choke VS resistor

rymac · 10-23-2008, 12:19 AM

I have a SF pro reverb I rebuilt. I changed out both transformers but
instead of a choke the amp had a 25 watt 1K wire wound resistor. I just replaced it with a new resistor. Is it worth replacing the resistor with a real choke tone wise?
If I replace it is a standard Fender choke OK or something from Mercury Magnets better?

Rymac

tubeswell · 10-23-2008, 10:18 AM

I take it you mean a choke in a Pii filter from the screen supply-node onwards?

The idea of a choke is to improve filtering in the B+. It will be quieter than a resistor filter, and there shouldn't be any hum. Compared to a resistor, it also has relatively little DC resistance, so you get more DC voltage at the screens (so you might need to add 470R-1k5 3W-5W screen grid resistors if the screen voltage rises more than 3-4VDc above the plate voltage in each tube), as well as increasing the B+ throughout the pre-amp, which increases the signal headroom (i.e.; if you don't change anything else about pre-amp stages) and so gives a bit more chime. The choke should be rated for enough current - if it is just for the screens and pre-amp B+, then 40-50mA will be fine.

Enzo · 10-23-2008, 10:27 AM

Didn't we just have like two threads on this exact topic within the last week or so? Do a search.

10-23-2008, 12:19 AM	#1
rymac Member Join Date: Sep 2008 Posts: 66	choke VS resistor I have a SF pro reverb I rebuilt. I changed out both transformers but instead of a choke the amp had a 25 watt 1K wire wound resistor. I just replaced it with a new resistor. Is it worth replacing the resistor with a real choke tone wise? If I replace it is a standard Fender choke OK or something from Mercury Magnets better? Rymac

10-23-2008, 10:18 AM	#2
tubeswell Supporting Member Join Date: Feb 2007 Location: Wellington NZ Posts: 2,661	I take it you mean a choke in a Pii filter from the screen supply-node onwards? The idea of a choke is to improve filtering in the B+. It will be quieter than a resistor filter, and there shouldn't be any hum. Compared to a resistor, it also has relatively little DC resistance, so you get more DC voltage at the screens (so you might need to add 470R-1k5 3W-5W screen grid resistors if the screen voltage rises more than 3-4VDc above the plate voltage in each tube), as well as increasing the B+ throughout the pre-amp, which increases the signal headroom (i.e.; if you don't change anything else about pre-amp stages) and so gives a bit more chime. The choke should be rated for enough current - if it is just for the screens and pre-amp B+, then 40-50mA will be fine. __________________ Building a better world (one tube amp at a time)

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10-23-2008, 10:27 AM	#3
Enzo Senior Member Join Date: May 2006 Location: Lansing, Michigan, USA Posts: 10,352	Didn't we just have like two threads on this exact topic within the last week or so? Do a search.

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