radiospares "standard" output transformer

[Maurizio]

I have just got one pretty cheap on ebay and I was wondering if anyone knows the specs of this old boy. Also any suggestions what amp build could I use it for? I haven't built anything in a few months and my hands are itching a little.
I know i probably should have asked this before buying it but it was sooooo cheap I could not resist!

[Rob Mercure]

I've nothing specific about your tranny but the name "radiospares" suggests to me that this is/was one of the "universal" output trannies common up until the 1970s. The better of these had multiple taps to match impedances but the commonest ones just "sorta" cobbled up to whatever you needed most being about 6-7K primary impedance if I remember correctly (and I could easily be wrong). Anyhoo, you can determine your voltage ratios between windings and from there determine impedance ratios. Oh the "udder hand" (as the farmer referred to dripping milk) if you know the power rating you can probably get away with some assumptions. If it's a PP tranny it's probably not good for more than about 10 W so 6V6, EL34s, etc. could be used. And if it's a SE tranny probably the same tubes <grin> unless it's a "wee little thing" (hmmm, perhaps this is Bush's problem?) with an outside core diameter of about 2" or less and then is was probably made to couple to a 50C5, 50L6, 50EH6, 25FX5 (ad infinitum for series connected less that 5 W output tubes) - but it would still work with the now more common output tubes as long as you limit plate current.

Hope this helps.

[Maurizio]

Thanks for your reply Rob!
I eventually found a datasheet for this OT. It's a "wee little thing" and it's also one of the universal transformers with multiple primaries taps. It is rated at 3.5W and with max primary DC current of 40 mA.