• 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.

Newbee looking to build Valve Preamp

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Hey Tony,
I'll assume you were talking to me. The grid choke is simple. Two bay bobbin, one bay reverse wound so that the turns next to the center tap are closest to the core stack. This way the capacitance works for you a bit better, and the signal ends of the inductor are farthest away from the center of the coil.

This works best for balanced drive. If you want to use it for phase splitting, you'll want to interleave the two halves.

I have them wound on a 1" scrappless EI lam. Square stack, with a .002" gap. I don't have the number of turns handy, but it works out to ~100 Hy per half/400 Hy end to end when stacked with M6 or M4 or even better still M3 or one of the high perm Nickel alloys will of course give more L, but with lower max flux density.
cheers,
Douglas
 
hi douglas,

at 400H and 1 in. sq. core, a #40 wire may be required, am i correct? i am thinking of winding it biffilliar, any thoughts?

i am building an output traffo with 8k anode to anode, i am using a 1 1/4 inch core stacked to 2in depth, i can make it 10k easy.

about the ccs, i am more comfortable with bipolar ones instead of mosfets, have you tried them on your amps?

again thanks a lot.

tony
 
They are not wound bifilar. One could make an interesting 1:1 TX that way. Single conductor, one bay wound each direction to fill it. I can consult the winder for the gage of the wire. Since they are not expected to carry any voltage to speak of( AC signal + bias ), the insulation is not extra thick.

I like the MOSFET, they can be made 2 terminal, instead of the three that is required for bipolar. If you're comfortable with bipolar, the CCS is for a current sink, and for a resistive voltage reference, there is no special reason to require MOSFET. I just am more comfortable with them...

cheers,
Douglas
 
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