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Registered Member #1225
Joined: Sat Jan 12 2008, 01:24AM
Location: Beaumont, Texas, USA
Posts: 2253
I recently got a small power transformer for an old audio amp (was HUGE, with a record player) that used vacuum tubes. I know that it has a 6.3 volt winding that powered the filament on 8 small tubes (3 used about .75 amps) with a 6.3 volt filament and it would be PERFECT for the filament on my 811A! Things seem to just be falling into place by themselves :P.
Well, i would like to know the pin out and i somehow came to the conclusion that someone here may have seen one or have one, as i know that at least Steve Conner messed with tube audio amps. Sooo, onto some specs no?
It is black, a bit smaller than 3 inches wide, little less than 2.5 inches tall, and a little more than 3 inches in length (this is while the transformer is sitting where the windings protrude from the core). It has 300188-1 on the top, and right under it is the numbers either 1386128 or 1886128 (or 3). It has 9 wires coming from it.
Registered Member #540
Joined: Mon Feb 19 2007, 07:49PM
Location: MIT
Posts: 969
If the transformer also had a winding for the plate's power then that would have the highest impedance. If it just powered the filaments then the winding with the most impedance is the line one. You can just connect up your meter to the pins and find which ones have the highest resistance. The windings with the lowest resistance would be for the filaments and other low voltage things.
If you are unsure if the transformer supplied power to the plates then connect the line to the windings with the highest impedance and measure the lowest impedance winding. Usually the lowest supply voltage in a tube amp is the filament so you should get something around 6.3V (depending on the tubes that were in it).
Registered Member #152
Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384
If you know what is your primary, just input some low voltage AC into it and measure other voltages. If you don't know the primary, input little AC voltage to the filament winding and measure other windings.
Registered Member #543
Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992
Make a map of the windings with the ohmeter, what is connected to what, what is the resistance between connected taps, and so on.
Unless you know otherwise, it is quite possible that the lowest voltage winding may be 5V - a very common rectifier valve heater voltage - and the next one up your 6.3V for the other heaters. Sometimes the same purpose will be served by having, for example, one 6.3V/1A winding for a 6.3V rectifier heater, and a second 6.3V heater winding of perhaps 2A for the rest of the valves in a small transformer like yours.
The unloaded voltage of the 6.3V heater winding will probably be about 7.5V.
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Unknown transformer pinout.
