Zenith 6A05R

3/1/2012 12:49:39 PMfrank goddard

Hi Folks.

The Power tube ( 6F6G is running hot. What would be some causes . I have no audio through the set but do have 'scratch noise' via anode touching

Frank.

3/1/2012 1:08:13 PMWarren

A 6F6 does run very hot. That's normal. A simple test of the audio section is to touch the grid of the 7B6. you should get a loud buzz. This radio does need a total re-cap job of all the old paper and wax capacitors.

3/1/2012 2:08:55 PMClifton

Frank,

I would check for a negative voltage on pin 5 of the 6F6 (G1). It should be several volts negative. If there is a positive voltage present on the grid, I would suspect a bad coupling capacitor to the preceding stage plate circuit. For a quick check, one could use a poor man's audio generator and connect a clip lead to the filament circuit and use a .01 mfd or so capacitor in series and inject the 60 Hz signal into the grids of the audio tube(s). Should hear a fairly loud hum sound.

Clifton

:
:
:Hi Folks.
:
:The Power tube ( 6F6G is running hot. What would be some causes . I have no audio through the set but do have 'scratch noise' via anode touching
:
:
:Frank.
:

3/2/2012 12:04:46 PMfrank goddard

Many thanks to you all. Been a great help

Frank

:Frank,
:
:I would check for a negative voltage on pin 5 of the 6F6 (G1). It should be several volts negative. If there is a positive voltage present on the grid, I would suspect a bad coupling capacitor to the preceding stage plate circuit. For a quick check, one could use a poor man's audio generator and connect a clip lead to the filament circuit and use a .01 mfd or so capacitor in series and inject the 60 Hz signal into the grids of the audio tube(s). Should hear a fairly loud hum sound.
:
:Clifton
:
:
::
::
::Hi Folks.
::
::The Power tube ( 6F6G is running hot. What would be some causes . I have no audio through the set but do have 'scratch noise' via anode touching
::
::
::Frank.
::
:
:

3/2/2012 8:50:24 AMEdM

:
:
:Hi Folks.
:
:The Power tube ( 6F6G is running hot. What would be some causes . I have no audio through the set but do have 'scratch noise' via anode touching
:
:
:Frank.
:
Common causes are audio coupling capacitor leaky (as previously stated), capacitor around cathode resistor leaky or shorted, leaky capacitor from plate to cathode (in some sets, in others plate cap goes to DC common or filtered B+). Also could be open / defective socket, open grid resistor, bad 6F6, or miswire by someone who worked on the set previously. Cathode should be positive with respect to DC Common and input grid. Check all 6F6 socket voltages. EdM

3/2/2012 8:54:56 AMEdM

::
::
::Hi Folks.
::
::The Power tube ( 6F6G is running hot. What would be some causes . I have no audio through the set but do have 'scratch noise' via anode touching
::
::
::Frank.
::
:Common causes are audio coupling capacitor leaky (as previously stated), capacitor around cathode resistor leaky or shorted, leaky capacitor from plate to cathode (in some sets, in others plate cap goes to DC common or filtered B+). Also could be open / defective socket, open grid resistor, bad 6F6, or miswire by someone who worked on the set previously. Cathode should be positive with respect to DC Common and input grid. Check all 6F6 socket voltages. EdM
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Oh, one more obscure problem I have seen: Someone replaced the output transformer with something wa-a-ay off, or miswired something, and the output tube is oscillating to beat the band. EdM

3/2/2012 10:02:36 AMClifton

Frank,

Also note from the schematic that the minus of C10 & C11 do not go directly to ground/chassis but to the center tap (circuit) of the high voltage winding. Might do an Ohm check of the center tap to make sure it is not connected directly to ground. The negative grid bias on the 6F6 tube is taken from the voltage drop across the field coil at the junction of R16 & R17.

Clifton

:
:
:Hi Folks.
:
:The Power tube ( 6F6G is running hot. What would be some causes . I have no audio through the set but do have 'scratch noise' via anode touching
:
:
:Frank.
: