# EF86 pre-amp mod



## taskforcestudios (Dec 21, 2007)

Hi guys,

So while I am in the process of repairing my Traynor head, I am going to attempt to change the first 12AX7 tube with an EF86, similar to the front end in a Vox AC30. I've heard a lot of good things about using an EF86 in the pre-amp, and I know people have done something very similar to this.

From what I've read on various forums, it was suggested to take the first preamp section of the Vox AC30/4 and replace the first 12AX7 in my circuit with this.

Here is the input section of my Traynor YBA-2A (with EL84 output tubes):









This is the input section of the Vox AC30/4 that I would be using to replace the 12AX7:









Now to my understanding, assuming I rewire the tube socket and connect all of the heater, B+, plate, etc. voltages to their correct pins for the EF86 this would work. Is there anything that I am missing, or should be aware of before trying this?

Any advice would be helpful, I just wanted to check with some more experienced techs on the subject. I know people have done this mod to Marshalls and Traynors with great success.

Thanks,
Brian


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## WCGill (Mar 27, 2009)

Brian,
This is one of my favourite preamp tubes and if you get all the connections kosher, it'll work fine. You may have to adjust values of some components to tailor gain and tone to taste. One suggestion would be to shock-mount the tube socket as the EF86 can be quite sensitive to outside vibrations. Try several specimens to find one that isn't quite as microphonic although in time it may turn out that way. Great tube, but demanding.


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## taskforcestudios (Dec 21, 2007)

*Ef86*

Thanks alot!

Do pins 3 and 8 have to be connected on the tube socket, or are they internally connected. Stupid question, I know. I'm assuming I have to jumper on the socket.


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## Scottone (Feb 10, 2006)

WCGill said:


> Brian,
> This is one of my favourite preamp tubes and if you get all the connections kosher, it'll work fine. You may have to adjust values of some components to tailor gain and tone to taste. One suggestion would be to shock-mount the tube socket as the EF86 can be quite sensitive to outside vibrations. Try several specimens to find one that isn't quite as microphonic although in time it may turn out that way. Great tube, but demanding.


Yep, would definitely require some tweaking of values, but would be a cool thing to try.

Would be really nice if you could keep the 12ax7 and add the EF86 stage, then put a switch in to select one or the other. Of course, this would require even more fine tuning :smile:


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## WCGill (Mar 27, 2009)

Hi Brian,
You have to connect pins 3 and 8, they're not connected internally, not a stupid question.


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