Is there such a thing as too much choke?

[eleventeen]

One of the surplus pieces of junk I got recently has a choke rated 19 henries. That seems a lot higher than the usual 4-10 henries I see most tube amp chokes rated. I note, as well, that it shows 420 ohms DC resistance...which seems like a heck of a lot --- you mean ---on a 420 volt supply it would produce 1 volt on the output?  Sorta doubt it. Rated 60 ma. I get the feeling that this choke is more suited to producing a clean clean clean output more for a high-freq radio, with teeny individual tube currents and no audio output per se (other than headphones) and indeed, that's the type of thing it came out of.

But the real question is, is this a usable choke for a non-specific say 6V6-fired amp? What happens if I got too many henrys? Or henries? Can you say "anti-sag"?

[HotBluePlates]

Is there such a thing as too much choke?

Generally only too much for your back or wallet. Or if you want sag, then obviously it's counter-productive.

One of the surplus pieces of junk I got recently has a choke rated 19 henries. That seems a lot higher than the usual 4-10 henries I see most tube amp chokes rated. I note, as well, that it shows 420 ohms DC resistance...which seems like a heck of a lot --- you mean ---on a 420 volt supply it would produce 1 volt on the output?

Only if you draw 0.9976 ampere of current through it; then 420Ω * 0.9976A = 418.99v  420v - 418.99v = 1.1v

Note that it is normal to see much higher d.c. resistance in chokes with more H... after all, more wire had to be wound around the core to get the high-henry count.

... it shows 420 ohms DC resistance...which seems like a heck of a lot ... Rated 60 ma.

This also seems in line with the other characteristics. With a given core size, to get more H you have to wind more turns of wire, but since the core size is fixed you need to use smaller diameter wire to fit more turns in the same winding window. That means d.c. resistance goes up due to both length and thickness of the wire; additionally, the skinny wire means allowable current may be small.

A small core could also limit the current rating of the choke, as the current's flux can't exceed the capability of the core for the choke to maintain its inductance. If the flux saturates the core, inductance falls.

I have a couple of chokes from a regulated power supply that are rated at 250mA and 500mA. The 500mA choke is bigger than a 100w output transformer put in a potting can.

... teeny individual tube currents ... that's the type of thing it came out of.

But the real question is, is this a usable choke for a non-specific say 6V6-fired amp?

The easiest way to figure out how to use it is to look at how it was used in the gear you took it from. You know it would likely be too small to handle the plate current of a push-pull output stage.

A class A 6V6 output stage idling at 24w total with a B+ of 350v draws 68.6mA of current. You could push plate voltage higher to reduce current draw, but if you get into class AB then peak current will exceed idle current so the reduced idle draw will mislead you.

But most guitar amps use a choke to feed the screens and preamp, and are unlikely to draw 60mA total. You might want to double-check current draw with an ammeter (or careful load-line plotting) if you use bigger tubes with high load impedances. If the loadline cuts below the knee of the 0v gridline, there is a chance for increased screen current draw during peaks of the input signal.

[eleventeen]

Excellent reply, HB, thank you!

[12AX7]

I don't know the technical aspects, but as a player i can tell you this. My main amp is a homebrew I spent a lot of years perfecting and i first used s 20H choke ala matchless chieftain. I since tried a 5 and i can tell you this much....no doubt the amp sounds better with the 20H. i swapped them back and fourth over a few years then just stuck with the 20 once It became clear it just sounds better. More punch and NO loss of sag at all, and my amp has a lot of sag generated in other ways. But sag may be an issue for a different type of amp like a non master you crack up for distortion. Mine is a 50 watt MV amp similar to a marshall JCM and the drive comes strictly from the pre. So for non master crank it and scream type amps i can't say. For a typical 50 watt MV amp with cascaded pre, the 20H is undeniably better in my mind. For what it's worth...

[Backwoods Joe]

To many Henry's for your amp? Yes. I built a PP EL84 amp with EZ81 recto for a guy and we decided to start with a 20H choke. Later we tried a 10H choke and the customer liked it much better. "His opinion" was that the 10H was "more responsive, faster & more solid feel". It seems like sounding great is not enough any more.... It's got to feel right too!

[tubeswell]

The RoT for HT whole-of-supply chokes in a CLC filter, is to make them the same DC-rating as the PT's high tension winding.

If the choke is only to be used for screen supply onwards in something like a 5G9 tremolux (with 2 6V6s in Class AB1 PP), then a 40mA DC-rated choke will be perfectly adequate, or a 90mA DC-rated choke in a 2 x 6L6 PP amp like a 5F6A.

If the choke is a whole-of-supply choke in a CLC filter for a SE Class A amp, then at least 1.2x the idle current of the 6V6s is a good idea (with 1.5x being a more reliable concept). YMMV

Choke-input filters require a higher DC-rating.