02-25-2021, 10:51 AM
Hello all,
I am hoping for some assistance with my Model 16 B (121 ) QAVC Potentiometer.
Please excuse any rambling as I am lost on this issue.
I've owned my 16B (121) since the mid 1970s.
Re-cap in 2010, and as you would expect, lots of smaller repairs over 45 years.
I have basically always let the set tune "wide open" with the QAVC Toggle Switch in the down position.
From time to time over the years I would at least check if the QAVC adjustment was still working.
And it was.
I checked it the other day, and it no longer works.
With the Toggle Switch Up, the adjustment does nothing until I reach total Counter Clockwise position.
Once I get to total counter clockwise, there is a quite loud THUMP from the set, and then NO sound at all.
Turn it ever so slightly Clockwise, and it springs back to life! And I do mean ever so slightly turn the knob.
I did check/test related tube(s) and even swapped them with other spare known good tubes.
Next I decided to remove the PN 33-5015 to test with an ohm meter.
With it laying flat, knurled knob facing up, three solder tabs at around 6PM position, here is what I get:
- Ohm Meter connected to Left tab and Center tab:
Knob turned totally Counter Clockwise reading briefly hits as high as 150 to 300 Ohms.
(I have watched it on occasion read some numbers into the "K" range but ever so briefly then falls back to 150 to 300 Ohms)
Now I just begin to turn the knob Clockwise and the digital meter goes to "O.L", no reading.
The meter continues to read no continuity as the knob is turned all the way Clock Wise.
I can only get a reading again by once again turning the knob all the way Counter Clockwise and I am back at approx. 150 to 300 Ohms
- Ohm Meter connected to Right tab and Center tab:
Fully Counter Clockwise reading reads "O.L.", no reading
Just barely start turning knob Clockwise and first readings varies between 18.5K to sometimes 21K ohms
Slowing turning the knob clockwise, meter readings continue to decline until around 200 ohms in fully Clockwise position
- Ohm Meter connected to only the two outside tabs:
NO reading at all in any position
My questions would be for anyone else who can recall ever trying to troubleshoot the QAVC Potentiometer.
1/ Does anyone know what the good ohm readings should be on the control?
2/ Has anyone ever successfully taken apart the control to clean it and get it working again?
If YES: do you remember how you were able to take it apart without destroying it's contents?
3/ Has anyone successfully replaced the original PN 33-5015 with available aftermarket Potentiometer?
If YES: do you remember what company you bought the part from, and hopefully what was the new part number and Specs?
And if YES: do you recall any issues connecting the new part into the QAVC circuitry, as in: just connect to the same lugs, etc.
If you've made it this far into my question, thank you so much.
Hopefully someone from our Philco community can offer some of their experience and knowledge on this QAVC issue.
Rod
I am hoping for some assistance with my Model 16 B (121 ) QAVC Potentiometer.
Please excuse any rambling as I am lost on this issue.
I've owned my 16B (121) since the mid 1970s.
Re-cap in 2010, and as you would expect, lots of smaller repairs over 45 years.
I have basically always let the set tune "wide open" with the QAVC Toggle Switch in the down position.
From time to time over the years I would at least check if the QAVC adjustment was still working.
And it was.
I checked it the other day, and it no longer works.
With the Toggle Switch Up, the adjustment does nothing until I reach total Counter Clockwise position.
Once I get to total counter clockwise, there is a quite loud THUMP from the set, and then NO sound at all.
Turn it ever so slightly Clockwise, and it springs back to life! And I do mean ever so slightly turn the knob.
I did check/test related tube(s) and even swapped them with other spare known good tubes.
Next I decided to remove the PN 33-5015 to test with an ohm meter.
With it laying flat, knurled knob facing up, three solder tabs at around 6PM position, here is what I get:
- Ohm Meter connected to Left tab and Center tab:
Knob turned totally Counter Clockwise reading briefly hits as high as 150 to 300 Ohms.
(I have watched it on occasion read some numbers into the "K" range but ever so briefly then falls back to 150 to 300 Ohms)
Now I just begin to turn the knob Clockwise and the digital meter goes to "O.L", no reading.
The meter continues to read no continuity as the knob is turned all the way Clock Wise.
I can only get a reading again by once again turning the knob all the way Counter Clockwise and I am back at approx. 150 to 300 Ohms
- Ohm Meter connected to Right tab and Center tab:
Fully Counter Clockwise reading reads "O.L.", no reading
Just barely start turning knob Clockwise and first readings varies between 18.5K to sometimes 21K ohms
Slowing turning the knob clockwise, meter readings continue to decline until around 200 ohms in fully Clockwise position
- Ohm Meter connected to only the two outside tabs:
NO reading at all in any position
My questions would be for anyone else who can recall ever trying to troubleshoot the QAVC Potentiometer.
1/ Does anyone know what the good ohm readings should be on the control?
2/ Has anyone ever successfully taken apart the control to clean it and get it working again?
If YES: do you remember how you were able to take it apart without destroying it's contents?
3/ Has anyone successfully replaced the original PN 33-5015 with available aftermarket Potentiometer?
If YES: do you remember what company you bought the part from, and hopefully what was the new part number and Specs?
And if YES: do you recall any issues connecting the new part into the QAVC circuitry, as in: just connect to the same lugs, etc.
If you've made it this far into my question, thank you so much.
Hopefully someone from our Philco community can offer some of their experience and knowledge on this QAVC issue.
Rod
