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RE: I think one needs to take that quote with a big grain of salt...

71.23.206.76

In Reply to: RE: I think one needs to take that quote with a big grain of salt... posted by unclestu on April 19, 2015 at 21:17:17

the Silver 7 prototypes used paralleled pair of A-451 outputs.

the Mk VI's used a model specific transformer that was never
offered as a catalog item. And it's primary impedance was
nomially 1650 ohms CT. As opposed to the A451's nim pri impedance
of 2200 ohms CT. The A-440 (and A-441) had a nom pri impedance of
4300 ohms CT and it is the 440 series that had the tertiary winding...

There was another Dyna output with a tertiary winding... though it never
went into production... the original tranneys developed for prototyping
the ST-70 amp had an ouput model A-460--- which had a 4300 ohm pri CT with separate screen windings.

MSL

Builder of MagneQuest & Peerless transformers since 1989

Follow Ups:

PS never worked on a Mk VI - unclestu 02:58:08 04/20/15 (0)
but the transformer sizes were similar hence my thinking they were 440's.
However if they indeed were custom and used only for the Mk VI and used a UL design, it would explain why they went ballistic so often . GE 8417's screens can not take more than 400volts continuously: oh they my work for a while but eventually they go up in smoke
Whoa !!! - unclestu 02:52:59 04/20/15 (1)
I'm getting senile.
I have what I thought are 441's with supposedly tertiary windings but IIRC the seller told me the primaries had a lower impedance of about 1650. Nice light blue potting cases, but no other id. Luckily I bought them before the Silver 7's came out.
Thanks for the info and crash course in dyna iron.
Funny that Dyna came out with those tertiary winding iron so late. I thought the whole idea of UL was to cut manufacturing costs by eliminating the fixed screen circuit as in Altec 340's, 350's and Allen organ amps which regulator tubes like OD-3's and such to power the screens.

UL transformers certainly paid off for Keroes and Hafler.

Edits: 04/20/15
- and.... - PakProtector 10:37:20 04/21/15 (0)
  That tertiary winding is also quite useful for CFB topology. That, with a fixed screen supply gives the same effective g2 U-L but with the CFB added to the mix. You can bring g2 to the cathode( with the extra winding attached to the g2's, and cathode grounded), or bring the cathode to the screen( using the extra winding tied to the cathodes and its CT grounded).
  cheers,
  Douglas
  
  Friend, I would not hurt thee for the world...but thou art standing where I am about to shoot.

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