Tweet
While I had this same amp here searching for output level dropping, I found Ch 2 once again had very nasty loud 60Hz buzz/hum from the Standby Switch coupling into the Ch 2 input stage immediately adjacent to the switch. I've normally been successful in dressing those two yellow Mains wires to the S/B switch, tightly twisting and wrapping spirally with the AC mains wires, and folding them away from the input connector. My notes from May 2018 indicated I had done so and got it quiet. Yet now, it was louder than ever.
On one of the SVT-VR's, I had gone as far as cutting up some 7mil Brass Shim Stock from a roll of it I've been using for the past 30 yrs, and folded up another shielded box to put the Standby Switch into.
After cutting the flat (4" x 2"), and punching a 1/2" hole a bit above center with a 1/2" dia Whitney XX Punch, I cut the flaps, folded the sides and back (2" deep, 1" wide, 1" side wall, 1/2" rear wall), along with the flaps, then soldered them together to hold it all together, and wrapped the outside walls and bottom with mylar insulation tape.
It's a snug fit, but goes in, and after connecting the switch back up, and folding those two wires back away from the input cable (which has been re-routed along the front of the PCB under all the pots, instead of along the rear of the PCB in parallel with the heater traces), I mounted the chassis back in to have a listen.
Buzz & Hum gone now. I can crank the Ch 2 Volume, Treble & Bass fully CW, Ultra-High & Ultra Low on, and just hear the normal tube noise without the annoying Buzz that comes with the stock amp. Sometimes on SVT-VR's, you have to go further than just lead dress, as was the case here. I don't know why it was so bad yesterday and not like that last year when I last serviced it.
On one of the SVT-VR's, I had gone as far as cutting up some 7mil Brass Shim Stock from a roll of it I've been using for the past 30 yrs, and folded up another shielded box to put the Standby Switch into.
After cutting the flat (4" x 2"), and punching a 1/2" hole a bit above center with a 1/2" dia Whitney XX Punch, I cut the flaps, folded the sides and back (2" deep, 1" wide, 1" side wall, 1/2" rear wall), along with the flaps, then soldered them together to hold it all together, and wrapped the outside walls and bottom with mylar insulation tape.
It's a snug fit, but goes in, and after connecting the switch back up, and folding those two wires back away from the input cable (which has been re-routed along the front of the PCB under all the pots, instead of along the rear of the PCB in parallel with the heater traces), I mounted the chassis back in to have a listen.
Buzz & Hum gone now. I can crank the Ch 2 Volume, Treble & Bass fully CW, Ultra-High & Ultra Low on, and just hear the normal tube noise without the annoying Buzz that comes with the stock amp. Sometimes on SVT-VR's, you have to go further than just lead dress, as was the case here. I don't know why it was so bad yesterday and not like that last year when I last serviced it.
Comment