I posted earlier about this H500 Trans Oceanic being acquired with all 5 filaments blown. Filament string runs normally with good tubes, but I've been troubleshooting a persistent hum/buzz for hours and can't find it. Even a strong station is deeply modulated with hum. All 5 electrolytic capacitors are fine. All tube voltages are reasonable (maybe with B+ a few volts low - but a temporary Si diode and resistor as temporary substitute for the Se didn't do the hum problem any good). All capacitors in the audio section, and all other screen bypasses, etc, have been trial-bypassed with no effect, and all resistors in the audio section check reasonable (in-circuit checking). The 2nd IF secondary is not open. Is there a common ground-loop / poor connection type of problem that crops up in these? Or something? I've never worked on a 5-tube Trans Oceanic before.

Thanks,
Eddie

:I posted earlier about this H500 Trans Oceanic being acquired with all 5 filaments blown. Filament string runs normally with good tubes, but I've been troubleshooting a persistent hum/buzz for hours and can't find it. Even a strong station is deeply modulated with hum. All 5 electrolytic capacitors are fine. All tube voltages are reasonable (maybe with B+ a few volts low - but a temporary Si diode and resistor as temporary substitute for the Se didn't do the hum problem any good). All capacitors in the audio section, and all other screen bypasses, etc, have been trial-bypassed with no effect, and all resistors in the audio section check reasonable (in-circuit checking). The 2nd IF secondary is not open. Is there a common ground-loop / poor connection type of problem that crops up in these? Or something? I've never worked on a 5-tube Trans Oceanic before.
:
:Thanks,
:Eddie

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Jumping a leaky capacitor with a good one won't tell you anything, neither will testing a capacitor in the circuit. Replace the electrolytics and any paper capacitors, then if you still have a hum we can troubleshoot it.

Dave

::I posted earlier about this H500 Trans Oceanic being acquired with all 5 filaments blown. Filament string runs normally with good tubes, but I've been troubleshooting a persistent hum/buzz for hours and can't find it. Even a strong station is deeply modulated with hum. All 5 electrolytic capacitors are fine. All tube voltages are reasonable (maybe with B+ a few volts low - but a temporary Si diode and resistor as temporary substitute for the Se didn't do the hum problem any good). All capacitors in the audio section, and all other screen bypasses, etc, have been trial-bypassed with no effect, and all resistors in the audio section check reasonable (in-circuit checking). The 2nd IF secondary is not open. Is there a common ground-loop / poor connection type of problem that crops up in these? Or something? I've never worked on a 5-tube Trans Oceanic before.
::
::Thanks,
::Eddie
:
:___________________________________________________________________
:
:Jumping a leaky capacitor with a good one won't tell you anything, neither will testing a capacitor in the circuit. Replace the electrolytics and any paper capacitors, then if you still have a hum we can troubleshoot it.
:
:Dave

Thanks Dave - I finally "googled" a few articles last night that imply this kind of trouble from capacitors that are merely leaky in T.O.s - and one with a very low resistor value - I guess I have to work a little harder tracking this one down. Any further leads will be appreciated. Eddie