Is There A Way.....?

[The Ballzz]

Hey All,
Just curious, is there a way to test an output transformer/amplifier to figure out it's specs? Nothing is broke yet, so testing "in amp" while fired up would be fairly easy. Bear in mind that even though there is only one power tube, that tube is a dual triode 12BH7 configured in a push/pull output scheme. The DSL5C is officially a 16 ohm output only, even though Santiago (from Marshall) says an 8 ohm load "should" be okay. The transformer in the amp and on the schematic is only listed as a part number, but no specs. I'd like to find a suitable replacement that would be correct for both 16 ohm & 8 ohm operation. Upgrading to a somewhat "beefier" hunk of iron would likely not be a bad thing either!
Thanks,
Gene

[Phil_S]

There is a long answer and a short answer.

The short answer is that a dual triode amp will be very tolerant of a variety of output impedances. I don't know the amp or the application so I can't say anything for sure. My gut reaction is that you can plug in 8 or 16 ohm load and it will work fine. I'm not sure I'd spend good money to "upgrade" the OT just to mate it to an 8 ohm load. What I think Santiago (whoever that is) is saying, is that it is correct enough and to save your money.

I should note that pentodes (and beam tetrodes) aren't tolerant like triodes and that your concern about impedance matching is a whole lot more important with those tubes.

The longer answer is the test the OT for turns ratio. The impedance ratio is the square of the turns ratio. IOW, if the impedance ratio is 8K:8, reduce to 1K:1, then the turns ratio is sqrt (1000) = 31.62:1. The test is described here: http://www.radioremembered.org/outimp.htm

This ignores other factors such as inductance, the wire size used, the actual number of turns, interleaving, etc., all of which are part of the dark art of designing an output transformer. But it will give you a sense of what you are working with.

[Reeltarded]

^^^ exactly

No problem, and no value added.

[The Ballzz]

Well Sir,
I'm the kinda guy who is not apt to leave well enough alone. I have also seen that many modern lower wattage amps, especially some of the Marshall offerings, have benefitted substantially from OT upgrades. From all that I read, it appears that Marshall, in particular, uses OT's that are just barely sufficient for their intended use. I'm one of those whacko guys that actually gigs with 5 or less watts. I'm simply looking to give this little amp the opportunity to be all that it can be! That was a good read, thanks for the link.
Thanks,
Gene

[Phil_S]

You know...it's your amp, the choice is yours. I seriously doubt you hear or notice a difference, even with a 4 ohm load.

If you insist, I believe want the OT5PP+, here: http://www.musicalpowersupplies.com/products/

Good luck.

[The Ballzz]

You know...it's your amp, the choice is yours. I seriously doubt you hear or notice a difference, even with a 4 ohm load.

If you insist, I believe want the OT5PP+, here: http://www.musicalpowersupplies.com/products/

Good luck.

Thank you Phil,
Please understand that this is not intended as part of a tonal quest, but simply wanting the amp to be utilized safely with a variety of speaker combinations, as some of my setups will use a 16 ohm load and some will use an 8ohm load AND I tend to run my amps fully or nearly fully cranked! The "probably" and "should" be okay at 8 ohms comment from the Marshall employee does not truly instill the confidence that I would like.
Thanx Again Sir,
Gene

[Reeltarded]

If I told you I had 50 year old amps that come mismatched backwards (small load/large impedance) from the factory and run like new with the original everything except filters would that build any confidence?

I tried.