S'men A2502 trouble, help please.

[ecluser]

do you think the 2N5415 or the 2N5416 is a suitable replacement?

Yes sir!

 

[goat67]

I take it the 2N5416 is the better of the two?

 

[ecluser]

In principle, but in your circuit the total supply voltage is ~140V, well below the limit of the 2N5415. You will not see the difference.

 

[Mazeppa]

ecluser,

Finally had opportunity to experiment w/different values at R4. Results were as you predicted. I progressed in +/- 4k ohm steps, DC offset steadily approached 0mv as R4 value was increased above the nominal 47K ohm value.

Initial DC offsets measured were:
A channel = 17.0mv
B channel = 22.2mv.
Both slightly higher than I measured before, I was using a different meter.
I stopped at an R4 value of 73.2K ohms (measured) which resulted in DC offsets of:
A channel = -1.0mv
B channel = 5.4mv

Mouser has metal film, 1/2watt resistors in 73.2K ohm, and 75K ohm. I'm thinking of getting both as the 75K ohm should center the span of difference closer around 0mv. Do these results seem consistent w/your assessment of this circuit?

Settled on 75K ohm, 2 watt, 1%, metal film resistor in R4 position.
Final DC offset measurements:
A channel = -1.6mv
B Channel = 4.6mv

Jacking up the R4 value worked like a charm getting the measurements closer to 0mv. 2+ hours of listening since then and the amp sounds very good.

Once again, my thanks to all that helped me on this project.

 

[goat67]

Enjoy the tunes, your project taught me some new things.