WTF: Buzzing Noise from Plate Xformer or Choke

[W1UJR]

Hi fellas and happy New Year.

My 310A Exciter has developed a loud buzz when the plate volage is on.
I checked the end ball bolts on both the xformer and choke, they are tight.
Also checked the mounting screws again tight.
This is a pretty loud buzz, the exciter works fine, but I wonder if I have loose laminations or a failing xformer?

Should I remove and inspect, perhaps repot to quiet it down?
How can I tell if its the plate xformer or the choke?

Tnx - Bruce W1UJR

[WB2RJR]

How can I tell if its the plate xformer or the choke?

Bruce,

I'd try using a piece of wood like a dowel. One end held to your ear the other end probe around until you find the source of the buzz. Works on car engines very well to find where a noise is coming from.

Could be a relay too with some dirt on the top of the electromagnet, I've had that happen.

73, Marty

[W1VD]

To identify the offending party...how 'bout a couple C clamps with wood spacers so you don't mar the bell edges?

Jay

[W2PFY]

Check out your filter caps. If they aren’t doing the job, the choke or transformer may make a noticeable hum.

[WA1GFZ]

The last lamination on top of the E/I stack usually comes loose. Many guys who built quality transformers cut the last E so the center is short and doesn't vibrate like reed. You can push a wood wedge in or maybe squirt some RTV in to damp the vibration. Make sure you don't have a shorted turn by checking the AC input current. The transformer will run a lot hotter if it is in the process of crapping out.

[W1UJR]

Thanks for the tips fellows!
Here is what I found:

1) Removed the exciter from the cabinet.

2) Used a long screwdriver to isolate noise to either the choke or power transformer.
I found if I applied pressure on the choke housing in a twisting motion the noise stopped.
But I also felt some noise/vibration from the power transformer, so I decided to tackle both.
These are old Thordarson units, very pretty with elaborate metal coverings.

3) Removed the retaining bolts from one end bell which hold the xformer to the chassis.
Removed the end bell and inspected laminations. As Frank offered the end lamination, the "I" part, was loose on both side.
There did not appear to be any varnish or lacquer on the laminations, just held together with the clamping force of the case.
Removed the "U" shaped center cover, the part that holds the core, and the two thin fiberboard side wedges.
I noted that these wedges appeared to have slipped down away from the core, rather than fully supporting it.

4) I reinstalled the core into the "U" shaped bracket and carefully positioned the fiberboard supports in the CENTER of the core, where I suspect they should have been to properly clamp the core. This was a chore, accomplished only with the careful use of a very small screwdriver to force the core to one side.
Reinstalled the two loose "I" laminations and then the end bell.

5) I carefully torqued the retaining bolts on the end bells, and then let the unit "bake" for an hour.
I still detected a slight amount of noise from the choke, so I loosened and then retightened the bolts on the end bells, problem solved.
I let it bake again for a bit and then reinstalled the unit back into the cabinet.

I also managed to tweak all the drive settings for the various bands, and now have drive on 10 meters, come on back solar activity.

Thanks once again for your help and tips, it got the job done!
The unit is now as silent as a church mouse, with just a slight hum under load.

73 Bruce W1UJR

[WA1GFZ]

Bruce,
I have shot laminations with varnish from a spray can when they appeared dry.
Glad you fixed it!

[W1TAV]

Speaking of Buzzzzzing, did you hear the one in Johnston 600 Tim (WA1HLR) was running last night when he came on with it around 5 PM! Later on he moved away from the PS and it was less of an issue.

Bruce, your buzz was small potatos!

Steve - W1TAV

[W1UJR]

Bruce,
I have shot laminations with varnish from a spray can when they appeared dry.
Glad you fixed it!

Hey Frank, these did not appear to have been coated with anything.
All were just bare metal.
Wonder if that's odd, or par for the course in 1940?

The sheetmetal is a work of art, very nicely done, with the big Thordarson tag on top.

[WA1GFZ]

All laminations are coated to reduce eddy currents but many times transformers were not potted or dipped. Makes sense that your unit was buzzing.

[W1UJR]

All laminations are coated to reduce eddy currents but many times transformers were not potted or dipped. Makes sense that your unit was buzzing.

Now I wonder if I should have removed the xformers and coated them?

Its a bit of a process, the leads are all laced into the cable harness, ala Collins style.

Guess that's my next step should this occur again, say in another 60 years or so. 

I tried your wooden wedge idea, but could not get anything thin enough, reposistioning the small fiber boards seems to have done the trick.