2SC2999 MOD ANALYSIS

[Handy Andy]

So in essence there are no easy answers?

Oh well. I just wanted to make a good thing a little better, if I could.

That's a tall order these days.

Well, the best way to answer the above is; - If it works - don't fix it...I mean that, just as it says.

Not trying to be cruel but a Cobra 2000 is like a 57' Chevy, nice to own, but a Bane to fix...

The better methods are to upgrade the older diodes to newer replacements - keep Germanium and as needed - use Schottky in the AGC negative - going part of the last IF output.

In the case of your Cobra 2000 - the section I'm suggesting you upgrade, to either newer Germaniums or Schottky - is D5, D6, D7, D8, D9 and D10 - all a part of the AGC, Meter Driver amp circuits. The PIN Diode section has D68 D14, D15 - these use a 1N4148 - so that can be Schottky as well.

I would only use 1N60 Germanium equivalents in the AM/ANL section. Like D21, D22 - and leave the ANL diode alone - if you decide to upgrade it, use one of the replaced Germaniums to see how a Schottky might sound in there.

TR14 is your conversion part - and you might need to add in some pF disc caps to this - the Base lead. It's a Common Base design. So if you have time to try a tweak, you might want to put in a simple vari-cap across using some old clipped leads from some resistors and make it stand up off the board - and try tuning the varicap as you tune for maximum signal - the original is 4pF per the schematic. I'm thinking due to the upgrade the cap may need to be replaced with a LARGER value in the pF range - say 10~22pF - although may seem small - this is an admittance issue for maximum transfer. There would be a small rise in gain - versus signal to noise - within the part itself with no signal applied - and it may be a narrow "blip".

Would love to talk more but XYL is home and is demanding Dinner for her and mom - so - not to be rude...
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[El Kabong]

Don't monkey around with a good thing, gotcha.

Do you know anyone who has done that diode extravaganza? Big improvement or small improvement?

 

[Handy Andy]

Small improvements - depends a lot on the SELECTIVITY and Band Pass - the more "traps" or Coils for narrowing the signal bandwidth and providing peaking - does help immensely. But it's a relative issue.

When you "swap diodes" you're just installing a new set of sneakers for the old car - does better driving and you get traction with less worry, but you still have the old car, it's performance and age of all those parts.

Not exactly stellar results, but diodes provide a performance in conduction - whether you use PN's like 1N4148's or 1N60s - the former has a voltage drop of 0.7V on average - but the latter gives you 0.3V or less on average voltage drop - one is a loss that is considerable in signal that you lose in the passing across the junction - the other suffers too but less signal is lost in the passage. The third, doesn't have a PN junction - just a N doped grain of sand, and a pellet of an alloy bonded/welded to it - it forms a junction but not a barrier type - so what happens is the N doesn't have to mix with a P-donor - instead it alloys with the pellet in a small region and the results give you a diode that acts like a diode - even provide reverse breakdown protection (steering ability) - and it's voltage drop is a lot like 1N60 types (Germanium).

Ok, sorry for all the above but it has to be said so you'd know what I mean by the noise figures and the performance changes to AGC and Noise abatement figures.

It can't remove the GOSH DARN duck running a homebrewed 100W Spread Spectrum linear - but what it can help in is how the receiver RESPONDS to the signals - RF gain becomes more selective, AGC "pushes down" receivers' RF amp gain - helping the band pass filters improve their response curve or "skirt" and the IF then can work with the Clarifier (Voice lock) to hone in on the signal you want to hear.

AGC can improve because the diodes' can rectify current with less drop across their junctions making them perform better than the original it replaced. Even noise floor can trigger the AGC reflex action and push down the noise - allowing the ANL to be more effective in removing noises.

Cannot help in PIN diode designs, they use a "cruddy high-loss" diode to provide a "window" that it doesn't remove so you can retrieve a signal out of a lot of other noise that would otherwise overload the receiver. Put a PIN diode swap in with the wrong bias drive (you have to change values in the circuit) driving the PIN section - might not work very well. It needs a tweak or two so it can work without driving too hard and damage the diodes or not enough attenuation action and damage the amp.

