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Grid stopper resistor question
Grid stopper resistor question
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Old 13th September 2019, 01:17 PM   #11
nigelwright7557 is offline nigelwright7557  United Kingdom
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Quote:
Originally Posted by sumotan View Post
Your comment that grid stopper resistor does not affect sound got me curious DF96.
Why would it not be when this resistor is directly in the signal path.

Thanks
Everything affects the sound.
However, in most cases it is negligible.
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Old 13th September 2019, 03:35 PM   #12
jhstewart9 is offline jhstewart9  Canada
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I've read that some have used surface mount resistors soldered direct to the socket terminal. Thus, very short leads.
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Old 14th September 2019, 02:29 AM   #13
PRR is offline PRR  United States
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Quote:
Originally Posted by sumotan View Post
...grid stopper resistor does not affect sound got me curious ...Why would it not be when this resistor is directly in the signal path....
The resistor is 1k or so.

The tube grid is over 100Megs over most of the audio band.

Look at it like a Voltage Divider. Huge variation of the resistor make "NO" difference to the voltage on the grid.

A high-Mu triode grid may come down past 200k at the top of the audio band. Still a few-k resistor makes about no difference.

Anyway carbon-comp is not THAT bad. It's all we had for decades.
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Old 15th September 2019, 01:16 AM   #14
Hanze Khronye is offline Hanze Khronye  Australia
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Quote:
Originally Posted by sumotan View Post
Your comment that grid stopper resistor does not affect sound got me curious DF96.
Why would it not be when this resistor is directly in the signal path.

Thanks
I realise there is no DC current through this resistor yet I wonder about contribution of noise from this resistor, 12AX7 is a high mu tube. Contact, thermal, Shot and or Johnson noise?.

Would a ferrite bead be a better solution?. 9 pin tube socket, cut the grid lugs down the centre, slip ferrite over the socket pin, solder to the lug tip.

If all we are doing is creating a LP filter, why not small value cap in parallel with the grid leak resistor?..

Anyway, I'm interested to see where this goes.

Cheers,
HK
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Old 15th September 2019, 01:25 AM   #15
PRR is offline PRR  United States
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Hiss from a ~~1k resistor at line level?

Do math. It's quite negligible.

FWIW: the hiss voltage at 12AX7 grid is OTOO a 20k resistor.
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Old 15th September 2019, 01:55 AM   #16
Hanze Khronye is offline Hanze Khronye  Australia
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I wasn't assuming line level, and what is hiss voltage?
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Old 15th September 2019, 03:24 AM   #17
dotneck335 is online now dotneck335  United States
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Quote:
Originally Posted by SemperFi View Post
Musical instrument amplifiers are often over driven (mostly guitar) and in those cases carbon comp is usually preferred, not just for their great pulse- and overload-tolerance, and non inductive properties, but also for sound. Carbon comps are the best for this purpose.
Quote:
Originally Posted by JonSnell Electronic View Post
Grid stoppers are best if they are carbon composition.
I am still not getting why the carbon comps are BETTER as a grid stopper resistor than a metal film one. WHAT makes them SOUND better?
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Old 15th September 2019, 04:25 AM   #18
Hanze Khronye is offline Hanze Khronye  Australia
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Why don't you build something, find out for yourself. Most of us have. And if you don't, then why come here with such comments?
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Old 15th September 2019, 04:54 AM   #19
Wavebourn is offline Wavebourn  United States
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Grid stopper resistor question
Grid stopper is needed only and only if the stage is unstable without it. Sometimes it even does harm, from example in a first stage of a power amp that has feedback to it's cathode, where a capacitor around 100 pF to the ground my work better. Sometimes it plays also other roles, like much bigger value resistor at input of a guitar amp, to work as a filter. Or, in the grid of output tubes where it increases time constant of a coupling capacitor when it's being charged through the grid current on overload.
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Last edited by Wavebourn; 15th September 2019 at 04:57 AM.
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Old 15th September 2019, 06:03 AM   #20
Hanze Khronye is offline Hanze Khronye  Australia
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100R + ferrite keeps high Gm and Mu from oscillating, I don't know how or why.. but it works, take away 100R and it oscillates. I'm not sure its strictly LP filter, suspect there is more to it than that. Low level <200mV.. as always could be wrong. Just saying from real world experience.

Last edited by Hanze Khronye; 15th September 2019 at 06:05 AM.
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