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Plate chokes for 10k Rp type tube

Posted on December 5, 2016 at 22:31:36

Posts: 324
Location: S.A.
Joined: March 27, 2004

I'm after a pair of plate chokes to suit a 10k Rp type tube which sets up at ~4mADC. Max voltage swing across the choke will be less than 40vAC peak.

I'm a little concerned about the affects on HF due to capacitance associated with high inductance, hopefully these concerns are misplaced.

Are you able to recommend something to me for this purpose?.



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RE: Plate chokes for 10k Rp type tube, posted on December 6, 2016 at 19:35:54

Posts: 4271
Joined: June 29, 2000
Hello Shane:

First let me ask a few questions about your application. I'm going to assume that this is a voltage amplifier whose plate will feed the grid of a succeeding tube (power tube?).

How will it be coupled to the succeeding tube? RC coupling? LC coupling? transformer coupling?

If transformer coupling tell me what the nominal impedance of the primary winding is.

If say your RC coupling... one rule of thumb to begin to estimate how much L you want in the plate choke is too take the value of what would be an appropriate plate load resistor for your operating points. Once we have that value it is a matter of calculating how much L is necessary to have that much inductive reactance at your lowest frequency of interest (say 30 hz).

At four mils of dc bias current... it's not going to be terribly difficult to be able to get a substantial amount of L and to keep the unit physically (relatively speaking) smallish in size. There are a wide range of design strategies and tricks that I can use to keep the C "small"... I don't anticipate a problem here from what I am now picturing.

Pricing is of course reflected in the course of action I take in wishing to minimize capacitance... the advanced strategies add to the cost of winding the coils. I would also recommend our PLUS strategy used in plate chokes and other special inductors. This involves winding symmetrical twin humbucking coils that are electrical equals but of opposite winding phase.

with the plus coil construction your capacitive gradients (potentials) will be the same irrespective of which one of the two lead wires you orient toward ac ground or ac high.


Builder of MagneQuest & Peerless transformers since 1989


RE: Plate chokes for 10k Rp type tube, posted on December 6, 2016 at 22:18:30

Posts: 324
Location: S.A.
Joined: March 27, 2004

Hello MSL,

Thanks for the response, the application is the input tube of the attached amplifier schematic.

Rp is ~10k and the bias resistor in that stage carries also the filament current, the 18R value is correct.

I really needed as much HF response as possible, and I'm not sure that I really need the ~300H that the EXO-010 might present, with the info provided is it possible to calculate the in circuit HF limitations with what you have in mind?.

Need a pair of plate chokes for the driver tube as well, much simpler I'm assuming.. Ip = 20mA.. Rp of the tube is ~2k.



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