Plate Choke for EF86 in triode?

[Tubenstein]

Hello!
My friend is working on EF86 in triode for line preamp application.

He wants to know what inductance of plate choke he should use?

I know operating current is low.

Thanks!

 

[Kay Pirinha]

To benefit from a plate choke, it's reactance at the LF audio end, say 16 Hz, needs to be at least as high as a common plate resistor, say 100 kΩ. Now do the math: L = 2πfR = 10 MH. Not really reasonable, is it?

Best regards!

 

[Francois G]

Not really reasonable, is it?

No, a 10 MH coil could be as big as a small house.

In stead, how about:

L=R/2πfc=2200 H? Almost doable at low currents.

 

[as_audio]

Confused - who is doing the math ?
As far as I can see many manufacturers in the past used physically small plate chokes.

 

[Tubenstein]

eBay is selling 250H plate choke that is made for EF86, and it is capable for 10mA.

https://www.ebay.com/itm/134393286931

 

[as_audio]

That would be like 25kohms at 16 Hz ?

 

[Kay Pirinha]

Francios G.'s formula is right, of course, and I was erratic. Sorry for that! Anyway, 100 kΩ @ 16 Hz requires an iductance of about 1000 H. Still doable? Reasonable? And what is it good for if the reactance rises proportionally with frequency?

Best regards!

 

[as_audio]

A general discussion on the use(fulness) of choke loads can probably be found somewhere

 

[nerdorama]

Lundahl has a plate choke that can reach 800H if gapped for max current of 5mA. This according to the Erhard Audio web page.