I recently finished a Weber 6A14 kit (BFPR 'clone').
(Voltages are more or less normal albeit slightly on the high side (425 on the plates) and the 6V6s are biased at about 26-28mA, which I know is hot. The heaters are at 6.5VAC.
I initially more-or-less followed the Weber layout (which follows the fender layout) and had quite severe hum issues. Then I re-did the grounding as follows:
Separate wires from each of the pots' ground lugs to one point on the brass grounding plate.
The main board grounds each going separately to the same point on the brass grounding plate
The reverb recovery stage (220k) grid load resistor and the RT secondary ground return going each separately to the same point on the brass grounding plate
A separate pre-amp filter cap going separately to the same point on the brass grounding plate.
The reservoir filter (off the cap can) and the screen filter (off the cap can) and the unused (former pre-amp) filter now tied to the screen filter, going to the same grounding point as the PT's High-Voltage winding centre tap.
The heaters are DC-elevated to 37V, and the ground return from this goes separately to the same point as the HV CT/main filter ground. The bias supply ground return also goes separately to the same point as the HV CT/main filter ground.
The hum is reduced substantially, however it is still there but it is intermittently affected/eliminated/reduced/enhanced by the vol pot and tone pot settings. (With the vol at zero I get a bit of hum, but it goes away completely when the vol is at about 1-3, then comes back with the vol at 4-5. Similarly when teh tone controls are at zero there is hum (when the vol pot is at zero, but when the vol pot is at 1-3 'quiet', I can get hum back by adjusting the tone pots). I guess this is inevitable as some of the main board ground returns are tied together before the rest of the pre-amp grounds are.
When I have scratch-built my own amps, I have learned to keep the ground returns separately wired to a common star point and never have any grounding issues.
How did Fender get the grounding quiet in his BF amps?
(Voltages are more or less normal albeit slightly on the high side (425 on the plates) and the 6V6s are biased at about 26-28mA, which I know is hot. The heaters are at 6.5VAC.
I initially more-or-less followed the Weber layout (which follows the fender layout) and had quite severe hum issues. Then I re-did the grounding as follows:
Separate wires from each of the pots' ground lugs to one point on the brass grounding plate.
The main board grounds each going separately to the same point on the brass grounding plate
The reverb recovery stage (220k) grid load resistor and the RT secondary ground return going each separately to the same point on the brass grounding plate
A separate pre-amp filter cap going separately to the same point on the brass grounding plate.
The reservoir filter (off the cap can) and the screen filter (off the cap can) and the unused (former pre-amp) filter now tied to the screen filter, going to the same grounding point as the PT's High-Voltage winding centre tap.
The heaters are DC-elevated to 37V, and the ground return from this goes separately to the same point as the HV CT/main filter ground. The bias supply ground return also goes separately to the same point as the HV CT/main filter ground.
The hum is reduced substantially, however it is still there but it is intermittently affected/eliminated/reduced/enhanced by the vol pot and tone pot settings. (With the vol at zero I get a bit of hum, but it goes away completely when the vol is at about 1-3, then comes back with the vol at 4-5. Similarly when teh tone controls are at zero there is hum (when the vol pot is at zero, but when the vol pot is at 1-3 'quiet', I can get hum back by adjusting the tone pots). I guess this is inevitable as some of the main board ground returns are tied together before the rest of the pre-amp grounds are.
When I have scratch-built my own amps, I have learned to keep the ground returns separately wired to a common star point and never have any grounding issues.
How did Fender get the grounding quiet in his BF amps?
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