transformer identification help

[joesatch]

i have a box of these transformers but dont know what their secondary current is. 24v how many amps?  19v how many amps?  they are beefy little PT's and i thought to use them in some preamp builds for the filament, relay sections.

[sluckey]

No way to know with the info you provided. You have a 60VA (watts) pie to be split up by the two secondaries. But how big a slice to give to each secondary? Don't know. It would be easy to figure if only one secondary.

[joesatch]

ah poop. i got 6 of em

[PRR]

I think one of that will power all the preamp tubes you could need.

Just do it and see if it gets warm.

[glass54]

Hi Joe
By any chance, would these transformers be from a Peavey MediaMatrix 8848 BOB (2RU) unit?
Regards
Mirek

[astronomicum]

It appears from the photo that the secondary wires are the same gauge so lets assume that the secondary current is split between the the 24V and 38V windings. That would yield about 37VA for the 38V winding and 23VA for the 24V. 23VA at 24V would be about 0.96A. If you were to test the 24V winding under load, you could get close to its actual rating. Got some power resistors lying around? Start with about 24 ohm (or higher) 50W (or higher) resistances (24 V across 24 ohms is 1A) and see what your voltage across the resistor is. Raise or lower the resistance until you get 24V. Calculate your current and split the 60VA difference between the secondaries.

[HotBluePlates]

It appears from the photo that the secondary wires are the same gauge so lets assume that ...

I don't think we can confidently infer that:

   -  The transformer leads that we can see are soldered to the actual windings that we cannot see.

   -  Many transformer leads are thicker than they need to be for current-handling, and are often much thicker than the winding-wire.

   -  It's easier for the transformer-maker to have 1 gauge of wire for all transformer lead-outs in a given class of component.  All my Fender replacement PTs have the same lead-out gauge despite the fact the heater winding support a lot more current than the B+ winding.

... If you were to test the 24V winding under load, you could get close to its actual rating. ... Raise or lower the resistance until you get 24V. Calculate your current and split the 60VA difference between the secondaries.

I think one of that will power all the preamp tubes you could need.

Just do it and see if it gets warm.

I think either of these are the way to go.

PRR's way acknowledges that "12.6v wiring" of a 12A_7 only pulls 150mA, and we need 2 of those tubes in-series for the 24v winding.

   -  2 tubes in-series is 4x triodes
   -  3 parallel groups is only 25.2v @ 0.45A ---> 11.34 VA
   -  3 parallel groups means 12x triodes available.  Does the cream need more than 12 triodes?

   -  Difference between "24v" and "25.2v" is immaterial; the under-loaded transformer voltage will likely rise anyway.