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Report: One-Electron PRC as input choke

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Well, since nobody seemed to have tried it, I got a couple of One-Electron plate chokes (PRC-2) from Antique Electronics to try as choke-input power supply chokes.

The power supply in question is a choke-input, ~300VDC @ ~110mA supply, using a 5V4GB or 5AR4 rectifier tube. The power xfmr secondary is 350-0-350, so there's close to 350V RMS AC across the choke. At 10H current ripple is fairly small, about 25mA (so peak current is about 125mA).

This is for a headphone amplifier project which I intend to sell (in small quantity).

Anyway, I compared several chokes:

#1: James 12H 200mA potted choke (not intended for choke input)

#2: Old stock Thordarson swinging choke, 8H - 20H @ 180mA

#3: Custom-wound power supply choke, requested spec 15H 110mA, for choke input service

#4: One-Electron PRC-2 parallel connected (12H, rated for 150mA as a plate choke)

Bottom line: The One-Electron works perfectly.


#1: The James choke performed pretty well, even though it is not (explicitly) designed for choke-input use. I know from a previous experiment that at ~180mA it buzzes in protest.

It is rated for 200mA, so one might expect it would be OK at 110mA. It did not make any audible noise, even at power-up, and did not vibrate significantly during operation. It exhibited a little bit of ringing (observing the rectifier cathode) but I wouldn't say it was ugly.

#2: This was an old choke designed for input service. Pretty big for it's rating; only the One-Electron PRC was bigger.

It was dead quiet and did not vibrate. Unfortunately I didn't bother observing the waveforms on this one because it's one-of-a-kind; even if I wanted to use it I've never seen another like it.

#3: Big dissapointment here. I asked a custom winder to make a choke for this exact application. It did not work out well. It vibrated significantly during operation - I think enough that I'd be worried about coupling noise into the tubes via microphony. It also made a nasty sound when the amp powered up - almost certainly it was saturating. When I asked the winder about it, the response was something like "choke input chokes always do that". :mad:

#4: The One-Electron PRC-2 was physically the largest of the lot, even though rated about the same as the others. Not the prettiest thing, but very well impregnated in varnish, which probably helps matters; it's dead quiet and no vibration. And the waveform observed at the rectifier was absolutely textbook perfect - no ringing at all. :)

Sort of makes sense, if you think about it... this choke was designed as a plate choke, so attention was no doubt paid to the winding arrangement. So from an AC standpoint it's pretty darn good.

Based on what I see I suspect that you could push the current up even more.

So, I'm going with the PRC. It's price is good ($60 from AES) compared to the other few "choke-input-specified" options (Sowter, Tamura, custom...) and it's performance seems perfect.

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