Choke ratings and substitutions

[leadtower]

Can anyone tell me what a guy would need to consider if he wanted to swap out a choke for a power resistor in a PS filter? I would model it on Duncans site but there are some variables i don't have; so I was wondering if I could get a short course in whats involoved.

[EWBrown]

First of all, just make sure that the DC resistance of the chioke and the current handling capability are compatible with those of the power resistor (or vice versa).

For examplee, in the DIY53 "baby blue", the power resistor is 50 ohms, and the Dynaco (or Triode Electronics)C-354 choke is about 56 ohms DCR and has a current handling ability of 200 mA. The choke will reduce 120 Hz ripple, the reactance can be figured by the formula XL = 2*PI*F*L F in Hz, L in Henries.

So a C-354 1.5H choke will have 6.28 X 120 X 1.5 or about 1130 ohms reactance at 120 Hz, with 56 ohms DC resistance.

/ed B in NH

[leadtower]

Thanks Ed; the resistor is 1800 ohms and 5 watt. I can see by the math that my 10 hy 150 ma Hammond should work. Thanks much I'll keep this posted.

[EWBrown]

Are you sure that the 1800 ohms resistor is the first one after the rectifier in the B+ chain?

That seems to be a rather high resistance value, typically 4 7591s are going to require 150-200 mA, and that would result in a 270-360VDC drop, at about 40-54 watts of dissipation. If it's the second resistor downstream, then a choke really isn't needed at that point.

Typically the first resistor after the rectifier should be in the 50-100 ohms range, 5 to 10 watts. A 2 to 10 H choke, 200 mA (or greater) would work well for that, just maintain the same or a reasonably close DC resistance.

/ed B in NH