Stancor 12.6 VAC Transformer

Stancor P-8130  heater transformer for tubes,

117 VAC pri to 12,6 with a center tap, 2 amps sec. juice,

that is all i have to report for now, Catalog Page:
http://www.alliedelec.com/images/products/datasheets/bm/STANCOR/70213238.pdf

Purchase 
http://www.alliedelec.com/stancor-p-8130/70213238/

print>

Primary inductance at 50Hz?

darn, forgot to measure L, 

have to use the lam catalog,

L=(0.3993^-8) K1 N^2 u-ac

L=(0.3993^-8)  x 0.9 x 711T^2 x perm
L=(0..3993^-8) x 0.9 x  505521 x perm
L=0.0018 x perm

barn roof lams lace 1 x 1 could yield 10,000 on a clear day,

so ballpark Henries might be  .0018  x  10 ^4  = 18 Henries

so reactance =  6.28 x 50Hz x 18 = 5652 ohms but wait!

we have an over stack which is probably used to get it to run cool at 50 Hz so

pump it up by 1"/.75" =1.33 times the whole mess, so 7.5K Ohms @ 50Hz,

60 Hz  would give 9 K Ohms

pri current = 120/7.5K = 16 ma excitation @ 50 and 120/9K=13 mils @60

heat?  current and voltage out by 90, so no heat unless DCR moves PF,

what do we use, cosine?  pri DC R at 17 ohms, 17/9K =99.99 PF, not bad,

lets wind 711T on some nylon and re-lace core, then we can get real numbers  for L and thus perm...


ok after rewind we get about 12 Henries, checked at 22 volts from the HP,

might go up at 120 vac, so barn roof perm goes down to

L=0.0018 x perm,  12=0.018*u-ac,  u-ac= 12H/0.0018,

1" stack  u-ac (18 mil non gr orient) = perm of 7333

reactance now at 4.5K Ohms, 5.25 ma at 22 v-ac excitation,

I was mostly joshing. But we do know that some tight-wound power transformers are fine audio trannies in less fussy work. 2-4-1?

> barn roof lams

I'll try that. I just tore a roof off a barn. It is corrugated tar-paper.

> heat?  current and voltage out by 90, so no heat unless DCR moves PF

There's heat because the non-infinite inductance passes a current which you have calculated:

> pri current = 120/7.5K = 16 ma excitation @ 50

From print: 17 Ohms. 17r*16mA^2= 0.004,3 Watts, which is indeed wonderfully small.

But that is not all.

There is also heat because of eddy currents in the iron. As an audio transformer this will appear as a shunt resistance across the "un-loaded" output. The shunt resistance varies with frequency. In bad work, this is messy. In good work, these losses are "small" and may be neglected or incorporated in fudge-factors (unless you pay a fortune, an audio transformer has a couple-dB loss and we don't try to figure how much is from what).

Anyway: It's crossing 7K impedance by 50Hz. Turns-ratio squared says the secondary could be 107 Ohms. Connected in these impedances we get -3dB at 50hz, probably very-smooth 200Hz-800Hz, and response above that depending on winding layout. Pri-Sec may support 5KHz, maybe another octave unloaded (line to mic). Dual-coil may be down at 1KHz.