Vibro Champ Conversion suggestions.

[GoghVan]

Long story short I recently picked up a '78 Vibro Champ with:

022905 Output X'former
022772 Power X'former

This amp is slightly different than the typical schematic I see for the VC in that it has (physically and on the schematic- old Groove Tubes book) 420V on the 6V6 plate V 342V on th AA764 version. BTW almost ALL of the listed voltages are either right on or very close to spec.

It needed some work to get it going and I've only looked at the signal on a scope. You guys are correct. The VC has poor bass response below 300Hz.

I'm looking to mod the amp to use as a practice amp and backup stage amp if I need to and 15-20W or so is plenty. I don't use a loud stage volume I mic the amp.

I like the sound of "Fenderish" 6L6 circuits but don't want the weight or power of a Bandmaster. I realize I'll have to change the X'formers to get the wattage.

Circuit suggestions?

[martin manning]

I'm confused... this is a 5W single-ended amp, right? 15-20W isn't in the cards for this. Seems like what you want is something like a Princeton with 2x 6V6 in push-pull. The PT is probably ok, but you'll have to find space for an inverter and another output tube.

[Firestorm]

You can get 15-20 watts in SE from much more powerful output tubes (KT88, 300B).You can get nearly 15W from a 6L6GC. But you'll need all new transformers, so you're really starting from scratch anyway. If you improve low frequency response in SE, you'll also have to solve the hum problem, which SE can have a lot of.

[GoghVan]

I know I'll have to change the X'formers. I can use a SS Rectifier and use the old rectifier tube socket for the second output tube.

If I'm reading the schematic right the Normal ch of a Deluxe (not including Rev or Trem) only uses 2 preamp tubes, the same with the Champ II, etc..

I'm curious if anyone has tried similar circuits with 15-20W where the sound impressed them. I can do mod's or complete rebuild. I also know there are a lot of people here who have more experience with a wide variety of amps.

I'm looking for an open, clean, well balanced sound.

[Firestorm]

You can probably shoehorn a 10" speaker into that cab. New baffle most likely. The challenge will be placing everything so the speaker doesn't hit an output tube or the OT. You can do the Normal channel of any BF Fender with two 12A?7 tubes: 1 pre, 1PI. 6V6, 6L6 or 5881 output with trannies selected accordingly.

[GoghVan]

I will use the chassis in a head cab so I'm not worried about hitting the speaker.

Thanks

[martin manning]

Do you have a schematic and layout for the thing as it is? I thought about using the rectifier socket, but wasn't sure if there was one since you said it is not AA764. If you dropped the trem there's another preamp socket, so you could do a Princeton circuit, or something like the normal channel on an AB763. If you went 2x 6V6 you could keep the PT.

[jjman]

This would not be a "mod." It would be a nearly-complete changeover from a vintage Fender to a non-vintage non-Fender. Why destroy the value and sacrifice it? There are now countless kits out there to build whatever you want. You could sell it and pay for most of a kit. And it gets to live on.