Steve Bench's LR Phono Stage - Cathode Bias Circuit Question

[Hearinspace]

Would anybody care to take a crack at why Steve put R10/R23 into this circuit? Steve himself went off the grid a couple of years ago and is no longer reachable for his comments. I heard from one person who built a version of it using the Sowter Transformers that it was to put the bias diode into a more linear operating range but if that's true , why not do it with the first stage as well?
Any thoughts on the design as it is or suggestions for variations or possible improvements etc. to explore would be much appreciated.

Thanks

[Sheldon]

Originally Posted by Hearinspace

Would anybody care to take a crack at why Steve put R10/R23 into this circuit? Steve himself went off the grid a couple of years ago and is no longer reachable for his comments. I heard from one person who built a version of it using the Sowter Transformers that it was to put the bias diode into a more linear operating range but if that's true , why not do it with the first stage as well?
Any thoughts on the design as it is or suggestions for variations or possible improvements etc. to explore would be much appreciated.

Thanks

That's an interesting one. The voltage figures for the respective cathodes don't add up. If it were done to bias up the diodes, then I don't know why it would skip the first diode in the string. Maybe to bias up the adjustment pot, or to lift the filament a little.

Sheldon

[Hearinspace]

No they don't add up. I've just been going through the curves for the diodes and the D3A and they don't really work out right. In Christian's schematic the pot is noted as being a 20Hz. adjust but with from 24mA up to 40mA going through the shared leg that pot is also needed for trimming the bias.
I'm going to build a simple version of it with AC heaters to start so no R10. We'll see how it works.

I don't know if you've seen his original article or not . Here's the link

[Hearinspace]

Steve Bench's original LR Phono Stage design uses the LL1623 as the output transformer which is followed by an LR filter stage with resistor R2 in parallel with the L (labeled transformer compensation resistor in Christian Rintalen's schematic - also linked in the top post this page). If building this with the 1660 instead of the 1623 how would the compensation resistor value be adjusted? Would it be the difference in source resistances (seen looking back from the secondaries) added to the resistor?