Picking the right PT - check my math!

[crazytooguy]

Hi all. I'm trying to choose the right PT for the current amp experiment I'm working on. Here's the setup:

2 EL34s, biased high class AB (~48mA)
2 6L6s, biased very nearly class A (46 mA), tetrode connected (plate and screen connected to OT)
4 12AX7s for preamp/PI duty
B+ of about 390V loaded

There's two Hammond PTs available that are in the range, both with 300VAC secondaries. One is rated at 250mA (372JX), the other 575mA (372KX). The higher capacity one is, of course, more expensive (and larger), but I feel like the lower capacity one is just not enough current capacity to safely operate this amp. Am I correct? I don't want to roast an expensive PT because I cheaped out on an extra $50. Thanks!

[Gingertube]

Voltage is about right. PSUD2 says 400V at 200mA DC.

DC Current at idle approx 200mA, need peak current capability for peak output power and then convert DC requiremnt back to the AC current requirement.

As a "quick and dirty" method simply look at the Hammond website for the replacement gutar amp power trannies. The one for a 100W JCM900 (be similar to what you need) says AC current 450mA and the Twin Reverb replacement says 514mA.

I would definitely go the extra $50 for the 575mA rated jobby.

Hope this helps,
Cheers,
Ian

[Zozobra]

Check out some of anteks torroidals. 575 mA does seem a little overkill to me for a pair of EL34s.

This for example is good for 420VDC unloaded and can supply 340 mA if you put the secondaries in parallel. $35.
Antek - AS-1T300

[crazytooguy]

Thanks! I'll go for the higher current capacity. Not interested in blowing up trannies. The toroidal is really interesting - they're my preferred choice for non-tube power supplies, but I was always put off by the high cost of toroids for HT supplies.