transformer question for a frankenstien vibrolux build

[mikepukmel]

Hey All.
With build #1 underway, finally, planning amp build #2.

Id like to build a vibrolux style chassis (no reverb) but with a solid state rectifier. The stock schematic from Fender AB763 has a 325 - 0 - 325 sec transformer, which according to the schematic anyway, is putting around 415v into the output tubes, which are 6L6gc's.

If I back out 410/1.414 (roughly) Id have to use a 290 - 0 - 290rms VAC secondary power transformer, to get roughly the same DC voltage at the output tubes. Mercury makes one, OK its pricey, but they do make one.

Am I way off here?

And since its a solid state rectifier, there is no restriction on the size of the first filter caps, so couldn't I put bigger caps in right after the rectifiers? Not so sure about the other side of the choke.


Wouldn't that leave the rest of the circuit about the same?

[mikepukmel]

vibrolux vs deluxe

Are the AB763 deluxe and vibrolux really almost exactly the same amp, just different PT and OT? I don't see any other component differences (couple of resistors, 2 I think)

[dstrat]

well overall circuit is same if your talking about ab763, but all the different models have subtle changes.
several were about the same wrt the reverb models as well for the 40w models.
but output transformers were different because different speaker arrangements.
most notably the difference is 100r tail PI, for a 2 8r speaker, vs the 47r for a single speaker.

[mikepukmel]

well overall circuit is same if your talking about ab763, but all the different models have subtle changes.
several were about the same wrt the reverb models as well for the 40w models.
but output transformers were different because different speaker arrangements.
most notably the difference is 100r tail PI, for a 2 8r speaker, vs the 47r for a single speaker.

Thanks dstrat.

[cjenrick]

i would not go too far beyond 40 uf for a pair of 6L6 tubes, you might start to lose the feel of the original amp,

push pull circuits cancel out B+ hum pretty well, you can always add more C for the preamp stages if you are worried about noise.

maybe put a 10 ohm surge resistor from the diodes to the first cap,

[pdf64]

No need for MM prices; Hammond make a vast range of transformers, or maybe contact Heyboer, Edcor etc and ask them if they can make what you want as a 1 off.
A bias tap isn't necessary, just amend the Princeton arrangement.