A 1960 Symphonic guitar amp has a power transformer (good) and a 50L6 power tube. I've replaced the old caps.
It still produces a bit of hum which increases with the volume setting.
The 50L6 heater is in parallel with the heaters of the 35Z5 and 12AX7 tubes.
The schematic shows a B+ winding and a separate 50 volt filament winding. In actuality, the manufacturer chose a transformer with a 50 volt tap on the B* winding. So there are only 3 secondart leads on the tranny, one of which is grounded to the chassis. B+ and the filaments are all using the chassis ground.

To remove some of this 60 cycle hum, should I add a separate transformer for the heaters? Lift the grounded secondary leads and run wires to the tubes?

:A 1960 Symphonic guitar amp has a power transformer (good) and a 50L6 power tube. I've replaced the old caps.
:It still produces a bit of hum which increases with the volume setting.
:The 50L6 heater is in parallel with the heaters of the 35Z5 and 12AX7 tubes.
:The schematic shows a B+ winding and a separate 50 volt filament winding. In actuality, the manufacturer chose a transformer with a 50 volt tap on the B* winding. So there are only 3 secondart leads on the tranny, one of which is grounded to the chassis. B+ and the filaments are all using the chassis ground.
:
:To remove some of this 60 cycle hum, should I add a separate transformer for the heaters? Lift the grounded secondary leads and run wires to the tubes?

John:
Er, excuse me, but 50L6, 35Z5 and 12AX7 in parallel?? That doesn't compute a'tall. If hum varies with volume, you are probably picking it up at the input. Grounding the input would be a quick check of that. A cheap transformer is more likely to cause smoke than hum, IMHO.
Lewis

Lewis, the 50L6 is paralleled to the other 2 which are in series. The filament supply voltage is 50 vac.

The hum is there on the 12AX7 preamp with the input jack disconnected. The hum is then amplified by the second stage. I am thinking the hum could be reduced by isolating the heaters from the B+, as the designer intended.

:Er, excuse me, but 50L6, 35Z5 and 12AX7 in parallel?? That doesn't compute a'tall. If hum varies with volume, you are probably picking it up at the input. Grounding the input would be a quick check of that. A cheap transformer is more likely to cause smoke than hum, IMHO.
:Lewis
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:

John:

Have you tried grounding the input of the 12AX7 to see if the hum disappears? If it does it may be coming from the 12AX7 input. If it doesnt there is another source.

Since the hum increases with the volume setting then it is coming somewhere from the input ( being ampified). One was of trying what you are thinking is to disconnect the transformer leads - filament supply and substitute a DC supply, 50 VDC.If the hum is still there, then that is not the problem.

You may also have a 12AX7 tube with a heater to cathode leak.

Lou

:A 1960 Symphonic guitar amp has a power transformer (good) and a 50L6 power tube. I've replaced the old caps.
:It still produces a bit of hum which increases with the volume setting.
:The 50L6 heater is in parallel with the heaters of the 35Z5 and 12AX7 tubes.
:The schematic shows a B+ winding and a separate 50 volt filament winding. In actuality, the manufacturer chose a transformer with a 50 volt tap on the B* winding. So there are only 3 secondart leads on the tranny, one of which is grounded to the chassis. B+ and the filaments are all using the chassis ground.
:
:To remove some of this 60 cycle hum, should I add a separate transformer for the heaters? Lift the grounded secondary leads and run wires to the tubes?
: