Workingman 15 thermal discrepancy

[x-pro]

Any ideas on which component(s) to potentially look at or tweak to get the DC offset less negative?

The zero balance at the output is determined by the input differential stage. Its transistors must be a matched pair. If this is not possible, additional balancing elements (labeled г1, #24), must be used.
You can play around with resistors R30, R30-A, R30-B.
Check the previously mentioned capacitors for leakage (labeled Helmholtz,#12).

[Delta362]

Well finally got it resolved. Call me an idiot for some of it as I stated earlier that R30A and R30B were spot on. I don't recall which resistors I was measuring around that circuit, but had confirmed whichever they were, they matched the schematic and mistakenly reported it as R30A and R30B.

The amp was a '98 version. It did not have the R30A, R30B or R39A resistors (22R1 ohm 1/8W). It did, however, have the updated other resistors matching the LA circuit values (R39 270ohm 2W, R36 180 2W, R23 2k7). I lifted the E legs on Q6, Q7 and Q8 and installed a 22R1 1/4W between the pad and each transistor emitter leg. The Dude, I'm very sorry for the confusion and mistake on my part. Your help has always been appreciated.

I powered the unit back on and the DC offset was less than 40mV. Woohoo! With a 4 ohm load, I then applied an input signal large enough to just barely hit the preamp clip input, then backed off just a smidge. I turned up the master volume to 100% and saw the output signal was a clean sinewave up to full power.

Thank you very much to everyone who helped me with this. I'm very appreciative of your time and knowledge.

[The Dude]

No need to apologize, I'm just glad you got it fixed!

[g1]

That's interesting. The only SWR schems I can find with no resistors in those positions are also from pre-2000 (hand drawn).
Glad you got it figured out!

[Delta362]

I had searched for the pre-2000 version schematics, but couldn't find any. The closest schematic I could find (which showed the headphone jack and speaker switch) ended up being the attached. It has the added resistors, but incorrect values for R36 and R39 (should be 1W180 and 1W270 respectively).

It also has Q6/Q7 listed as KTA-1268 (ECB) vs the MPSA56 (EBC) on my version (which is what's silkscreened on my board) so if someone else attempts to replace those transistors, please watch the pinout vs what's on your board. You may need to trace the connections to ensure it's correct with whatever transistor you might be installing.

[Delta362]

That's interesting. The only SWR schems I can find with no resistors in those positions are also from pre-2000 (hand drawn).
Glad you got it figured out!

Can you post the hand drawn version that you saw?

[g1]

The ones I have are not for the Workingman, see attached

[Delta362]

The ones I have are not for the Workingman, see attached

Thanks! Definitely seems like it's a cross between several of the amps over time.

[Tom Phillips]

This is a very informative discussion. Thanks for following up with details of the solution and schematics of the various circuit versions.