Ranger made radios RT1 invasion

[Nowurtalkin222]

Specifically, it was this comment that is not consistent with the results "performance tests show them to do the same or better than the old toshibas". Until the base and collector impedance match the 2879, the counterfeits are not the same. Most telling is the fact you have to drastically decrease the value of the loading cap used in the output before the power will peak out. That means the output impedance has to be higher than the real part and this is one of the most important specifications in terms of output capacity. You need a lower output impedance to increase output power.

I don't mean to sound rude but Texas Star is really one of the worse ever deigns made in the history of CB amps. While it has a following because it sounds cleaner than a class C amp on SSB, everything from the unregulated resistive bias circuit, to the routing of RF through all of the push buttons and unshielded PC board traces, is a disaster. Combine that with boards that have very poor ground plane surface area intact, with positive ground wiring and these things can be very unstable. Drive them a little too hard and the 10uh choke burns up and allows RF to leak right back into the bias circuit. Then you get oscillations and pills popping. That fatal flaw is because they didn't want to spend an extra 75 cents on a 3 pole relay to isolate bias.

Don't be fooled. The builders you mention know full well they have never used a 12 volt transistor, that is as rugged as the original Toshiba. Showing equal power under ideal bench conditions, for a short time, after the mic was already keyed, is much different than hot switching the amp, into an antenna while talking skip for an hour.

Specifically, it was this comment that is not consistent with the results "performance tests show them to do the same or better than the old toshibas". Until the base and collector impedance match the 2879, the counterfeits are not the same. Most telling is the fact you have to drastically decrease the value of the loading cap used in the output before the power will peak out. That means the output impedance has to be higher than the real part and this is one of the most important specifications in terms of output capacity. You need a lower output impedance to increase output power.

I don't mean to sound rude but Texas Star is really one of the worse ever deigns made in the history of CB amps. While it has a following because it sounds cleaner than a class C amp on SSB, everything from the unregulated resistive bias circuit, to the routing of RF through all of the push buttons and unshielded PC board traces, is a disaster. Combine that with boards that have very poor ground plane surface area intact, with positive ground wiring and these things can be very unstable. Drive them a little too hard and the 10uh choke burns up and allows RF to leak right back into the bias circuit. Then you get oscillations and pills popping. That fatal flaw is because they didn't want to spend an extra 75 cents on a 3 pole relay to isolate bias.

Don't be fooled. The builders you mention know full well they have never used a 12 volt transistor, that is as rugged as the original Toshiba. Showing equal power under ideal bench conditions, for a short time, after the mic was already keyed, is much different than hot switching the amp, into an antenna while talking skip for an hour.

I'm having trouble using my phone to field these emails and to post my replies. As. I've noted before, my phone simply doesn't play well with this forum, so apologies if any of my posts or replies are not where they are supposed to be or anything like that. I'm having great difficulty wth the screen not looking right or showing me where to put my replies. Doing the best I can t ok deal with it. I tried to reply to one email in the email but it bounced and I knowno have to come directly to the forum but it's a mess on my phone. Anyway, this is a partial reply to Mr Shockwave I think. I can't even see what's what on my screen. I want to try to reply to the rest of what you said on the matter also, because I keep getting the feeling here that you are going beyond what I have actually said, as tho in rebuttal. I'm not an amp builder or a technician. I've been doing repairs for many years tho and know enough to be dangerous. I make my comments which only went so far to Lake whatever point and then you and some others seem to want to twist what I sad or contradict me or go deeper into some contraversy that I never intended to go into. The stiff I say, I know what I'm talking about or have good reasons to back up what I've said. Like the comment about Texas star is not a reputable company because they sell illegal amps. That's BS in my book and I gave my reason why. So now you go into Texas star design. It's like you keep baiting me. I'm not gonna debate design w/you if you are a designer or know deeply about it. I know that Texas star boxes have very well filled a need for many years and there are many thankful ppl. I know they are made up of some real nice ppl. I know they stand behind there stuff as much as possible. I know the amps are not fully true AB1 boxes, not the cleanest not the best ever amps built. That is not anything I came here to debate or cite about. They have put out a pretty decent product rust has worked well for many ppl for many yrs no matter what you say. They are not trying to be Ameritron or some type accepted ham amps. They have their place in this world. They filled a big niche. They have provided alot of joy to literally millions of ppl for many years. They are what they are and all you are doing is putting them down and telling me what bad about them. What other American company has done so much for so many ppl in this realm for such little $ for all these years and then stood behind their radio imports and the amps they build right there and employed those ppl for so many years? No one that I know of. They've helped me out many years times. More ppl have had more joy with galaxy radios and t/s amps than anyone else in my opinion. And while I know they aren't the most hi quality in every way, they still have gotten the job done for many for relatively cheap money. And I don't for a minute believe your point about how they chose not to make some circuit be better becsuse of 75 cents. I have no doubt in my mind that merely conjecture on your part becaudenit doesn't hold up to common sense. In other words if they could have a substantially better product for a lousy 75 cents, logic dictates that it would make far more sense to increase sales then to save a crummy 75 cents per box. So obviously there is more to the scenario than simply choosing the right save 75 cents. No way they are that stupid to cut their nose to spite their face. They have been around for a long long time very successfully because they had a clue what they were doing. And they are still going strong even with covid and all the rest of the things that you say are wrong with them. If you can do better, then you ought to... They are an American company who has kept the same ppl for so many years as a family and treated ppl real well and real fairly. And they always answer calls and emails and timely. The best amp design is not what they are all about. They are an American institution as far as I am concerned and never rip ppl off. Good folks...in a state of crazy ppl (California). They deserve at least as much praise as your criticism. And their amps have held up quite well for many ppl for many years in many cases. Amps are abused terribly and texas star has done reasonably well to take the abuse and they are not hard to fix dither & parts are modular and always readily available. My hats off to TEXAS STAR AMPS! They have done a great job for the prices and the risks they take to provide the public what it wants. And they have made improvements over the years as well. And they bring in the most popular radios of all time in my opinion. And their resale values are unreal. Just take a look on ebay. Ok well I got that off my chest. I didn't even come here to debate Texas star amps but I'm glad i said my peace be use they have been very good to me over the years and I am thankful. They have done their job for many years and been fair in business dealings. Ok, rant over.

