How to determine current requirements for a circuit

[deuce42]

Hi guys

I know this is a rudimentary question but I'm a little confused - I have a power xformer which has 100ma for the HT, 3A for the 6.3v winding and a 5v winding of which I'm unsure of its amperage.

I want to power a 45w Super Reverb type circuit however condensed down so that the circuit is just a single channel AB763 without the tremelo part of the circuit and no tube rectifier (just diodes).

I am wondering whether this xformer is rated high enough.

My thinking is that the circuit will require 2 x 7581A tubes, and 4 x 12ax7 tubes. The 4 different 12ax7's are for input, reverb in/out and the PI tube.

I believe the 7581A's usually require about 900ma for the 6.3v but I cant seem to understand their HT requirements. I believe the 12ax7's use about 300ma for the 6.3v and maybe about 6ma for the HT however I may have got this wrong.

Am I right in saying that I may be on the verge of the xformers maximum rating for this circuit and the xformer may not have enough power?

Thanks for in advance

[martin manning]

7581A are interchangeable with 6L6GC, with a little higher (35W vs 30W) max plate dissipation. You aren't really reducing the HT requirement very much relative to a Super Reverb, which uses a 200mA PT. If you look at the simpler 2x 6L6 Fender amps (Tweed and Blonde/Brown/Black Bassman, e.g.) you'll see 200mA and higher HT ratings.