In our Drake T4XB, AM is produced by modulating the screen grid of the 12BY7 driver. This is an inconvenient position...
Instead of moving the modulator to the left (ring modulator) we now move it to the right (output tubes).
Modulating the output tubes should be better. Just give it a try.
http://www.ing.unitn.it/~fontana/HiFiAMT4XB.pdfhttp://www.ing.unitn.it/~fontana/TrueAMT4XB.pdfI use both and I receive excellent reports.
Giorgio