Calculations for an AIKIDO

[gionag]

Hi guys,
i'm intended to build an aikido pre-amp with 2 of ECC88 (6922).

the voltage i'm intended to use for B+ is 200V and then here the calculations for the PSU:

Toroidal transofmer with a primary of 225Volt / 142Volt Sec. 70 VA.

(my calculations : 200V + 1.3V(drop of rect-diodes) = 201.3 / 1.414 = 142.3V and i estimate that 50mA is enough for both channel of Aikido).

Then... for what concern the rectifing i intend to use a "silly" Gretz-Bridge with 0.01uf bypass cap on each section (of the bridge) then a 100uf ELECT cap.

I'm right ?

And ... the last thing... i based the project about the schematic on the tubecad PCB pdf : http://www.tubecad.com/Aikido_9-pin_Mono_Rev-A_PCB.pdf) Do you think it's ok ?

thanks for support
Michele

[Andypairo]

Ciao Michele,
if you haven't already bought the transformer I'd suggest to use a higher voltage (200V ac) and to "drop" the excess voltage with multiple R-C cells, in order to bring ripple to lower level.

BTW with 200V B+ be careful not to exceed dissipation limit of the Ecc88, especially on the output tubes (been there, done that )

Aikido has a very good PSRR figure but feeding it from a clean supply doesn't hurt.

Ciao!

Andrea

[gionag]

what do you suggest to me for the Rc filter ?

and... how i have to use the "heater bias" ? how does it works ? thanks !