Cobra 29 High Power mod with 2sc1969 transistor

[Chris Millas]

I installed an authentic 2sc1969 final in my 29 and left the stock driver. It produces about 20-23 watts.and has been running this way for years. I personally prefer the 1969 over any other final for a 29. It works well and sounds good if the radio is tuned correctly.

 

[Mr.715]

Ok back to another question that was raised here earlier maybe 3 pages back has anyone tried the new 2030+ or the hg1969+ I'm here there is one of those out now as well from hg.

I've been playing with the new HG2312s inside of the 29 chassis. Leaving all other components in the radio with the expection of changing a couple caps. C71 and the 1000uF south nearest audio transformer to a 3300uF (16-25v) after a tune with clean waveform we see it produce 28-34s peak depending on the radio. Each will slightly vary. Of course if it's a newer 29 chassis we need to remember to remove a turn off the coil of L14.

But I hope to repost a thread shortly after some further experimentation is done. And we have a complete guide for installation.

 

[Chris Millas]

I've been playing with the new HG2312s inside of the 29 chassis. Leaving all other components in the radio with the expection of changing a couple caps. C71 and the 1000uF south nearest audio transformer to a 3300uF (16-25v) after a tune with clean waveform we see it produce 28-34s peak depending on the radio. Each will slightly vary. Of course if it's a newer 29 chassis we need to remember to remove a turn off the coil of L14.

But I hope to repost a thread shortly after some further experimentation is done. And we have a complete guide for installation.

Mr.715,
Have you had a chance to do further testing with the HG 2312's in regard to the cobra 29?

 

[MKwrench]

Mr.715,
Have you had a chance to do further testing with the HG 2312's in regard to the cobra 29?

I used one (HG2312) in a pinch to repair a side mic. 29 LTD a while back, then monkeyed around with some trial and error stuff. It seems to make easy power the way it is. A clean 23pep without tweaks. These are from my notes some add a little more oomph, or help keep things sharp and clean:
It liked a 1957 driver with a 1ohm for R58, 330p or more (total) at C62, and a 22p across R55, the 22ohm bias resistor is fine. I used a 47uf at C71 (any smaller causes a bounce that I didn't like) changing C73 higher widens the voice frequencies that "pump up" the limiter, it needs experimented with if its needed, otherwise its fine as is. I have a 2.2 in one (very wide banded) radio. Beefed up the power filter caps at the inlet and audio chip/Transformer (C42 can help hold up the whole Radio). Keep the limiter (don't do the D11 or potentiometer mods), leave R48 alone too, but instead swap R67 (33ohm) for a 10ohm. The C67 and C38 changes are gold, but can cause a "bassy" voice output that doesn't sound good on some receivers, removing C69 seemed to add some highs to balance it out, but something should be there to keep TR18s "clicks" out of the mic line. Using 2SC1845 for TR17 is another thing to experiment with, for clear audio.
Lots of this stuff applies to more than the "high power mod". I just thought it would be cool to share for those of us who like to tinker and experiment with our radios.
To me the 2312 seems broader and the 1969 seems peakier, (if that makes sense).

 

[Harley3315]

I used one (HG2312) in a pinch to repair a side mic. 29 LTD a while back, then monkeyed around with some trial and error stuff. It seems to make easy power the way it is. A clean 23pep without tweaks. These are from my notes some add a little more oomph, or help keep things sharp and clean:
It liked a 1957 driver with a 1ohm for R58, 330p or more (total) at C62, and a 22p across R55, the 22ohm bias resistor is fine. I used a 47uf at C71 (any smaller causes a bounce that I didn't like) changing C73 higher widens the voice frequencies that "pump up" the limiter, it needs experimented with if its needed, otherwise its fine as is. I have a 2.2 in one (very wide banded) radio. Beefed up the power filter caps at the inlet and audio chip/Transformer (C42 can help hold up the whole Radio). Keep the limiter (don't do the D11 or potentiometer mods), leave R48 alone too, but instead swap R67 (33ohm) for a 10ohm. The C67 and C38 changes are gold, but can cause a "bassy" voice output that doesn't sound good on some receivers, removing C69 seemed to add some highs to balance it out, but something should be there to keep TR18s "clicks" out of the mic line. Using 2SC1845 for TR17 is another thing to experiment with, for clear audio.
Lots of this stuff applies to more than the "high power mod". I just thought it would be cool to share for those of us who like to tinker and experiment with our radios.
To me the 2312 seems broader and the 1969 seems peakier, (if that makes sense).

 

[Harley3315]

Seems to me it saw earlier nomadd mentioned using 2166 as the driver which means we could likely use the 2078 we swapped out for the fet. Now that said we would also want to swap in a larger predriver I've alread done this in the past. Although 1973 is hard to find now. Some of this is likely how drail gets crazy watts out of his radios. Ive also seen a mod where a relay is installed fed by the d11 traces is I remember right to provide voltage to the gate only on key up.

 

[Squints]

I was asked by a few people how to do this mod, so I figured I'd just post it up.

Please don't copy and paste this mod to other sites/forums, but feel free to link to it.

Also applies to:
Uniden 78
Cobra 25 & Uniden 76 mod is similar, although you'll need to cross reference against the schematic.

1: change the final to a 2sc1969
2: change the driver to a 2sc2314.
3: change the electrolytic capacitor by the audio IC (C42, 1000uf) to a
3300uf, 16v.
4: Take a turn off the output tuning coil (see tuning coil note below)
5: Remove the AMC potentionmeter (VR4), and put a 1K resistor in it's place.
(only two connections are used on this pot, use those two connections
for the resistor)
6: add a 1K in series with D11.
7: Change R48 to a 33K ohm resistor.
8: Change R55 to a 10K 1 watt resistor.
9: change C37, and C68 to a .2 monolythic (this changes the A.F.
response on TX)
10: Now align the radio, start with the output coil, the the predriver
stage for peak output.
11: Tuning notes: Tune L17 for max with audio. Then, tune L23 for max output with audio, this will upset the radio's frequency. So, after L23 is set, adjust L24 to put the radio back on frequency.

Tuning coil note: If the radio says "made in China" on the back, you must remove 1 turn from the output tuning coil with the slug in it. If it doesn't then you may or may not have to. Count the turns, if it has 4, leave it alone, if it has 5, it's too many and won't tune, remove a turn. You may have to add a 68pf capacitor from the left terminal of the coil to ground, with the solder side of the board up. This method produces better results than just removing the tuning slug.

This mod will consistently produce output between 10-12 watts AVG and 45-50 watts peak. If I can find my video clips of Bird 43P power meter and spec analyzer I took after doing this mod, I'll follow up with those.

If all those steps are necessary just to switch from one bipolar to another similar but not identical bipolar transistors in final output that's a little more radio butchering than it does to accomindate a MOSFET conversion.
I'm gonna need to study more on this mod I can't decide how I feel about it at this moment

 

[Squints]

If all those steps are necessary just to switch from one bipolar to another similar but not identical bipolar transistors in final output that's a little more radio butchering than it does to accomindate a MOSFET conversion.
I'm gonna need to study more on this mod I can't decide how I feel about it at this moment

I had no issues from switching both driver and final to a 2sc1306 and a 2sc1307 and the 1307 has near identical specs as well, they worked fine in my cobra 29 without any additional butchering