2nd gainstage: ef86 switchable with 12ax7

[makepeace]

Hi guys,

This is my first post, so an intro is probably due. My name is Jono Makepeace and I'm writing from a small town in South Africa, Hermanus. I'm 20 years old and I started playing guitar 2 years ago, although my interest lies more in the technical workings of guitar and music related equipment. I've built a couple of effects pedals, and have recently finished building a modded 5E3 (a selection of either tweed or blackface tonestack, classA/classAB switch, switchable negative feedback loop and soon to be switchable B+ so that I can effectively swap out 6V6's for 6L6's if I want - made possible by a Woden 380-0-380 pt).

I'm busy building another 5E3 for a friend as a gigging amp. It was intended to be a clone of mine as it stands, but as it happens, the chassis we're using has an extra hole for a 9 pin tube, so I'm looking for something to do with it that doesn't require much control panel, or turretboard space.

A friend suggested that I put in an EF86 gainstage. So, my plan (Please bear in mind that my knowledge of these things is VERY limited, but I'm learning all the while..):

-keep the 12AY7 as the input stage
-implement the 1st triode of the 12AX7 as a gainstage (as its set out in the 5E3 schem), switchable with an EF86 gainstage.
-take this into the 2nd triode of the 12AX7 (PI)

The all my tone controls would be before my EF86/12AX7 stage, as goes the 5E3 topology, so I will retain the control that I have, just with a different flavour.

Could anybody suggest, 1st of all, how I could implement the EF86 as a gain stage that will work similarly to the 12AX7's triode in this position (before the PI and after the tone controls) and secondly how to make the two stages switchable.

Example schematics would be ideal.

Thanks,

Jono

[tubeswell]

my plan ...:

-keep the 12AY7 as the input stage
-implement the 1st triode of the 12AX7 as a gainstage (as its set out in the 5E3 schem), switchable with an EF86 gainstage.
-take this into the 2nd triode of the 12AX7 (PI)

The all my tone controls would be before my EF86/12AX7 stage, as goes the 5E3 topology, so I will retain the control that I have, just with a different flavour.

Could anybody suggest, 1st of all, how I could implement the EF86 as a gain stage that will work similarly to the 12AX7's triode in this position (before the PI and after the tone controls) and secondly how to make the two stages switchable.

Example schematics would be ideal.

So you've looked at the Matchless Clubman? Sounds like what you want is similar to that.

As for the channel switching aspect, that is a matter of incorporating relays. Look at any Crate/PV etc where they use channel switching to see how that can be implemented

[Chuck H]

The ef86 option for amps like the 5e3 is usually as a first gain stage. Having almost twice the gain of a 12ax7 triode, the ef86 is a higher gain option. Sure you could stick it anywhere in the circuit, but it's real advantage for gain and voicing is as an input stage. I would just make one of the input triodes switchable with the ef86.

[MikeM]

So you've looked at the Matchless Clubman? Sounds like what you want is similar to that.

As for the channel switching aspect, that is a matter of incorporating relays. Look at any Crate/PV etc where they use channel switching to see how that can be implemented

I've read that the higher input signal means you'll be less prone to microphonics from the EF86. I think the Clubman is a great example for this case.

[makepeace]

Thanks for the replies. Yeah actually the clubman design did play a part in the idea, but it was actually MikeM who suggested it .

Tubeswell, thanks for your input. To be honest, I'm a little averse to relay switching as well as anything solid state.. I don't really want things to get too complicated in that respect.

There must be a way to just have a manual switch on the control panel I could flick to switch between EF86 mode and 12AX7 mode. But I understand that this will be inflicted by the pop of doom. Is there a way to get around that to a relative degree?

Chuck H, thanks for that bit of info. Very interesting, and I'm sure you're right, but in this case it wouldn't really work as I currently have my tweed stack following one triode and my blackface after the other triode.