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Connex CX-3400HP, practically new, questions

Hawkeye351

Well-Known Member
Jun 27, 2021
463
330
73
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Explain something to me everyone:

I've had a practically brand new connex cx3400hp on my desk the past few days. This radio was not hacked up at all. My bench is running 14.1v dc.

R238 is still intact and the value is just what the schematic says.

R249 still intact.

TR32 is still intact.

TR53 is still intact.

There was no diode/resistor on the reg.

No mods no where.

It came in because of low power. I replaced several things.

Passthrough Regulator (tip36c)
AF Regulator (2sa1012-y)
2 - 1000uf 25v
1 - 330uf (beside passthrough)
1 - 100uf (C190)
both bias caps (1uf and 2.2uf)
All 3 mosfets (vishay brand)
Driver bias vr (100k)

Biased all mosfets to 3.80v
Realigned rf stage

Cannot get any more than 30w out of it, no matter what I do. I even tried removing R249, same watts. I even tried the diode/resistor on the collector of the passthrough, no change, same wattage. Tried a diode and resistor at the R238 location, same thing. I tinkered with the coils a little, no change.

How in the heck are you guys getting 50w out of these 3400hps?

Now, I'm using a peak reading meter, not a pep meter and 30w peak (X) 1.414 = 42.43w pep. But I hear people saying their dosey or pdc (which are peak reading meters also) is showing these radios doing around 50w peak on their meters, how?
 

Luck of the draw.

As for that 1.414 thing, it doesn't apply to PEP, only to peak amplitude of a sine wave. Your voice audio is not a sine wave, so this rule doesn't apply.

A 'scope makes PEP easier to explain. You make a mark on the screen at the highest point your voice peaks reach. This is your peak amplitude. Not power, amplitude.

Now connect a radio to the same dummy load that can deliver a carrier big enough to reach the same mark on the 'scope screen. Now you have a carrier with the same amplitude as the voice peaks from the first radio.

Read this carrier wattage from an inline wattmeter. This is your peak envelope power.

PEP is the wattage an average-reading meter would show with a carrier that has equal amplitude to your voice peaks.

If you are using a Dosy or similar "passive" peak meter, click up to the 200 Watt range. You'll usually find that the peak readings are stingier on the lowest power scale.

Might be your whole problem.

73
 
Thank you for responding nomad. I know this seems like a dumb thread.

No sir, I don't use a dosy or pdc meter. I use an mfj 873 and mfj 868. I was just testing to see if I could see those watts I hear others saying they're getting out of these radios, wasn't gonna leave it like that, just messing around.

I tried all the typical mods,
Diode/resistor at r238
Diode/resistor on regulator
Clipping r249
Removing tr32 and tr53
Etc...

Never did see any increase in peak swing watts, but rms swing watts increased.

I put everything back like I had it, realigned it and put the covers on it.

I called the customer and told him I tried everything I could to get him more swing, but he said he's not worried about all that swing. He said that's not why he sent me his radio, he said he wants clean watts and a radio that will last and he heard I was the one to go to. So, his radio is done.

I'm not testing this mess anymore, I'm just gonna stick with what I do best, spectrally clean power from a cool running performer. I was just trying to give my people more than usual.
 
Ok, this is all I did as far as mods go:

1. R174, R187 (both 10k) changed to 2.2k on each.
2. R165 (270k) changed to 330k.
3. C133 tied with a 22k resistor.
4. Replaced C195 with 1000uf 25v.
5. Replaced C190 with 100uf 25v.
6. Replaced C194 with 1000uf 25v.
7. Replaced VR11 with 100k
8. Replaced passthrough reg (2SB817)
9. Replaced AF regulator (2SA1012)
10. Replaced all 3 mosfets (vishay).
11. Rebiased for gate voltage of 3.80v on each mosfet.
12. Adjusted current draw for each mosfet.
13. Realigned RF stage.

Runs very cool. Whispers every syllable up to 30w easily. Whispers 2w average.

Does anyone see anything I should reconsider or does everything seem about right to y'all? Does anything I done seem as though it may conflict?
 
Just curiosity, what board is in that radio? I remember that being so with some of the early ranger 696 pcb with dual mosfets. I once owned a ranger freedom with dual mosfets and after tune would only do about 30 pep maybe a smidge over and was a common complaint with those radios. Almost behaved like a 959 with dual final mod because that's about all you could get out of them in my attempts.

If it is that pcb, it's as if there's something in that final section not letting it do higher. Capacitance on the final stage it seems but I'm no tech, just trying to achieve the radio practitioner status.
 
The board in this 3400hp is the EPT360015C.

I was just attempting to get more out of this one for a friend, but 30ish watts is all its gonna do.

Mosfets, regulators, etc...run very cool. Power is very stable (no creeping up or down). Extremely sensitive to whispers, peaks on every syllable and holds at the peak with every word. Very clean signal on analyzer.

It's all she's capable of I guess, lol... I threw every swing mod I could find at this one, no more than 30ish watts peak is all I could get out of her.

I just hope the brand of TIP36C and mosfets I'm using are good quality.

For the mosfets, I use vishay brand.
For the passthrough, I use ST Micro brand.
For electrolytic caps, I use nichicon.

Are those brands decent or should I consider a different brand?
 
Are those brands decent
Yeah, all of them are. I'm baffled. You have covered all the ground I can think to suggest. The only thing that comes to mind is heat. If any final or driver circuit components, especially a capacitor is getting hot, that would be a lucky find pointing to a component swap. Might make a difference, maybe not. But checking for a passive part that gets too hot is the one thing I don't remember seeing in the story so far.
73
 
I also thought of a heat issue preventing power from getting out. Nothing, nowhere in this one runs hot at all. I couldn't get the power out of it but I sure did get the audio sensitivity, lol...

Already put the covers back on this one, delivering it to the owner this weekend.

On my desk now is an oldie, but goodie, a uniden Washington in pristine condition. Just needing a complete realignment. Almost done with this one too. Next is a 2950 input dc circuit repair.

Still got a couple 2980s, few Saturn's, few cobra 2000s, about 6 galaxy type mobiles to get done, then I may be caught up.
 
By the way,
Just wanted to end this post with another thank you to nomad and Andy for chiming in to help. You 2 guys/gals? have been of great help to me, and to my locals around here who are happy with the end result of certain radios they were told weren't worth fixing or couldn't be fixed. I couldn't have helped them if you two hadn't helped me.

I recommend anyone needing help with this stuff to look you two up. Very knowledgeable, patient and kind.

And no, I'm not making money off the info given. I've been told by everyone that I should charge, and when I do charge then they say I don't have faith in my work and I should charge more. But, I always tell them I'm not in it for money, I'm only wanting to help since y'alls decades old local tech passed away.

Thank you again. Have a safe blessed day.
 

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