HELP. PLEASE!!!

[Sonar]

Does anyone know if there's another audio tube besides the 12at7 (driver) and the two 6bq5's audio tubes in a sonar FS 2340?
I replaced the driver with one I purchased from an eBay seller. The audio quickly drop down from 12 Watts pep to 4 after about 5 minutes of use. I then removed a 12at7 from a parts radio. And the same issue.
I then replaced both 6BQ5's with two NOS RCA's I also purchased from eBay. After a few minutes the same issue occurred.
I then thought it could possibly be my wm1 meter having an issue when it warmed up. So I changed the meter to my backup wm1. And the same issue continues. I have the radio sitting here opened and was hoping someone knows if there is another tube that is associated with the audio section in this radio.
I should have one of each tube in the 2340. But unless I know which other two besides the ones I mentioned are associated with the audio I will unfortunately have to send the radio out. Thank you very much.

 

[midnight special]

have you adjusted r105?

 

[BJ radionut]

Since you don't have a tester...it's tough...
I would also look at V10 & V11...those are the RF and Power amp tubes

 

[scout943]

Check here for tubes and substitutes http://www.kenselectronics.com/

 

[Shadetree Mechanic]

Looking at the schematic from CB Tricks, it looks like the tubes you replaced are in the audio section. I think the 6BQ5 tube in spot V11 is the final output tube for RF. Someone correct me if I am wrong.

 

[Shadetree Mechanic]

Since you don't have a tester...it's tough...
I would also look at V10 & V11...those are the RF and Power amp tubes

It says in the manual that if V11 is replaced that it might need to be neutralized. How would a person know if this is needed?

 

[Shadetree Mechanic]

V11 is at the back of the radio kind of between the antenna connector and the transformer. In that general area.

 

[unit_399]

Sonar -
Does the deadkey remain the same when the audio pep drops, or does the DK drop off too??
- 399

 

[Sonar]

Sonar -
Does the deadkey remain the same when the audio pep drops, or does the DK drop off too??
- 399

Yes. There's no problem with the Dead key.
When the rig is first turned on and cold I get the 11/2 watts DK and 12 pep.
After about 10 minutes the pep drops. It's a slow continuous drop over the 10 minute. After approximately 10 minutes there's a final reading of 1 1/2 Watts dead key and 4 Watts pep. The DK stays at 11/2 and doesn't change. Even after the rigs been on for hours. Thanks for replying. Any information helping me to figure out what the issue might be would be greatly appreciated.

 

[Sonar]

It says in the manual that if V11 is replaced that it might need to be neutralized. How would a person know if this is needed?

That third 6bq5 at the rear of the radio is indeed the final. When the final goes (soft) it will affect the DK,. That has happened once to one of the several FS 2340's I've owned. I had it replaced, and neutralized. Keep that in mind for your 2340. If you ever need to replace the final 99% of the time it will need to be neutralized. If not 100%. There's no issues with the rigs dk. It starts out at 11/2 watts cold and doesn't drop even after the rigs been on for hours. I'm beginning to believe the drop in modulation might be the audio Transformer. I'm beginning to believe the rig will have to be sent out. Anything beyond replacing one or all three audio tubes (which was already done) will have to be done by my tecnitechn. I'm already looking for a box. I've already got the bubble wrap and styrofoam ready. I want my backup 2340 back!!! LOL! I jest. I'll send it out sometime next week unless I get some information through the replies giving me another idea of the possible issue causing the audio drop. Even then the chances of me being able to do the repair myself are very low. Having an idea would be nice even if I can't do the repair myself. Thanks for replying.

 

[Sonar]

It says in the manual that if V11 is replaced that it might need to be neutralized. How would a person know if this is needed?

What usually happens is the same as when a transistorized final goes bad. Your dead key output will drop some if not in totality. If that happens you know it's time to replace that 6bq5 final.

 

[Sonar]

Looking at the schematic from CB Tricks, it looks like the tubes you replaced are in the audio section. I think the 6BQ5 tube in spot V11 is the final output tube for RF. Someone correct me if I am wrong.

You're 100% correct. The 6bq5 in the V11 spot is the rigs final.

 

[unit_399]

OK. Two more questions: 1.) Do you have the speech clipper board in the circuit, or has it been bypassed?? 2.) When you first turn the rig on and have the receive volume set at a certain level, does the receive volume decrease over time, or does it remain the same??

- 399

 

[Shadetree Mechanic]

The tube V10 is 6AU6A and appears to be the driver for V11. Maybe this could be the cause?

 

[Sonar]

Since you don't have a tester...it's tough...
I would also look at V10 & V11...those are the RF and Power amp tubes

The DK doesn't drop. It's 11/2 and doesn't drop even after hours of the rig being on. It's just the modulation that's dropping. This drop in Modulation is very quick
(10 minutes after turning the rig on.) Do you have knowledge that it's possible for the 6bq5 final to affect the audio without affecting the DK (output?) Thanks