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previous: Lee MacMillan What kind of tranny do you get to g... -- 4/5/1999 3:36 PM view thread

Re: Optimum B+ for EL84s

4/5/1999 6:00 PM
Bob S
Re: Optimum B+ for EL84s
I must confess I have actually looked for a new one. I've worked on a bunch of AC-30's (old ones) and just about all them run @ 330 volts on the plates and about 327 volts on the screens and that's with about 85ma. per pair. I bought an old AC-15 about a year ago and when designed these things in 60's the voltages in the U.S. were'nt as high as they are today. So when I got it home I checked it out and it had about 360 volts on the plates.(about 310 volts on the secondaries). I pulled it out and had it rewound for 285 volts, which will give you about 330v. on the plates. I'm going to be talking to a guy I know in Texas who winds transformers about making some with those specs. In the mean time I have used 10 watt resistors right after the rectifier tube to reduce voltage,(100 to 300 ohms). I'm probably going to here about this but I'm telling you it works. I currently have 3 AC-10's that have Mojo Deluxe Reverb trans in them and this mod has been in them for 2 years.(I bought them this way, they were brought in to the states with 220v. trans in them). Anyway it's certainly not the way I would prefer but they have been very stable.  
You're going to need no more than 370 volts B+  
in order to get to 330v.on the plates. Look for a trans with 285 volts on the secondaries and you should be fine. And remember that a SS rectifier will raise the voltage and what I've been talking about was also with a GZ34.  
Let me know if you or anybody else knows where there might be some stock trans with these voltages.  
Good luck  
Bob S.

Carlo Bob, what about a Hammond 270HX? It... -- 4/6/1999 8:35 AM