The power transformer in my 222C Amplifier is shorted, and I need the
voltages, (HV Secondary, etc) in order to locate a replacement.
The transformer is marked TR12-3-1,
The tube complement in my 222c is:
one 5ar4, two 6GH8, four 12ax7, four 7189
Any info is appreciated.
Dan,
You'll need a five volt winding for the rectifier tube filament (unless
you use a pair of diodes to sub for the tube) and a six volt winding for all
the other tube filaments. Those windings will be pretty hefty to carry that
much current, perhaps 1.5A for the rectifier and 4 or 5 amps for the other
tubes (wild guesses). Look at the thickness of the wires on the old tranny.
If you can scrounge up a receiving tube manual, you can calculate the totals.
To get a rough estimate of the total B+, look at the voltage rating of
the filter caps on the rectifier tube. There is normally about 10% "headroom"
so the caps never see anything at or over their rated voltage even if the AC
line goes high. Keep in mind that if you substitute diodes for the rectifier
tube, the B+ will not be loaded until the other tube filaments warm up, so
the B+ will go immediately to the peak value when the unit is powered up.
Also, there is some voltage drop when using a tube as a rectifier, so subbing
diodes with the original transformer (if you find an exact replacement) may
exceed the cap voltage rating.
Multiply the transformers rated secondary voltage times 1.414 to get the
peak value. For example, for a secondary rated at 260 volts, you multiply
that by 1.414 to get the maximum voltage the input filter has to handle. That
comes to about 367 volts DC (unloaded). With some overhead so the filter is
never pushed beyond it's voltage rating, it would likely be rated at 400
volts. If the filters in your amp have a different voltage rating, you can
recalculate to get an approximate value for the transformer voltage rating.
Ray
