How to use (in a guitar amp) some ECC82 (12au7) tubes that I've

[kagliostro]

I've some ECC82 tubes, they are rarely used in guitar amps (maybe, sometime, as PI or in the send of FXLoop)


To find an use I can use it also in CF configuration, but I was wondering if is possible to use it in other collocations on a guitar amp circuit


as V1 or V2 in Cascode configuration or simply as Anode Follower putting two in series to be used as something like a single triode of a 12ax7 tube


Often I've read that each gain stage adds harmonics so my idea has this thing on the basis


K

[rzenc]

Hi K,


I used it to drive tonestacks with great results. It was plate-driven and I had to adjust TS caps to taste. Basically a 5879 gain stage - gain control - 1/2 ECC82 - Tonestack + vol. - 1/2 ECC82 - PI - PA


I need to find the schem, but if you are interested, pm me.


Best regards


R.

[eleventeen]

Find an old CONN organ in the garbage and you'll have 36 of them.


Some folks use them in reverb driver position in a Fender amp which can increase the usable range of the "reverb" control because they have much less gain than a 12AT7.

[tubenit]

I like them in the D'Lator type active FX loops & sometimes use them there.

With respect, Tubenit

[HotBluePlates]

Often I've read that each gain stage adds harmonics ...

Only if you're driving the tube hard enough to push it beyond clean amplification (or mis-biasing enough to ensure there is little clean amplification).

Seems like a good tube to deliver moderate current in a preamp (a reverb driver might be a decent application), to act as a unity-gain mixer (though the relative levels of the individual signals need to be pretty close; closer than what you might offset with a 12AX7 as a unity-gain mixer), etc.

[Merlin]

If you cascade enough of them you can get as much distortion as you like, but be prepared to tweak everything.

Some examples of use, AX84 blues preamp:
http://www.ax84.com/static/corepreamps/Blues/AX84_Blues_Preamp_Schematic.pdf

Doug's Firefly, which uses a 12AU7 as the output stage:
http://ax84.com/media/ax84_m276.gif

[kagliostro]

Many thanks to ALL you friends

@ Merlin

is this the Blues preamp that you mean ?

http://www.mrdwab.com/john/Blues-pre.jpg

on the two link you posted there is the same schematic (both are FireFly rev.3)

Franco

[kagliostro]

I'm spending some time on research on old amp schematics

I discovered that Univox used the 12au7 in different positions on their amps

a pair attracted my attention, one has a 12au7 tube as driver and recovery of the TS (as Rzenc told  )

The other was in a position at which I've think sometime but was never sure if convenient (may be in the 1236, that is a Bass amp, it was), I mean V1





on the 1236 there is also a 12au7 after the PI before the Power Tube

I think the purpose was to drive at the max the 6L6GC tubes, is this correct ?

K

[PRR]

> purpose was to drive at the max the 6L6GC

6L6 are not hard to drive. Almost any reasonable driver can over-drive them.

And the U-1075 would need more drive than the 1268 because of higher 6L6 voltages.

It's a cross-word puzzle.

Put in a tube. Not enough gain. Put in another tube. Too much gain. Throw in a tone-stack. Or a mixer. Less gain. You move things around and change them until you have a reasonable gain-structure from input to output. You also want a reasonably minimum cost, which suggests dual-triodes, but you have to get the right halves in the best places.

The U-1075 has a lot of inputs, so has a lossy mixer, and has to start with high-gain preamps and individual gain controls. After the mixer the level is too weak to go to a tonestack, but too much gain added may overload. So a low-gain stage. Then tonestack. The output stage is lifted direct from Fenders, needs pretty strong input, so need a little gain after the tonestack. While two low-gain stages seems complex, they are just one dual-tube. This also allows a 2.2K+0.3uFd cathode network, twice, to provide a lift and shelf in the midrange, a classic guitar EQ.

The 1263 looks like two hi-gain stages before the tone/volume network but the NFB around these stages means a very clean input with moderately high gain. All the tone/volume loss is in the middle, and then it needs fairly high gain to the output. The 1263 is unusual for a guitar amp in that all the gain happens in just two NFB sections. It might be very low coloration before over-load.

Also I am sure the guy who designed the Japan-made UniVoxes had the same problem as everybody here. He just wanted to try something different each time.

[kagliostro]

I like your guidance on those old circuits if well explained there is a lot to learn there


As always Many Many Thanks PRR

Franco