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Re: Dynaco A-440 Transformer - Tertiary Windings

I don't have the schematic drawn up, but would be happy to - I can describe it briefly...

The main circuit is based on the design on PAE's site at:

http://www.paeng-design.com/

The driver is a 6C45pi choke loaded (BCP-15) using the 290v windings of the TP-550 thru a Bendix 6106 for very slow turn on. I needed the driver stage to come up after the 211's had stabilized to avoid noise at turn on. Coupling caps are some old oil's - you can see them behind the input jacks.

The main B+ is around 825v - I used a pair of 866jr's, then a damper diode in a LCLC circuit with oil caps and some old Thordarson swing/smooth chokes. The 866jr's pre-warm for 4 minutes with a small timer circuit before the B+ is applied - then "slow started" thru the damper diode to avoid flash over. Dave Slagle taught me lots about Hg rectifiers - they are pretty looking but picky. Bias is set for around 65ma thru the 211's.

Output is around 6-8 wpc, nice sounding imho, though not exactly portable.

- Gary




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