Film-Tech Forum ARCHIVE: Rectifier buzzing

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Posted by Matthew Taylor (Member # 2310) on 06-29-2005, 03:23 PM:

My 500w rectifier has always made a loud buzzing noise when the lamp is ignited. it has always done this and it does get quieter the longer the lamp is on.

What would cause this and what components would be causing the buzz?

Unfortunately I can't tell you which recitifer it is because it isn't marked up in any way.

Posted by Dave Macaulay (Member # 813) on 06-29-2005, 04:43 PM:

The transformer itself usually is what buzzes. Most transformers are made of lots of steel E plates stacked up and the alternating magnetic field makes them vibrate. Dipping the thing in tar or attaching bolts and clamps is the normal factory solution, this is hard to do in the field. An SCR controlled rectifier is usually more buzzy because of the current spikes developed, but passive rectifiers do it too.
Open the case (main power feeds OFF!!) and see if there are bolts or clamps on the transformers that you could tighten. You can drive wooden wedges into the frames of some transformers to tighten the plates too. Irem rectifiers in particular have clamping screws to reduce buzzing.
It may even be some loose sheet metal panels inside that are rattling.

Posted by Mark Gulbrandsen (Member # 72) on 06-29-2005, 07:35 PM:

quote: Dave Macaulay
You can drive wooden wedges into the frames of some transformers to tighten the plates too.

This is true but you mist forst determine if its the laminations of the frame that are buzzing or if the actual core is loose in the frame and causing the problem. The latter is VERY common in older 68000 series Strong rectifiers and in Christies on occasion. Determining which it is regquires probing with an insulated tool whilst the rectifier is operating. Ten poking and prodding at the laminatiions and or the core to see what quiets it down. Then appropriate measures can be taken. Loose laminations can sometimes be kept quiet with siome silicon seal applied in between the loose layers. Cores can be quited down by pounding in a wooden wedge very carefully to tighten it up gainst the frame. Great care must be taken and all standard electrical precautions need be adheared to!!

Mark

Posted by Ken Layton (Member # 133) on 06-30-2005, 10:32 AM:

Sometimes the contactor coil can get noisy too.

Posted by Jack Ondracek (Member # 1466) on 06-30-2005, 12:25 PM:

"Wooden Wedges", eh?
When I had that happen with one of those old Strong 4kW supplies, the guy I bought it from suggested I push popsicle sticks between the laminations. I put up with the buzzing for 2 more weeks... not believing such a procedure could possibly work.

but... it did.

Posted by Mark Gulbrandsen (Member # 72) on 06-30-2005, 07:55 PM:

quote: Ken Layton
Sometimes the contactor coil can get noisy too.

Especially where it is damp and the ends of the contactor pole pieces get corroded..... these will buzz REALLY LOUD! For what ever reason I've experienced this alot on Irem rectifiers.

quote: Jack Ondracek
the guy I bought it from suggested I push popsicle sticks between the laminations. I put up with the buzzing for 2 more weeks... not believing such a procedure could possibly work.

but... it did.

What flavor did you use and how did the flavor affect the level of the buzz... or should I say what flavor gave the lest buzz? Now I do know that if you get too much flavor it will actually increase the buzz....... especially alot of that chocolate flavor.

Mark

Posted by Rick Long Jr (Member # 541) on 06-30-2005, 08:47 PM:

You've got to be carefull not going too far too fast with the adjustments on a Kneisley rectifier transformer or similar model. I've seen more than once a rectifier that had happily buzzed for years go up in smoke because someone learned what those bolts do and overdid it.

Posted by Jack Ondracek (Member # 1466) on 06-30-2005, 10:46 PM:

quote: Mark Gulbrandsen
What flavor did you use and how did the flavor affect the level of the buzz...

