In need of help (again) identifying some mystery (allegedly Fisher 125) transformers

[AlexHempel]

Somewhat off-topic but do DC screen ratings apply in the same way when operating in UL? Since the plate and screen voltages move in tandem in UL it seems intuitively that maybe some tubes could handle more DC screen voltage in UL than they could otherwise. Anecdotally, Jack from electra-print told me about a UL 803 transmitting pentode amp he built with B+ at twice the screen rating (!) that had no reliability issues. Maybe this is a special case because these huge transmitting tubes are so rugged and that screen voltage rating was probably set based on the assumption they'd be used in a very different application than a SE audio amp.

 

[TriodeLuvr]

The 6146/A/B is a derivative of the 807/1625 and exhibits similar characteristics in this regard. The screen is rated for 3W dissipation. This is what sets the limit. I don't know if any of the data sheets show the relationship of screen current to screen/anode voltage and output power.

 

[trainbuftony]

The big Acrosound transformers for 6146 tubes had an Ultralinear winding that was separated from the plate winding.
That's what you need for big power on low screen voltage tubes.
Maybe someone will make you a copy...

 

[gadget73]

I have what seems to be a functionally identical spreadsheet for doing impedance tests. Plug in the voltage and load and it does the rest. Much easier than manual calcs.