FX Loop Advice for Hot Cat with VVR Build

[bcmatt]

See limiting values p5
https://frank.pocnet.net/sheets/010/e/ECC83.pdf

Thanks for the link and page number. I've learned something new. So the max cathode to heater voltage on a 12ax7 is 180V.

So now with my changes it's about 120V difference (177V-58V). That seems better.
Anything else look out of wack?

[lonote]

Thinking 58V elevation is right in the zone. I seem to recall Merlin suggesting 30V-60V.

[martin manning]

So the max cathode to heater voltage on a 12ax7 is 180V.

Not always. Some are rated as low as 100V and some as high as 200V, and the positive and negative limits may be different.

[bcmatt]

So the max cathode to heater voltage on a 12ax7 is 180V.

Not always. Some are rated as low as 100V and some as high as 200V, and the positive and negative limits may be different.

Oh, interesting. I guess I shouldn't assume. I should check what I have in that position. I popped a somewhat modern (less than 20 years old or so) Tung-Sol in the loop position. I just have a box of preamp tubes with varying levels of labels still visible. That one's label was still bold and clear, so it earned a spot in an amp.

[pdf64]

... Some are rated as low as 100V and some as high as 200V, and the positive and negative limits may be different.

I get the impression that the h-k limit is 180V design centre, 200V design maximum

https://frank.pocnet.net/sheets/093/1/12AX7.pdf
https://frank.pocnet.net/sheets/093/1/12AX7A.pdf

[martin manning]

You may be correct Pete, but IDK what the current manufacturers are doing with respect to quality control.

A look at the current 12AX7 Vh-k specs as published:

JJ Electronic 180 "Limiting Value"
New Sensor +100/-200 "Not More Than"
PSVane 180V "Limiting"