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moleculo · #11 03-30-2009, 11:28 PM

OK, I had to go over the schematic, and the ones on CBTricks are hard to read. I'm not that good at understanding what everything in a circuit does, but here's my take:

Steps 7,9 go together. They change the circuit values around the Audio power amp and the AMC (modulation control) transistor. Basically it's widening up the audio response and allowing the radio to modulate a little more free.

Step 8 : Not sure I understand it, but it looks like it's the first resistor on the collector of the final transistor just past the low pass filter. Adding more resistance to ground at this stage seems to me like it would allow more current to flow through the final to the load (antenna). This part of the mod is eliminated with the MOSFet mod.

Step 3: Not sure...it's supplying more capacitance to the audio IC, but since I don't have a pinout handy of that IC, I can't be certain what part of the IC it's affecting. I'm guessing it's just providing a little more sustained drive to the driver and final.

Maybe someone who understands the circuits better than me will come along and help me out.

You can't change the driver to the mosfet if you're going to do this mod. You need to do one transistor design or the other but not combine them.
However, it looks to me like you could do steps 3,5,7,9 with the mosfet mod. Regarding the output coil: It doesn't really matter which side you remove it from; you'll have plenty of adjustment range once you have the correct number of turns. You should be able to do this with the mosfet mod also and fine tune the output a bit better than just discarding the slug.

If you do this, let us know how it turns out. I've been thinking about trying this out myself but just haven't gotten around to it yet.

Rob KI6USW · #12 03-31-2009, 01:08 AM

Although the mod sheet provided points out the use of the 1K ohm resistor with D11, it doesn't say if the resistor goes to the right of the diode banding. That is, looking from the front of the radio twards the back. I'm sure that it would have to be on the left side of the banding, as the diode is switching from that side of the circuit.

If I'm wrong, please correct me before I start with that mod. My plan is to do one mod at a time. I'm going to do the MOSFET final mod first, then the TX/RX audio enhancement with the .2 monolythic/33K ohm, then the 3300mf cap/variable pot removal/1K ohm resistor replacement.
But-
Isn't it redundant to put a 1K ohm resistor in place of the variable pot AND the 1K resistor in series with D11 diode?
I thought the variable pot WAS feeding D11 - or is that wrong?

Q: Why wouldn't the addition of the 2SC2314 work? Doesn't the MOSFET final get fed from the stock bipolar driver as well?
So, if the MOSFET gets a bigger boost from a better driver; wouldn't that potentially drive the MOSFET final harder?
Or - would it be too much? Especially since I am using a IRF520N as Exit 13 suggests? But I can use either the ERF2030 or the IRF520N; as I have both. And either MOSFET can be driven with the same EN1230 - rrrright? My point in saying this is purely speculative and needs correction - that is why I saying it here to be examined and considered.
What's right/wrong with these ideas?
Please comment!

BTW - Does anyone know when CB Tricks will be fully operational again? They still don't have everything available like they used to. That info provided from that site is indispensible and essential. It's too bad someone wrecked it for everybody else...

moleculo · #13 03-31-2009, 10:10 AM

Regarding the resistors around the VR and diode...I'll have to look at the schematic again tonight. I don't have it here at work with me and CBTricks is still down. Maybe someone else has it and can look at it. Remember, I didn't come up with this mod, I just documented it here.

I think the main issue with changing the driver also (this is speculation on my part) is driving the FET too much. There was a thread about runnign these Mosfets too hot from too much current causing them to pop here:
http://www.worldwidedx.com/tech-repair/26775-erf-2030-a.html

CBTricks has a warning about running them with too much current or overdriving them here: CBTricks MOSFET Experimenter's Information Notes

I'm not sure, but I would bet that changing that driver will push the FET too much. BTW, check out some more notes on increasing the carrier of the MOSFET mod here:

mosfets

Rob KI6USW · #14 04-01-2009, 03:33 PM

I put in the MOSFET final kit. It keys at 1/2 watt and swings waaay over to 5 watts. Is it because the driver is working, and the final isn't?

