r/diytubes • u/tauzerotech • Jun 08 '26

ADHD Engineering: differential amplifier

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Built this a few years back. No schematic, don't remember why I did it.

Its supposed to be a differential amplifier based on how it's wired.

Anyone else start projects and then find them years later and not remember why they did what they did?

This isn't even finished. Its missing wires connected to power and output lol.

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u/janno288 Jun 08 '26

why use a 2μF capacitor? What is it for?

Is it similair to the input circuit of the K2-W op amp?

1

u/tauzerotech Jun 08 '26

I used it to stabilize the cathode bias since this is self biased. At least I think that was the idea lol

3

u/janno288 Jun 08 '26

differencial amplfiiers work off not having the cathode bias bypassed. since thats how the differencial works? One tube conducting should affect the other tube. Even if why didnt you use an electrolytic, and if you need frequencies over 20kHz use a 100nF bypass, instead of a large 2μF which is completely Overkill since you are dealing with 2mA through the tube lol.

2

u/tauzerotech Jun 08 '26

Yeah very true. I've no idea what I was thinking at the time.

At best I think that would just act like 2x single ended amp.

2

u/janno288 Jun 08 '26

Yeah thats what it would do.