 

[Shockwave]

And I don't for a minute believe your point about how they chose not to make some circuit be better becsuse of 75 cents. I have no doubt in my mind that merely conjecture on your part becaudenit doesn't hold up to common sense. In other words if they could have a substantially better product for a lousy 75 cents, logic dictates that it would make far more sense to increase sales then to save a crummy 75 cents per box. So obviously there is more to the scenario than simply choosing the right save 75 cents. No way they are that stupid to cut their nose to spite their face. They have been around for a long long time very successfully because they had a clue what they were doing. And they are still going strong even with covid and all the rest of the things that you say are wrong with them. If you can do better, then you ought to...

I do apologize for my somewhat abrasive responses. Sometimes I even make an ass of myself and get things wrong. However, in this case all it takes is the ability to read a schematic and following simple amplifier basics, of keeping your bias isolated from RF. If you think TS didn't know they had a bias issue directly related to being cheap with the number of poles on the relay, take a look at everything they made from the 667 down, and compare the bias switching in the sweet 16.

I've seen more 5 transistor TS units with blown 10uh chokes along with output combiners and transistors than I can shake a stick at. The problem is so bad, they knew they could never get away with that design in any 8 transistor amp and finally deiced to do the right thing and separate RF switching from bias switching. They also had to eliminate all of the front panel push buttons and unshielded PC board traces, to get rid of all of the stray RF pickup they created.

 

[Nowurtalkin222]

I do apologize for my somewhat abrasive responses. Sometimes I even make an ass of myself and get things wrong. However, in this case all it takes is the ability to read a schematic and following simple amplifier basics, of keeping your bias isolated from RF. If you think TS didn't know they had a bias issue directly related to being cheap with the number of poles on the relay, take a look at everything they made from the 667 down, and compare the bias switching in the sweet 16.

I've seen more 5 transistor TS units with blown 10uh chokes along with output combiners and transistors than I can shake a stick at. The problem is so bad, they knew they could never get away with that design in any 8 transistor amp and finally deiced to do the right thing and separate RF switching from bias switching. They also had to eliminate all of the front panel push buttons and unshielded PC board traces, to get rid of all of the stray RF pickup they created.

Ok Mr Shockwave, apparently, despite the unreal difficulties I have using this forum w/my dumb smartphone, my responses seem to be getting thru regardless so.......

#1) no need to apologize for whatever you feel strongly about.. You say what you feel needs to be said as I do the same. You've been a bit much for me or let's say more than I bargained for today, but I don't see you as having been rude to me or anything like that so I'm a big boy and will either try to deal with it or just duck out. I'm a talker and well known to be as engaging as anyone else and can argue about almost anything, but never unless I believe it's a valid & worthwhile thing to debate or argue.. In this case I no longer even remember why I came here today but I'm pretty sure it had nothing to do with Texas star amps & their design... I don't even remember how it even got on that subject but once you get me started, it's not easy to get me to stop. I have little business debating amp design with you but I feel kind of wrangled into into it somehow. All I know is regardless of how the orig discussion got to Texas star design, when I saw them dismissed as nothing more than a useless piece of junk company, which is how it came off, well I wasn't gonna stand for that and I think I made some good points in defense of them as a company. They are not some Chinese fly by night here today gone tomorrow, could care less company. I felt they had plenty to be praised about aside from award winning amp design, so I did. I see them as an all American success story who has never ripped off anybody & fulfilled a certain need. But I thought I came here tonight or yest, whenever it was, because I rcvd an email from this thread which was originally about the RT1 & evolved into the IRFZ24NPBF. I am not a design engineer nor a full fledged tech, but I have been doing nothing but buy/sell/trade/repair/tune/modify/customize & install, for more than 25 yrs mostly on my own but I have also worked for a couple of major cb shops for maybe 5 or 6 of those years and I got into radio in the mid 70s when everybody had one. I have no formal traininh in electronics but I order to do this, I've made it my business to research everything I can wrap my head around, and spent much time talking to & questioning techs along the way. I have successfully repaired many thousands of radio systems, mostly in the cb realm and related. Prolly more like tens of thousands all told and all self learned plus a certain knack almost like a divining rod, to get pointed to the source of the problem or at least some way to fix it, even via unorthodox means. Ok, so now you know what I'm about... There is very little that I havent fixed or found a way to fix in radios and antenna systems and to a much lesser degree, amps. I have fixed quite a few amps just because lots of failures are obvious and because I've hung around this stuff for so long. I could tell you the basics, the bare basics I suppose, of how an amp works, ie, I'm not clueless, but very limited. Mike Hawkins, the Texas star repair guy for so many years was good enough to teach me alot about how to test and repair them, both on a personal basis and via his videos that he so graciously shared his knowledge with so many ppl. There's alot to be said for that. He'd be the 1ztnone to admit he's no amp engineer but he certainly knows how to fix them and make them do their job and has been at it for about 40 yrs. I even sold a few amps for him to help us both out when t/s laid him off.

Ok, so enough about all that...

This latest spate of emails with me & wwdx began when I took in a job that was pretty big for me. It was an old customer of mine, a trucker who likes big radios and amps for many years. He brought me a newly purchased (by his kids as a birthday present) N3. I know now that the N3 has been out for perhaps over a year, but when he brought it to me, I had not yet even heard of them. I knew about N2 & N4 but not N3 with 4-500 watts... He got it from gi Joe less than 90 days ago as the present. So when he brought it to me, it was maybe less than 2 mos old. It was all blowed up and real good. Fire & brimstone blowed up. Barbeque pit blowed up..

