JTM-60 OT needed

[lowell]

Interesting: https://marshallamps.com/support/faq/marshall-bits/

Checked parts is parts and full compass to no avail. Any suggestions on a genuine Marshall replacement? Or are we left with modifying mounting for an after market part?

thanks!

[The Dude]

I think the Hammond 1750NA might be a drop in replacement. Here's a link to the datasheet.

http://www.hammondmfg.com/pdf/EDB1750NA.pdf

[Enzo]

What is the part number for the original OT? And by checking those sources, did you contact them and ask about that part number? Or did you explore their web site and not find it?

WOn't this work? Yes, it is a replacement
50W / 60W Marshall JCM900 & JCM2000 Style Upgrade / General Replacement Output Transformer, 4/8/16 Ohms, 784-348

TXOP-00002 is a standard 50/60 watt Marshall OT. That would be what I'd hunt up.

The JTM60 print says the OT was Drake 292-772

[The Dude]

According to this site, https://www.etronic-parts.com/Transf...L401::507.html, the Marshall part number is TXOP-00012. Hence, my suggestion. But, not discounting Enzo's either.

[lowell]

It says Drake Transformers. With a sticker that says T402. All I got. I'll check those thanks!

I did email them as well.

This transformer has the pins and clips. The transformer itself has not "leads." No biggie there at all...if it's a drop-in, like to avoid drilling when necessary.

[lowell]

That looks right, but is Euro... so $$ and shipping etc... All good options, just looking for cheapest option for customer. May indeed go with one of these. Thanks!

[lowell]

And why the hell is there a 30watt OT in this amp. Hmmm... wonder why it blew.

[Leo_Gnardo]

And why the hell is there a 30watt OT in this amp. Hmmm... wonder why it blew.

To get that "stressed" tone ? ? ? And of course, to increase profits. No wonder this line of Marshalls didn't make much of a splash.

[g1]

And why the hell is there a 30watt OT in this amp. Hmmm... wonder why it blew.

Isn't it a pair of EL34 running at fairly low plate voltages? I'm not sure why they called it '60', maybe to differentiate from the 2 x 6L6 JTM30? It's the same OT, TXOP-00012 (also used in 4x6BQ5 DSL401)

[lowell]

No they're at 500vDC. However, maybe that's because the OT is messed up. I get 70ohms/30ohms from CT to each end. Big difference.

[Enzo]

Which may or may not be normal, all depends how it was wound. The test for transformers is to go to RG Keens Geofex site and make his simple transformer tester.

If they wind half a primary, connect a center tap, then wind the second half, those second half windings are around the first half, so they are wider in diameter, and that means the wire is longer for the same number of turns. So its resistance will be higher. Other transformers are wound with two pieces of wire that are then joined at the center tap. Winding both halves at once makes them the same length and thus the same resistance. Transformers work on turns rations, not resistance, so it doesn't matter.

[lowell]

Right on. I did sub my bench OT and it fixed the issue. I also have a Blue Ring Tester from AnaTek for SMPS inductors. Haven't researched using it on transformers.

[Enzo]

Go chek out Geofex, his tester is a battery and a neon bulb, you can literally make on in a couple minutes.

[lowell]

I read about it. So wouldn't my meter show a short? Is that more accurate? I'd think it only would show an "open" when the neon bulb is lit. By short, does RG mean a dead short to the core? I can't imagine the bulb would change with a short versus 50-100ohms. I must be wrong cause RG is clearly a veteran in the world of electronics.

[Enzo]

If your winding shorted end to end, then your meter would detect a short instead of 100 ohms or whatever it should be. But what if two turns are shorted together. Your meter might change from 100 ohms to 99.5 ohms, and you'd never know the difference. And it is way more likely that two adjacent turns would short together than for the two ends to short together.

But all it takes is for one turn to short to the next to kill the field inside the transformer. The test relies on the inductance of the transformer to kick up the battery voltage enough to flash the bulb. A shorted turn anywhere in the transformer would dampen that inductance to the point the bulb would not flash.