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Hi All
I have a Fender Blues Jnr in the workshop at the mo' that buzzes @ 2x mains freq (100Hz here in the UK), so pretty sure it's from the FWBR'd line somewhere.
The buzz fades up when 1st powered on, so would suggest related to gain of valves. There is a lot of ripple on the B+ line, (about 5VAC p-p) and someone in the past has added a parallel cap to C25 47uF 450V, not badly done IMHO, but it hasn't stop the buzz or the ripple. I tried breaking the track between the original 47uF and the added cap and bridging with a 5W 1K resistor, to form a pi filter. This reduced the ripple to practically zero, but the buzz remained, possibly at slightly less volume, but still noticeable.
I have checked the HT voltages and the bias all are well within 20%, bias is particularly good at 10.54V (spec'd 10.6V).
Pulling the PI valve stops the buzz, but swapping the PI with known good valves doesn't cure the problem.
Don't know what else to try.
(btw many thanks to Enzo for posting the service manual with all the variants - the incorrect part Nos on the schematic I had was driving me nuts
)
I have a Fender Blues Jnr in the workshop at the mo' that buzzes @ 2x mains freq (100Hz here in the UK), so pretty sure it's from the FWBR'd line somewhere.
The buzz fades up when 1st powered on, so would suggest related to gain of valves. There is a lot of ripple on the B+ line, (about 5VAC p-p) and someone in the past has added a parallel cap to C25 47uF 450V, not badly done IMHO, but it hasn't stop the buzz or the ripple. I tried breaking the track between the original 47uF and the added cap and bridging with a 5W 1K resistor, to form a pi filter. This reduced the ripple to practically zero, but the buzz remained, possibly at slightly less volume, but still noticeable.
I have checked the HT voltages and the bias all are well within 20%, bias is particularly good at 10.54V (spec'd 10.6V).
Pulling the PI valve stops the buzz, but swapping the PI with known good valves doesn't cure the problem.
Don't know what else to try.
(btw many thanks to Enzo for posting the service manual with all the variants - the incorrect part Nos on the schematic I had was driving me nuts
)