EF86 LITE w/ dissimilar EL84/6V6 power section

brownnote · Post by **brownnote** » Thu 04/26/07 12:18 pm

Hey everybody,
Here's a possible weekend project for someone, this is based on a proven design, but there may be some errors so give it a careful look...
It's untested but I think it will get you about 99% there.

...just posted this for discussion on the BN forum:

dartanion · Post by **dartanion** » Thu 04/26/07 12:32 pm

Hey Rocco,

Looks like a fun project, although I have remodel work to do this weekend

Have you tried the differential output pair like this before? Just curious as to how well this works. Any specific reason for the grid stopper values as such on the power tubes?

nomad100 · Post by **nomad100** » Thu 04/26/07 2:05 pm

is this implying 1 6v6 and 1 el84 in a push pull config?

briane · Post by **briane** » Thu 04/26/07 2:41 pm

This is very cool to see... I had been wondering how this might sound....Now I have a layout to try out.

Thanks a lot rocco!

Looks PP to me based on the OT.

Bringing up a plexi 1986 this weekend, so this build is not on my short list.....

Anyone have any theories on how this migh sound? How might the phase-cancelation common to PP be affected, in regards to noise floor and harmonics?

tarzanalog · Post by **tarzanalog** » Thu 04/26/07 2:47 pm

This is JUST what I was looking for...

THANKS ROCCO!!!

brownnote · Post by **brownnote** » Thu 04/26/07 3:36 pm

Yes, PP.
I haven't built it yet, maybe someone will beat me to it

I'm just taking a stab at balancing the pair...I'm sure a scientific approach would be more effective.

tarzanalog · Post by **tarzanalog** » Thu 04/26/07 3:38 pm

Scientific approach?!? I think your signature line says it all...

Alexo · Post by **Alexo** » Thu 04/26/07 3:39 pm

Just curious - Why the 25UF cathode cap on the 6V6 and 50 on the EL84?

Michael · Post by **Michael** » Thu 04/26/07 3:49 pm

Rocco,

Built something like this using a modified HO in SEL. Would like to try the PP next. For the SEL, using a 12AX7 instead of an EF86, but was just recently pining to try an EF86 in the first stage. It works great. I added a balance pot between the two power tubes, so you can swap many different tubes. So far we have run everything from 6EZ5s to KT88s in the octal socket. The pot lets you balance in that most scientific of ways, live, using your ears.

Note that these are two separate pots, not a ganged pot. The first is the master volume; the second is for signal balance. Maxed one way or the other, it essentially shuts down one tube.

brownnote · Post by **brownnote** » Fri 04/27/07 2:16 pm

Alexo wrote:Just curious - Why the 25UF cathode cap on the 6V6 and 50 on the EL84?

I haven't done any calcs but based on proir builds this is where Im starting.

Alexo · Post by **Alexo** » Fri 04/27/07 3:03 pm

Cool, actually that makes sense since the 6V6 has double the resistance of the EL84's cathode resistor, you would need to halve the capacitance of that cap to keep the same corner frequency.

nomad100 · Post by **nomad100** » Mon 04/30/07 3:41 pm

would that design cause highs to be attenuated differently to each tube, and differently threw out the travel of the pot?

brownnote · Post by **brownnote** » Mon 04/30/07 9:17 pm

nomad100 wrote:would that design cause highs to be attenuated differently to each tube, and differently threw out the travel of the pot?

The grid-stoppers on each tube are different, so you’re going to have some band pass filtering there...

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EF86 LITE w/ dissimilar EL84/6V6 power section

EF86 LITE w/ dissimilar EL84/6V6 power section

Built similar SEL...