replace 6N1P with 7308

[dsavitsk]

I built a pair of Welborne DRD 300B amps. They use 6N1P's for the driver tubes, and I am wondering whether it is a) safe, and b) a good idea to put 6DJ8/6922/7308's in instead. I have a pair of Amperex PQ 7308's that I have no other use for (no, I won't give them to you -- I am sure I can find something to do with them,) and it seems a shame to leave them in a drawer.

As I understand it, the tubes are pin compatable, the 7308 will draw less heater current, but I am unsure how different the operating points are?

[gorgon53]

bifilar winding of the transformer is a keyfactor in reducing distortion of other than class A biased PP operation. If we choose PP we should go parallel-PP (circlotron, McIntosh) because only then we can go bifilar with lower winding capacitance and hf-copper losses. One of the mainprobs with transformer windig are the core dimensions. They are optimized basically for 50/60Hz use and low production costs. What we need in audio is a WIDE and NARROW window, like we have in a toroid. Unfortunally, toroids without airgap arent what we need. If we introduce a distributed airgap it will increase copper losses and winding capacitance far more in the toroid than in a conventional EI cored transformer. So why not forget about PP transformers alltogether and make a real big airgapped EE-core and go single ended?
What would we loose? Power? Efficience? Sure... BW? Not so sure...if we get the right core...
What would we gain? I imagine small signal linearity....
might be worth it....

[gorgon53]

oops...
went into the wrong place...
should have been a new thread....
sorry