I have DAC which uses tubes and the grid leak resistor and the grid bias resistor are originally Allen Bradley 1W
I have tried to replace them with lower noise vishay cmf55 which like rn60 or rn65
But the sound became worse!!!
Seems since those resistors connected to the ground and carbon resistors are limited in their frequency response....less noise at high frequency enter the tubes or am i wrong?
I have red in diy audio that the recommendation is to go for carbon resistors in those places.
The actual question is there are 2 types of carbon carbon film and carbon composition
Carbon film has a bit less noise than carbon composition.
Do you have any experience with that?
Best regards
Nehoray
I have tried to replace them with lower noise vishay cmf55 which like rn60 or rn65
But the sound became worse!!!
Seems since those resistors connected to the ground and carbon resistors are limited in their frequency response....less noise at high frequency enter the tubes or am i wrong?
I have red in diy audio that the recommendation is to go for carbon resistors in those places.
The actual question is there are 2 types of carbon carbon film and carbon composition
Carbon film has a bit less noise than carbon composition.
Do you have any experience with that?
Best regards
Nehoray
Is "grid bias" the grid stopper (series from input to tube's grid)? There is AB (100R..few kOhm, depends of tube) -or any carbon comp resistor- is OK.
If it's a cathode resistor, there is any good (metal, wirewound or carbon film like Kiwame) resistor would be better.
The grid leak resistor -from point where input connected to grid, to ground- usually has large value (about 100k..1M).
If it's has larger value, the resistor own noise would be problematic ... if the signal is very low (for example phono input stage).
If it's in line stage (signal value is Volt magnitude), I don't think that AB vs. Dale is the problem.
If it's a cathode resistor, there is any good (metal, wirewound or carbon film like Kiwame) resistor would be better.
The grid leak resistor -from point where input connected to grid, to ground- usually has large value (about 100k..1M).
If it's has larger value, the resistor own noise would be problematic ... if the signal is very low (for example phono input stage).
If it's in line stage (signal value is Volt magnitude), I don't think that AB vs. Dale is the problem.
Thank you for your reply
The tube is 6SL7
Both resistors are 470k ohm
I will try to write the schematic
The tube is 6SL7
Both resistors are 470k ohm
I will try to write the schematic
The sound became worse?
More noisy?
More distorted?
Worse frequency response (sounds rolled off at the high frequencies, or sounds more rolled off at the low frequencies?
Apparent mid range frequency roll off?
Or what?
I agree, troubleshooting without a schematic is like a blindfolded archer shooting 100 arrows trying to hit the target.
More noisy?
More distorted?
Worse frequency response (sounds rolled off at the high frequencies, or sounds more rolled off at the low frequencies?
Apparent mid range frequency roll off?
Or what?
I agree, troubleshooting without a schematic is like a blindfolded archer shooting 100 arrows trying to hit the target.
You should't be able to hear 1 resistor , probably just a crappy marginal design sensitive to any changes ...
470K is way too low for grid leak bias so it is just the grid resistor to ground
470K is way too low for grid leak bias so it is just the grid resistor to ground
The schematic in Post # 8 shows the 71A connections:
The grid is connected to the output transformer
The plate is connected to the signal from the driver tube.
I did not check for any other errors, I stopped looking when I saw those two errors listed above.
Your circuit might be connected properly, and operating correctly, but the schematic needs to be checked over, and corrected where necessary.
Happy listening!
The grid is connected to the output transformer
The plate is connected to the signal from the driver tube.
I did not check for any other errors, I stopped looking when I saw those two errors listed above.
Your circuit might be connected properly, and operating correctly, but the schematic needs to be checked over, and corrected where necessary.
Happy listening!