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Given one 12AX7 how would you run it given the rest of the amp is SS?
Given one 12AX7 how would you run it given the rest of the amp is SS?
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Old 23rd November 2017, 01:57 AM   #1
Printer2 is offline Printer2  Canada
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Default Given one 12AX7 how would you run it given the rest of the amp is SS?

Heard some of the Joyo amps running one tube and PWM output, sounds pretty good. I was wondering what the circuit was like and nobody bothered to dissect one yet. So I was just wondering what you would do given few constraints.
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Old 23rd November 2017, 03:53 AM   #2
dotneck335 is offline dotneck335  United States
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Put it as the FIRST preamp stage, like a Fender AB763 circuit.
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Old 23rd November 2017, 06:57 AM   #3
artosalo is offline artosalo  Finland
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One halve as voltage amplifier, the second as cathode follower (to get lower output impedance).
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Old 23rd November 2017, 08:03 AM   #4
chris661 is offline chris661  United Kingdom
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I'd swap it out for a 12AU7, run it push-pull into a transformer with a load and get some of that sweet saturation that valve-based output stages are great for.

Chris
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Old 25th November 2017, 01:12 PM   #5
thoglette is offline thoglette  Australia
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If I have to stick with 12ax7, with cold cathodes.

Frankly, with Just One Tube(tm) I'd be going for a triode/pentode tube, with the triode set up with a cold cathode and the pentode feeding into a transformer& speaker emulator to get that overdriven output stage sound.
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Old 25th November 2017, 10:10 PM   #6
Printer2 is offline Printer2  Canada
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So a Champ of sorts. Not bad.

The 12AU7 in P-P is something I never considered either, there are a few dual pentodes with a shared cathode. Might be interesting also.

I drew up a 12AQ5 amp with a 12AX7 with cathode follower, actually had it wired up. Just needed some input gain. I chickened out and went with two triodes in series as a BF Fender circuit.

Well we can't get any more varied than that can we? I will have to think about it some more. I have been more concerned in the last week with a 12V6 amp I want to build. I think I got it down to a sort of 5F6 Bassman - Paraphase Deluxe.
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Old 25th November 2017, 10:18 PM   #7
Mark Johnson is offline Mark Johnson  United States
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Given one 12AX7 how would you run it given the rest of the amp is SS?
As cathode followers to drive the VIN- and VIN+ inputs of a bog standard LM3886 chip-amp.
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Old 26th November 2017, 12:50 AM   #8
Printer2 is offline Printer2  Canada
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Quote:
Originally Posted by Mark Johnson View Post
As cathode followers to drive the VIN- and VIN+ inputs of a bog standard LM3886 chip-amp.

But the reverb goes between the CF and the chip!


Anyway. just for kick might try this with a high voltage convertor running off a 12V laptop brick.

Click the image to open in full size.
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Old 26th November 2017, 02:23 AM   #9
AquaTarkus is offline AquaTarkus  Canada
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Quote:
Originally Posted by artosalo View Post
One halve as voltage amplifier, the second as cathode follower (to get lower output impedance).
Seconded. And have the voltage amplifier triode as your second preamp stage, so that it can be overdriven for some nice valve distortion. Then have the cathode follower DC-coupled to the voltage amplifier triode,for more 2nd harmonic warmth.
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Old 26th November 2017, 02:44 AM   #10
thoglette is offline thoglette  Australia
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Quote:
Originally Posted by artosalo View Post
the second as cathode follower (to get lower output impedance).
Waste of a triode. Might as well use a MOSFET.

Or do you have a clever scheme to drive the CF to clipping/cuttoff?
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