Going forward, the Transistor Swap only provides a sensitivity factor with a low-noise figure attached. Means it has a "knee" that has a sharp bend (it's RF - UHF band stuff) so it amplifies - quickly. Can provide that "Window" to capture or detect a signal - but also can saturate and distortion is your end result. You still have to provide an R1 and R2 factor to "preset" the operational window and still be in it's Safe Operating Area without going into oscillation. You also have to factor it an admittance issue - its' an RF transistor so it sees lead length as a highly inductive antenna - so you'll need to do some Reactive Conjugate work to make the transistor work in an otherwise hostile environment it's not designed for. It's why I mentioned the capacitor swaps - because the transistor is so broadbanded - it'll amplify anything - even stuff you or the original engineers never expected to find - like Birdies...self-resonant images and mixing byproducts.

As far as any quick suggestions, each radio will react differently - but most radios' will do better with diode upgrades and swaps - due to the performance and lower losses. They improve the radios own ability to receive - but they are not a cure-all because the radio is set to a standard for the day it was made - so some results are nothing more than a loss of time and a waste of money. I'd spend more on the effort of diodes swap than a transistor - because of the image issue I mentioned earlier - never expected it but then PC68's are very broadbanded and the tweaks after the install, to the AGC, Re-tuning of the RF amp and IF sections - as well as Cap value tweaks - was it worth it - yes, because I can say I've done it. But - Is it worth it - only if you plan on spending a lot of time in dollars to get back a couple of dimes for your efforts.

Sorry for the long explanation - but this is how I see these - they are challenges and formidable too - so you don't throw a lot into this unless you are willing to do side-by-side and really be willing to take on the effort.

 

[El Kabong]

Wow, thank you for all your information. I read every word. I even understood most of them.

I think I will leave well enough alone. Since positive results aren't necessarily reproducible the work would mostly be a teaching moment and not so much a radio upgrade.

The question that haunts all long time CBers bugs me too. Why if it's well known how to build a superior radio hasn't somebody done it and advertised it as such! I've seen better looking radios, smaller radios, larger radios, futuristic radios, industrial radios. Even radios with disco lights. But no radio made to work great, and sold that way. The radios with a reputation of quality I suspect are just flukes and not much better then their contemporaries. I mean 40 years of just-okay? Not a single engineer put his foot down to use better parts and a few more of them? Never understood that.
Maybe that's why CB died as a pop trend. It bored itself to death.


Thanks.

 

[StrangeBrew]

It's all about price point. The goal is to make money not radios, they know most buyers will look for "a good deal" so those are the buyers they try to accommodate.

Everyone says they would be willing to pay more for quality but when it's time to open the wallet that's rarely the case.

 

[Handy Andy]

Well, to give you an idea. You'd have to call up the "datasheets" on a part and look at the "test jig" they used to get the results and charts the did - testing that part.

Due to a previous issue with interpretations - I must issue this Disclaimer...

This Message Contains Graphic Images Of Exposed Circuits
Some Content May Be inappropriate For Some Readers With;
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Viewer Discretion Is Advised
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But has been tested to show it does not contain LEAD (Pb),
However, it can be distributed and viewed by devices that do contain this substance
that IN CALIFORNIA has been known to cause metal health issues...
In Michigan - we just smile give you a glass of water and wave a hand back to ya'

​

The engineers' say - this is what we use...

But what you see schematically from the radio maker - is something totally different.

Ok, let's take a look see....

Here's a 1674/1675 stuff - note; I'm only going to locate datasheets that have honest efforts, meaning, they are willing to post the circuit they used to publish these results.

You've seen this...


But, you work with this...


Ok not exact, and note the Cap value of C13 - which I think is an awesome demonstration of "improving selectivity at the cost of sensitivity". It is presumed that L3 peaking contains the 30pF vari-cap as a fixed value (about 22pF)

But what gets strange and comical at the same time...
The 2SC2999 shows us this...from SANYO


Nothing Comical here, but there is a LOT of inductance used and not quite sure if it's fair to use that circuit as the means to go against the 1674 - but remember this is what they designed/made - as a functional test jig, to produce the charts they did...

Here's the comical...PUN intended...

The circuit on the left, is from Stryker RF amp section - but the Circuit on the right looks more like the IF output of a Cobra 25 or Cobra 29? I'm not saying it's bad, just remember what engineers do, is not always what a radio manufacturer does...

