got a small toroidal power transformer for a decent price and figured I'd use up some stuff I've got lying around (fender reverb transformer, 25l6 power tubes) for a little single-ended build. just looking for confirmation that this voltage doubler (I've got some 4700uf 25v radial electro caps that I'll likely use) for the 12.6v heater string
my other question is just a general one for the preamp: should i go full old style and use a single 12au6 or go more modern and use a 12ax7 with gain->tone stack->gain->power stage?
guess I'll be needing a big cement resistor to drop b+ and the 25l6 is wanting to see 200v on the plates (assuming 300v unloading b+ with a bridge rectifier)
anyway any thoughts or input is appreciated
PRR wrote:
Plotting loadlines is only for the truly desperate, or terminally bored.
thetragichero wrote: ↑Sat Jan 09, 2021 9:10 pmjust looking for confirmation that this voltage doubler (I've got some 4700uf 25v radial electro caps that I'll likely use) for the 12.6v heater string.
The doubler circuit is ok, but with 12.6VAC input it will produce about 33V DC, which is too much for your 25L6. The filament requires 300 mA at rated voltage, so you will need to add a series resistor to drop 8V at 300mA, which is 27Ω, and it will need to dissipate 8*0.3 = 2.4W (so use a 5W). 4x 4700u caps should be adequate. Note that if the 12.6VAC winding has only 0.8A, that is not going to be enough.
