heater current

[ninjadave7]

Hey guys, I'm building an amp with an AO35 PT and wanted to make sure I wasn't going to pull too much heater current. The spec for the PT shows 1.8A max, and I was planning on running 2 12ax7s, 2 EL84s and an ef86. Similar compliment as the original amp but with an ef86 added. Will this be a problem? Thanks!!

David

[guitician]

.3A x 2 for 12ax7 and .76A x2 for EL84 and .2A for EF86 = 2.32A at 6.3V

[ninjadave7]

hmmm, maybe I have the wrong info on the transformer then, because the original amp would still be at 2.12A, which is more than the spec I found.

[guitician]

.5A more than the rating may not burn the windings. I would wire up your heaters and run it for a while and see how hot it runs. If you can still keep your hand on it, your OK.

[Chuck H]

Better yet... ire it up as planned and read the voltage to see if it drags down below spec. If it does, pull a couple of preamp tubes. If the voltage comes up to spec by pulling tubes then your over loaded and can just add a small 6.3V tranny for the power tubes.

[guitician]

Yeah, but read the no-load voltage and graph the voltage drops as each tube is added to see were the "knee" is. It's the point where the voltage starts to drop faster than the other "drops". The "spec", 6.3v, may not be what you have with modern line voltages too.

[Chuck H]

+1