• 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.

Which 6SN7 preamp should I build?

Here's the one I'm using:
53188d1131713130-12ay7-6sn7-preamp-psu-check-6sn7-with1n4007.jpg

A lot of people here helped me with the circuit design.
I think removing the .047uF cap is the only change I've made.

Glenn
 
You know, I should mention that this is not really a preamp. I think it has unity gain.

Trying to figure out why it is a unity gain config.

Common cathode followed by CF no?

Won't there be an amplification of ~20?

Please correct me if I'm wrong or not understanding something here.🙁

If this provides no gain then maybe a better option to a CF between my cdp and ss power amp for that tube warmth.
 
I am planning on building this preamp, what is the diode for on the connected to the grid of the second triode?

It's a polarity protect diode that keeps the control grid from going positive during power up. It shouldn't really be necessary since 6SN7GTBs were designed for operation in Class *2, and the control grids were hardened and equipped with radiator "wings".

You could also avoid the diode by separating heater from DC power. Power up the heaters before turning on the HV DC, and positive grid voltage won't be a problem.

Otherwise, the diode adds a non-linear, voltage variable capacitance to Cgk. Not having nasty, non-linear, voltage variable capacitances is one of the advantages that hollow state has over solid state.
 
Thanks! I'll search for a 6SN7 preamp circuit. :wave:

I've built the following circuit, and many variations thereof, many times over the last ten years or so. It's a very adaptable and clean circuit, with less distortion than the SRPP circuit. If you will use it with multiple sources, leave the input capacitor in to block DC from the input tube grid. It's very easy to build, and if you use a decent power supply you will be very pleased 🙂

Here's the one I'm using:
53188d1131713130-12ay7-6sn7-preamp-psu-check-6sn7-with1n4007.jpg

A lot of people here helped me with the circuit design.
I think removing the .047uF cap is the only change I've made.

Glenn


The 6CG7 will work perfectly in it, and will require no parts changes. Gain should be ~10 or so. The diode isn't strictly necessary, but wont hurt a thing or effect sound quality in any way. It protects the grid during power-up and then reverse biases itself out of the circuit.
 
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> Between pin 2 and 4 mess a coulping cap?

No.

Pin 2 probably sits around 125V. Pin 4 "wants" about a 125V bias to be happy, to get significant voltage and current in its cathode resistor. We could block V1's plate voltage, then re-establish bias for V2, and sometimes that is best. But this way works, and is *simple*.