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Questions about tubes and gear that glows. FAQ

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Original Message

Re: Awesome info, thanks

Posted by Jim McShane on April 3, 2003 at 07:46:25:
"Thanks for the in-depth reply"
Glad I could help.
"On second check I can barely see the number 35, possibly followed by a W, on the mystery tube."
Yep, a 35W4 7 pin rectifier. So look for a big resistor like I mentioned. Be sure it's in good shape.
"Someone started to make a tube layout diagram on the inside of the cabinet, but the only value filled in is the 12AU7, and of course I pulled both other tubes without noting their original locations."
The 12AU7 number is probably 12AU6. All the sockets are 7 pin, right?
"How would I figure out which tube goes in which socket?"
Okay, if you know where the 12AU6 came from, then the 35W4 goes to a socket that connects to one side of the line cord - probably through that big resistor I've been talking about. If you find that, then the 50C5 goes in the only remaining socket.
"The sockets are on either side of a smallish paper-sided transformer (is this the "choke?")."
No, that's part of the filament supply for the 12AU6 IIRC.
"There is also a bigger, all-metal transformer, "Tranco 44 36 NOV 1963", and a 3-section filter cap can. Is this a power trans?
No, that's probably the output transformer. And the triple cap is a power supply filter cap.
If it'll help, here a link to a site that has a schematic that's probably pretty close to your amp's:
http://www.deltabluesman.com/
Scroll down and click on "Bargain Bin Amps", then click on the Harmony H-400 amp. That schematic is pretty typical of the old transformerless 3 tube amps.
Be safe, but have fun!