The Defpom Forum, for RadioMods, S&M Software and Music by The Defpom

Here's one for the old timers. I have an old sbe console 2 , 23 channel am ssb radio, it was given to me to have a look at,problem is that the tx audio is very low even with a Turner + 3 mic turned up all the way, it sounds like a hand mic, when using a hand mic there is almost no tx audio.I have managed to find a service manual for it and checked out the mic amp circuit and it seems to be ok.Does anyone have any hints as to what could be happening?
The output power is fine but audio is so low, tried adjusting the amc and alc but still no good?
Tnx Bob

Check electrolytic caps as it?s a old radio and SBE are known for there bad caps and cold solder joints.

Tnx Rick, I will take a look at the caps and the joints.Could it be something to do with the push pull audio amp, it is using 2 , 2sc1061's , I know this an old radio but the guy that owns it doesn't have the $ to get another one so I am just trying to help him out.It does have some old mylar caps that are cracked and split and was wondering could I replace them with some other type of caps? I have replaced some of the crystals that were bad and I notice that there is a wire that was cut from somewhere that comes from the transformer and shows a lot of ac voltage (about 200 volts)?? whats up with that??.It rx's fine but the agc seems to be a bit wonkie. Output power is about 10 watts on am but ssb seems to be down quite abit.With the turner + 3 the tx audio is like what you would get with a hand mic? Oh well I will start re doing the joints to nite and see where that get me.Tnx for the info Rick and I always respect your info , you are the man.
Bob

It has been a very long time since I last work on one, about 25 to 30 years ago.

I have had a look for the schematic diagram but with no luck, but I did find some notes I made, which refers to low TX audio in SSB, fault found to be D37 short, Q29 low gain, R508 o/c and C505 leaking, C508 o/c. Maybe you have the same fault

In any case the fault you have is most like to be in the mic amp stage, from memory, the stage is in the top left hand corner of the PCB the transistors are Q28, 29 and 30. The capacitors and resistors you need to check all start with the number 5 like R501 and C501 and so on.

The push pull amp is only used in the RX mode.
As for replacing Mylar capacitors, they must be Mylar or Polystyrene type.

Tnx for the info Rick,I just got home from work and I spent an hour checking things, I also made a few adjustments and now have the audio up quite a bit on am and ssb with the turner + 3 .I am done playing with the old thing and am now going to try a few things with my old 139xlr.As always Rick I thank you for your knowledge and input .P.S. I also did the mod on the new 158 edx for 24 to 29 while the Mrs was in town and it seems to work just fine so its back in the box till Christmas
Bob