Replacing power supply resistors with chokes

[debk]

Had to see what it looked like without the Choke

40Hz/div No Choke
(https://forum.bottlehead.com/proxy.php?request=http%3A%2F%2Fi566.photobucket.com%2Falbums%2Fss102%2Frktdoc%2FEros%2Feros5.gif&hash=0e48d5d5af1407c5df67319e99fa7bfe76349545)

20KHz/div No Choke
(https://forum.bottlehead.com/proxy.php?request=http%3A%2F%2Fi566.photobucket.com%2Falbums%2Fss102%2Frktdoc%2FEros%2Feros6.gif&hash=e254f7a932156dc567e9915ccca78bd15fa11b6a)

One more 20KHz with Choke ( Not sure if I captured the trace in the previous post correctly)
(https://forum.bottlehead.com/proxy.php?request=http%3A%2F%2Fi566.photobucket.com%2Falbums%2Fss102%2Frktdoc%2FEros%2Feros7.gif&hash=7b62614d63268763dff62611f9f97b8d4340ab91)

Debra

[Doc B.]

I my limited experience with vacuum tube audio design I have come across things one wouldn't think audible, like digital filters that can radiate spikes in the 10MHz range. Under Buddha's tutelage I wrestled with filtering that kind of stuff out and found that the difference was audible.

[JC]

debk, I'm curious about the program you are using, and what is "acquiring" the signal for it to analyze.

[debk]

Check out
DPScope.com

Debra

[JC]

 Thank you, I most certainly will.

[johnsonad]

The PC board was designed around that time, and it retains the optional terminals for a choke.

Paul, the chokes are here and I'm curious if there are different terminals for the choke or simply removing the 270 Ohm resistor and wiring in the choke (Paramount use)?  There will be a shorter wire run if I I use the present terminals when mounted above the filament choke.  Lastly, will twisting the wires reduce potential hum pickup? 

Thanks,

Aaron

[Paul Joppa]

Paul, the chokes are here and I'm curious if there are different terminals for the choke or simply removing the 270 Ohm resistor and wiring in the choke (Paramount use)?  There will be a shorter wire run if I I use the present terminals when mounted above the filament choke.  Lastly, will twisting the wires reduce potential hum pickup? 

Thanks,

Aaron

I'll attach a picture of the missing silk-screen layer. The two terminals at the far right, labeled "L," were for the choke. (This design is six years old...) Twisting is generally a good idea, and using the resistor terminals may in fact be better than using these terminals, which run through a large loop area on the board. In simplified theory the magnetic field should be pretty symmetric and orthogonal, hence not a problem either way, but the real world always holds unanticipated surprises for us!

[johnsonad]

Thank you Paul.  I'll post some pictures once finished.   Another thing, I measured the chokes and one is outside 10% at 238 Ohms and the other is 251 Ohms.  This is to be expected with the tolerances Triad specifies.  Am I looking at any potential problems?

[Paully]

Yep, I just measured both of mine and they both came back almost exactly 236 ohms.  But they do state 20% tolerances, hopefully that isn't an issue for the Paramount either.

[Paul Joppa]

I think the C-7X design by Triad goes way back. When we first bought them, they were actually labeled MagneTek (they had bought Triad from Litton Industries in the seventies) and made in Mexico. I dug one out of the stash and read 256 ohms.  The current Triad web site has an interesting summary of ownership changes, and are currently owned by Axis of Taiwan, who were by that time (2004) actually manufacturing 95% of the product line. But the current production sold by Allied appears to be made by Hammond (look, feel, and boxes are distinctive) and has changed from the original layer-wound to modern nylon bobbins. No way to tell if anybody changed the internal design during any of those iterations. The C-7X is listed in the current Triad catalog, but I have no idea where it might be made, or if it is the same as what Allied sells.

Anyhow, since this is past the first cap, you can estimate the voltage loss fairly accurately. In a Paramount drawing 80mA, the 30-ohm difference will become 2.4 volts; less with other amps that draw less current. It's nothing in comparison to the effect of different power line voltages!

[johnsonad]

My chokes are clearly labeled "Made in China"...

I'm not an electronics wiz unfortunately but it doesn't sound like 2.4 volts will make a huge difference in B+.  My voltage is regulated at 120v.  Had a thought; as it looks like the two sets of pads are in series.  Could one use one set of pads for the choke and use the other set for a series resistor (30 Ohm, not sure on the wattage) to get a little closer to a total of 270 Ohms or is this overboard?

[Paul Joppa]

They are in parallel, not series.

[Paully]

We went ahead and installed the chokes.  Will try to see if I can figure out how to downsize a picture and post it.  We put shrink tubing around the wires and also put some thick wire mesh type material under the chokes to try to give some more shielding from the filament choke.  On first blush it seems to us that what it did was make the highs a little clearer and sweeter if that makes any sense.  But it did seem to make some difference so I am happy we did it.  As far we can tell we didn't pick up any additional hum.  Guess I will have to order one for the Eros!

[johnsonad]

They are in parallel, not series.

Thanks Paul!

[dbishopbliss]

I was just about to start my own thread related to using chokes in the power supply when I remembered this one. 

I have a more basic question... what parameters are "better" when designing a power supply that uses a choke?

For example, the C-7X is rated 10H, 90mA, DCR 270 Ohms while the C-3X is rated 10H, 50mA, DCR 500 Ohms.   I realize there will be a larger voltage drop using the C-3X, but is there any benefit to using the C-7X over the C-3X when my circuit draws only 20mA?

Also, the C-14X that is rated 6H, 200mA, DCR 150 Ohms.  Assuming I don't need the current capacity (which I don't), is more Henries better?