• 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.

Transformer Options

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Howdy there, I’m building an over engineered preamp that is one half Salas DCG3 powered with the DCSTB to boost my turntable signal the necessary 10dB gain, and one half Aikido ACF tube buffer powered by his PS-Tube to help any digital source that doesn’t need any gain but needs that little bit of help after encountering a 50K potentiometer. They’re gonna be boxed together, signal and convoluted relay selection circuits in one box and the power supply just an umbilical cord away. This is my first tube build and I didn’t realize how much different choosing a transformer is compared to solid state, especially if you decide to use a tube rectifier.
So first transformer (of a total of 4 in the PSU box) for the ACF I tried was a 500V CT /6.3V/5V Hammond and when I brought the 6NS7s up for the first time, I was pleased to see that both channels were dead on the same plate voltages, however, I was quite bummed to see the plate voltages sitting at an unfortunate 158V at the first triode and 75V at the second.
So obviously, the Hammond 270CAX ain’t gonna cut it.
What would a good voltage be to handle the voltage drops and other fools in the way of reaching the 200-300V necessary? And what is it I’m looking for? Should I try for 285V first a d approximately 215V at the second triode? If anyone has a better (cheaper) option than the Hammond, I’d be nothing but ears for that.
Regardless, thanks for advice hints and bonuses.
 

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What are you using for the rectifier tube? Right off the bat I see that the design says you can use a 5y3 or a 274b, but as far as I can see it doesn't mention that you have to change the value of C1 if you use those tubes.

I am probably being blind, but I don't see why you couldn't hit a b+ in the mid 200v range with your transformer.
 

PRR

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Joined 2003
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> 500V CT

250V per side, 30mA current, 5Y3 bottle, you should have 300 VDC at C1.

Not that I would flip-out about 75v per tube, when you can't need over 3V peak output. It should play perfectly fine.
 

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Now the question is, what exactly do I want at the first triode, the second triode, and if I add a choke at J1, what values should I look for, and how will that mess with the voltage? I would assume I would treat it as resistance in series, but I know just enough to know that nothing in this scientific discipline is that cut and dry. So now you know what I had done to suck that voltage, what should I do to optimize the circuit for a 01dB gain buffer at most, would actually like to come in as close to 0dB as possible. Thanks again all y’all who got back at me so quickly. If you could even point me in the way of some formulas, I’d be really excited to figure it out myself. One concern still lingers, and that is that even under no load, my dim bulb is nowhere as dim as I’m used to it being. Normal with tubes? Or maybe a four transformer PSU? Have a great day...
 
Shouldn't that be pretty close to no gain as-is?


Voltages look balanced enough to work fine and as far as adding a choke, you want to look at the DCR or DC resistance of the choke, that'll tell you what you can expect for voltage drop by swapping out R5 by applying current times resistance.



With 4 transformers your bulb will light up a bit, even with no load, as each transformer will have its own parasitic power usage.
 
Thanks, I’ll start looking to see what’s a normal choke value other people have used in this build maybe. I’m wanting to keep a smaller value at R5, just to even out any ripple and add the choke as well for as flat a line as possible, so it’s off to the interwebs! I appreciate your help.
 

PRR

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Joined 2003
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....what exactly do I want at the first triode, the second triode,.......

How much, exactly, money do you want in your wallet?

"More than enough"? Not an exact number.

For specific signal level, THD will go down as long as you keep jacking the supply voltage.

Until something blows-up.

And if 900 Volts gives 0.01% THD, maybe you could get to the same place with a 19 cent chip?

And some guitarists deliberately low-Volt their amplifiers for a more pronounced tone.

Anything 160V-260V seems plenty good to me, "more than enough" for hi-fi demands.

The lower goal incidentally allows more ripple filtering, less buzz (though this amplifier circuit has some rejection).

Don't over-think. And don't think that there is a "magic voltage".
 
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