ST35-BCU Bias Control Upgrade

[Thor61]

Does anyone have experience with the ST35-BCU Bias Control Upgrade by Dynakit ? If so please let me know ones thoughts good, bad or other ect... Thanks !

[EWBrown]

I recently found this one, too, it looks to be a nearly direct copy of the biasing circuitry used on Shannon's DIY35 boards. It should work perfectly well, just use it to replace the single 95W resistor and can cap section. THis will allow you to individually set each tube's cathode bias.

The general approach is to pre-set the 10K pots so that the total resistance from cathode to ground is 400 ohms, then "fine tune" from there.

/ed B

[Thor61]

Ok great to here cause I have one of Shannon's DIY35 board's ! How is it that he can claim it as an improvement in the new ST35 and old alike ? I had looked at the pics posted there and wondered how it could be as stated. So is our set-up is pretty much the same or better ? PS still waiting to receive the 6P14p-ev tubes I ordered 12

[EWBrown]

It would be a definite improvement for the "old style" ST35 (and SCA-35), either vintage or the new Dynaparts clone, which is a pretty faithful copy of the original.

THe original Dynao/Dynakit scheme of the single shared 95 ohm, 5W cathode resistor is fine, if all four 6BQ5s are closely matched.

The upgrade kit allows for balancing those 6BQ5s / EL84s which may not be so closely matched.

/ed B