Rca rs188

[Eli Duttman]

If you're going to add global feedback (that includes the output transformer secondary) you will want to use the specific output transformer specified in the schematic. It has to do with tuning the amp for best performance, which is output transformer specific.

Otherwise, if you don't want global feedback (many SE fans do not) then you might start your learning journey by looking at the RH topology. (Google "RH84 tube amplifier".) This topology uses plate to plate feedback (output stage to driver stage). Or if you have an output transformer with a UL tap, you could try an approach where feedback is taken from the UL tap to the plate of the driver. If this is your first build, I might suggest the RH topology to get you going.

However, I prefer a little global feedback even in SE amps, but that's just me. Also see my PM to you for some additional thoughts.

Total no NFB requires triode mode, but only 2 W. are available from a SE triode wired 6BQ5. Also, better quality (read $) O/P magnetics are in order.

Loop NFB of some kind is essential when full pentode and UL modes are employed, lest an inadequate damping factor be present. I too prefer GNFB, as low cost O/P "iron" gets linearized. However, the short loop found in RH84 does avoid the core saturation/headroom issue.

 

[redride27]

Little update for my friends.

 

[redride27]

Wow!!! I'm still using the stock output transformers and this thing gives me goosebumps!!!!!