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    Building, troubleshooting and testing of these amplifiers should only be
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Resistor design?

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oemcar

oemcar

Member
Joined 2020
#1
Spent extra time & $$ sourcing carbon composition resistors for EL84 PP project attempting to minimize noise. Most values were not in tolerance- especially from ebay vendors.
Investigating using carbon film or metal film for next build- any noise advantage of carbon comp's vs those other designs? Film resistor tolerances seem to be much tighter- perhaps beneficial in PP design for balance.
Thanks,
Jim
 
#2
Carbon composition resistors are known for being noisy and having poor tolerance.

Carbon film resistors are quieter but tolerance is still a bit of an issue.

Metal film resistors don't really require these considerations for AF amps. Just buy those and use them.
 
#3
Carbon Comp are the worst with regard to noise,
and noise increases with time, current, temperature and they exhibit high temperature coefficient, too.
One thing they are good with is that they swallow huge energy pulses without blowing up, maybe the only good ...
 
#10
No need for CC as grid stopper... This is an old wives tail debunked by many including the late DF96.

1% MF types are perfectly fine. For power, I use MO though - I like the pulse and flameproof properties.

if you MUST use CC for whatever superstitions you might have, just buy the DALE parts for $$$ and be done with it. How many do you need for an amp? They last for te life of the amplifier anyway usually. I just found Stackpole makes CC for 1/3 the cost of Dale...

RC12JT1K00 1k Carbon Composite Resistor - Stackpole Electronics
 
#11
astouffer said:
I doubt you would be able to hear resistor noise unless you are running ridiculously high gain stages.
Click to expand...

agreed mostly, at least when we talk thermal or current noise;
but the O.P. was hunting for carbon comps explicitely to reduce noise in his amp, and this is generally not the way to go;
incidentally, I was able to "hear" a resistor's noise once, namely a sort of not very loud but enoying crackling in one channel; I re-soldered, replaced the tube, then the screen decoupling cap, then the socket, until I finally found the root cause: a 330k screen dropping cc resistor in a state of de-composition;
agreed, it was a high gain pentode; and a high gain phono circuit; and the resistor had had an unknown shelf time before; and using a cc was purely accidental (just mixed up in the box) ...
 
#16
payloadde said:
incidentally, I was able to "hear" a resistor's noise once, namely a sort of not very loud but enoying crackling in one channel; I re-soldered, replaced the tube, then the screen decoupling cap, then the socket, until I finally found the root cause: a 330k screen dropping cc resistor in a state of de-composition;
agreed, it was a high gain pentode; and a high gain phono circuit; and the resistor had had an unknown shelf time before; and using a cc was purely accidental (just mixed up in the box) ...
Click to expand...

This makes sense to me from an electrical cause and effect standpoint-
Thx,
Jim
 
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