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"The black can cap next to the blue 20uF is a dual 33uF450V"
So I would assume that there is a 1 k 10watt resistor between the 2 33uF
cap halves as in the diagram , therefore there must be 2 x 20uF caps after that seperated by a 22k 1 w and 47k respectively.
What I meant by "piggybacking" is temporally connecting a suitable capacitor
(ie 20uF 500v) across the existing one and see if the hum drops in level.
This should improve the filtering to the PI and the first 12AX7.
It may not be this but at least can eliminate the powersupply ripple.
Is there much distance from pin 2 of V1 to the input socket?
Is the wire shielded?
I would also try piggybacking i mean connecting across the 5.6meg from
pin 2 to ground with a 1 meg.. maybe its picking up stray hum...
Another thing to check would be the centre tap of the heater supply.
The schematic shows a .5uF capacitor to ground.
Its common practice to directly ground the centre tap or as in some early Fenders run 100ohm to ground from both legs of the heater supply disconnecting the centre tap of course.
Was the tech who replaced the capacitors aware you would be recording with it? the hum may be acceptable for general use particularly considering
the age of the amplifier.
Maybe this needs the "fine tooth comb" repair .. where the amplifier is practically rebuilt with all the connections reterminated with particular
attention to lead dress (thats how the wires lay in the chassis).
When you turn the amplifier off does it take a while to die away ?
If so does the hum disapear instantly the switch is turned off ? or does the hum die away with the signal ?
Maybe a dc heater supply may be of use particularly to the first valve.
So I would assume that there is a 1 k 10watt resistor between the 2 33uF
cap halves as in the diagram , therefore there must be 2 x 20uF caps after that seperated by a 22k 1 w and 47k respectively.
What I meant by "piggybacking" is temporally connecting a suitable capacitor
(ie 20uF 500v) across the existing one and see if the hum drops in level.
This should improve the filtering to the PI and the first 12AX7.
It may not be this but at least can eliminate the powersupply ripple.
Is there much distance from pin 2 of V1 to the input socket?
Is the wire shielded?
I would also try piggybacking i mean connecting across the 5.6meg from
pin 2 to ground with a 1 meg.. maybe its picking up stray hum...
Another thing to check would be the centre tap of the heater supply.
The schematic shows a .5uF capacitor to ground.
Its common practice to directly ground the centre tap or as in some early Fenders run 100ohm to ground from both legs of the heater supply disconnecting the centre tap of course.
Was the tech who replaced the capacitors aware you would be recording with it? the hum may be acceptable for general use particularly considering
the age of the amplifier.
Maybe this needs the "fine tooth comb" repair .. where the amplifier is practically rebuilt with all the connections reterminated with particular
attention to lead dress (thats how the wires lay in the chassis).
When you turn the amplifier off does it take a while to die away ?
If so does the hum disapear instantly the switch is turned off ? or does the hum die away with the signal ?
Maybe a dc heater supply may be of use particularly to the first valve.
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