6v6 push pull build, Altec 1594B destruction!

rage · Jun 1, 2012

I'm in the process of converting this Altec SS rack mount amplifier into a 6v6 push pull tube amp.

It was one of those swap meet buys...$20... and the thing has sat on the shelf taunting me to do something with it for about a year now.

Anyhow, pics and a mock up on the schematic...not all values are determined...and I need help setting up the CCS for the tail of the differential input. Hopefully Douglas will excuse my Medwinite experiments and lend a hand!

Initially I'll be running the 12ax7 LTP as phase splitter/driver direct coupled into the 6v6...Which will be triode strapped and no feedback.

The power transformer is the Antek 4T-320. Outputs are Edcor 15 watt 8K to 8 ohm.

Tubes will be JJ6v6.

Wish me luck! I have a habit of wrecking things!

All input and suggestions as well as criticism is welcome.

rage · Jun 1, 2012

few more pics, partial schematic.

dcgillespie · Jun 1, 2012

Rage -- based on the basic schematic topology and values you have already provided, your CCS will need to operate at ~ 2.5 ma.

Good luck with your project!

Dave

GordonW · Jun 1, 2012

I'm guessing Kegger will be along any time now... I'd expect he'll suggest maybe using a 12AT7 instead of the 12AX7, due to "distortion cancelling" nature of the match of the 12AT7 and the output tubes. I like that concept, personally...

Regards,
Gordon.

djnagle · Jun 1, 2012

You might want to talk to Doug about his e-linear design as well.

With all these amps you are building, you might want to look at building the Steve Bench tube active crossover as well.

Kegger · Jun 1, 2012

Yep Gordon got it, 12at7 is the tube I'd use there.

(with no feedback the 6bk7/6bq7/6bz7 looks good to)

rage · Jun 2, 2012

I'll look those tubes up Keg.

I'd be pretty flexible on different dual triodes to try out there... in retrospect I wish I would have put holes for two more 9 pin sockets in that plate...then I could have used pentodes in an LTP.

I've got some homework to do on setting up the LTP.. I've ordered the parts for the cascode based on what Pak told me to use...just need to figure out how to set it up for ~ 2.5ma quoted above or in the ballpark. I *think* I can use the 70 volt taps on the Antek transformer to feed the CCS.

Gordon - Is the 12at7 higher in distortion vs the ax7 hence the cancellation? Some cancellation is done in the output stage of distortion too?

dcgilespie thanks for the suggestion!

Dennis - I'll look at that active you mention! Sounds interesting.

djnagle · Jun 2, 2012

You are not that far along to rip out on the stuff and drill 2 more holes.....easy peasy!

Hell, I'll time you......GO!!!!

Kegger · Jun 2, 2012

If you look up the distortion spectrum of that 12at7 LTP you'll see it has a very nice
waterfall with good/even distortion distribution, I believe if you search for baby huey
you'll find an very similar setup as your trying to put together, 6v6 push pull with the
12at7 in an LTP with CCS. (I believe that's the amp I'm thinking of)

If you give some info on your CCS I may be able to Sim it, and set the current for it.

djnagle · Jun 2, 2012

Is this the one you are thinking of Keg?

http://www.diyaudio.com/forums/tubes-valves/72536-el84-amp-baby-huey.html

Kegger · Jun 2, 2012

No that's not it, I'll try an find what it was.. (must be different name)

It's a well established push pull 6v6 amp schematic though.
(maybe it was the updated musical machine)

Kegger · Jun 2, 2012

AHH, I was just a bit off!

El' Cheapo was what I was thinking of..
(search and you'll find plenty on it)

I think Doug had a hand in the CCS for El, Cheapo..
(so maybe it's the same as your contemplating) ?

Here is 1 schematic link.. (6AQ5 an 6V6 are the same basic tube in different bottles)

jaymanaa · Jun 2, 2012

Micah has an awesome CCS circuit he designed. I have 4 of the boards he made, I doubt if he has any left though.

jaymanaa · Jun 2, 2012

That 4th pic reminds me of a Fisher 80 or 100. Are you going to build a cage?

djnagle · Jun 2, 2012

I would think he would set it up vertical with that pretty Altec green showing.

Kegger · Jun 2, 2012

Here is a couple Diyaudio threads for El' Cheapo......

http://www.diyaudio.com/forums/tubes-valves/169914-el-cheapo-builders-thread.html

http://www.diyaudio.com/forums/tubes-valves/208340-want-use-el-cheapo-p-i-scott-lk72-rebuild.html

rage · Jun 3, 2012

Ok I'm leaning toward 12at7 for several reasons now.... and considering "e-linear" as well as pentode mode. Allows me to eliminate two caps.....even if it means feedback.

I've got some nice 120uf motor runs on hand as well, pretty sure I can neatly stuff at least one of those underneath.

Will study El' Cheapo.... looks like that CCS setup will serve me well.

Since my voltage supply for the CCS is lower vs whats used in El cheapo, pretty safe to assume a different resistor value on the bottom of the cascode?

Shadowdog · Jun 3, 2012

Here is Poinz's Musical Machine. Well regarded as the previously mentioned ones. Threads @ diyaudio etc. There is also a non CCS version using a 5965 tube.

Shadowdog · Jun 3, 2012

5965 may be similar to 12AT7 , & you could always add CCS.

dcgillespie · Jun 3, 2012

I have seen diodes used to connect the plate to the screen grid in pentodes configured for triode service before, but for the life of me, I have no idea what it is supposed to accomplish. Anyone want to weigh in on this one?

Dave

6v6 push pull build, Altec 1594B destruction!

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