Thanks if anyone can help with any ideas; what to do next. Thanks.
:I have a 1939 silvertone with a 6U5 silvertone. I recapped it and also replaced the 1 megohm resister in the 6U5 socket. I measure a steady AGC negative voltage irrespective of signal strength. I wonder if it could be the 2nd det/AVC 6Q7 (metal with grid cap) is possibly bad? I do not have a tube tester and I can't find any other problems. I don't have a known good 6Q7 to swap out. I am curious, if all other things being equal, a tube can cause poor tuning indicator response. One final note: when I switch to SW and get a whistle at a certain point on the band, I can trim the oscillator section of the tuning capacitor and get a full close of the eye with a little overlap. When I read AGC at that point it goes from about - 3.5 V to over -10 V (just as it is supposed to I imagine). I don't have the slightest idea why it does that.
:
:Thanks if anyone can help with any ideas; what to do next. Thanks.
Don't think the 6Q7 is bad or you wouldn't have a signal. Try attaching 10-20 feet of wire for antenna.
You will find a large value resistor off the volume control. It's usually 1 meg or greater. This resistor starts AVC and may be open? There will also be a capacitor on the AVC line. Value is usually .05 mfd. It could be leaky?
Your IF amplifier is going into oscillation when the eye closes the way you noticed. Be sure the IF tube is shielded. If metal tube, pin #1 must be grounded. This may also be an indication the AVC line has a problem leaving the IF tube grid return opem?
Norm
:A 6U5 silvertone? I meant a 6U5 tuning indicator. I didn't notice my mistake until I posted the message...
:
::I have a 1939 silvertone with a 6U5 silvertone. I recapped it and also replaced the 1 megohm resister in the 6U5 socket. I measure a steady AGC negative voltage irrespective of signal strength. I wonder if it could be the 2nd det/AVC 6Q7 (metal with grid cap) is possibly bad? I do not have a tube tester and I can't find any other problems. I don't have a known good 6Q7 to swap out. I am curious, if all other things being equal, a tube can cause poor tuning indicator response. One final note: when I switch to SW and get a whistle at a certain point on the band, I can trim the oscillator section of the tuning capacitor and get a full close of the eye with a little overlap. When I read AGC at that point it goes from about - 3.5 V to over -10 V (just as it is supposed to I imagine). I don't have the slightest idea why it does that.
::
::Thanks if anyone can help with any ideas; what to do next. Thanks.
Can I ask some more questions? 1. Can you think of a reason why tuning eye response would be better on the high end of the BC band but not on the low end? 2. Why don't we just connect the antenna directly to the grid of the 1st detector (it always seems to be better that way on all the radios I have ever seen). Thanks norm for your help.
Nelson
:Hi Nelson
:
: Don't think the 6Q7 is bad or you wouldn't have a signal. Try attaching 10-20 feet of wire for antenna.
:
: You will find a large value resistor off the volume control. It's usually 1 meg or greater. This resistor starts AVC and may be open? There will also be a capacitor on the AVC line. Value is usually .05 mfd. It could be leaky?
:
: Your IF amplifier is going into oscillation when the eye closes the way you noticed. Be sure the IF tube is shielded. If metal tube, pin #1 must be grounded. This may also be an indication the AVC line has a problem leaving the IF tube grid return opem?
:
:Norm
:
::A 6U5 silvertone? I meant a 6U5 tuning indicator. I didn't notice my mistake until I posted the message...
::
:::I have a 1939 silvertone with a 6U5 silvertone. I recapped it and also replaced the 1 megohm resister in the 6U5 socket. I measure a steady AGC negative voltage irrespective of signal strength. I wonder if it could be the 2nd det/AVC 6Q7 (metal with grid cap) is possibly bad? I do not have a tube tester and I can't find any other problems. I don't have a known good 6Q7 to swap out. I am curious, if all other things being equal, a tube can cause poor tuning indicator response. One final note: when I switch to SW and get a whistle at a certain point on the band, I can trim the oscillator section of the tuning capacitor and get a full close of the eye with a little overlap. When I read AGC at that point it goes from about - 3.5 V to over -10 V (just as it is supposed to I imagine). I don't have the slightest idea why it does that.
:::
:::Thanks if anyone can help with any ideas; what to do next. Thanks.
Your first stage may not be aligned properly or antenna coil open? By connecting your antenna directly to 1st detector grid it bypasses the tuned circuit.
Have you tried adjusting the padder? This cap should be adjusted toward the low end of the band while rocking tuning back and forth. Adjust for loudest signal. This is usually the reason for low end of a dial being weak.
Norm
:Thank you Norm.
:Adding 10 ft of wire to my existing 10 ft antenna, and playing with the value of the large value resistor finally gained some tuning eye response. The resistor was 3 megohm (per schematic and as installed, and read over 2 megohm on my meter); I unhooked it and put in various values over 1 megohm, and 1 megohm in series with a 1 meg potentiometer. I have some more testing to do before I substitute a fixed value.
:
:Can I ask some more questions? 1. Can you think of a reason why tuning eye response would be better on the high end of the BC band but not on the low end? 2. Why don't we just connect the antenna directly to the grid of the 1st detector (it always seems to be better that way on all the radios I have ever seen). Thanks norm for your help.
:
:Nelson
:
::Hi Nelson
::
:: Don't think the 6Q7 is bad or you wouldn't have a signal. Try attaching 10-20 feet of wire for antenna.
::
:: You will find a large value resistor off the volume control. It's usually 1 meg or greater. This resistor starts AVC and may be open? There will also be a capacitor on the AVC line. Value is usually .05 mfd. It could be leaky?
::
:: Your IF amplifier is going into oscillation when the eye closes the way you noticed. Be sure the IF tube is shielded. If metal tube, pin #1 must be grounded. This may also be an indication the AVC line has a problem leaving the IF tube grid return opem?
::
::Norm
::
:::A 6U5 silvertone? I meant a 6U5 tuning indicator. I didn't notice my mistake until I posted the message...
:::
::::I have a 1939 silvertone with a 6U5 silvertone. I recapped it and also replaced the 1 megohm resister in the 6U5 socket. I measure a steady AGC negative voltage irrespective of signal strength. I wonder if it could be the 2nd det/AVC 6Q7 (metal with grid cap) is possibly bad? I do not have a tube tester and I can't find any other problems. I don't have a known good 6Q7 to swap out. I am curious, if all other things being equal, a tube can cause poor tuning indicator response. One final note: when I switch to SW and get a whistle at a certain point on the band, I can trim the oscillator section of the tuning capacitor and get a full close of the eye with a little overlap. When I read AGC at that point it goes from about - 3.5 V to over -10 V (just as it is supposed to I imagine). I don't have the slightest idea why it does that.
::::
::::Thanks if anyone can help with any ideas; what to do next. Thanks.