The Pentode (Preamp) Homage to HAD

[didit]

Hello —

Cool package and project. Late I know for this particular party so apologies now. However, why not simply series connect the pentode filaments and use your 12VDC power feed?

Best .. Ian

[ElectronAvalanche]

Hi Ian,

Thanks for your feedback. Indeed a nice little project and most satisfying.

Heaters: Indeed, the 7812 would probably been able to supply the 150 mA for the 12DW7 and 400mA for the two EF86 easily. I did some reading about EF86 heaters in series and maybe I was wrong, but I concluded that this can be problematic (unequal current situation).

See here:

https://www.freestompboxes.org/viewtopic.php?t=7398

Indeed a single regulator would have been more elegant and easier, but each pcb plus parts was only about 5€, so negligible. Also now the tremolo oscillator and 12DW7 are nicely separated DC wise from the EF86 heaters.

Best, Electron

[martin manning]

Heaters: Indeed, the 7812 would probably been able to supply the 150 mA for the 12DW7 and 400mA for the two EF86 easily. I did some reading about EF86 heaters in series and maybe I was wrong, but I concluded that this can be problematic (unequal current situation).

See here:

https://www.freestompboxes.org/viewtopic.php?t=7398

Indeed a single regulator would have been more elegant and easier, but each pcb plus parts was only about 5€, so negligible. Also now the tremolo oscillator and 12DW7 are nicely separated DC wise from the EF86 heaters.

Not a problem in your case. Connections would be like this:

[didit]

As Martin has already helpfully summarized and illustrated it works fine. To generalize, any pair of identical 6.3V tubes or even two dissimilar 6.3V tubes that happen to have the same current requirements (and therefore same filament resistance) can be series connected successfully.

Best .. Ian