May 24th, 2012, 02:15 AM
Recently acquired an old 65ish Vox AC50 what had been converted to run 4 EL34s. I am currently in the process of restoring it back to its original specs. The power transformer has also been replaced, and I am just trying to figure it out, so that I can ensure that everything is hunky dorey before I eventually bring it up to power. Not much info on the PT, but it has "5023" stamped on the top. I am just trying to figure out what all the leads are. Looks like the way they have it wired, the smaller red wires are the high voltage, the large cloth wrapped are the heater supply. Not sure what the red/yellow is up to, maybe center tap? Curious as to what the other cloth wrapped, larger red, and larger black leads might do? ANy assistance would be greatly appreciated!
May 24th, 2012, 07:48 AM
I see cut leads in unfinished projects all the time. Did it ever function with EL34s or is it another "great idea" that never made it?
The way to work through a PT is with a multimeter. Leads that have continuity are the same winding. They may not read zero ohms because wire has a little bit of resistance. Then make your best guess by color codes. It's a good guess that the red leads are high voltage and there's a center tap. So... hook up the primary and check voltage. Ah, now we're into the expert program. Heed all warnings about working with lethal voltage. Most "tube" transformers have at least 600 volts and frequently more from one side of the secondary to the other. So you should meter 300v-350v on either side of the center tap. Then find 5v and 6.3v. Once you know for sure what you have hook it up.
BTW 4x EL34 with a tube rectifier is generally a bad idea. Take a couple rectifiers to push that much current which is why we usually see SS diodes in 4x EL34 amps.
May 24th, 2012, 10:11 AM
Thanks for the advice. I think that's the way to go. I haven't ever tried powering it up. Since it looked like the electrolytics were all original and since I knew right of the bat that I wanted to put it back to AC50 specs, I was not planning on powering it up until I had done those things. Seemed a little odd to me that the leads going to the heater circuit were such a massive guage. There are like 5mm wide ribbons of copper.