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.


  1. Hi Robert,
    I love what you did and I want the same !
    Only issue I see : I live in France.
    Any suggestion ?

  2. Parts ought to be generally available in your part of the woods. I think I would try and get an international voltages Champ size power transformer or use a stepdown transformer-you use 230v AC I think, you need to get down to 120. Tube Amp Doctor in Germany probably has much of what you need on hand. This is a relatively easy conversion. It took me a few hours on a sunday. Speakerwise is where the important choices come in; and these amps don't sound right with modern speakers. Get yourself a new old stock six inch radio speaker or a 6x8 radio speaker like a Cletron or Rola or Heppner. For these I'd look in the antique radio parts section of ebay. They've got that scratchy tone that makes an old Champ what it is.

  3. Thanks Robert.
    You gave me a nice roadmap.
    I'll start the job in 2 weeks.

  4. Sure I'll do it.
    Here is my roadmap :
    - Changing capacitors with orange drop,
    - Changing transformer, as you suggest,
    - Changing speaker as you suggest (hard to find suitable vintage speakers, even on ebay), so I'm afraid I'll go with a Jensen mod6 ... I would love to try some oldies before making the definitive choice ...
    - Changing tubes coz I have the chinese crap ...
    - Changing some resistors here and there, still have to figure out which ones ...
    - Changing other things, maybe, inspired from this blog. Could be interesting for you also :

  5. ... and after that training, I'll go modding my Blues Deluxe ...

  6. I've seen you'r looking for old speakers, maybe these ones could go ...