Posted by Damir [ 213.202.85.22 ] on August 20, 2005 at 16:41:27:

In Reply to: matchless chieftain transformers posted by tomgillou on August 20, 2005 at 14:20:44:

Hm, 20mH seems like pretty small choke in tube amp PS, it`s more likely that it`s 10-20H choke. I don`t have PS schematic, but I suppose that`s "guitar amp classic" - B+ for output tubes is from the first cap, then Pi-filter (choke+another cap) for screen grids (g2), then RC filters for splitter/preamp tubes. I found amp schematic, and it shows about Uak~390V "through" each EL34, cathode biased - each EL34 with Rk=270 Ohms+cap. On schematic, Uk=24V. That means that current through the EL34 Ia+g2 = Uk/Rk = 24/270 = 88,9mA. And dissipation through the each tube is Pa+g2 = 390*0,0889 = 34,6W!
Much more then Pa+g2 max. for EL34.
Well, maybe I found not so good schematic on the web - can you post the link of your schematic? And schematic is not everything - layout, choice of parts make much difference.
IMO - if you have tons of experience, good schematic and known layout - go on with this project. But, if not - maybe first try some books by Kevin O`Connor. There are some with complete schematics, layout, etc. - see "London Power" site for more details.

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