Like this...(This as an article I posted on CBT about this - back in 2015-16)

The above was from a YT dealing with someone taking out the TOSHIBA 2714 and replacing it with a 2999...

Why?

Now, note - the 2SC2714 - the Toshiba test jig versus the STRYKER production run...



IN the example above the TOSHIBA test jig isn't an "overlay" - note the use of the Varactor diodes in the Stryker run, and the use of bypass as well as bias design - looks more like the 2999 one - scroll up an compare!

So someone's part selection, was not necessarily based on the test jig for the engineer, appears more like, if it can be dropped into another designed for some other part...

Which is why the 2999 versus everything else argument - shows up...

To me it raises more of the question...
If we use the STRYKER RF amp design - does the 1674, 299, 535 also work?

How well?

Or was it that the 2714 was "Discovered" to work; better or same or just because, at the time the runs were made- it was decided that the 2714 part provided similar acceptable performance at a lower cost than the 2999 part the radio was originally designed for?

Interesting day over here - Hi! How are you?
:+> Andy <+:

 

[Martian]

@Handy Andy
They would have used the 2714 over a 2999 because it's been EOL for a long time.
Availability has been questionable for over decade now and not via very many reputable sources or in large enough quantities.

We have to correct the newbies sometimes. They seem to ignore that "not recommended for new designs" plastered on the datasheets. They use it. We point at that. They walk away with egg on their face.

I think we have established in this thread that the screwdriver guys think that bigger numbers are better.
But they don't understand that these circuits are designed to work within tolerances.
Just like this "matched pair" fad going around.
These are HF radios. not medical devices or spare faring vehicles.

I have seen a video where someone painstakingly matched every single transistor in the receiver chain that they could replace with a 2999 in an 8719 chassis radio and claimed it was better.
No calculations done, no before/after testing. Just "my ear says its better"
it was "just better because all of the transistors are matched"

We have a name for these types of people in our industry.
Audiophools. the "golden ear"

It's alive and well in the CB community.

 

[El Kabong]

I would say The Community wants quality they are not getting and are willing to do silly things to get some.

 

[Martian]

I would say The Community wants quality they are not getting and are willing to do silly things to get some.

Okay, but that leads me to ask what quality does the community feel it's not getting?

What I have seen repeatedly is the community care about the numbers when it suits a narrative, like to make a sale. The 2999 swap is an example of looking at certain numbers to fit a narrative to make a part swap sale.
This isn't going to get more "quality" but it will make your coin purse lighter.

There is only so much that is economically feasible.
There is also only so much that people will pay for that "quality" as well.

Here is the dilemma.. let's assume there are no regulatory hurdles...

If you get "quality" the screwdrivers, most of which are dealers, won't sell it because they won't be able to add on screwdriver type mods like "tunes" and transistor swaps like this 2999 nonsense. That means the manufacturer won't sell many or fast enough to warrant production. The price will be out of reach for some, further depressing sales.

Now there is the balance or middle, which most all the manufacturers aim for with most of their product lines. Leave room for the screwdriver crowd to sell you "tunes" and parts swaps you don't need but they can do since they don't help but don't hurt, like the 2999 thing. Doesn't help but doesn't really hurt either.

Then you have the low end. The radios that cannot be screwdrivered since there are no controls. You can make a radio that requires virtually no adjustment because of the advances in electronics today. Part tolerances are really high and they are cheap.
These are the beginner radios. It was cheap, it works well, and if you want more you will buy the next tier up that can be screwdrivered to death.

But I still fail to see how the 2999 being done is for quality, if that's what you are saying.

 

[Handy Andy]

I'd just like to add this to an otherwise very productive discussion on "selling ideas"...

What I see from the various datasheets, are more like templates - they are a simple circuit that they can attach their equipment to and generate outputs - plotted by using inputs - plotted and we get these "Charts" of what that transistor does when it's treated this way.

We have X-Machine over here that measures its output across a bridge of known parameters...

We have Y-Machine - over here, that also measures it's output across a series of detectors set up along a line here using these known elements...

Ok, I could go on, but if you can think of this as a science lab and kids playing in it - respectful of the elders that put this test site bench together. Working together, can arrive at a series of numbers, graphs - plots from the data and give it back to the engineers that loaded the die, prefabed the chip wafers - designed the overlay masks and worked on the heating, chemistry, pressures and purity as well as which gasses were used in the making of the chips

These guys use a "template" on a bench of known values - to obtain the variables of the part that was exposed - tested - using these machines.

