#1
This isn't a guitar build though i guess it would go under here. I'm currently designing and prototyping a ,5 12ax7 4 el-34 in push n pull pairs, tube amp. I have all of the schematic worked out and i have the power supply but i have a few questions for anyone that knows about it. Should i have 450 v going from the psu to the plates of teh el-34's. How would i also determine how to correctly bias the 12ax7 tubes without building it if i have teh voltage that will go through the resistor. I have tried some sites, and this is being designed partially with duncan psud II, the power supply is on the site as Spitfire. If anyone can answer any of my questions i would greatly appreciate your help.
#2
you should get in touck with the creator of the my tube amp thread not a hypothetical build this is the real thing, he can help you, but you didnt hear it from me..
#3
you don't need to bias your 12ax7's

and for christ's sake, please don't run 450v lines from your power transformer to your tubes. They might explode or melt or something.

You want to run 6.3v lines to your fils from your pt. That should be the only thing directly connected to your tubes from your pt.
#4
Quote by greenbox

and for christ's sake, please don't run 450v lines from your power transformer to your tubes. They might explode or melt or something.


thanks for that information, i've been working on the design and all of the other people that i have talked to have given me mixed messages about that.
#5
yeah, that and I don't think power transformers have 450v lines...

They usually have 6.3v (for the pilot light/tube fils), maybe 5v (some rectifier fils) and 12v lines (i forget what these were for), and the lines that go to your rectifier (I forget the voltage for these lines). And some ground wires. That's it. (The trim pot typically is, circuit wise, controling the voltage to the control grid, or pin5 for el34's).

However, from your circuit, you'll want to measure the plate voltage (pin3 if you're using el34's, or any octal tube), and use a trimpot to adjust the voltage. There are charts online for whatever tube you're using, so you know whether you're biasing your tubes cold or hot.

Also, I believe the plates should be connected to your output transformer.
Last edited by greenbox at Jul 3, 2006,