Ironically, years earlier, he brought me a fully blowed up 98vhp which I repaired but in that case it seemed the most prudent thing for me to do was to buy a new amp board and install it which I did and the rebuild turned out well. Also ironically, another mosfet amp. The more I read here the more I get it, thst mosfet amps, esp w/8 fets, are nothing more than an accident waiting to happen. In fact, I never liked mosfets in radios much either ever since they began to surface due the Mitsubishi shakeup. I remember getting into a bit of a hassle with Mr Lewis (Sam) before he died because so many of his early mosfet conversions and factory mosfet radios were failing and I wanted him to take of them via warranty but after the same radio blew up a few times he saod he wasnt going to keep covering and I had a problem w/that because I knew something was wrong about these mosfet radios continually blowing up. At the time, was the controversy going around that his ekl 2030 fets were just rebranded irf520's and many were absolutely convinced that was the case. So. Since he didn't want to warranty some of the radios he already fixed, one day I innocently asked him if I could use the irf520's instead of the erf2030s (because they were much cheaper and I just happened to have a supply of). Well, I hit a major nerve and he went ballistic on me. All I did was ask but I must have been the straw that broke the camels back on that question. Once he calmed down he told me they were not the same and not to use them. Around the same time I had some kl60 rm Italy stinger boards that had blown or missing rm3 (or was it rm1?) fets and I decided to try using the irf520's but they were definitely not the same output pwr but they worked. So anyway, some time later Mr Lewis sent me a letter (I think i still have it from around what, 10 hrs ago or more?) where he basically admitted that there was indeed a problem with those radios and he included a bagful of parts & the instructions how to install in the magnum mosfet radios. After that, his radios held up much better ot seemed. I didn't know what I was doing, but I suspect it had something to do with a more appropriate biasing circuit?

So let me get back to your email about the Texas star design thingy..
I dx ont doubt what you say about the rf & switching pwr supply circuit conflict. All I said is that common sense dictates to me that if they knew about this issue and it was only a matter of 75 cents to correct, sorry but you'll never convince me that they chose 75 cents over a design so much better and so much absolutely necessary, which obviously would bolster their rep and create more confidence & sales, I simply refuse to believe that. I have no doubt in my very inyltuitive mind that there must have been more to to it than that. They are not stupid ppl. It's not very sensible to cut your nose to spite your face in business. And that's why they have been in business for so many decades now, going back to those pre Texas star boxes that started with an O. (temporarily forgot the name) oh yeah, Outcomm.. Whether it was a design mistake or lack of knowledge or whatever, I don't know. All I know is it makes no sense to knowingly have such a catastrophic design flaw as you have characterized it, which could be solve by a mere 75 cents and then to CHOOSE as a business decision, not to. If you believe that's what happened, I would reconsider.

Oh and by the way, I've fixed a fair number of them and only remember 1 or 2 that had burnt chokes and/or combiners. Early on, I believe it ass Mike H who explained to me about the issue with some of the pcbs and the metal standoffs & how they were causing shorts that would burn the chokes and how I had to be on the lookout for that issue. I could never understand why they didn't just use plastic standoffs but it just occurred to me that it's prolly a matter of the metal washers connecting board ground to chassis/heat sink ground to make a better ground plane??? I thought board ground & chassis ground were supposed to be kept seperate to help eliminate rfi?? In any event, only have had to replace 1 or 2 chokes and no splitters/combiners that I recall. Just lucky I guess. This leads back to the 98vhp I got to fix.

So it was the 1st time I saw the RT1's. I started to research and wound up here where I saw this RT1 thread which I don't think was too old of a thread and someone wanted to know about what the hell the remarked RT1's really were. So there were a few comments & opinions in general about how crappy it was to make these mosfet amps esp 8 device. I believe it was NOMAD who gave me some advice but either him nor anyone else seemed to have much insight about the RT1's. Then, a day or 2 later, I 4get who it was posted about what he had determined the RT1's to be. And then there was a followup tomit that seemed to confirm they were IRFZ24NPBF but I didn't pay that much attention to it because by that time I had already contacted my regular wholesale supplier and asked for RT1's. He told me he had some but there was some sort of problem about them and he would have to look into it and get back to me. A day or 2 later he got back to me and said he d he had them so I ordered a set thinking I would be getting a set of RT1's. But when he sent me the digital invoice, they were not as RT1 but as IRFZ24NPBF. I couldn't u derstand that and I was quite concerned, because I had already learned that apparently this radio could do over 400w pep. In fact, the owner of the radio said his meters (dosy & no dummy load) were telling him 550w. I told him to forget about 550 but maybe 250 or 300 was my guess after tune. It says 100w am & 300.ssb on the box. But then I saw the cb shop guy in Florida, oh yeah, Bells, video showing the N3 doing 400 and out of the box and 450 after tune. I was astonished! But then I knew that these RT1s were much higher pwr than the old irf520 version of this amp.

So immediately I contacted my salesman and asked why my order for RT1's was invoiced as IRFZ24NPBFs? He explained that over a year earlier, he had a curomer request some RT1s which they did not yet carry so he contacted their supplier (most likely in China) to get some and the the supplier said they were actually IRFZ24NPBF being buffed and rebranded by Ranger in Malaysia or whatever. My salesman was maybe not aware of that at the time as he doesn't make the orders. So when they came their computer system had them marked as IRFZ24NPBF as far as the stockroom goes. But they were marked as RT1 as far as the general company part #. So that's why there was confusion at 1st when I ordered because my salesman couldn't the stock room could only find IRFZ24NPBF. Then he found out that the supplier had said they were RT1 same thing. Then I remembered the post here in this thread that ID'd them as one and the same IRFZ24NPBF. But I still wasnt fully convinced because now I knew that anyone could take any workable mosfet & buff it out & mark whatever he wanted to on them. Which is why I now think it's a horrible practice to do.

