Super Twin Reverb

[imaradiostar]

Have one on my bench that belongs to a friend of a friend...missing a 6L6 and the other 5 are terrible and mismatched.

I have this really strong desire to re-engineer it to have individual bias controls per output tube and a bunch of current sense resistors since I seriously doubt 6 6L6's won't drift at 500+ volts in ultralinear mode!!

Why the hell didn't Fender use a pair of 6550's?

How bad are these things really?

jamie

[Gibsonman63]

This amp will need new tubes anyway before you will get decent tone from it. Why not start there and then see what it needs before putting some serious work into it.

BTW, with 6 power tubes, I bet you find at least one pair of heater wires crossed.

[imaradiostar]

I'm sorry if I didn't say- I do intend to put new output tubes in it! I'm not going to go ahead with it till I'm sure the rest of the amp is in order. I have a lot of 6L6's laying around and if I can find 6 that match closely enough I'll at least be able to fire it up and see how it sounds.

What do you mean by filament wires reversed? As in if they're wired correctly it helps to cancel hum because the outputs are push-pull? I've heard about this but never really taken time to mess with the concept.

I don't know if just any old 6L6 would hold up in this circuit- being ultralinear and having very high screen voltage I'd imagine it can be hard on 6L6's. I've never worked on an amp like this before, only the normal earlier garden variety Fenders and Marshalls and the occasional modern amp. I suppose if it's truly ultralinear it prevents the screen current from getting out of hand but the nominal current and voltage just sitting there seems to be pretty high.

I've read that it's not an ultralinear amp in the traditional sense, meaning it has 20% screen taps instead of 43% taps. I intend to measure when I get it apart but I thought I'd mention it.

It seems like it's a great platform for mods- if you wanted to build a bass amp it would easily support an SVT style preamp and a pair of KT88's. If you wanted a marshall major style thing the transformers would be a decent match. There are enough gain stages available (and graphic EQ!) that one could probably build any of a number of really cool channel switching designs.

Anyway, all food for thought. For now I haven't had time to get into it and see just what's going on.

jamie

[Jazz P Bass]

Fender Super Twin

Here is a link to a nice little distortion channel mod.
http://music-electronics-forum.com/t15622/

[Gibsonman63]

Apparently, Fender didn't pay attention to the polarity of the heater wires. Correcting this problem has worked very well on my Fender amps to reduce hum.

On my 100W amps, I sometimes pull two power tubes so I can run at lower wattage. I would suppose that you could run your amp with four power tubes and still have plenty of power to spare.