I checked my work before I turned it on; so I'm stuck now.
I'm using the EN1230 bias; is it the right one?
Maybe I should use the EF369, or change the driver.
I can't use a diode checker on the MOSFET final, because they need at least 3v to open up - right?
I gotta think about my next move first.
Any suggestions?

This 29 radio came with the 2SC2028/2SC2029 driver/final setup...

moleculo · #15 04-01-2009, 03:54 PM

Yeah, sounds like the FET isn't doing it's job. Use the link I gave you to that other thread and check everything out with a multimeter along the way.

Rob KI6USW · #16 04-01-2009, 05:02 PM

What I did to make it work, was put all of the parts back in. With the exception of the driver; I put in a 2SC1307 that I had.

Now, should I put in a different bias resistor at R56?
I know this final is capable of getting 5-25 swing. But with the current bias resistor in it - it is doing no more than the stock 4-8 watt swing. Just as anemic as the stock final.
Back to square one - or is it???

moleculo · #17 04-08-2009, 12:17 PM

Rob,

I just thought of something last night while I was working on one of these 29's.

On the tuning coil, did you take a turn off or just pull out the slug? If you removed a turn, don't forget that the coil wire has a coating on it. You have to scrape it off to re-solder it to the pad. If you didn't do that, then the tuning coil isn't working for you.

The other thing is those .2uf monolythic caps...make sure you got the right one, or put the stock ones back in for testing. I bought some .2's a while back, used a couple of 'em and it screwed up the modulation on one radio. When I looked at the values on the caps, I found that the package was mislabeled

Rob KI6USW · #18 04-08-2009, 12:53 PM

Quote:

Originally Posted by moleculo

Rob,

I just thought of something last night while I was working on one of these 29's.

On the tuning coil, did you take a turn off or just pull out the slug? If you removed a turn, don't forget that the coil wire has a coating on it. You have to scrape it off to re-solder it to the pad. If you didn't do that, then the tuning coil isn't working for you.

The other thing is those .2uf monolythic caps...make sure you got the right one, or put the stock ones back in for testing. I bought some .2's a while back, used a couple of 'em and it screwed up the modulation on one radio. When I looked at the values on the caps, I found that the package was mislabeled

When I looked into this early 29, it didn't have the 5-turn coil. So, no problem there.

I took the tuning slug out as per instruction, and it did worse. So, I put it back in and re-tuned it for peak output.

As far as the caps go - that is another issue. I didn't put them in. Are the .2 monolithic caps supposed to be as big as a match-head in size? The ones I would be taking out were much bigger, so I thought that didn't look right to me. I know we are talking about two different kind of cap construction; but it didn't make sense to me that the difference in size should be so great.

I'm going to have to find a 1969 and a 2314 transistor to do this right. I had some ERF2030's and some IRF520N's that arrived DOA in the mail. Seems that they cannot handle all of the static they get exposed to in the mail. Where is the best place to buy this stuff online? Anyone on this site sell these parts - I will buy some! I can get all kinds of caps, switches, resistors, etc, out here in Silicon Valley; but I haven't found a single place that sells RF finals and drivers. I need some 1969'a, some 2314's, and some 2091/2092's.

I'm also looking to replace the finals in a Uniden Honest Abe. Someone posted a mod her on another thread I started to find mods for that gem I found. I'd put the 2091/2092 diver/final in it as suggested; but where can I get them w/o having to buy more than I need? Same problem with the 29 too. Is there any mod - similar to the Cobra 29 C42 cap/resistor change to improve audio output on the Honest Abe? The mods for the Honest Abe are the same as the Cobra 29 XLR. I need a swing mod for it - too.

I need the parts to work on stuff - who has them for a REASONABLE price? If they have them and can sell me what I need - I will continue to do business with them!

moleculo · #19 04-08-2009, 01:02 PM

Yes the .2's are really small. I'll send you a PM about the transistors in a bit.

bob smith · #20 04-08-2009, 05:00 PM

I have a few 1969 finals I could part with for cheap. I know for a fact that one works and the other 2-3 should work as they are in radios that did work before I started pulling parts out of them and they turned into parts radios.

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Cobra 29 High Power mod with 2sc1969 transistor