Some uses for old transformers

[mashaffer]

I have a bunch of PTs for solid state equipment with secondaries ranging from 12V to 70V output and one microwave tranny. Not wanting anything to go to waste I have a couple of ideas to run by you folks.

1. I have searched on the topic of using E lam PTs as PS filter chokes and am getting seemingly conflicting opinions so maybe we can clarify that a bit. It seems that the big concern is DC current saturating the core and reducing inductance. Some say that it won't work while others seem to have been able to make it work with reasonably low currents.

I would be looking at using fairly substantial (SS power amp) trannies and running no more than about 120ma through them. I would only need between 2 and 5H for my purposes. Any personal experiences with this? Worst case I suppose would be to disassemble and re do with air gap but that is a lot of work.

Also on this topic would it be safe to assume that in a step down transformer the primary is likely to give the higher inductance?

2. I want to cobble together a ghetto static gm tester and was trying to come up with a parts bin B+ supply. Normally a microwave oven tranny (MOT) would not be of any use unless testing big transmitter tubes but then I thought of all of those little amp designs I have seen with back to back filament trannies and thought why couldn't I do something similar here.

If a MOT puts out say 2KV when fed 120V input feeding it with a 12V filament tranny should give us about 200V. Why not? By feeding 6V, 12V, 30V etc one would have a wide range of voltages to choose from.

Thoughts?

[Eli Duttman]

Mike,

The trafo that puts out 70 V. has to be pretty hefty. Consider that P = V²/R. You can make use of that trafo to energize the B+ rail of a tubed power amp. The last circuit here gets the job done.

TANSTAAFL applies. You have to use AC motor run caps. in the "arm" positions. 'Lytics are fine in the central "spine", as polarity is fixed.