Ef86 circuit changes

[BigBob]

Hello everyone, what I need to know if when using an EF86 in a TMB amp, are any circuit modificatons required. I am going by Richie's 18 watt TMB with master layout. I want to leave the master out and use the EF86 for the TMB channel. I know the 86 is a pentode and the wiriling is a little different for the socket. So do I just build the circuit, leaving out the master and doing the correct wiring for the EF86? Any help would be very appreciated.

Bigbob

[dartanion]

Using an EF86 to drive a TMB tonestack is not going to work very well as the EF86 has a high output impedance and the TMB is very lossy. You really need a buffer stage such as a cathode follower to overcome this obstacle. This requires a single triode and should be doable. The easier route is to use an EF86 in the normal channel using the Trem channel tone control (low loss) and leave the TMB channel alone.

[Freddy]

You could run the EF86 signal into a single knob type tone control and it will work. The EF86 pushes out a lot of gain so you have to be careful not to swamp out anything downstream with a big signal. They do sound good though when once you get the gain under control.

[zaphod_phil]

Using an EF86 to drive a TMB tonestack is not going to work very well as the EF86 has a high output impedance and the TMB is very lossy. You really need a buffer stage such as a cathode follower to overcome this obstacle. This requires a single triode and should be doable. The easier route is to use an EF86 in the normal channel using the Trem channel tone control (low loss) and leave the TMB channel alone.

Or you could replace the first stage of the TMB channel with an EF86, so that the rest of the TMB channel is the same. You would need to attenuate the signal after the pentode, since EF86s have a lot of gain, which could end up making the amp sound blatty.

[Cathode_Ray]

I built a 36 watt with standard 18 watt tremelo channel and EF86 for the other - a treble/bass tone curcuit worked nicely to tame the gain from the EF86.
2 12" cab contains a Private Jacke and a Patriot - best of both worlds as I use one or the other. Really LOUD with both...

[klingo]

Hello,
is it a Dr Z treble/bass tone set up or a princeton one ?

[dotfret]

Nobody mentioned the Vajra?

http://www.18watt.com/storage/Vajra%2018%20scheme.jpg

LOL

If you want a single triode buffer like Phil suggested, a 6AQ4 is probably first choice to give the desired effect and put enormous amounts of the gain down the toilet ... WTH it should make for a very low noise design!