Blown PT to OT conversion???

[Paul1453]

Probably another one of my silly questions.

I've got a couple of blown PTs that I was about to trash.

Before I did that, I thought maybe this won't work as a PT anymore,
but what about using it as an OT instead?   

I had one with CT 6.3 V and CT HV secondaries.
I put 6.6VAC on the filament tap and measured the HV tap.
Got a Z of 975 so in theory an 8 ohm speaker connected would give me 7.8K load on the HV tap.
That could work for my little PP 6V6, 6BQ5/6AQ5 circuits.

I haven't tried it out yet.
I understand that this iron wasn't designed for this,
and probably won't give the proper frequency response for an OT.
Has anyone else given this a try?
I searched the forum and didn't find any threads along these lines.

I am cheap, and if I could repurpose a blown PT into a reasonable sounding OT, I'd likely do that instead of just trashing the iron.   

[HotBluePlates]

I've got a couple of blown PTs that I was about to trash.
...
I had one with CT 6.3 V and CT HV secondaries.
I put 6.6VAC on the filament tap and measured the HV tap.
Got a Z of 975 so in theory an 8 ohm speaker connected would give me 7.8K load on the HV tap. ...

So just the 120vac primary was damaged? It's not shorted to anything, is it?

If not (just burned open), then sure you could try that as an ~8kΩ:8Ω OT. Worst case, it might not have all the high frequency response you want.

[Paul1453]

Actually, this PT wasn't completely blown.
I've got another where the 5VAC opened,
and at least 1 more after that so I appreciate the feedback.

On this one, all of it's windings were still intact, and not shorted to something else.
I think the problem was the 6.3VAC would get very hot and start smoking.
If I recall properly, this was powering a PP EL84 projector amp with 4-5 tubes.
When I put my 6.6VAC on that winding, it still got hot but no smoke during my Z testing/calculations.
The voltage on the HV tap rose as it heated up.
Not a huge amount, less than 10%.
I waited until it stabilized z=975, and the iron was hot but not smoking then.

Maybe as the secondary winding of the OT it wouldn't get as hot?   
2 6AQ5s put out around 10W max output power, maybe OK for that?

I might just have to try it on my BB with a PP 6AQ5 circuit and see how it sounds.
If it does sound good, will it get hot and smoke with cranked up usage?
Maybe it is worth a try.  I've got lots of 6AQ5s and,
Dummyload's K10 circuit mod really ROCKS!

Thanks for the feedback.   

[PRR]

If a transformer gets hot no-load, it has an internal short.

This will suck-up all your signal.

[Paul1453]

Thanks PRR,

I guess this one is trash then.

I feel better about dumping this stinky one now.

I will see if the other ones that don't get hot, have a potentially usable Z like this one seemed to.

Otherwise, in the trash they go.

[Paul1453]

I checked a different PT's 6.3VAC to HV tap turns ratio and calculated it's Z.

It was nowhere near a common OT's Z like the 1st one.

Another one to dump in the trash.