1.) On the "roehrentechnik.de" web pages, there are data for their two anode chokes:
-70H/1300 Ohms/Ce~300pF
-200H/2800 Ohms/Ce~90 pF (2 Kammer Wicklung)
Both chokes are good for 35-40mA at least.

2.) Measurements of (quality) S&B grid choke by Thorsten, see the link. He found Ce~65pF.

Well, 65p-90pF is not too much, but 300pF in parallel with 80pF input capacitance of 300B is 380pF. And with high impedance driver (cascode, pentode, high rp tubes common cathode...), say Rout~15kOhms, we have f-3= 1/(2*3,141*15000*380*10^-12) = 27,9 kHz , limited frequency response of the driver.
Do anybody has some more informations/measurements about "typical" shunt capacitance of grid/anode chokes?

• http://groups.yahoo.com/group/Thunderstone_technical/message/556

you were saying;

::::-200H/2800 Ohms/Ce~90 pF (2 Kammer Wicklung)
Both chokes are good for 35-40mA at least.::::

are you sure there isn't a typo in the above description?

reason I ask is.

at 35 mils and 2800 ohms DCR you'd have a voltage drop of
98 volts.

the I squared R losses would be equal to close to 3 and a half watts.

and this before you even add in any ac current and add the two vectorally to arrive at the heating current.

dropping 98 volts across an anode choke would be fairly "expensive" in terms of using volts efficiently... and would most likely be one hot little critter to the touch.

If we were to allow a 20 volt drop then our max dcr should be approx 575 ohms. And then our I squared R losses (dc only) would be approx seven tenths of one watt compared to 3.43 watts.

just curious.

msl

Resistors are usually esy to put into the 'single parameter' category. If you're choosing a choke to present a load, you need to consider frequency response of the inductor. This frequency response is also not going to remain constant, as other parameters of the choke begin to surface. Capacitance being the primary paramter which causes chokes to behave like things other than inductances.

As Damir was pointing out, measuring these effects is not always simple.
cheers,
Douglas

• http://www.roehrentechnik.de/html/anodendrosseln.html

you asked rhetorically:

:::I really don`t know can we use those chokes with "working quiescent DC current" of say, 40mA?:::

well... like you said... it depends...

1) can you afford to drop 98 to 112 volts depending on if you run at 35 or 40 mils dc. And what is the ac vector addition to the heating current... which we don't know and will be determined by the core losses and the inductive reactance of the choke and the magnitude of the ac volts across it...

by any standard notion or industry practice that I've seen... this level of voltage drop and winding resistance would be considered too high for the stated current levels.

2) other thing you'd want to consider... what is the resultant temp rise of the unit... is the temp rise so high that it really puts the unit in danger (by danger I mean in excess of it's ul ratings for insulations, and magnet wire type used and etc)...

but I don't want to monday morning QB another company's design or etc... I was just pointing out... the obvious... what the voltage drops and the copper power losses were under the conditions published.

perhaps it would work just fine for someone, somewhere....

msl