Power in Perspective / Transistors Verses MOSFETS

[Switch Kit]

I had dropped out of the hobby for about 8 years or so and came back a few years ago . I knew back then that MOSFETS were the growing trend and they seemed a lot cheaper to use and I've still been trying to shake hands with them ever since ? (to have a better understanding of them) I was old school and still had a appreciation for Motorola and Toshiba transistors , they just seemed to be a lot tougher then the MOSFETS ? But it looks like the times have changed . it's looking more and more like a MOSFET world to me ? Rangers doing 100 to 600 freaking watts out the box ! That's almost scary to me along with the price tags on those radios but yet MOSFETS are cheap ? and then I read about the Chinese knock off transistors work but there not as tough as the Moto's and Toshi's were ? but yet they will work well if you don't over drive the snot out of them ?
I see the RM Italy stuff and have been impressed with the RM 703 amps running 16 x 13N10s and sound great on SSB ...........500 big ones taxed and shipped ! when the 13N10s are only about 1.25 cents a piece (about 20 bucks to replace if blown in the 703s) Now that's cheap ! and fairly easy to replace in those amps (same as the KL 503's that run 9 of them although I'm not sure how well they would sound on SSB) I guess my confusion and question just comes down to , is one power source better then the other ? Transistors Verses MOSFETS .........Doesn't look like MOSFETS are going away to soon , especially when there powering some of the nice HF radios on the market theses days. Thanks for any input on this subject , I'm just getting older by the day and more and more plug and play , you know , if it works , don't fix it . Thanks again Switch Kit

 

[Enterprise312ok]

I got started in the mosfet world, I like them personally you get good power with low amp draw and if bias is set properly they are plenty durable.

 

[9C1Driver]

I think ohm's law still applies to mosfets. I saw recently that the 13n10 has been discontinued and they are now very tough to find. Switch Kit the 2030 mosfet's that Magnum radio's used are also gone as well as the 7530 mosfet in the RFX-75's. It's like Toshiba finals all over again.

We can then look at newer mosfets like the RT1 that Ranger is using. Can't find the thread now but it's not even a transmitting final. They are used as switching transistors in power supply's. RCI buys them in bulk and has RT1 stamped on them.

Welcome back Switch Kit, good to see you posting again. The way I look at it is we are pretty much stuck with mosfets for better or worse. Mostly for the worse. I am not at all interested in an amplifier with 16 mosfets that does 400-450 watts. There are plenty of posts here where RCI N2 and N4 radio's keep toasting their finals. Mosfet's don't seem to like a higher SWR or a mistuned bias setting.

Anyway take care

 

[Enterprise312ok]

On the new President Washington the 2 Irf 520 finals run at 19 volts and are capable of 100 watts clean on the spectrum analyzer.
Were there ever any BI-polar transistor in the same package that were capable of this?

 

[9C1Driver]

Nothing old school ran reliably at 19 volts. That's a nice radio, hate to see what would happen if a mistake was made by keying up with no antenna connected. What has some potential to be interesting for a base amp would be those ldmos finals that run at 50 volts. Something class AB in 10 and 11m would be neat.

 

[Shockwave]

I think the biggest thing to consider is the MOSFET transistors used in amateur and Commercial radio equipment, are not at all related to the garbage seen in CB equipment. Other than things like the 1500 watt LDMOSFET amplifiers, you literally can't find a single linear rated RF transistor being used in any CB equipment today. The difference between a linear rated RF transistor, and a fast switch mode transistor, are astonishing. There are huge differences in power capabilities and reliability.

While I might consider using a small amplifier with these cheap transistors, I would never consider purchasing an expensive radio, that had these in its final output stage. It just doesn't make sense to spend that type of money, on this type of unreliability. Buy the radio without the cheap amplifier they are making a lot of profit on.

 

[Enterprise312ok]

Nothing old school ran reliably at 19 volts. That's a nice radio, hate to see what would happen if a mistake was made by keying up with no antenna connected. What has some potential to be interesting for a base amp would be those ldmos finals that run at 50 volts. Something class AB in 10 and 11m would be neat.