So I tried to do more research on them. I contacted all sorts of industry peeps, even eric Lewis (as he had previously been involved with Ranger) but neither him nor anyone else knew a damn thing about these RT1's or weren't divulging...

I tried looking on Ranger website but they have no mention of N3 there, lol. I tried to email them but they did not answer several emails. Finally I tried calling and I reached someone (Roger) who said he was the only one working in the building due to to covid I guess. He had a very thick chinese? accent and was real hard to understand. He said he worked there for around 35 yrs. I asked him if he could tell me what the RT1's really were or what I could use. He immediately knew what I meant and he had some notes in hand to look it up. I did not tell him anything before hand about the IRFZ24NPBFs I ordered. And he then told me to use IRFZ24NPBF. At that point I was convinced the IRFZ24NPBFs were either the same thing or close enough to use. I had some more questions about the biasing but it became too difficult to u derstand him plus he spoke of a special Chinese measurement tool he used to the biasing and he the. told me to call Chris Holland in calif to get the rest of the procedures. I did so.and I completed the job with Chrics telling me I had done it correctly. But as I mentioned earlier, there is still a problem.

So as far as I recall, I came here today to reiterate to someone that reported 2 different IRFZ24NPBFs that the ones that say IRFZ24NPBF on them are the right thing as far as I know. And then, somehow it evolved into what transpired today! Yikes!

 

[Shockwave]

So let me get back to your email about the Texas star design thingy..
I dx ont doubt what you say about the rf & switching pwr supply circuit conflict. All I said is that common sense dictates to me that if they knew about this issue and it was only a matter of 75 cents to correct, sorry but you'll never convince me that they chose 75 cents over a design so much better and so much absolutely necessary, which obviously would bolster their rep and create more confidence & sales, I simply refuse to believe that. I have no doubt in my very inyltuitive mind that there must have been more to to it than that. They are not stupid ppl. It's not very sensible to cut your nose to spite your face in business. And that's why they have been in business for so many decades now, going back to those pre Texas star boxes that started with an O. (temporarily forgot the name) oh yeah, Outcomm.. Whether it was a design mistake or lack of knowledge or whatever, I don't know. All I know is it makes no sense to knowingly have such a catastrophic design flaw as you have characterized it, which could be solve by a mere 75 cents and then to CHOOSE as a business decision, not to. If you believe that's what happened, I would reconsider.

Oh and by the way, I've fixed a fair number of them and only remember 1 or 2 that had burnt chokes and/or combiners. Early on, I believe it ass Mike H who explained to me about the issue with some of the pcbs and the metal standoffs & how they were causing shorts that would burn the chokes and how I had to be on the lookout for that issue. I could never understand why they didn't just use plastic standoffs but it just occurred to me that it's prolly a matter of the metal washers connecting board ground to chassis/heat sink ground to make a better ground plane??? I thought board ground & chassis ground were supposed to be kept seperate to help eliminate rfi?? In any event, only have had to replace 1 or 2 chokes and no splitters/combiners that I recall. Just lucky I guess. This leads back to the 98vhp I got to fix.

I agree with just about everything you said, except the two paragraphs above. Maybe it's 50 cents more, maybe it's $1.50 more to buy a relay with 3 poles. In any event, the schematic proves one fatal error in their bias circuit is the direct result of combining RF and bias DC, on a single relay contact and then relying on a small choke to separate the two. They had to know about this problem because they fixed it on the 1200 power plate and the sweet 16, while it still exists where they could get away with it, in most of their smaller amps.

Do a little more research into this issue and you'll note it's connected to the problem of the amp not unkeying until you switch it off. Oscillations that smaller TS amps are well known for due to poor circuit board layout and design. Only the ones with front panel meters have this particular bias issue and believe it or not, the light behind the meter contributes to their problem, because it is also powered by the same shared relay contact.

 

[Nowurtalkin222]

I agree with just about everything you said, except the two paragraphs above. Maybe it's 50 cents more, maybe it's $1.50 more to buy a relay with 3 poles. In any event, the schematic proves one fatal error in their bias circuit is the direct result of combining RF and bias DC, on a single relay contact and then relying on a small choke to separate the two. They had to know about this problem because they fixed it on the 1200 power plate and the sweet 16, while it still exists where they could get away with it, in most of their smaller amps.

Do a little more research into this issue and you'll note it's connected to the problem of the amp not unkeying until you switch it off. Oscillations that smaller TS amps are well known for due to poor circuit board layout and design.