Well, that's pretty KEWL - now they have a part that can do what all the fussing of the masks, doping and baking did - and can do it consistently and get these results.

Only now, someone in a different part of the building or even across the street - has designed their bench with their versions of what a "Template" should be.

There may be a problem here, what was once considered "Standard" is now being questioned because the guy across the street is able to sell others on using their parts by showing their data - that the part they produce can suit their needs better than anyone else's can.

Questions like "How can we validate that claim?" - Do up the circuit - ok it does what it says it will do, but what about it's predecessors? Will the older parts work in this newer circuit template? Will we be ridiculed by our peers for even trying this? Seems people forget the very shoulders that they stand on was provided by the ones that led the way in developing the very means used to make that part perform.

Radio hasn't changed - we have, and so has the technology used to make the radio work - but the elementary principles' have not. They are still there - our understanding of them may have improved but we don't change the principle element that radio is, electromagnetic waves - it's just how we use them - has expanded.

So when the "If it works - Don't Fix it" adage comes into play, we should not have to question it. So why the "doubt"?

Because again, someone changed the playing field and the claims that theirs is better is making the rules right now, unless we could come up with something better - we keep confirming it thru "Urban Myth and Legends".

How about?

... more like someone got tired of all the noise and same old same all - and wanted to improve the level of performance and perhaps a level of enjoyment added in as a bonus. But did we improve the performance and make radio better? Or did we make a radio that just hears better so therefore it's better...because we said so....

Interestingly enough - again if the paying field was equal - everyone wins - or loses - depending on how you look at that glass half-filled with water.

Because we need something to apply ourselves to. What drove the change in the receiver performance - was it from lack of hearing? Unable to hear? Or just got tired of seeing same old stuff? Perhaps more of all three and then some others not even included here...

Look back at the YT graphic above - I said something back then and I still stand by it now. I wish more radios were made like this - because of that design - you can see it - you can review the details and know that when it's all put together correctly - is a functional unit with great possibilities.

But is it Needed, or just Wanted - comparisons are so hard to define...

That's why I posted the "comparisons" for that reason, a 2999 versus a 1674 - the test circuits aren't the same - neither are the results. So even with these two "strikes" against formulating a conversion process and being successful at it - there is still the nagging level of "What about...?" looming overhead circling the camp...

:+> Andy <+:

 

[El Kabong]

Ohkay, thanks all.

 

[Klondike Mike]

... I took a C1730L from a junked D858 chassis and replaced the C1674 in my President Madison (MB8719 chassis) with the C1730L. It actually made a noticeable improvement.

Thanks for sharing this information ExitThirteen. I ordered a few C1730L's from the seller below and will use them for MB8719 chassis upgrades in the future. I will also continue to use these "enhanced Schottky" diodes that I have listed on eBay as well. These are "real" and not sourced from any Chinese distributors/eBay.

https://www.ebay.com/itm/10PCS-2SC1730-L-C1730-L-100-Genuine-NEW-NEC-TO-92/171396620529?ssPageName=STRK:MEBIDX:IT&_trksid=p2057872.m2749.l2649

https://www.ebay.com/itm/142835493697

 

[OldTech03]

In reality, there is no real value in substituting the 2SC2999 for whatever transistor is being used in the first stage especially because its job essentially, is to amplify everything that hits the antenna and that is quite a bit. Yea there are some restrictions in the first stage but the real discriminating circuits come after that and really those are the stages that could use more gain/selectivity especially after the first IF stages. Just saying if you want real receiver performance do something there if there is a 455 stage as most radios have? do something there otherwise, all that is really happening in the first stage is the amplifying of everything that still has to be dealt with later. Now for the controversy, I'm going into hiding now.

 

[El Kabong]

Anyone have a good picture of where these parts are found in a 2000 GTL, in case I get bored one afternoon? My eyesight sucks. Thanks!

 

[StrangeBrew]

....
:+> Andy <+:

If I'm reading your posts right it seems as though how well a part works with the rest of the circuit is more important than any measure of "quality" of a particular part on its own, so all bets are off if you swap a part into a different design. Is this anywhere close to right?