bought myself another project

[gadget73]

I've purchased another project. I think this is a homebrew amp, but I'm not really sure. I'll know more once it graces my doorstep. No tubes, but the tube sockets look to be an octal, a pair of 9 pins, and a 7 pin. I've got plenty of tubes around here that will fit that lineup, even if I do have to re-wire the amp. Worst case, I'm thinking mono P-P 6BQ5 amp, 5U4 rectifier, and a 6J6 or whatever that triode/twin diode tube is that I have a bunch of.


http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&rd=1&item=260268856657&ssPageName=STRK:MEWA:IT&ih=016

Worst case, I should end up with a nice power transformer, an OPT, and a good chassis for a project.

[gearhound]

That is some SERIOUS iron!
Those trannies and the chassis are well worth the price of admission.

Steve

[cademan]

Can't really tell by the pictures, but the tube layout could be a pair of 6BQ5's, 5U4, and 12AU7 or 12AX7 tubes. Pretty basic design!

[clydeselsor]

Interesting looking unit...

[gadget73]

Can't really tell by the pictures, but the tube layout could be a pair of 6BQ5's, 5U4, and 12AU7 or 12AX7 tubes. Pretty basic design!

Thats kind of what I was thinking. I've got all of those tubes laying about, so it should be pretty easy to make something work. If not, I could always make it work with the tubes I have.

[gadget73]

I got the amp today and did some fiddling. Its got some interesting iron, and the circuit layout is sort of different than anything I have experience with so far. If I'm reading this right, I think its ultralinear? Transformer is a Chicago Standard BO-13 or something similar to that. The top part of the first letter is worn off, could be an E, and the O could be either a zero or a Q, not 100% sure. I also could use some help figuring out what tube needs to go in the v3 position. The others I can guess at and probably get something going, but v3 I'm stumped on.

Schematic is linked below. I know its backwards from the standard input on the left, output on the right arrangement but I started at the output transformer and worked my way back.

http://lunar.gadget73.com/images/mystery_amp/mystery_schematic_L.jpg
http://lunar.gadget73.com/images/mystery_amp/mystery_schematic_R.jpg


I may re-wire this to make v3 some known value, but I'm just curious what it sounds like it would have been originally. The voltage in the power supply is also awfully high, 400 vdc at the first tap, down to 250 vdc at the last. This might drop some with a full tube compliment, but I suspect I may have the wrong rectifier in there. Using a 5U4 right now, but if need be, I can either change the first resistor to drop the voltage, or see what other rectifiers I have to get less B+.

[Tom Bavis]

You'll find the BO-13 in the Chicago catalog on my web page, page 24. 10K to 4,8,16 @ 20W.

http://www.audiophool.cjb.net/Techno.html

[gadget73]

Thanks for the info, good to know what exactly I've got for iron.