EF86 as a later gain stage?

10thTx · Post by **10thTx** » Sat Nov 03, 2012 12:06 pm

Just a couple more with the 5879. I built these also.

with respect, 10thtx

jon · Post by **jon** » Sat Nov 03, 2012 4:01 pm

Dr.z prescription ES

JazzGuitarGimp · Post by **JazzGuitarGimp** » Sat Nov 03, 2012 4:45 pm

I think you're on to something, Lefty - in his preamp book, Merlin suggests that pentode preamps like to be driven hard to really get their unique sonic imprint.

M Fowler · Post by **M Fowler** » Sat Nov 03, 2012 4:48 pm

Jon I was thinking the same thing about Dr Z RXES but it only has one triode not two before the EF86, same for the Z28.

Mark

LeftyStrat · Post by **LeftyStrat** » Sat Nov 03, 2012 5:02 pm

JazzGuitarGimp wrote:I think you're on to something, Lefty - in his preamp book, Merlin suggests that pentode preamps like to be driven hard to really get their unique sonic imprint.

That was part of my inspiration. I think I might try something like two triode stages with a tone stack between them then into the pentode with Merlin's morph control on the pentode.

212Mavguy · Post by **212Mavguy** » Sat Nov 03, 2012 5:14 pm

I am wearing my nomex suit...

IMHO ef86's are not all that suitable in a v1 situation in a guitar amp where that tube's socket is configured for high gain. There are plenty of stories about folks having microphonic issues with ef86, including a close friend with a very spendy Divided by 13 boutique amp fighting this issue.

Drive an ef86 with a 12ax7 or smething else in front?

Yes. I have some experience with a lightly modded Mullard circuit (6x5 rec, ef86V1>12au7PI>pair 6v6gt cathode biased Class A. Mod was revoicing for flat freq response after disconnectiong the single knob tone control circuit, which was voiced for the speaker and cab.

It's a 60's vintage HIFI Ampex amplified speaker with Mullard circuit tube amp and JBL d208/Ampex speaker. On it's own it's use for guitar is as a clean, not very loud practice amp.

Because I don't follow rules well or pay attention to guitar tube amp dogma, I stuck a vintage Peavey Rockmaster 3 channel preamp with footswitch in front of the input. The Peavey is filled with VOS tubes, a 12at is subbed for the 12ax in V1, other than that stock. The Mullard circuit effin' SCREAMS when a strong enough signal smacks that ef86. Can be a strong boost clean, can be a dirty channel, when you set the preamp right in front of that ef86 i'ts just plain glorious, a sleeper blues and rocker with amazing variety of tones clean to scream exuding from a big fat heavy Triad OT...Tha main volume becomes the "master" with this setup, good grind at lower volumes is easy.

tubeswell · Post by **tubeswell** » Sat Nov 03, 2012 8:57 pm

LeftyStrat wrote:Very nice design! I'd love to hear some clips. Are you able to get some decent distortion at lower volume levels?

Its got quite a bit of gain in the parallel V1 input jack and with triode/pentode morph control in pentode mode and the NFB switched off. Not a screaming SLO lead overdrive type amount of gain, but plenty of gain to clip the 6V6 grids and to get a bit of feedback going (with just humble SC p'ups). It would have even more if I changed the LTP to a driver-cathodyne pair, but I like it in this incarnation.

I'll post some soundbytes next time I grab some.

renshen1957 · Post by **renshen1957** » Sat Nov 03, 2012 11:26 pm

Reeltarded wrote:Selmer Zodiac 30! No scheme here. It is on this forum though!

-boats off to deeper water-

+1 Good Call!

renshen1957 · Post by **renshen1957** » Sat Nov 03, 2012 11:27 pm

Reeltarded wrote:Selmer Zodiac 30! No scheme here. It is on this forum though!

-boats off to deeper water-

+1 Good Call on the Selmer Zodiac 30!

rdjones · Post by **rdjones** » Sun Nov 04, 2012 1:11 am

bb5000 wrote:The Weber 6S100:

https://taweber.powweb.com/store/6s100_schem.jpg

a Sunn 100S-inspired amp with lots of clean headroom, I use it for bass.

Yeah, various Sunns use the pentode side of a triode/pentode (7199 or 6AN8) as a driver before the cathodyne inverter.
There are a few Univox amps with a similar scheme.
Neither of these lines were renowned for their overdrive character, though.

There might be room for tweaking the design if the direct coupling of the stages is replaced with a master.

rd

LeftyStrat · Post by **LeftyStrat** » Sun Nov 04, 2012 4:34 am

Would love a way to compensate for the gain changes in the Merlin morph control. Maybe a dual pot with one post pentode with another resistor to ground?

Reeltarded · Post by **Reeltarded** » Sun Nov 04, 2012 4:41 am

Divide divide divide.. then conquer.

That Zodiac.. if Selmer had a distribution deal when they designed that amp Brian May would be playing through piles of them, and the British invasion would be based on the amps made by "that trombone company".

Masco · Post by **Masco** » Sun Nov 04, 2012 3:25 pm

Blackstar artisan30 has a 2nd stage EF86 w/ feedback. Something I've never seen before.
http://www.el34world.com/Forum/index.ph ... 4731;image

Andy Le Blanc · Post by **Andy Le Blanc** » Sun Nov 04, 2012 10:17 pm

thats a pretty clever feedback arrangement for a tone control.

Post by **Colossal** » Sun Nov 04, 2012 10:50 pm

Andy Le Blanc wrote:thats a pretty clever feedback arrangement for a tone control.

Interesting...10M input grid leaks...

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