What to do with the extra triode?

[allsavy]

Many, if not all of the trainwreck clones use only 2 and 1/2 dual triodes in the preamp. What might be done with the unused triode? Parallel it with the other half to help reduce noise? Add an extra input stage with marshall values? Make it a switchable extra gainstage? (does a franchesca need that???!) Ignore it and dream about solid state?

[paulster]

I would say try to forget it's there, enjoy the amp, and you'll be a more fulfilled person as a result!

The beauty of an Express is in its simplicity. Why try to complicate it more than it needs purely because there is an extra triode available?

Paralleling two triodes will decrease noise. However it will also increase gain (not particularly desirable in an Express) and, if I could find the really good graph that compared them, reduce the desirable second-order harmonics at the expense of creating some higher-order less-desirable harmonics.

The other uses for a triode all involve complicating the circuit, which is kind of the antithesis of what the Express is about. You can do it and may have some success, but its unlikely to retain that Express sound.

If you really want to use the triode then why not build a Concorde instead, which is probably its spiritual successor?

[Roe]

try an extra gainstage

[wrathchild]

I've been looking at that possibility also. If no one ever tweaked or added gain stages to Fender or Marshall we would never have Mesa, Saldano, ENGL, Bogner, etc. It would be very obtuse to say don't try it.

[Cliff Schecht]

A lot of older amps (Gibson, Silvertone/Sears amps, etc..) used a cool single triode tremolo circuit. Without the second tremolo tube (ala Fender) to act as a cathode follower, you get a more distorted tremolo waveform that is characteristic of most vintage tube amp tremolos. I thought about adding this into my Express build but I have a pedal designed that does the tube tremolo sound quite nicely already.

TBH, I'm with Paul. If it was good enough for KF then it's good enough for me as is.

[gearhead]

I've been looking at that possibility also. If no one ever tweaked or added gain stages to Fender or Marshall we would never have Mesa, Saldano, ENGL, Bogner, etc. It would be very obtuse to say don't try it.

Welcome to the Amp Garage.

Thing with an Express/Liverpool, there is tons of gain already; but significantly different beast wrt Mesa, Soldano, etc. And it's not that anyone hasn't ever tried, because that was one of the obvious mods to do once folks had a handle on the circuit and especially topography (with that extra triode hanging out there).

It's just that just about everyone that did it, ended up undoing it. And precisely for the reasons paulster gave.

But give it a whirl, maybe it will tickle your fancy.

[FYL]

What might be done with the unused triode? Parallel it with the other half to help reduce noise?

Use a selected 5751 instead of a 12AX7, scale the passives, parallel the sections and you've got app. the same gain, lower hiss and noise, a more expressive sound and a better touch sensitivity (yes).

While the soldering iron is still hot, add a decoupling cap + R as close as possible to the plates as well as a 10K to 33K grid stopper right at the socket.

OK it's not canonical, but who cares if the mods result IMO in a better sounding amp and are 100% reversible, huh?

[Bob Reinhardt]

I use it as a footswitchable extra gain stage in one amp. Its not a direct express clone, but started from that. you have to be careful with it.....

[ampdoc1]

Hook up the unused 1/2 as a cathode follower, ala the Komet Concorde. There have been some criticisms about Komet's design philosophy there, but I think it adds a slight compressive "bloom" to the response, somewhat like the Dumble.

ampdoc1

[j-po]

Parallel the first stage, half the value of all the pots in the tone stack/vol and double all the caps to keep loading similar. Plate resistor also, obviously.

[jjman]

In my pseudo-Express, I use it to amplify the return from my post-3rd-stage parallel effects loop. Then blend and on to the PI.

[Andy Le Blanc]

Diode bias the first gain stage.

[Bear]

If you want to do the single-triode tremolo, look at the 6G3 Fender Deluxe schematic as a starting point.