Monday, August 1, 2011
Vintage Parts Excursion Part IV: Son of Judybox Champion 600?
A friend of mine dropped off an early fifties Fender 5C1 Champ for an overhaul and it sounded so good I decided to make my own. Looking around the shop I found my Champion 600 reissue that has been lounging around with the occasional task of testing preamp tubes for excessive noise. I also gathered up a trio of tube sockets, some capacitors, a bit of perf board that had been used as a bookmark, and the main ingredients-a Stancor new old stock power transformer and a Thordarson output transformer, both of which had come out of the split window Dodge van. It took a few hours to gut the Champion 600 innards and repurpose it.
The first thing I did was ditch the speaker out jack and bore the hole out for a fuse holder. At that time I also installed a SPST power switch and, using a Greenlee type punch from Harbor Freight, installed a trio of tube sockets. Then a trio of 22 uf capacitors and suitable resistors completed the power supply setup. A test confirmed proper voltages at all the important places. Then, I wired up the 6V6 power tube and the 6SJ7 preamp tube.
It sounds remarkably like the old 5C1, but the speaker's a little more hi fi, so I'm looking for a nice period Cletron or similar fine speaker. The combination of the 6SJ7 pentode and grid leak bias is the tonal ticket. It'll slide right into a nice greasy blues tone, and with the right pickups it's a joy.
You could probably re-use the Chinese iron if you wanted to use a 6AX5 rectifier and reutilize the output transformer. But you might miss out on the magic.
To reproduce this project for you, it would cost you about $120 in parts and shipping for Magnetic Components iron, shipping both ways, and about $120 in labor. Tubes would be about $24 extra for a NOS rectifier and preamp tube and a vintage serviceable 6V6. If you like the idea, drop me a line.
I did have a few issues with this circuit that it is worth knowing about. The lead between the 2-75k ohm resistors and the preamp tube is very sensitive to positioning and has a bad tendency to create oscillation.
After a few fits and starts and some blind alleys I ended up taking some hookup wire and wrapping about thirty turns around a pencil. I then stuck the lead through this coil and grounded one end. The Jensen Mod came in at about the same time so that got installed, offset a bit for clearance. The result's a lot cleaner and the volume can be maxed with no oscillation or interference. I'm still looking for an older 6" speaker-that'll really do the job of recreating a classic.