5e3 clone PT-> OT coupling inducing speaker hum

[Cirrus]

Apologies to anyone who's also on TDPRI for the cross post!

I've built a 5e3, all works fine, voltages are good, sound's good... but even with all tubes removed, there's 50hz (I'm in the uk) hum through the speaker that's *just* loud enough to be annoying. It's due to the physical proximity and orientation of the OT to the PT, and by laying the OT flat I can remove it almost completely.

So I know what the problem is and am debating on how to fix it.

If anyone could shed any light on why these two transformers might interact more than other 5e3 builds when the physical layout and orientations are pretty standard, it'd help. Because while jury rigging a bracket of some kind to mount the OT at an unusual angle will fix the issue... it'd be nice to have a neat build, and maybe a different Power transformer would also solve the issue.

The PT *is* actually oversize - 2 inch stack, current capability for 6l6 & GZ34 operation too. It's giving me bang on voltages with 5y3 and 6v6.

[sluckey]

pics???

[Cirrus]

Layout with problem induced hum:




Layout that silences induced hum:





Power Transformer: https://modulusamplification.com/deluxe-power-transformer---megastack-3073-p.asp

Output Transformer: https://www.tubeampdoctor.com/en/output-transf.-for-fender-tweed-deluxe-5e3

[EchoSonic37]

I would find a piece of thin steel plate to shield the power transformer on the side facing the output trans make sure its grounded near the P.T.
If that solves the hum I would fabricate or find something suitable to make it permanent. Maybe not the most aesthetically pleasing though.
 Is that a copper shield I see on that P.T.? Too bad its 90 degrees to the wrong side because that might be the answer if oriented toward the O.T.
I'm not sure if it could be a factor but is your chassis chrome plated steel or stainless steel?

[JB]

I have the same issue with my 5E3. I haven’t tried laying down the OT but angling it helps. I’ve put a vertical piece of mu-metal in between OT and PT which has reduced but not cleared it completely.  I’ve tried two different PT’s - a Hammond and one from Michael at Modulus (I’m also in the UK). Same level of hum with both, and neither are oversized for the job.


It’s fine with a band, just at home in a quiet room it’s noticeable. 

[Cirrus]

OK JB, really appreciate the reply! Glad to know it's not just me then.

Yeah I'm emailing Michael at the moment to see if he has any suggestions. I had been wondering if a different PT might solve the issue, sounds like it could be an expensive dead end.

So your PT is the non "Megastack" 5e3 one he sells?

What OT are you using?

[Cirrus]

I would find a piece of thin steel plate to shield the power transformer on the side facing the output trans make sure its grounded near the P.T.
If that solves the hum I would fabricate or find something suitable to make it permanent. Maybe not the most aesthetically pleasing though.
 Is that a copper shield I see on that P.T.? Too bad its 90 degrees to the wrong side because that might be the answer if oriented toward the O.T.
I'm not sure if it could be a factor but is your chassis chrome plated steel or stainless steel?

I'll have a look in the garage later and see if there's anything I could try as a temporary fix.

It's a steel chassis, don't think it's plated.

At the moment my thought is, I'm really happy with the build, and most 5e3 builds don't have this problem so it must be something to do with this particular combination of PT and OT. JB in his comment above said he tried a second PT, a hammond, and Hammonds are used *all the time* on 5e3 builds yet the internet isn't littered with forum posts about this issue.

So... I'm of a mind to get another output transformer, and see if that helps. It doesn't need to be silent, it just needs to drop the hum by say 5dB and it'll stop being an issue.

[HotBluePlates]

I'll have a look in the garage later and see if there's anything I could try as a temporary fix.

Since laying on its side kills the hum, I would simply get two L-brackets and mount the OT on its side.

Perhaps unnecessary, but I might put a plastic sheet between the paper insulation & chassis.

[Williamblake]

It might be easier to turn the power transormer. Looks pretty square.

[JB]

OK JB, really appreciate the reply! Glad to know it's not just me then.

Yeah I'm emailing Michael at the moment to see if he has any suggestions. I had been wondering if a different PT might solve the issue, sounds like it could be an expensive dead end.

So your PT is the non "Megastack" 5e3 one he sells?

What OT are you using?

It’s just his ordinary Deluxe power transformer, not for 6L6’s. My output transformer is a Mercury Magnetics tone clone I bought from Mike Garton. I played one of his 5E3’s at a Les Paul Forum meet up in Stockport and it was incredible. Might not make a difference but I decided I’d always be wondering if I didn’t use the same OT as him. He ordered me one which was nice of him.


Let me know how you get on! I think you’re also on tFB? I’m Springhead on there.

[JB]

It might be easier to turn the power transormer. Looks pretty square.

I tried that with mine when I had the Hammond PT in there. Sadly it didn’t make much of a difference and neither did the replacement PT I tried. It’s quite low level hum, no problem for gigging, just a bit irritating at home. But then these aren’t really home amps unless you have no neighbours!  Might be annoying in a studio perhaps.

[DummyLoad]

Have you tried at 45deg angle? 90deg?

--pete

[Williamblake]

Thats a bugger. In europe we dont have bells on transformers, so i cant tell the orientation. While you are remounting the OT anyway you could give it the extra mile?