The minimum (recommended) capacitance
in the power supply for a 55 Watt stereo
amp with a 480V B+, like the MKIII is:
Watts = 55W x 2 = 110W
E = 480Vdc
C = total power supply capacitance
W = 110
E = 480
C = 110 / 480 x 480
C = 110 / 230400
C = .00048 F
C = 480 uf
Look at the multi-cap lug #3 in the MKIII
manual. The voltage there is 330Vdc. You
might get away with a JJ 220uf 385Vdc
electrolytic, like the one pictured here:
http://us.st11.yimg.com/us.st.yimg.com/ ... 6_19305451
JJ also makes a 330uf and 550uf in this
series. Might be worth looking into.
If you have not yet decided on a power
tranny and were going solid-state on the
rectifier, but feared that the resulting
voltage could touch the ratings of the
capacitors, you could make a hybrid
solid-state/tube full-wave bridge rectifier.
http://homepages.ihug.co.nz/~rwillis/al ... ifier.html
With this configuration, you get a nice
voltage drop and a delayed turn on. No
real necessity for a slow start mechanism.
A 350@425ma non-center tap supply
should be about right.