Well Mr Shockwave, you seem to want me to engage you in something I know very little about. You insist on this design flaw & as I've said, I know almost nothing about design and/or rf engineering. But you're kinda making me know something about it, so I can't just leave it alone. I already have enough trouble keeping enough synapses firing to stay focused on what I'm doing, and I've already proferrred my opinion that it doesn't make sense to me that they would know about a critical design flaw yet choose to allow it to stand due to cost to change. It is you who chose to say 75 cents as the amount needed to make it right. I assumed you were using a reasonable number but now you are saying it could be more or less that amount, but we're STILL talking a relatively small amount (50 cents to a buck fifty). And again, I still find it very hard to believe they would consciously choose to allow such a flaw as you've described to me, for even that amount. Especially when you describe it as "a fatal flaw". Possibly you're overstating the problem? For example, you say that originally the same flaw existed in the hot plate & sweet sixteen and they HAD to fix it. That's not something I've ever been aware of but I'll take your word for it. However the small difference in cost would be even smaller in those units. I'm guessing that in the past a sweet 16 retail price must've been in the $700-$800 range & the $600-$700 range for a hotplate? I know it has to be somewhere in that general range. So 50 cents to $1.50 would be somewhere in the range of 1/10th to about 1/5th of 1 percent of retail. I also am guessing that Texas star has never been turning out like millions of these units, say, per year. I really dont know but I've been in this business for a long time so I should be able to make a reasonable guess that they made the smaller boxes (1 pill/250/350/400/500/667) in numbers more in the range of thousands to maybe ten thousand per year it couldn't, I don't think, be much more than that, could it? And on the big boxes, far less in number, I think more or less made to order. And that would, I think, be in their hayday, certainly not in recent years, where the numbers must be far lower than estimated above. They don't even make 250 anymore. I would guess the 350 is their flagship box in terms of sales & popularity. Those are what....around $275-$300 retail? So even there, we're talking far less than 1 percent of retail. Possibly approaching 1 percent of cost? Those, of course are estimates but I think they are within reason. So let's go with under 1 percent of cost in a 350 and much less on all the bigger boxes. Pretty sure they don't make a hot plate anymore. Last time I spoke to John there, which was less than a month ago, he laughingly didn't even know that hg/dei made a 2290 i had to assure him they did (although now I'm not sure about that. What brought that up was me asking him why they quit making the 250. In any event, I think i have reasonably established that the cost to them, all above factors considered, to use a 3 pole I stead of a 2 pole relay, would've been pretty small in a business sense compared to knowingly putting out a fatally flawed product., as you state it is/was.

To be honest with you I don't have a clue how a choke seperates rf (ac) from DC? I thought a choke was a kind of rf resistor. I think i understand that the torroids were combiners & splitters of the rf signal which is ac, but I didn't know that texas star were combining rf & DC on a single pin of a relay or how the choke seperates that. If the choke seperates the 2 components, then what's the problem? Obviously the choke burning up is not like an automatic thing that happens. If it did, then yes, I would call that "fatally flawed" and it simply would not work. I've looked at a fair number of t/s boxes and not seen that many burnt chokes on the relay. I don't know how often it happens but I know many t/s boxes operate for a long time w/o burning out the choke. I'm now interested in knowing just how a choke seperates ac (rf) from DC? The only thing I knewnabiut chokes was long ago, when I got my 1st A99 antenna, the enclosed paperwork said to make a choke by wrapping several turns of coax around the bottom of the antenna where the mounting is to help mitigate RFI. But I never went in to study the characteristics of a choke or as may be in this case, an "rf choke"... Hopefully I can remember long enough past finishing this post to look up exactly how chokes or rf chokes actually work. So thanks for the impetus to do that. Does it mean that an rf choke blocks ac but passes DC, similarly to how caps block DC but pass ac?? Are the torroids that are wrapped with wire, which are used as noise filters often on DC input, is that a choke? I DO know that the most astonishing feat of blocking real bad RFI was solved 100% by a large torrid that had the wires from the identified source of the bad RFI (in that case, the wires from about 7 very dirty electronic devices (I forget what they were but some kind of signal splitter for many devices in a computer shop which caused terrible RFI in the cb shop where I worked back then and we used an rf sniffer to track it down to the computer shop that had just moved in down the hall) causing HORRENDOUS, unbearable RFI, were wrapped several times through a large torfoid obtained from a gas pump. We had tried all sorts of conventional filters but nothing helped until some very smart guy brought that big toroid on and wrapped all of the (output?) wires from the offending splitter boxes and like magic, after days of fighting this noise, it vanished, 100%, like magic. So I'm guessing that "RFI" was composed of RF signal which I know is AC and the toroid acted as an rf choke, seperating the RFI (RF A/C) from somehow capacitively coupling (??) into our test equipment in the cb shop? Am I on the right track? Anyway, it was definitely the best example of curing bad RFI that I ever saw. Years later, when I worked at the other cb shop, I fixed a pretty bad interference problem on a big truck by wrapping the pwr wires, I think it was, of very "dirty" inverter, around a sizable torroid ring. I know that the wrapped toroids in the amps are called splitters & combiners. Are they essentially rf chokes as well that seperate ac from DC?

OK, so are you happy? Now you've exposed just how dangerous I am....
....and all I started out to do was to tell that poster about the little bit of knkwledge I had about the IRFZ24NPBF mosfets. I'm way out of my league and prolly sounding like an idiot....

Can you at least admit that many many t/s box owners, when they don't push their amps too much and let them cruise along happily, staying on the side of underdrive and staying under 15V, that they can get years of service from them w/o any "fatally flawed, catastrophic fails?

 

[Shockwave]

It is you who chose to say 75 cents as the amount needed to make it right. I assumed you were using a reasonable number but now you are saying it could be more or less that amount, but we're STILL talking a relatively small amount (50 cents to a buck fifty). And again, I still find it very hard to believe they would consciously choose to allow such a flaw as you've described to me, for even that amount. Especially when you describe it as "a fatal flaw". Possibly you're overstating the problem? For example, you say that originally the same flaw existed in the hot plate & sweet sixteen and they HAD to fix it. That's not something I've ever been aware of but I'll take your word for it.

While it's very possible to upgrade a 2 pole relay to a 3 pole relay for 75 cents, you only have this option prior to designing the PC board and mass producing them with layouts for a 2 pole relay. Maybe, they got a 50% off deal on NOS 2 pole relays that are much more common. Don't feel too bad because Black Cat did the same thing with a cheap 2 pole relay, on many of their JB "modulators".

TS really only made one PC board with 2 transistors on it, and stitched them together without a continuous ground plane, as individual pallets, to make all of their bigger amps. You'll note the sweet 16 has the same board as the 350 and they didn't put any RF on the board where the pushbuttons and relay are. That whole section needs to be bypassed because a choke cannot remove enough of the RF to make that micky mouse design work at higher power. Then they hardwire a separate relay off the board, for RF.

