Output xfrmr?

[ALBATROS1234]

I was given a box full of transformers. A handful are 12v or 24v output and a few high voltage industrial control type like I used in my build recently.  One small one has multitap and odd markings. I think it's an a universal output type .  Basically one side (secondary?) Has 3 leads one had a c (common) one says 3-2 and the other says 6-8. The other side has 5 leads one says c and each of the other 4 have a number 500, 1000, 1500, 2000. My guess is that the latter is the primary and you can choose the common with the other of your choice btw 500ohms impedance to 2000ohms. The other side I assume is ohm range 3-2 and 6-8.  It's small in size like the type you might find in a radio. Has anyone seen something like this? Am I on the right track? If so maybe I can used it with a low powered output tube to make a small amp with a 6 inch speaker? If anyone has any ideas I would love to hear from you.

[PRR]

Does it have any maker? Part number?

How much does it weigh?

Picture?

[ALBATROS1234]

no markings other than whats written on the paper shell wrapped around the secondary as stated above. its old, my guess is 1950s the sheet metal mounting bracket which wraps the laminated iron seems to have been painted several times so perhaps if i strip the paint i can find a part number. it has typical heft for a small transformer about 1 3/4" x 2" x 2" its bigger than some of the radio output transformers ive seen but not as big as the one i got out of my western electric 100f powered speaker. it just looked imediately like an output type and when i read the numbers seemed to be although the secondary(?) side with the "c" and "3-2" "6-8" kinda didnt make much sense, the primary did kinda as i know load impedence for small tube amps would average 5000 to 8000 kohm impedance. the fact that this one is multitaped and ranges a 500 incriments from 500 to 2000 seemed to make me think this was input side for a low output single ended radio. i have been wanting to build a tiny/poratbel perhaps 1watt in the shell of a 1950s radio guitar ampette using the included 3 or 4 inch speaker and thought this might be good ot for that type thing

[92Volts]

You can apply a small AC voltage across some of the taps and measure the result at others to determine the ratios.

Impedance ratio = voltage ratio squared... so if C & 500 see 6.3v AC across them you'd expect C & 2000, a 4x greater impedance tap, to show about double that voltage. Also, 2000 is about 1000x greater impedance than 2 ohms, but this corresponds to a voltage ratio of 31x.

If that pattern holds true it seems like an OPT but you don't automatically know the voltages or current (especially unbalanced single-ended current) it's meant for. Likely on the low side, as you'd seen in a low power radio with B+ of 100-something volts
O

[kagliostro]

May be it is a line transformer (you put it on a speaker to connect it to an audio distribution line)

dismant the transformer (only the mounting belt) and control the disposition of the E and I laminations

if E are all in one side and I all in the other side, easily it is an SE OT

if E and I are mixed, may be it is a line OT

basing on your description it didn't seems to be a PP OT

Franco

[ALBATROS1234]

great thanks guys. output transformers are something i need to learn more about among other things, i am new to tubes not to electronics so i have been mainly studying signal path, how to tweak tone, tube types etc. i know that you should match tubes output load to the ot input range 2000 seems on the low end of the spectrum but 500 and such seem ridiculously low, i suppose this could be for a 1 watt se radio. but i seem to remember reading that if you overload the impedence somewhat you can get a nice nasty tone. i will check it out.

[92Volts]

Impedance depends on plate voltage as well as the tube.

Consider an EL34 at 500v, it idles at 50ma at the 25w dissipation limit.
Change in current through the cycle can symmetrically be at most +/- 50ma (can't draw less than 0ma). We want +/- 50ma current difference to correspond to +/- 500v voltage difference, to use the whole available voltage supply*. That's a huge 10,000 ohms load!

Consider an EL34 at 125v, it idles at 200ma** for 25w dissipation. We have the potential for +/- 200ma change in current. Yet we want this larger change in current to correspond to a smaller change in voltage (125v*) because we have less voltage to work with... we want a load around 625 ohms.

By lowering the voltage 4x we lower the ideal load 16x.

* Tubes cannot continue drawing current until the plate voltage reaches 0v, so the ideal load is smaller, giving a voltage swing smaller than the available voltage... but this illustrates the general idea
** Tubes have current limits as well as power limits, so an EL34 (for example) may not actually work for this sort of high-current low-voltage use

See this page for info on calculating this yourself with greater accuracy: http://www.valvewizard.co.uk/se.html

[ALBATROS1234]

thanks, i already got that concept but will read that to refine my knowledge,thanks sir