transformer current capacity

[jestaudio]

scored on a all valve no name amp which for once looks as if someone tried to do a good job, i,m pretty much going to scrap the pcb and take it from there, however i have no info on the transformers, i,ve got a 50-60 v tap for bias and i,m getting about 400 odd on the plates of the 6l6 which points to it being about 290-0 290, at the moment theres only 2 12ax7s but i need to determine if i have the capacity to run another for a Wreck style build.
Anyone know how to work it out

[surfsup]

One more preamp 12ax7 is going to draw only a few extra mA at the most, so I personally wouldn't worry about it. But maybe someone else will chime in.

Do you see any identification markings on the PT?

[jestaudio]

One more preamp 12ax7 is going to draw only a few extra mA at the most, so I personally wouldn't worry about it. But maybe someone else will chime in.

Do you see any identification markings on the PT?

Not a thing, i suspect its chinese in origin but to be fair the amp actually sounds pretty good as it is with some half decnt valves in it

[tubeswell]

So the amp's got one 6L6 and one pre-amp bottle (of some description?)?

[surfsup]

I think it is push pull since he speaks of the 6L6 plates in plural. I would worry about the heater supply but not sure how to measure capacity.

Did you try to remove the PT? I know edcor puts markings on the bottom face (up against the chassis) so you can't see it unless you unmount the PT.

[Cliff Schecht]

There was an old scanned article posted a good while back detailing how to find the current capacity of an unknown PT. I can't find it but I bet somebody else has it.

[tubeswell]

carefully hook up the PT primary to a mains supply and measure the secondary AC voltages. They should be about 10% higher than what it will be safely loaded.

But, if you are unsure which country the PT came from, then hook up a 6.3VAC supply to the heater winding and measure the Primary VAC first. That will tell you what mains VAC to apply to the primary.

If the PT has been powering 2 x 6L6 plus a few pre-amp bottles with parallel AC-connected heaters, then the heater winding is probably good for at least 3-4A. And the HT winding is probably good for at least 150mA.

But if you want to be more scientific in testing it, there is a procedure described in Ch 1 of Merlin Blencowe's 2nd book for estimating the capability of a power transformer based on measurements of temperature and resistance - but you really should look at his book for that.

JM2CW

[passfan]

There was an old scanned article posted a good while back detailing how to find the current capacity of an unknown PT. I can't find it but I bet somebody else has it.

https://tubeamparchive.com/viewtopic.php?t=13747