Time to build another amp using as much as possible parts I have on hand. Transformers I have would lend themselves well to a Fender Harvard, which I also understand makes the basis for a very sweet harp amp. A few questions though, directed especially to anyone with experience with these amps (Goose?):
1. How much of the Harvard's character comes from the 6AT6/6AV6 preamp tube? Some have maintained that these are basically 1/2 of a 5751/12AX7, and since I have plenty of the latter but none of the 7 pin tubes or sockets, I may opt for this if there's no tonal reason not to do so. Also, having 2 input triodes would let me use grid leak biasing on one, with the other set up in the normal Harvard fashion.
2. The Harvard schematic shows no grid load resistor to ground on the input. I would think this would be a problem for mic elements that want to see a
high impedance, esp crystals. Anyone with any experience here?
3. Anyone with experience or thoughts on preamp plate voltages for a Harvard harp amp? Stock values are 160, 170 and 207V on the 1st and 2nd preamp stages and PI, respectively. Normally I'd go a bit lower, 100-125V on the first stage.
4. Coupling caps--I have lots of .1 on hand, which is my default value for a harp amp. Any reason not to use these to couple all stages?
5. The schematic shows a 25uf cathode bypass cap on the 1st preamp stage, none on the 2nd. I'm inclined to add a switchable 50-100uf bypass cap to the 2nd stage, to provide the option for more punch. Again, anyone with experience/thoughts here?
Any other comments from people with experience with this circuit will be appreciated.