Few Power Supply Questions For 5C8 Twin

[rp]

1) Does the 6J5 tube really draw 20mA (not filaments)? I'm about to source a PT for a 5C8 Twin (all octal low power cathode bias amp) and wonder if I can get away with 150mA, I think not and 200mA would be better, but that would force me to cut out for a laydown in an fancy expensive chassis. Strange that the IGPW trany for a JMP45/50 is only rated 150mA.

This is the PT I'm looking at:
http://www.tube-town.net/ttstore/produc ... rsion.html

Otherwise it's:
http://www.tube-town.net/ttstore/produc ... rolux.html

2) The PT voltage is very tricky here as I'm trying to hit 370-390V on the plates as I plan to (also) use Coke bottle 6L6Gs and so want absolutely no more than 390V but don't want any less than 370V as that seems lame for 6L6s. You all think the Vibrolux PT above w/ 325VAC sec (I assume unloaded) used w/a 5U4G (ST) will get me there? Or maybe go with a 300VAC sec? Hammond has that (372HX) as a stand up with export taps but I worry it'll be to low.

My experience is the math never really gets you there as it's all about the loaded/unloaded values and wall voltage (237VAC in the house) and the current draw... Maybe someone has direct building experience? Maybe make it a poll: 325V or 300V?

[tubeswell]

A 6J5 is similar in characteristics to a 12AU7 triode. So yes it can draw up to about 20mA, depending on how you set it up. But the way its set up in the 5C8 (with a 100k load) won't draw anywhere near 20mA. (more like 2mA)

[rp]

A 6J5 is similar in characteristics to a 12AU7 triode. So yes it can draw up to about 20mA, depending on how you set it up. But the way its set up in the 5C8 (with a 100k load) won't draw anywhere near 20mA. (more like 2mA)

so I'm looking at about 88mA total, with the Power tubes at 40mA, so maybe that odd Marshall PT @ 150mA will do. It's likely conservatively rated.

[tubeswell]

Yeah 150mA on the HT winding ought to be alright for that amp

[Firestorm]

You have to take them with a grain of salt, but the old Fender transformer lists show the same Triad PT (#7993) in all the Tweed Twins. That's what's in my 5C8/5D8 transitional Twin; I've also seen it in some Bassman models. The later schematics with this PT show secondary voltage of 300-0-300. The B+ voltages don't exactly make sense considering that different models had 2x5Y3, 5U4, 2x5U4, 83 and GZ34 (and the 5E8-A had a choke input), but 300-0-300 doesn't seem out of hand.

You might consider trying the Heyboer 5199 (x-mount) that is used in Express builds: 300-0-300 (or 260-0-260) @ 300mA. Depending on the rectifier you use, you should be able to dial in your preferred voltage.