{Collins} Re: 516F-2 mechanical hum

I received several responses off-list - thanks all. The consensus seems to be that the L1 choke itself is noisy and needs to be reworked, using one material or another (varnish or epoxy were suggested), to stabilize the core laminations. There was also a suggestion that the filter capacitors might be leaky - but it's unclear to me, in this case, what would cause the vibration to cease under load. I will investigate further.

Chris, W2PA

Chris Codella, W2PA wrote:
Hi Collins folks. I'm in the process of restoring an S/Line (75S-3B, 32S-3, 516F-2). The project has gone very well - I'm almost finished - but the 516F-2 power supply has a mechanical hum that I'd like to get rid of. Here are the details:

- To my ear, it seems to be coming from the choke stack L1/L2. When I pull the 5R4 (V1) it goes away, so it looks like L1 is the guy.

- It starts a second or two after powering up. If I power up after having it on for a little while, the hum starts immediately.

- It goes away under load - i.e. when I transmit.

- I have tightened all the mounting hardware, top and bottom - no effect.

- I have not yet replaced the original capacitors, although I have replacements ready to go in.

Any advice would be greatly appreciated before I start testing and replacing parts. I would have searched the archives first but the link to them on the CCA site seems to be broken (http://mailman.listserve.com/archives/collins/).

Chris, W2PA

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