I have a transformer that I pulled out of an old reciever...
with all the talk about the Firefly..  I'm thinking of it a lot..

So how do I identify what on earth I have here?  
"-)

:?  Same here!
I have some transformers that I know they're from audio tube amps but I have no idea what each one is or specs, voltages, impedances .....

Does this issue deserves an """Audio Transformers FAQ"""  

Best regards
Kleber AG

Question #1:
is it an output or power transformer (or a choke)?
Question#2:
what were the original operating conditions and tubes/speakers connected?
Both questions you should have an answer to if you took apart the original.
From the original operating voltages and tubes (and operation the tubes are running in) you can deduct what the n:m transformer ratio is, what it's approx. power rating is and how much DC current it can take on it's primary.
A firefly is a wee amp (if great), just have a look at the dimensions of the Hammond 125 transformer. And that gives you a world of impedance options.

so let's start with :
do you remember what tubes were in there,
run at what voltage,
into what impedance,
etc.
if not, well, as long as youre sure it can hold a whopping 3 Watts, just hook it up and see what it sounds like. Both firefly circuits sound good, so if it's crappy there's a significant mismatch (assuming the rest is ok). DO be careful not to exceed the trannies ratings, so start slowly, very slowly. When something appears to be wrong, cut power.
This might sound very gung-ho, but we're still in low-power regions. Voltage is rather high, but as long as you're not drawing massive power through the transformer you should be fine with a quick test. Keep in mind DC power also runs through it though.
The Hammond is small, but sounds surprisingly well.
Actually *measuring* an output tranny is really a handful, and it still doesn't tell you how far you can go as far as power is concerned.

Identifying transformers,being power or output is not hard but it could be dangerous if you are not careful.
Just do a Google with "Identifying transformers" or similar.You'll get something.
Aharon

Hmm..
the amp I pulled this out of was solid state, not tube..  NO idea what the power rating was (it was dead, I just cannibalized it for parts)..

this transformer MAY be completely useless to me, but hey - if I can use it, great.

I'll pull it out and see if there are any identifying numbers on it.
"-)

Quote from: Mike Burgundy.
Actually *measuring* an output tranny is really a handful, and it still doesn't tell you how far you can go as far as power is concerned.

No but educated guesses can be made according to size,more so if you know what was connected to it like what tubes and stuff.
To find out impedance involves using voltages so I'm not going to get into that but like I said there's a couple of tutorials on the subject out there
Take care
Aharon