5G9 PT, OT and Choke layout

[tubeswell]

Some Help Please?

Been working on making holes into a piece of 1.2mm thick (18 Gauge) Aluminium sheetmetal and thinking about laying out the various components (PT, Filter caps, Choke and OT) on the back of the Chassis.

Which layout would be most optimal? A, B or C? (Hopefully it is A or B - then I can keep the Choke and filter caps near each other)

All comments welcome thanks

Cheers

(PS also if someone is able to comment on my earlier post about designing an FX loop in this amp, http://music-electronics-forum.com/s...ead.php?t=6802 , I would be most appreciative, cheers)

[J Martin]

When I build amps I put the iron in order of use, pwr, choke. opt. I would turn the power transformer 90 deg. so its side of least radiation faces the rest of the circuitry.

[tubeswell]

THanks J Martin. I've always wondered about which side of the PT gives off the most EM radiation in relation to the iron. (For some reason I'd worked out in my head that it would be higher in-line with the axis of the iron?, because I thought the Electric current would magnetise the iron in bi-polar fashion, where the axis of the iron represented the alignment of the opposite poles.) I haven't yet found a diagram on the net to show this. Finding space on the back of this chassis is challenging. I don't want to move the OT too close to the inputs, so everything else is squeezed in between them. and I was hoping to keep the choke close to the filter caps. I guess I could rotate the filter caps through 90 degrees so that their positive ends were away from the PT (but then would their positive ends be affected by the OT?)

[J Martin]

Don't worry too much about the output transformer being too close to the inputs. My Sunn amps, my Plush amp, Ampeg amps, and many others I have seen have the output transformer right over the inputs. I think it is only an issue with very high gain amps if at all. In my Sunns the first preamp tube is just about touching the output trans. Route the output trans primary wires away from the pre amp circuits inside and you will be ok. Ampeg used a metal tube to shield them, I just use plastic ty wraps to hold them in a safe place. Cap orientation should not be an issue either. In many of my builds I'll use a 32/32 can cap for the plate and screen nodes and distribute and ground the rest of the caps near the part of the circuit they serve. That can could be a 50/50 or 100/100 also depending on your needs. It saves space.

[tubeswell]

When I build amps I put the iron in order of use, pwr, choke. opt. I would turn the power transformer 90 deg. so its side of least radiation faces the rest of the circuitry.

As an afterthought, would I be better off (in terms of EM interference with the filter caps and OT/Choke) mounting the PT on one side (i.e. through a rectangular holde in the chassis) as per the stock tweed setup?

Its easy enough to do, and would save some space - I'm just a little bit lazy, but will do it it its 'better'. :-)

PS what direction/orientation is the source of greatest EM radiation coming off the PT? (in line with the iron, or at right-anges to it?)?

[Bruce / Mission Amps]

Unless you know where the null and nodes of the flux lines are in the PT, it's a crap shoot.
All the tweed chassis I have, use a Z mount power tranny.
Besides pushing the center of the pt into a different plane, it rotates the core of the PT another 90 degrees from an X mount.

[martin manning]

You could always try the "headphone trick" as described here:

http://aga.rru.com/FAQs/build.html#ot_pos_1

Basically, mount the PT and power it up (with secondaries taped-off). Then, hook cheap headphones up to the OT secondary and position the OT for minimum hum. I've never tried it, but it sounds like a good idea.

MPM

[tubeswell]

Unless you know where the null and nodes of the flux lines are in the PT, it's a crap shoot.

Well Dang!


All the tweed chassis I have, use a Z mount power tranny.
Besides pushing the center of the pt into a different plane, it rotates the core of the PT another 90 degrees from an X mount.

Excuse my ignorance of the terminology - by 'Z mount' I presume you mean mounted 'lying down sideways' on the chassis (as opposed to standing up off the chassis)?

[tubeswell]

You could always try the "headphone trick" as described here:

http://aga.rru.com/FAQs/build.html#ot_pos_1

Basically, mount the PT and power it up (with secondaries taped-off). Then, hook cheap headphones up to the OT secondary and position the OT for minimum hum. I've never tried it, but it sounds like a good idea.

MPM

That is interesting. I don't have cheap 'phones (By 'cheap', I presume you mean 8 Ohm ones? The only phones I've got are 150 Ohm ones (still I don't suppose that matters if the OT primary is not live. All you would be needing is for the secondary to act as an EM field antenna?)

[Bruce / Mission Amps]

Excuse my ignorance of the terminology - by 'Z mount' I presume you mean mounted 'lying down sideways' on the chassis (as opposed to standing up off the chassis)?

Yes.. an X mount has the transformer standing up right.. like on legs... with the lamination perpendicular to the chassis
The Z mount allows the laminations to be in parallel and the PT is usually "let into" the chassis so it is partially inside the chassis too.

[tubeswell]

So if I took an X-mount PT and lay it down on its side like a Z-mount PT, I could call it a Y-not-mount PT?

(All joking aside, as an afterthought I suppose I would need to make sure both shield covers were grounded to the chassis with this Y-not-mount?)

[tubeswell]

What I did

Well after much pondering I decided to keep the X-mount X-mounted.

I shifted the OT right over to the input side and it gives a bit more room for the Choke and the filter cap doghouse.

I guess I'll just have to see how it goes.