From your last post, you do understand how a choke works. It provides a high resistance path to RF and a low resistance path to DC. Unfortunately, it never reaches the resistance of an open to RF and some small degree of RF will still get by. In most cases that's not a problem because we typically do not rely on a choke to remove 100% of the RF, from the DC line feeding the sensitive bias circuit, due to the designer, directly combining the two, because they didn't provide a dedicated relay contact.

I call this a fatal flaw for one reason. When one of the two 10uh chokes gets a little hot from too much RF, it overheats the enamel insulation and turns brown. Therefore, it can no longer provide as much resistance to the RF and more passes by. Now it can be enough RF feedback from the output, back to the input, to sustain a self oscillation and hold the relay keyed when you unkey the mic. If you don't turn it off fast enough, it can take out a transistor and the output combiner too.

Yeah, if you run a TS on 13.8 volts (not 15) and don't drive it too hard, your 10uh chokes may stay bright gold color and not act up to the point of destroying the output transistors. On the other hand, the unregulated bias circuit, lack of good PC board RF grounding and stray RF all over the board, introduces numerous issues not found in other amps, that reduces the reliability of the TS.

 

[AudioShockwav]

And I don't for a minute believe your point about how they chose not to make some circuit be better becsuse of 75 cents. I have no doubt in my mind that merely conjecture on your part becaudenit doesn't hold up to common sense. In other words if they could have a substantially better product for a lousy 75 cents, logic dictates that it would make far more sense to increase sales then to save a crummy 75 cents per box.

I am probably the one of biggest TS fan on this board but you are just wrong with the above quote.
It's not conjecture, go download the Texas Star schematic from CB tricks and look at it.
You can believe what you want but that tells a different story.
Yes, for a " production built" amp they "used" to be fairly consistent and if you were careful to not over volt and not over drive and put a fan on it and make sure it is getting enough current the TS 350 and 500 are usable.
Donald is correct, just to save the cost of a relay they are using a choke to keep RF out of the bias.
TS has no real thermal tracking of the bias
TS does run input RF through its signature push button switches.
The old TX series Palamor amps with electronic voltage regulation and thermal tracking were a much better design but since they went out years ago TS is about all that is left.
They are far from the best 11 meter amp ever made.
Personally if Ray was still building Messenger, it was a better built amp, I would take them over a TS today.

73
Jeff

 

[AudioShockwav]

Now it can be enough RF feedback from the output, back to the input, to sustain a self oscillation and hold the relay keyed when you unkey the mic. If you don't turn it off fast enough, it can take out a transistor and the output combiner too.

I have personally seen a Yaesu a FT-897 that was being used with Texas Star amp and the front end of the radio was damaged because the amp broke into oscillations after the radio was un keyed.
The amp , ts 500 , had a roasted choke in it because he was overdriving the amp.
I will never run a TS amp behind a HF rig because it is not worth the risk.

73
Jeff

 

[Shockwave]

I am probably the one of biggest TS fan on this board but you are just wrong with the above quote.
It's not conjecture, go download the Texas Star schematic from CB tricks and look at it.
You can believe what you want but that tells a different story.
Yes, for a " production built" amp they "used" to be fairly consistent and if you were careful to not over volt and not over drive and put a fan on it and make sure it is getting enough current the TS 350 and 500 are usable.
Donald is correct, just to save the cost of a relay they are using a choke to keep RF out of the bias and it is on all the time.
TS has no real thermal tracking of the bias
TS does run input RF through its signature push button switches.
The old TX series Palamor amps with electronic voltage regulation and thermal tracking were a much better design but since they went out years ago TS is about all that is left.
They are far from the best 11 meter amp ever made.
Personally if Ray was still building Messenger, it was a better built amp, I would take them over a TS today.

73

The only thing off a little is TS didn't do what Black Cat did and hold the bias on all of the time. The idea of the choke was to be able to combine DC with the existing RF on the 2 pole relay contact. Now TS found a shortcut to turn the bias on when you key and made sure to pick up a little more stray RF, by running those DC wires up to the front panel meter lamp so it comes on with the keyed bias too. I also liked my Messenger much more than the TS and it even had some degree of output filtering with an LC matching circuit, after the last output combiner. While it's a little lacking in the heatsink department, it was much easier to add a fan, than to redesign a poor RF layout.

 

[Shockwave]

I have personally seen a Yaesu a FT-897 that was being used with Texas Star amp and the front end of the radio was damaged because the amp broke into oscillations after the radio was un keyed.
The amp , ts 500 , had a roasted choke in it because he was overdriving the amp.
I will never run a TS amp behind a HF rig because it is not worth the risk.

73
Jeff

I didn't even want to mention that fact. I know of several people that lost the front end in their rigs, when they unkeyed and the amp didn't.

 

[AudioShockwav]

"The only thing off a little is TS didn't do what Black Cat did and hold the bias on all of the time"

You are correct I posted in error on that point.
Thank you.

73
Jeff

 

[Nowurtalkin222]

While it's very possible to upgrade a 2 pole relay to a 3 pole relay for 75 cents, you only have this option prior to designing the PC board and mass producing them with layouts for a 2 pole relay. Maybe, they got a 50% off deal on NOS 2 pole relays that are much more common. Don't feel too bad because Black Cat did the same thing with a cheap 2 pole relay, on many of their JB "modulators".

TS really only made one PC board with 2 transistors on it, and stitched them together without a continuous ground plane, as individual pallets, to make all of their bigger amps. You'll note the sweet 16 has the same board as the 350 and they didn't put any RF on the board where the pushbuttons and relay are. That whole section needs to be bypassed because a choke cannot remove enough of the RF to make that micky mouse design work at higher power. Then they hardwire a separate relay off the board, for RF.

