Cathodyne before VAS

[mashaffer]

Just curious as to why the cathodyne is always after the VAS. It seems it would have more headroom if it came first as it would not have to swing as much voltage.

 

[PRR]

Look at Williamson. Gain stage, cathodyne, another gain stage.

Cathodyne has 100% NFB. It rarely distorts before the tube which drives it. It can use a low-Mu tube of HIGH current, a better fit for the low resistors on power tube grids.

Cathodyne has no convenient place to inject NFB.

You can do it any which way. Gain-cathodyne is neat and sweet.

 

[Lingwendil]

You could o it that way if you want, but it's not needed in most cases. The split load is a fantastically linear topology, and is very capable when given plenty of voltage to flail around in.

As an example of my favorite method of swinging lots of volts, I usually do a 6SN7 volt amp, into a 6SN7 concertina, and feed the outputs into a 6SN7 LTP standing on a CCS with a negative rail, with a bit of cathode degeneration per triode. With a supply voltage upwards of 375-420 volts, it'll swing all the drive you could ever need, and if fiddled correctly, you can direct couple source followers between the LTP and a following power stage.

 

[stocktrader200]

with little NFB, separate gain stages may not be perfectly matched. using the concertina as the driver ensures the gain is balanced into both output tubes.

 

[6A3sUMMER]

concertina are matched gain, unless there is filament to cathode leakage. Keep the cathode to filament voltages in spec, otherwise the 'insulation' will degrade over time. And if that happens, the gain is not matched.