mwhouston wrote:
This requires a look:
http://www.audionotekits.com/agrove_interstage.htmlI'll assume a 6SN7 could be used. Or could it?
Yes a look is in in order. I do agree with most of what Mr. Grove has to say concerning SE interstage coupling transformers. However his comments about PP interstage and high frequency response I do find a little dubious. After running the calculations I don't see the inter-wire capacitance limiting the upper frequency response anywhere in the audio range. And his comments about design history, especially "Circuit designers became lazier as the physicists and engineers designing the valves improved them...", are way off the mark. But we must remember that he has a product to sell so he needs to talk it up to some extent.
As to Mark's question about the 6SN7 as a driver, I wholly agree with his assessment. Following are the two driver load lines, first for the 6SH7 and then for the 6SN7.
Attachment:
6SH7 Load Line.jpg
Attachment:
6SN7 Load Line.jpg
These two load lines are first approximations assuming an interstage transformer with the input characteristics of a Hammond 124B transformer and the circuit values given by Mr. Grove in his circuit. From what I see here, I have to say that not only is it possible to use the 6SN7 here but it is a superior choice to the 6SH7. It should have both lower distortion and lower noise. If the Hammond 124B were used in place of the 1:1 transformer indicated then it should make for one quiet and sensitive amplifier.
Anyone out there want to give it a try? (I don't have any interstage transformers lying around.)