Hammond 290GX Transformer laying down?

[timbraun]

I have Marshall JMP 50 Mk II which blew the power transformer (it wasn't the original transformer). The amp is from about 1978. I bought a replacement PT - the Hammond 290GX and when I went to bolt it into place this evening - I found out the chassis cutout expects a laying down version, while the PT bell sheet metal expects it to be standing upright.


I have 2 questions:
1. Are there adapter bell housings to allow me to use this PT laying down?
2. Are there issues running the PT horizontal vs. vertical for power dissipation or noise from magnetic coupling?


Thanks, ev-a-body.

[DummyLoad]

1. Are there adapter bell housings to allow me to use this PT laying down?

probably, but i can't find any - there is an issue with the upright in that all the leads don't exit on one side of the bobbin as they do with a laydown. that's the problem and probably why you won't be able to convert unless you want to cut the bobbin's outer insulation and move the wires to one side.

2. Are there issues running the PT horizontal vs. vertical for power dissipation or noise from magnetic coupling?

some - can't answer that question definitively until tested. best to get the proper replacement.


if you're in western hemisphere, then the classictone part is probably the one you want. you have a model # 1987 mkII lead?

possible calssictone replacement. do check the hole spacing on your chassis and compare to spec sheet before ordering. ;-)   
otherwise a chassis hack may be in order.

contact heyboer transformers as an option, and of course there's mercury magnetics if you want your wallet raped.

--pete

[PRR]

> Are there issues running the PT horizontal vs. vertical

1) Marshall thought lay-down would be fine.

2) This rig is already on its *3rd* PT after only 39 years?? (Actually that's not too bad.)

It IS very odd that Hammond says "Designed for drop in replacement of original units" and gives you a stand-up for a lay-down. Are there several runs of this Marshall with different PT mounts? You might call Hammond on this. Unless you missed a trick, you bought a PT and paid for *shipping*, and can't "drop-in". They should at least tell you where/how to stick it.

The primaries are all on one side. In a bind, *ME*, I would pop the bell on the secondaries side, mount it, then put sleeving on the 0-120-240 bundle and run it down through a grommet into the chassis. If it reaches. If I am sure the kid and cat can't get in there with a butter knife. If I'm not trying to sell it to someone.

[TIMBO]

Like This

[kagliostro]

+ 1 for PRR & TIMBO

Wires can also be collected in a small tube to get a better aesthetic

Franco

[sluckey]

I have Marshall JMP 50 Mk II which blew the power transformer... ...the chassis cutout expects a laying down version

This pic of a Marshall JMP 50 Mk II shows a standup PT. Has your amp been modified to accept a laydown PT? If so, just cover the big hole with a piece of sheet metal and mount your standup PT like the originals.

[DummyLoad]

Has your amp been modified to accept a laydown PT?

example here. if i had i 1973 marshall i wouldn't be cutting the chassis up to make a part fit when one is available that does. just my 2 cents.

--pete

[kagliostro]

May be someone think that that is an improvement against humm due to iteration of the magnetic field of transformers ?


Franco

[timbraun]

Hi, folks. It's been a while... thanks for the comments, photos and suggestions.


It turns out that this Hammond PT will lay down just fine - the mounting bolts and chassis cutout fit perfectly. The problem is the end bell and the primary side coming out the top of the chassis. I am going to deal with that the suggested way - drill a small ("9/32) hole, grommet that, and run the primary wires through that. There's lots of lead length.


Chassis is labelled for 1975 and that matches the date codes on the blue electrolytic can caps. I'm pretty sure it shipped with a lay-down style PT, which means I'm returning it to factory configuration. The PT that was in it when I got it (stand-up mount) was under-powered, IMHO.


Hope the hum doesn't get loud.


Thanks, again, folks!