From your last post, you do understand how a choke works. It provides a high resistance path to RF and a low resistance path to DC. Unfortunately, it never reaches the resistance of an open to RF and some small degree of RF will still get by. In most cases that's not a problem because we typically do not rely on a choke to remove 100% of the RF, from the DC line feeding the sensitive bias circuit, due to the designer, directly combining the two, because they didn't provide a dedicated relay contact.

I call this a fatal flaw for one reason. When one of the two 10uh chokes gets a little hot from too much RF, it overheats the enamel insulation and turns brown. Therefore, it can no longer provide as much resistance to the RF and more passes by. Now it can be enough RF feedback from the output, back to the input, to sustain a self oscillation and hold the relay keyed when you unkey the mic. If you don't turn it off fast enough, it can take out a transistor and the output combiner too.

Yeah, if you run a TS on 13.8 volts (not 15) and don't drive it too hard, your 10uh chokes may stay bright gold color and not act up to the point of destroying the output transistors. On the other hand, the unregulated bias circuit, lack of good PC board RF grounding and stray RF all over the board, introduces numerous issues not found in other amps, that reduces the reliability of the TS.

Mr SW, you continue to "shock my waves"...
That's a good thing.. I must thank you for hanging in their, with my obvious technical ignorance, you seem to allow for that and see fit to educate me on this t/s design flaw.

I can't help but wonder....is there not any other way to mitigate the troublesome mixing of RF & DC, which you say causes the described problem? I mean is there some other way to upgrade the board via diodes or something? What about a heavier choke? Yes/no? Also, what would it take to modify the board to accept a 3 pole relay? Or are you saying there's simply no fix? What about adding additional chokes or torroids in that circuit. Is that possible? And put another way, what is the amps are simoly not overvolted & over driven? Are they then reasonably reliable boxes for the money?

Also, I can't help but wonder what is so difficult in creating a continuous ground plane between the boards? Also, is there or is there not, any sort of feedback circuit present and if not how difficult is it to make one? I mean on the rangers, it's just a resistor & cap across ea side of the transformers.

Thanks for your patience with me and the info

 

[Nowurtalkin222]

I have personally seen a Yaesu a FT-897 that was being used with Texas Star amp and the front end of the radio was damaged because the amp broke into oscillations after the radio was un keyed.
The amp , ts 500 , had a roasted choke in it because he was overdriving the amp.
I will never run a TS amp behind a HF rig because it is not worth the risk.

73
Jeff

Again, "because he was overdrivinv the amp". Shouldn't a ham know better than that just on general principles? Also, I'm not a ham, but I thought ham rigs employed a keyer circuit rather than have the radio key the amp directly. Maybe the answer to that, is the keyer circuit is built into the ham amp as opposed to a texas star amp. If I ever get this N3 working right and after listening to what Nomad radio guy tried to tell me, I wondered if I might be able to construct a simple keyer for the amp. I mean I know how easy it is to manually key the Texas star amps by shorting the resistor in the relay circuit. So how hard could it be to tap a couple wires in there that lead to a foot pedal or something so you could key the amp up before keying the radio? Isn't that how it's supposed to be done anyway, to avoid that "kickback" or that momentary open circuit w/high swr that nomad was describing to me? Or am I just way off base? Let me back up a sec so you know what I'm talking about. I don't know if you read my initial post where I described how the N3 blew up. The owner was using the N3 to hit a 12 pill box (pretty sure 2979s). The demise of the N3 came about during one of those keydowns as he told me after nomad asked me about that. So I don't want the same thing to happen again (yes, I intend to measure the swr between the N3 & the 12 pill, before proceeding to let it all be hooked up again) if I ever get the N3 fully fixed. I rebuilt it, replaced all the mosfets with a matched group, also replaced the burnt output side torrid, replaced the "ok looking" 100 ohm, "flame proof" resistor that parallels that torrid, which I surprisingly found to be open, and replaced the input side resistor because it measured 208 ohms. I used texas star torrid/resistor combos to accomplish this by cutting the resistor free from one of the torroids to use on the input side and on the output side I figured out how to just connect the torrid/resistor combo by cutting some leads and using the extra pads there. Same thing. I also very thankfully was advised by Chris Holland to look carefully at the 56 ohm smt resistors associated with the mosfets on ea side of the transformers. It's a damn good thing he told me to look because my eyesight is no longer good enough & those resistors are way too small for me to have casually noticed they were toast. So I then looked closer and could just barely see the dark spots on the front where the numbers are and I confirmed w/o meter they were bad. I didn't have any replacements in 56 ohm in that pkg so I opted to install 4 quarter watters. I wound up losing a couple of the mosfet pads and a couple of the smt pads and so I very carefully put in some jumpers to correct that. It was really hard for me to do but I ohmed them after and they all checked out as best I could tell (no opens no shorts). I then did the radio biasing and then the amp biasing according to the instructions from Chris. When it was all done, I didn't have a large enough pwr supply to test so I used my large, deep cycle battery power supply which has a fairly clean charger that let's me monitor the voltage at the battery. I keep it at close to 14v but sometimes let it get close to 15v. Nice clean DC power... Unfortunately, after all that work, it only was outputting approx half the expected power at about 200 pep and the output 100 ohm resistor was burning up quickly. I was super careful along the way but something got missed or messed up. Of possible note, it was the output side torroid that burnt in the orig fail so maybe something I missed in the rebuild?

 

[Shockwave]

Mr SW, you continue to "shock my waves"...
That's a good thing.. I must thank you for hanging in their, with my obvious technical ignorance, you seem to allow for that and see fit to educate me on this t/s design flaw.

I can't help but wonder....is there not any other way to mitigate the troublesome mixing of RF & DC, which you say causes the described problem? I mean is there some other way to upgrade the board via diodes or something? What about a heavier choke? Yes/no? Also, what would it take to modify the board to accept a 3 pole relay? Or are you saying there's simply no fix? What about adding additional chokes or torroids in that circuit. Is that possible? And put another way, what is the amps are simoly not overvolted & over driven? Are they then reasonably reliable boxes for the money?