Perhaps we should disable the swr protection and do a few tests. I often forget to switch my bench radio back to antenna that is where I run my Washington.

 

[Shockwave]

Nothing old school ran reliably at 19 volts. That's a nice radio, hate to see what would happen if a mistake was made by keying up with no antenna connected. What has some potential to be interesting for a base amp would be those ldmos finals that run at 50 volts. Something class AB in 10 and 11m would be neat.

While you could certainly question the level of reliability, old school original Toshiba 2SC2879s could be run on 18 volts worth of battery, charging at 21 volts. The trick to keeping it reliable, was class C operation and a matter of keeping the drive and carrier level within safe limits. Which is noticeably lower than the level you would drive it at under normal voltages. Still able to achieve peak outputs 50% higher than what you could see at 12 volts. That part did a wonderful job at handling higher than its rated collector voltages, as compared to higher than its rated collector current.

You cannot exceed the total current that the amplifier operated at safely, on 12 volts. You can make a 50% increase in voltage and output power, by reducing the drive level so that the amplifier doesn't draw any more current at the increased voltage. Failing to reduce the drive level would result in the amplifier trying to produce 100% more output power, and quickly fail.

At up to 21 volts of charge, the amplifier only runs reliable under precisely controlled operating conditions. It is not tolerant to operator error such as overdrive and high SWR. Yet, it can last for years if you don't screw up or, nearly indefinitely if you place some type of current limiting protection on your output transistors.

Then you have to ask yourself if a 1.5 db increase, is really worth having to operate within carefully controlled limitations or, install elaborate over current protection?

 

[Shockwave]

I should mention that overcurrent protection is a very effective safety tool on the output devices used in any power amplifier. It also has the ability to detect the most commonly destructive SWR faults, that shift the load impedance below 50 ohms and force the final stage to draw more current. Decent SWR protection through current limiting, goes right out the window as soon as you operate the finals at or close to their breakdown voltage. That's because any increase in load impedance also creates a proportional increase in RF voltage which goes all the way back to the anode, collector, or source of the active component. That will take it right over its breakdown voltage, when you're already operating close to it.

 

[Switch Kit]

I think ohm's law still applies to mosfets. I saw recently that the 13n10 has been discontinued and they are now very tough to find. Switch Kit the 2030 mosfet's that Magnum radio's used are also gone as well as the 7530 mosfet in the RFX-75's. It's like Toshiba finals all over again.

We can then look at newer mosfets like the RT1 that Ranger is using. Can't find the thread now but it's not even a transmitting final. They are used as switching transistors in power supply's. RCI buys them in bulk and has RT1 stamped on them.

Welcome back Switch Kit, good to see you posting again. The way I look at it is we are pretty much stuck with mosfets for better or worse. Mostly for the worse. I am not at all interested in an amplifier with 16 mosfets that does 400-450 watts. There are plenty of posts here where RCI N2 and N4 radio's keep toasting their finals. Mosfet's don't seem to like a higher SWR or a mistuned bias setting.

Anyway take care

Just getting older (by His graces) and rolling with the changes the best I can . Thank you gentleman for your input . Reminds me of Microsoft in a way , they stop making security updates for older models so your hands are tied to buy there new software . Discontinue this and discontinue that and match it up with something else and show us the money . (RCI N2 and N4 radio's keep toasting their finals.) been hearing that one for years ! I remember about 18 years ago testing out a 800 watt mobile MOSFET box for the builder , he told me it wouldn't be a problem if I blew it up because it was just a test run anyway, It seemed to work great the times I was in and out of my car , went up on a perch I hung out on and was really doing some modulating with that thing , I started to cost down the hill I was talking on and that thing blew up like a smoke bomb ! I couldn't see or breathe and had to pull over and get out , open both doors and let the smoke out ! talk about toxic ! My car stunk like those things for a month ! and here it is 18 years later and I'm still trying to shake hands with those damned things ! (my guess would have been when I was costing down that hill it wasn't getting the amperage and voltage the box needed) Wish I would have had a camera that day , but I doubt I ever forget it . Thanks again