• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

An all DHT push pull amp.

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I'm on my way to building my first all DHT amp - time to use DHTs all the way through. It will be all balanced. I've fixed the tubes for the first experiment - 3A5 diff pair cap coupled to the volume control, 1J6 driver and either cap or transformer coupled into 2a3 output stage. Danbury output transformers in the first instance - they're pretty good and I've used them before. All on a stereo chassis. The ultimate amp will be two monos, and more like 30 into 26 into 2a3 with O-netics iron. This is a dry run. Rationale:
a) 3A5 is surprisingly good and very clear, 1J6 is a decent driver and between them they should have enough gain.
b) volume control is after the first stage since I intend to drive the amp straight out of my DAC digital board, which has DC superimposed on it. I do this at present and it works very nicely.

Definitely DC current sources and Morgan Jones CCSs for the first two stages. I thought of using AC for the 2A3s.

I'm quite excited about this - I've been building up to it for 6 months with various experiments. I'll try and write out a circuit diagram when I have it working.

Any comments so far? Andy
 
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Any comments so far?
Only to say it sounds like a recipe for success, so long as your speakers are satisfied with the modest output from PP 2A3s (but I'm sure you have this in mind). An all-balanced design is THE answer for low noise. I doubt if you really need a CCS in the tail of the second stage but it won't hurt.

Good luck with it.
 
I doubt if you really need a CCS in the tail of the second stage but it won't hurt. >>

It's not direct coupled, because the volume control is between stages one and two, since it has to cope with DC on the signal to the first stage. I made the volume control 100k in the first instance - may need tweaking. Andy
 
Hi Eusebius

Sounds pretty nice to mee! Will you be using the shunt kind of pot for volume? I mean the one with the two resistors of same value going into the extremes of the pot, and the wiper connected to either side of it? I have never seen it done, but shall work, although I don't know how heavy a load it will represent for the 3A5...but then, I don't know a lot of things..

I am curious how this turns out. Any chance of a schematic of what you have in mind (also to clarify the connection of the volume control). It just makes understanding easier!

Good luck with the project - winter has just begun!

Erik
 
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