Following EF86 V1 w/ Cathode follower and TMB?

[Jalmeida]

Hey folks,

I have been mulling around and research amp ideas based around the EF86. I love the sound EF86 in V1 preamps. And I have found lots of suggestions of using a EF86 following another V1.

However I am searching to see if anyone has played with or had success following an EF86 V1 with a cathode follower and then additional gain stages. I have found that the EF86 is a
Fickle microphonic devil to work off of. But my hope is that by following with a cathode follower and then a TMB stake I could incorporate a cold clipper and gain stage before the PI. My hope is that the tone stage can attenuate enough to be able to not have horrible feedback. And possibly worse case if needed split the EF86 plate load into two separate resistors and pick couple between the two resistors to maintain EF86 behavior without overloading the following gain stages. Here is what my proposed flow would be:

EF86<Cathode follower<TMB stack<Cold clipper<triode gain stage< PI etc.

Any input on experiences with this would be appreciated. My search hasn’t turned much up.

[sluckey]

Just search the forum for "EF86 cathode follower". Here's one example...

     https://el34world.com/Forum/index.php?topic=29702.msg326994#msg326994

[shooter]

^^^
reply #26, the DCCF option, although i'd hunt up Merlin's "fixes", they work well, I'd also start with an AU, properly biased.

[HotBluePlates]

Hey folks,

... I love the sound EF86 in V1 preamps. And I have found lots of suggestions of using a EF86 following another V1.

... EF86 V1 with a cathode follower and then ... a cold clipper and gain stage before the PI. My hope is that the tone stage can attenuate enough to be able to not have horrible feedback. ...

I think you already found the best advice:  Put the extra gain before the EF86, so you minimize the impact of microphonics, and distort the stage you find most interesting anyway (the EF86).  Experiment with the screen voltage (by changing the dropping resistor value) as it affects the EF86's harmonic content.


If you keep the EF86 as V1 and then put a bunch of tube stages afterwards, one of those last stages will almost certainly distort first.  Meaning, you get the sound of that 12A_7-whatever distorting rather than the sound of the EF86 distorting.

[bmccowan]

I'll join the pentode in V2 position parade. I tried doing what you suggest awhile back with poor results. Members here helped me to change course. Pentode in V1 with a simple one knob tone control works fine - I have a GA-40 that is sweet.
I built a Z-28 type amp with a 5879 in V1. I loved it at first, but then grew tired of the tone. So I added a parallel wired 12A_7 in V1, followed by a gain pot into the 5879. The tone stack, PI, and power amp are straight up Z-28. I adjusted the resistor and cap values on V1 and V2 until I had total gain to a reasonable level. Those values ended up very close to the values Tubenit has used on his various 5879 amps.
I also built an all octal version of the Matchless Clubman circuit - parallel 6SL7 into a 6SH7 - another keeper.

[Jalmeida]

I totally get the challenges. I knew this prior to this. I guess what I am inquiring about is if anyone has tinkered with and has been able to get the Cathode follower and any form of cold clipper to work and how. That is not to say that I am looking for an easy build as much as a challenge to solve. So my thought is to split the plate load into two resistors and couple between the two as below as a means to keep the EF86 operating parameters while having the coupled signal significantly less as a means to be able to do the Cathode follower, TMB and cold clipper.

I completely agree and acknowledge this is the hard way versus using an EF86 in V2 and so on. 

[zendragon63]

Hi Jalmeida - I think you will find the slightly overdriven EF86 yields not only a unique tone but can add some compression--which you may or may not like. I rebuilt and refined an amp I built several years ago into a switchable preamp LND150->EF86 and a sort of 18 Watt TMB. Used the FETs to simplify. Actually, turned out well. FWIW, I experimented with power supply time constants as much as anything but didn't hit on any revelation. But maybe an idea in there somewhere to consider. Happy 4th. Regards


dennis

[Jalmeida]

Hi Jalmeida - I think you will find the slightly overdriven EF86 yields not only a unique tone but can add some compression--which you may or may not like. I rebuilt and refined an amp I built several years ago into a switchable preamp LND150->EF86 and a sort of 18 Watt TMB. Used the FETs to simplify. Actually, turned out well. FWIW, I experimented with power supply time constants as much as anything but didn't hit on any revelation. But maybe an idea in there somewhere to consider. Happy 4th. Regards


dennis

Thanks for sharing. I am studying it. Creative solution for sure.