Do swingers always buzz when they swing?

[pjanda1]

I've gone through several iterations of the power supply for my "El Cheapo" (6V6 PP). I am using a choke input supply with a tiny cap in front of the choke (.22uf in there now, IIRC). I started with a couple of Heyboer chokes, but the measly 2.5lbs of the first choke didn't convince me that it could last terribly long as an input choke (despite what the manufacturer said). At that point, I had a 10K bleeder resistor to maintain critical current.

Then, at a Ham fest, I stumbled upon a giant NOS looking Stancor Swinging choke (C-1404 17-3hy at 40-400ma). It's weight (11.7 lbs) and intended purpose (choke input duty) made $10 seem like a no-brainer. I switched to a 15K bleeder resistor, and felt good about it.

If since swapped power transformers and now the choke is the loudest thing still buzzing. The entire supply actually makes a faint 60hz buzz, but I can deal with that (it is semi-enclosed). The choke intermittently buzzes louder though, and I assumed it was buzzing when it saturated, as it is intended to do at low current. I swapped the bleeder back to the 10K.

Now it buzzes in much shorter bursts, but thus far, I've still got the problem to some extent. It is quite possible that this is just a buzzy choke, and as it is probably 50 yrs old, that seems excusable.

But, my larger question is, is this a typical problem with swinging chokes? I like the idea of choke input supplies, and I'll probably build another at some point. Big old swingers don't bring much dough on Ebay, but are any of them going to be quiet?

Paul
Wild Burro Audio Labs - DIY Full Range Speakers

[nullspace]

Hi Paul,

I've had very good luck with chokes from Heyboer in choke-input supplies, as long as the current rating is sufficient for both average + peak AC current.

You probably already know this but it bears repeating, if your choke meets critical inductance, then it'll see current from zero to twice the average and should be spec'd accordingly. If the inductance is twice the critical minimum, then the AC curent peak is half the average, so a choke rated for 1.5 times the average current will work. And so on... PSUD2 is a big help in pinpointing what's needed.

Regards,
John

[Sch3mat1c]

It is typical for ferromagnetics to expand around saturation. The physical phenomena is magnetostriction.

I was once testing a high permeability ferrite toroid. Everything was going fine until I turned up current slightly more, hit saturation, and suddenly the ring became about ten pieces! I'm guessing the magnetic field was slightly stronger on the inside, causing it to expand and fracture the rest apart. The same effect, plus Lenz' law, causes transformers to buzz.

Tim