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In Reply to: RE: I would not use wire-wound resistors in grid stopper positions posted by Tube747 on March 03, 2017 at 21:34:51
Carbon film resistors are LASER trimmed, with a spiral cut. The spiral's presence makes the part inductive, which is a negative in grid stopper service.
Carbon film resistors are what I recommend for plate stopper service. The current in the plate circuitry is substantial and CC noise is an issue. So, some inductance can't be avoided, but at least the non-metallic nature of the resistance element is retained.
Eli D.
Follow Ups:
So good quality carbon film resistor should be good for R2, R4, R8 and R11 then, right?
CF will do nicely. Buy KOA/Speer parts from Mouser, of an appropriate wattage rating. Remember, Kiwame "audiophile grade" resistors are, in fact, KOA/Speer.Frankly, the fascination with "boutique" parts eludes me. Yes, there are hyper-critical situations where noise factor, low ESR, non-inductive ... matter and a costly part makes sense. Otherwise, good grade ( not "bargain basement"), industrial parts yield eminently satisfactory results. Every last one of us is highly vulnerable to the "Emperor's New Clothes Virus". :> ((
Eli D.
Edits: 03/05/17 03/05/17
Are you talking about this one??
A Mouser search is linked below. The parts branded Kiwame are of the higher rated wattages. I suggest you use parts of an appropriate wattage in any given position.
Good stuff at a reasonable price is hard to beat.
Eli D.
Can I use Mills MRA-5 and MRA-12 for the power supply circuit?
That would be a complete waste of money . The inductance of "ordinary" WW resistors is of benefit (small) in a PSU filter. For Pete's sake, chokes ( inductors ) are part of many an excellent PSU filter.
Eli D.
Edits: 03/06/17
I have no choice as some of the good sounding and dirt cheap inductive wirewound resistors do not have all value for the PSU.
However, Mills has everything I need for this purpose.
What about a few loops of wire around a ferrite bead (i know they can be lossy at high frequency) or the old-timers trick of a wrapping the leads (or another piece of wire) of a CC resistor around the body to make a little air cored inductor in series with the resistance?
dave
A tiny ferrite bead, just big enough to clear the socket lug, cemented to the socket's insulating base has been used. FWIW, I find that idea appealing on the (ostensibly grounded) grid of a cascode's "top" triode.
JMO, anything that truly suppresses parasitic oscillation is fine. "There's more than 1 way to skin a cat."
Eli D.
As politically incorrect as it is, I agree with the cat skinning and was making just that point when I questioned your insistence of a carbon comp because it was non-inductive.
dave
It's a question of Q. Will those devices exhibit sufficient dampening at the frequencies over which the tube exhibits a tendency toward instability? I've seen transmitting tubes oscillate when the carbon comps in anode suppressors (the second device you mentioned) were replaced with spiral-wound carbon film. Depending on the tube, the circuit and the physical layout, this can be a tricky thing.
--------------------------
Buy Chinese. Bury freedom.
What about non inductance wirewound resistor for R2, 4, 8, 11 and Vishay naked for R15 and 16?
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