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In Reply to: RE: any one here using kiwame resistors on grids stopper ? posted by FenderLover on May 11, 2016 at 07:55:59
what i concern about the use of carbon comps is noise , carbon film seem to be better in this regard .
what value riken 1/2 watt you got ?
LT
Follow Ups:
Since the current through the grid stopper is miniscule the "microarcing" noise from a carbon comp resistor is not an issue. I try to use them whenever possible. The near total lack of inductance makes them the right part.
thanks Jim.
i also think how much resistance to use is importance as well .
i always use as small value as i think it get the job done , however i seen some people use up to 10k on grids stopper and i think this is way too much .
Yes, carbon composition is the "correct" construction for grid stoppers, as that type of resistive material is both non-metallic and non-inductive. Hold the amount of metal attached to the socket lug to a minimum. An antenna for parasitic oscillation is very bad here.
The value used for grid stoppers depends greatly on the gm of the type being employed. High gm types are much more vulnerable to parasitic oscillation. A 100 Ω part is fine for the 12AX7 triode. OTOH, a minimum of 10 KOhms should be used at each of the 4 grid connections of a 5842.
Eli D.
"a minimum of 10 KOhms should be used at each of the 4 grid connections of a 5842."
That's really interesting. Because all the grids are connected internally, I have only put stoppers on the signal input. I have seen photos of a little pyramid of grid resistors connected to the input signal, but have never tried it.
"I have seen photos of a little pyramid of grid resistors connected to the input signal, but have never tried it."
That's exactly the way to do things. The 5842 and its Russian counterpart, the 6C45П (6s45p), come annoyingly close to oscillating inside the cardboard box. :> ( The slightest bit of stimulus will trigger those VERY high gm types, which were designed for grounded grid RF service, into oscillation, when they are set up common cathode. Even a 200 MHz. o'scope might not catch where those buggers can oscillate. Take no prisoners! CC stoppers on all grid connections, a carbon stopper of some kind on the plate, and ferrite beads on the heater wires are very much in order, when "in box oscillators" are to be employed.
Eli D.
"Even a 200 MHz. o'scope might not catch where those buggers can oscillate. "
That's what scares me! My 60 MHz Tektronix would be blissfully ignorant. Thanks, Eli.
And that tube's parameters (voltage and current). If instance, most Fender amps use 1.5K-ohm resistors on their 6L6GC amps. Marshall uses 5.6K-ohm resistors on their EL34 amps.
Noise only occurs where there is current. There is virtually no current driving a grid.
One of the problems using a spiral-wound component in this application is the difficulty in testing for spurious responses (oscillations). Such responses may occur only when signal is present, and may appear only for brief intervals as the signal crosses the zero point, or on positive or negative peaks. The only definitive tool for this is a spectrum analyzer with a bandwidth of several hundred MHz. Lacking this instrument, the only resistor safe for a DIYer to use in either the grid or anode is carbon comp. Failing to hear anything amiss after installing something else is no guarantee that the amplifier isn't oscillating.
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Buy Chinese. Bury freedom.
Variety of values. I have primarily 1800-ohm, 1-watt used to replace grid stoppers in most Fender amp that use 1500-ohms. Can't seem to find any 1/2-watt resistors close to 1500-ohm value.
I like them too for grid stops, but where can you get them these days, if anywhere?
I got some from Parts Connexion, about a year ago.
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