Rca SE 6BQ5 output transformer.

E

Edward STL

New Member
Rca SE 6BQ5 red plating new tubes but not old ones. (Renamed)

I have an RCA RS-199a power amp in a console I'm restoring. I've recapped the power amp and preamp/tuner. I Am still having very weak output from the right side of the amp, left side sounds great. I have traded speaker wires, and preamp 6FQ7 tubes, and the problem stays with the right output. No problem with the output tubes either. This leads me to believe that it's an issue with the output transformer. I can buy one, but I don't want to just throw money at this amp. Am I on the right track?

All help is appreciated!
 
Last edited:
Worst case, swap your output transformers. If that moves the problem, you'll know. Might also be worth doing a simple ohm check of the transformer windings to see if they are significantly different side to side.
 
gadget73 said:
Worst case, swap your output transformers. If that moves the problem, you'll know. Might also be worth doing a simple ohm check of the transformer windings to see if they are significantly different side to side.
Click to expand...
Thats the way to go-chances you will find the OT good. They usually work or don't.
 
Ok, one of the resistors that's 47 ohm 10% is reading over 60 on the cheap-o-meter. I know it's out of spec, but is that enough to fade the sound to almost nothing? It's in the right side audio output path, and the left side resistor (where it sound good) is at 49. Every other resistor in the power amp is within spec, all the caps are new and were exact or slightly higher, and again, the left side sounds great. When I balance it all the way to the right, I barely hear anything. With the balance in the center, I get a little bit more but not much more out of the right. Should I be looking in the preamp? Maybe a dead pot? ( it has dual volume pots on one stem... Any direction would be appreciated.
 
I'd still do what Gadget said and ohm out the OT. Pull the power tubes and you won't even need to desolder anything. What your e hearing could be crosstalk, all from one channel.

I wouldn't think the 47 ohm resistor that reads 60 would cause these symptoms.

another thing you can swap is to take the input from the grid of the good side and put it into the grid of the bad side. That will rule the preamp and driver in or out.
 
Ok, I flipped the OPT's and the problem is still in the right channel. ( switched the line from the output tube and the speaker jack being fed, basically connected them to the opposite side of the amp).... This means it's a preamp problem right? Any ideas on where to start there?
 
Edward -- Swap the signals coming from the tuner/preamp to the power amp chassis. With them swapped, if the problem now moves to the other channel, then the problem is in the tuner/preamp unit. If the problem remains in the same channel, then the problem remains in the power amp unit.

Let us know!

Dave
 
I'll get some alligator clips and try to reverse the input from the preamp... its got those dumb RCA 3 prong inline plugs which I'll have to go around. I'll update you this evening on the progress. Is there a way to directly post pictures, or do I need to have them on a hosting site?
 
Ok, when I reversed the channels coming from the preamp, the reaction to the balance control was reversed, but the right side was still a dead output, other than some faint sound when I had it balanced almost but not quite to the right side. I switched the output transformers, traded the output tubes, replaced the 6cg7 which feeds the output tubes... replaced all caps and checked resistors for spec...what's missing? both sets of speakers sound great when hooked up to the good channel...turning into a head scratcher.
 
So the problem is in the power amplifier unit, since the same channel speaker is not working even with the signals swapped to the power amplifier. Either a new component has been incorrectly installed in that unit, or is bad. That's about all that's left.....

Dave
 
The only thing is that it had this issue before I did anything to it. This is the original complaint.... Guess I'll pick up a SAMS and trace the whole thing through till I find it. I'll let you know when its resolved.
 
Ah! I guess that's what the "still" means in your first post. If anything, it shows that the cure-all of recapping a unit isn't the cure-all it's thought to be!

Your best bet then at this point is good old signal tracing. Use another amplifier that has a level control and an input coupling cap to probe around in the amplifier between both channels, and seeing where it quits in the bad channel, versus that of the good one. You'll find the problem that way real quick.

Dave
 
Dave,

I'm sure this happens to all of us at some point, but when I checked all resistors to spec, I must have missed one, because there is a resistor dead that's feeding the plate on the right channel side of the 6fq7. The left side plate on pin 6 is getting the 110v or so, and the left side is negligible.... So I'll pick up the resistor tomorrow and hopefully report back with good news. I wish I had found this in the first resistor check a couple night ago, but live and learn I suppose. Update to follow!
 
Fixed! The right channel is still very slightly weaker than the left, but it could be the 1961 dated 6bq5's that no doubt have quite a few hours on them...
 
Cool, glad you found it. If nothing else, you now know everything is as right as it can be.
 
You must log in or register to reply here.

Similar threads

Speaker Fan
RCA 6BQ5 SE console amp... need help
Replies
7
Views
4K
Speaker Fan
Speaker Fan
D
new 6bq5 SE amp Build
2 3
Replies
52
Views
4K
Don P
D
doctor fuse
Help identifying this 6BQ5 SE tube amp
Replies
11
Views
595
NikiNick
NikiNick
ToxicTele
Lack of volume/power
Replies
6
Views
493
ToxicTele
ToxicTele
dspear99ca
RCA 6BQ5 PS voltages too high
Replies
13
Views
848
dspear99ca
dspear99ca
Back
Top Bottom