Help!!! Again, SEX monos

[najo49]

Doc and Paul you have commented on this , perhaps Paul B might help on this latest post. I have about 20% drive ac out of the .47 coupling cap, as compared to the working amp. Each of the amps are wired as parafeed,  with a c4s , as suggested in the C4sing the sex amp, in the old valve issue.  I have checked the cap and the connections from the input half of the 6dn7 which goes of course to the output in parellel at  pins 1,2,3.  I have bent the connections in the tube sockets and checked if any of the 9 pins are shorted somehow.i have checked each wire connecting the tubes to see if any are shorting.. all voltages are the SAME ,as the working amp. including the output of the C4s which is right on at 250V Only difference is the attenuated AC voltage At the screen pin 1 in the amp that just whispers. please note the one amp works perfectly, and I have tried everything I can think of. Do you think I should replace the tube sockets? Or What?? Please take pity on me and help if you can. PS DOC these are NOT the amps i am giving you. Jan Olsen

[Paul Birkeland]

You can play a 60Hz signal from your smartphone into the amplifier, then measure what comes out of the first stage (measure the AC voltage on the side of the cap with no DC voltage).

If you provide the incoming AC voltage, and AC output voltages of each amps, we may have some ideas.

[Doc B.]

Check the resistance of the output transformer primary winding on the good amp, vs. the bad amp.

[najo49]

With .223 volts AC in and with a 1k test signal I got

Good amp 2.59 volts AC at the .47 cap ac side
Bad amp .052 volt AC at the .47 cap ac side
Will test the   opt when I get home. But please note I have tried several opts of the same unit. none changed anything.

[Doc B.]

So maybe the cap is bad. Try swapping them? Or at least try measuring the AC signal at the plate side of the parafeed caps.

[najo49]

Doc, I have already tried swapping the Caps. I get 250v DC on both amps at the plate side and no AC reading as you would expect. I am not gettin I think any voltage gain at the very first level. I get consistant readings  at the plate side of the parafeed cap or put another way. The readings are a consistant 10% of the working amp when measured aT ac side of the .47 cap and the parafeed cap AC side then on to the opt. untill I get the inital voltage gain at the plate of the first tube I will be dead in the water. I am thinking of replacing the tube socket in that tube. because I see no way there is no voltage gain from the input pin 4 to the plate at pin 5 where there is the intersection of the c4s and the wire over to pin 5. I have tried also swapping the plate chokes also.  the problem amp has all the same voltages at all the pins,as the working amp. What do you think. Jan

[Doc B.]

Then you just need to go through very methodically and figure out where the first point is that you find the reduced signal level compared to the other amp. Try checking the resistance at the grid resistor at the input tube and then at the output tube. If either has gone to a low value it would reduce the signal.