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~ The fix for whistling tubes ~
Discussions on the topic @ Vinyl Asylum:
http://www.audioasylum.com/scripts/t.pl?f=tubes&m=120675
http://db.audioasylum.com/cgi/m.mpl?forum=tubes&n=178906&highlight=Conrad+Johnson+PV10A+w/phono&session=
Anumber1 @ the VinylAsylum helped me with this. He said:
"...we changed the 47.5 ohm resistor on the grid of V4 (R29, right channel) leading to the Volume Control pot to 1k ohm. You would need to do the same for the left channel (V5 IIRC).
The Whistling/Microphonics are not really bad tubes but a parasitic oscillation that occurs due to the zero feedback design of the circuit. If you have tubes that will not work now they may be viable after the resistor swap. IIRC the job took me less than 20 mins to accomplish so it 'aint "Rocket Surgery". "
I took his advice and it only took 20 minutes. Dead quiet now.
For reference here is the entire board and the Schematic for the PV10B. It applies to the PV10BL minus the phono stage.
http://www.audioasylum.com/scripts/t.pl?f=tubes&m=120675
http://db.audioasylum.com/cgi/m.mpl?forum=tubes&n=178906&highlight=Conrad+Johnson+PV10A+w/phono&session=
Anumber1 @ the VinylAsylum helped me with this. He said:
"...we changed the 47.5 ohm resistor on the grid of V4 (R29, right channel) leading to the Volume Control pot to 1k ohm. You would need to do the same for the left channel (V5 IIRC).
The Whistling/Microphonics are not really bad tubes but a parasitic oscillation that occurs due to the zero feedback design of the circuit. If you have tubes that will not work now they may be viable after the resistor swap. IIRC the job took me less than 20 mins to accomplish so it 'aint "Rocket Surgery". "
I took his advice and it only took 20 minutes. Dead quiet now.
For reference here is the entire board and the Schematic for the PV10B. It applies to the PV10BL minus the phono stage.
Before
w/ the 47k resistors
After w/ 1k resistors
After w/ 1k resistors