Nahhh... you've got to lick 'em down to nothing first [Razz]

The real trick is to make sure they're very dry before using them. The first one darn near zapped my hair straight !!! [Big Grin]

Posted by Demetris Thoupis (Member # 833) on 07-01-2005, 02:30 AM:

Hey Mathew,
You failed to mention the rectifier model. Is it an Irem? If it is an Irem there are some adjustment screws inside which you can adjust to eliminate buzzing.
D

Posted by Eric Robinson (Member # 2966) on 05-05-2006, 09:27 PM:

I'm going on service call soon for a buzzing Christie CC10. I'll try poking it with a wooden dowel rod to see if I can track down the loose laminated plates. If I find loose plates, I'll try to wedge some wood in to minimize the vibrations. Or, like Mark said, I can use some silicon seal.

Anybody have any other suggestions for this model?

Posted by Frank Angel (Member # 248) on 05-05-2006, 11:56 PM:

Dip the whole thing in tar? [Eek!]

Posted by Mark Gulbrandsen (Member # 72) on 05-06-2006, 07:18 AM:

Most buzzing christies that I have seen (a fair number) have loose laminations. Locating them and then spreading them apart and applying a little silicon to stop the buzzing has worked for me a number of times. This de-lamination of the plates usually occurs at one of the upper corners of the transformer block. If its not due to loose laminations then get yourself some oak wedges at the lumber yard to use between the windings and the steel core. Sometimes it cannot be made quiet...

Mark

Posted by Richard Fowler (Member # 893) on 05-06-2006, 12:29 PM:

The "tar" is insulating varnish....recently upgraded a 30 year old IREM up to almost good as new...the lamphouse was restored from hurricane water damage but the projector is another story [Smile]

Posted by John Pytlak (Member # 331) on 05-08-2006, 10:06 AM:

Putting real "tar" or asphalt on the windings of a transformer would create a fire hazard. [Eek!]

Some can run quite hot.

Posted by Eric Robinson (Member # 2966) on 05-08-2006, 07:15 PM:

Thanks for all the help. I made the service call and was able to locate two different areas of loose laminated plates by poking around with a dowel rod. I then had to move some assemblies out of the way to get access to the plates. Afterwhich, I used silicone seal injection under the plate edges as best I could. I followed this up with some wooden blocks which keep pressure on the potentially loose plates. The rectifier runs as silent as a kitten now.

Posted by Mark Gulbrandsen (Member # 72) on 05-08-2006, 09:19 PM:

quote: John Pytlak
Putting real "tar" or asphalt on the windings of a transformer would create a fire hazard. Some can run quite hot.

You're right! Insulating varnish is a special sort of thing that is also flame resistant at least to some degree.

Mark

Posted by Thomas King (Member # 2745) on 05-09-2006, 05:17 AM:

We've got a big T&R rectifier from circa 1950. It buzzes like a madman, but I can't get into it to tighten its mountings because genius! we have a false floor in the booth which the unit goes through, meaning I can't get the side panels off because there are screws under the floor level.

Posted by Pete Naples (Member # 761) on 05-09-2006, 05:43 AM:

Thomas, your T&R is not that old! (Assuming it's the 123/B? model)

Good rectifiers those, will last forever as long as the cooling fan is OK.

Posted by Thomas King (Member # 2745) on 05-09-2006, 06:21 AM:

Pete; you've made me doubt myself now. I'll check the manufacture date on it when I get a chance and get back to you! I'm not sure how it's doing in terms of voltage stability; we've got an engineer coming up this summer so I'll get him to check it then.

Posted by Pete Naples (Member # 761) on 05-09-2006, 07:00 AM:

T&R made really 3 models, there's the 100A version which is about 18" all round, there's the 123/B series which are good for about 75A, those are the most common, about 18" square, and a couple of feet tall. Then there's the compacts, which are maybe a foot square, and a couple of feet tall, but won't push as much current as the others.

Post a photo, I'll ID the beast for you.

Posted by Josh Jones (Member # 447) on 05-10-2006, 12:39 AM:

Matthew, is this the baby kniesly "kni-tron supply and lamphouse that both look very similar? I think the model is l-100-3 for the lamphouse. I've got one too and mine has always buzzed, just let it warm up for about 10 minutes and it purrs like a kitten, well, nearly so [Smile]

Pics of the setup are in the warehouse.

JJ