Also, I can't help but wonder what is so difficult in creating a continuous ground plane between the boards? Also, is there or is there not, any sort of feedback circuit present and if not how difficult is it to make one? I mean on the rangers, it's just a resistor & cap across ea side of the transformers.

Thanks for your patience with me and the info

While you could use a heavier choke to provide more headroom, it's still just like putting a bigger Band-Aid on the problem. Changing the existing relay is not really necessary, since it's able to do two of the three switching jobs just fine. If I had one today, I would just add another small single pole relay coil in parallel with the existing relay. Lift the side of L2 that connects to R30 and the output combiner, from the board. Use the normally open contacts on the relay to supply 12 volts to the lifted side of L2, so it gets 12 volts applied only when the mic is keyed. This breaks one problematic connection, to the output RF, through the choke. However, from what I recall, you'll also want to remove L1 so that the second path back to the input side, is also disconnected.

The TS does use negative feedback on each transistor through a .1uf cap and 39 ohm resistor. This is good practice but cannot be relied upon to compensate for RF getting into the bias or a poor ground plane surface area around the PA circuit. There are very high RF currents flowing through the ground plane surface of the PC board around the transistors and output transformers. Sharing an unbroken large copper connection area between these points and all output transistors, reduces circuit inductance and provides the greatest stability. That issue in not really fixable in the TS but it's also not its weakest link.

The bias problems are fixable and if you add the relay, you should also consider some basic regulation for the bias so if it ever gets more than 13.8 volts applied, the higher bias current, doesn't force the thing into thermal runaway. Just add 1N4001 diodes across the 1.8 ohm resistors (R16 & R23) With the cathode (banded side) towards ground. Go one step further and add some thermal tracking by sticking those diodes on top of the nearest output transistor, with some thermal compound.

We can keep going... The bias voltage used here is often not enough to produce true class AB. The use of the 1.8 ohm (or 1.6 ohm) resistor is to hold that bias voltage down to a safe level. Since the vehicle electrical system can fluctuate between 12.6 and 13.8, TS had to compromise towards the low side, to put safety in front of spectral purity. Now if you feed an adjustable, regulated bias voltage into L2 through a 3 terminal regulator like the LM-317, you can remove the 1.8 ohm resistors (replaced with diodes) and precisely set the idling current with the pot connected to the 3 terminal regulator.

Make sure the pot is set for minimum voltage first and then ease it up until the desired idling current is reached. This part is critical because if you start too high, you can kill all transistors instantly. Don't even connect the output of the LM-317 regulator to L2, until you test what that voltage is first. Without the 1.6 ohm resistors, I'd be comfortable starting with a voltage around 6, before connecting to L2 and dialing up the correct idling current. That's 100 ma. of collector current, per transistor with no RF applied.

One last thing I forgot is to check the torque on all of those hex screws holding the boards, transistors, SO-239 connectors and case to the heatsink. Ones that got used in vehicles, can loosen up over time and cause havoc without any defective parts starting the problems.

Thanks for your patience with my critical comments. If that's not a deal stopper for you, I am able to answer questions.

 

[Shockwave]

I didn't have any replacements in 56 ohm in that pkg so I opted to install 4 quarter watters. I wound up losing a couple of the mosfet pads and a couple of the smt pads and so I very carefully put in some jumpers to correct that. It was really hard for me to do but I ohmed them after and they all checked out as best I could tell (no opens no shorts). I then did the radio biasing and then the amp biasing according to the instructions from Chris. When it was all done, I didn't have a large enough pwr supply to test so I used my large, deep cycle battery power supply which has a fairly clean charger that let's me monitor the voltage at the battery. I keep it at close to 14v but sometimes let it get close to 15v. Nice clean DC power... Unfortunately, after all that work, it only was outputting approx half the expected power at about 200 pep and the output 100 ohm resistor was burning up quickly. I was super careful along the way but something got missed or messed up. Of possible note, it was the output side torroid that burnt in the orig fail so maybe something I missed in the rebuild?

I feel your frustration and how aggravating it is to think you're running out of options. The good news is it's working again, you just need to figure out what the difference is between the left half of the amp and the right half, that is causing the imbalance that heats the output combiner resistor. It could be as simple as one capacitor across an input or output transformer, has shifted value due to stress during the last transistor failure. Or, the old shorted transistor could have damaged the bias circuit feeding one half of the amplifier.

If you can figure out how to get it to key and apply bias without RF drive, it makes testing for proper bias voltage on each bank, easy. Otherwise you may find an inexpensive thermal temperature gun with the red laser pointer, can spot a pair of transistors that are either running cooler due to lack of bias or drive, or running hotter because they are doing most of the work. Bad caps that shift value with heating, can also show up here. Every part used on one pair of transistors, should run at the exact same temperature as that same part, on the other pair.

Likewise, everything on one side, should look symmetrical to the other side. For example, when you replaced the surface mount 56 ohm resistors with standard ones, did you keep the lead lengths as sort as possible and the same length for all four? Do any of those resistors have their leads bent so one is noticeably closer to any adjacent part, or the PC board ground?

Does the 100 ohm resistor across the input splitter get warm at all? It won't burn like the output since it has much less power here, but If it even gets warm, the imbalance is all the way back at the input and could easily be blown bias on one side that caused the impedance to shift up on one banks input, or a bad cap across the input transformer. Do these boards use the so called "companion part" for bias like Palomar does with the 1N4148 diode and two resistors? If so, look there first, they often burn that diode out when the FET fails.

If all else fails, post some high resolution pictures of the board here and let more eyes see if we can spot something that was overlooked.