EF86 vs ECC83

[leadfootdriver]

I have ZERO experience with an EF86. I wanna' redo my little project amp from a single ended JCM 800 to a Vox circuit, and was thinking an AC4 would be the ticket since I only have 3 tube sockets to use.

I'm hoping for some low volume preamp distortion so I was wondering if it would be better to go ECC83 or even 81 instead.

Here's a schematic. What would you do?

[mozz]

I'd say go for the pentode, be different. I just bought some evaluation type boards and have a 6688 in there now, gain of 200 with some stock values.

[Justin Thomas]

Built two EF86 amps; one with an LTPI & one with a Cathodyne fed by the other half an AX7... The one with a Cathodyne had 2xEL34, the other had 2x6V6/6L6.
The first was EF86>Volume & Tone>Driver>Cayhodyne>EL34s. Grinds like a mofo.
The 2nd was EF86>Volume & Tone>LTPI>6V6s. This one is still in process, as I'm trying to get rid of some excessive brittle highs.

I don't know how much "preamplifier distortion" you'd get with a single pentode, but it can certainly drive a PI harder than a paralleled AX7. I think the difference is more in the "character" or "flavor" of the distortion. Both my EF86 amps have more Presence than my straight-up Spitfire. Definitely in the Slice&Dice department - cuts through a mix.

Justin

[Jazz P Bass]

The EF86 is a wonderful tube.

I have seen them used in preamps of 1960's console stereo's. (RCA)

[leadfootdriver]

Thanks for the replies..

So, what is it about an EF86? Does it have a lot of clean headroom? I like the idea of parallel Triodes. It was fat when I tried it years ago.

[pdf64]

I don't see how you will get low volume pre-amp overdrive with an AC4 / 3 tubes, one being a rectifier, the other an SE power tube?

[leadfootdriver]

Maybe I could run 2-ECC83's with 3 stages of gain before the Cathode Follower. I'm not hung up on reproducing the schematic exactly. I'm definitely not doing a Tube Rectifier..

[leadfootdriver]

I need a new PT. I think this would do. What do you think?

https://www.hammfg.com/files/parts/pdf/269JX.pdf

[eschertron]

I need a new PT. I think this would do. What do you think?

https://www.hammfg.com/files/parts/pdf/269JX.pdf

I'm using that one in a 2xEL84 amp. 3 preamp tubes. It's a decent PT, however I think next time I'll step up to the 270CX (550vct), mostly for the 2nd filament winding to use for control circuitry.

[leadfootdriver]

Cool then. My original PT was designed for 1 preamp and 1 el84. I put another 12 a x7 in there and it sounds a bit thin, especially when I plug it into a 412 cab. It just doesn't sound right. I'm hoping a more powerful PT will fill the sound out.

[Loogie]

If you're looking for lots of gain from one bottle without pre-amp distortion you could try a cascode. I've been experimenting and its definitely possible to create enough gain to overdrive an EL84. I'm using a 12AT7 with a 68k anode resistor and a 820R cathode resistor. Its sort of non-standard for guitar amps, but it sounds very good in my prototype. I settled on 68k just by trial and error.

[TimmyP1955]

I'd avoid the EF86 like the plague. My experience with them is in Matchless DC30s. I have to go through 8 to 12 tubes to find one that's sufficiently low in microphonics that our clients don't complain.

[leadfootdriver]

LOL

I will then. Parallel Triodes is sounding good.

[Zozobra]

The issue that most EF86 designs have is that they try to screw every last drop of gain out of them, rather than run them sensibly and focus on their tonal properties. Lower the gain and the microphonic issues go away.