Bias test points for PCB amp

[Jon434]

There's two EL34's on a separate daughter board with pin 1 and 8 tied together and then connecting to main PCB via a 4 pin connector going to ground.

I'd like to add some test points for cathode current, and just wondering if what I've done in the picture below would work ok, or if there would be any potential problems to doing this?

Both tubes have pin 1 and 8 together, would it also be worthwhile cutting the trace separating the tubes cathodes from being tied to each other? Or would this be pointless? Just wondering if anyone with more experience.. if I've overlooked anything or if there is any potential complications? I have a spare output tube PCB to experiment on, but obviously would like to get it right first time.

[g1]

No point separating 1&8. But you will have to also cut the trace on the other side of the board that connects the 2 tubes together.

[Tom Phillips]

Situations like yours (with the traces on PC Board) are a good candidate for using a bias probe socket adapter. You may want to consider building a bias probe instead of cutting into your PCB. A plus is that you will have it available for use on other amps.

[Jon434]

Thanks g1.

I do have a bias probe but in the case of this amp, I also have a spare output tube PCB making it easier to experiment with mods or add test points etc. And being able to revert back to the stock board if necessary.

The main advantage being that the chassis wouldn't need to be removed, if a quick tube change was required.

[Enzo]

Suggestion: You disconnected the cathodes from ground then put in 1 ohm resistors, and then ran a ground wire from the rear panel off to somewhere. I would recommend running that ground wire back to the point you disconected from on the board. That way the tube currents won't have a new ground path that COULD cause hum or stability problems.

[Jon434]

Thanks, I'll try that idea.