WA88 Pi filter and Schottky diodes.

[bob orbell]

Good morrning all, does any one have information on upgrading the heater supply on a WA88 please, I already have some diodes (schottky) but need to know what value of capacitors to buy and I would think that a resister will be necessary to lower the voltage a bit. Just fitted Evox Rifa capacitors and Hex-fred diodes to the HT, sounds very good so far, although the Rifa's were pricey, any help please. BOB

[John Caswell]

Hi Bob,
The "official" circuit shows C14/C17 to be 10,000µF/16V capacitors with the pi series R30 to be between 0R47 to 0R68 depending on whether you have input relay switching or not. Because the actual heater current can vary with different makes of valves I prefer to "tack in" a 0R47 then adjust finally to give 6.1 -6.3v on the heater pins of the last valve in the heater chain.
I always aim to underrun the heaters slightly.

John

[bob orbell]

Thank's John, that gives me a guide to work to. BOB