SILVERTONE 7036

2/16/2010 6:24:07 PMAndy

Need ADVICE Please,
Just replaced all Caps. It now works, but has a background 60 Cyc. Hum. Would appreciate any help finding cause.

2/16/2010 7:19:45 PMEdd

Sir Andy . . . . . .

How about localizing its source ?
One wants to initially ascertain if introduction of the problem is prior to the audio and AF output sections.

Step one:

Tune the radio off station and listen for the hum, then decrease the volume control to zero to see if the level decreases, if so it must have some degree of its introduction from circuitry that is feeding into the top leg of
the volume controls input.

Step two:

If that test was ineffective in reducing the hum level, then leave the vol control at minimum and short the 1st grid of the 6k6 AF poutput tube to ground for just a few seconds to see if the hum abates.

If the hum remains you might additionally do a tempory shunting . . one at a time, of each of the three power supply electrolytic filters, with yet another like value capacitor.

Tube possibilities ?

If there is filament to cathode leakage within the 6SQ7 and 6K6 tubes, hum could be introducd in that manner also.

Fill us in . . .

73's de Edd

2/16/2010 9:04:22 PMAndy

:
:

:
:
:

:
:
:
:Was a SHORT between Filament and Cathode.. Thanks
:
:
:
:Sir Andy . . . . . .
:
:
:How about localizing its source ?
:One wants to initially ascertain if introduction of the problem is prior to the audio and AF output sections.
:
:
:Step one:
:
:
:Tune the radio off station and listen for the hum, then decrease the volume control to zero to see if the level decreases, if so it must have some degree of its introduction from circuitry that is feeding into the top leg of
:the volume controls input.
:
:
:Step two:
:
:
:If that test was ineffective in reducing the hum level, then leave the vol control at minimum and short the 1st grid of the 6k6 AF poutput tube to ground for just a few seconds to see if the hum abates.
:
:
:If the hum remains you might additionally do a tempory shunting . . one at a time, of each of the three power supply electrolytic filters, with yet another like value capacitor.
:
:
:Tube possibilities ?
:
:
:If there is filament to cathode leakage within the 6SQ7 and 6K6 tubes, hum could be introducd in that manner also.
:
:
:Fill us in . . .
:
:
:73's de Edd
:
:
:

:

:
:
:
:
:

2/16/2010 7:24:40 PMBill G.

Hi Andy,
The first thing to check is for interference. Modern switching power supplies can be problematic with these.
You can tell if it is interference if the 60 cycles is not uniform over the band, or if it is more or less intense in different locations. I get it here mainly at the low end.

If it is uniform over the band and has 60 cycles anywhere you place the radio, check for low voltages around the 6K6GT.

Best Regards,

Bill Grimm

2/16/2010 8:08:37 PMAndy

:Hi Andy,
: The first thing to check is for interference. Modern switching power supplies can be problematic with these.
: You can tell if it is interference if the 60 cycles is not uniform over the band, or if it is more or less intense in different locations. I get it here mainly at the low end.
:
: If it is uniform over the band and has 60 cycles anywhere you place the radio, check for low voltages around the 6K6GT.
:
:Best Regards,
:
:Bill Grimm
:
Bill,
Right on, Bad 6k6 Thanks for your reply, Andy