I have a melody cruiser that has a loud ocsillating chirping sound that is ser off by wigglling the volune control. Schematic is in rider vol 14 page 2, model is a majestic 1S49. Originally the radio would not work at other than squeal and osccilate. Tubes check out ok. replaced filter caps and it seems to work fine except when oscillation occurs. Volume ocntrol is grounded to chassis on one lead, in parrell with a 250 pico mica cap, center tap of winding islinked to 2nd det grid via a .002mfd elec and to ground via a 15 mg resistor. this unit is very compact and has a roughly a 5 X 7 planform s i suspect it is subject to interference oscillation. inside of cruiser cabinet is lined with coper sheet that looks original. Due to the pitch I would suspect the 12q7GT. Any clues as to how to debug this thing would be greatly appreciated. I hate to take out the mica caps if I don't need to. Thanks, DWG

Hi Dave

You might try spraying some tuner cleaner into the volume control. It may not be making good contact. If the wiper doesn't make contact the grid of the 12Q7GT is open with only 15 meg to ground. This could cause oscillation.

Does the 12Q7GT and 12K7GT have shields?

Norm

: I have a melody cruiser that has a loud ocsillating chirping sound that is ser off by wigglling the volune control. Schematic is in rider vol 14 page 2, model is a majestic 1S49. Originally the radio would not work at other than squeal and osccilate. Tubes check out ok. replaced filter caps and it seems to work fine except when oscillation occurs. Volume ocntrol is grounded to chassis on one lead, in parrell with a 250 pico mica cap, center tap of winding islinked to 2nd det grid via a .002mfd elec and to ground via a 15 mg resistor. this unit is very compact and has a roughly a 5 X 7 planform s i suspect it is subject to interference oscillation. inside of cruiser cabinet is lined with coper sheet that looks original. Due to the pitch I would suspect the 12q7GT. Any clues as to how to debug this thing would be greatly appreciated. I hate to take out the mica caps if I don't need to. Thanks, DWG

No shields, but that side of the radio compartment is copper lined. By the way the line caps are 24 and 16mfd at 150v. hese are hard to find, so im using a 33/47 @150V seems to work ok any other ideas space is at a premium in this set. Will try the volume when I get off. DWG

: Hi Dave

: You might try spraying some tuner cleaner into the volume control. It may not be making good contact. If the wiper doesn't make contact the grid of the 12Q7GT is open with only 15 meg to ground. This could cause oscillation.

: Does the 12Q7GT and 12K7GT have shields?

: Norm

:
: : I have a melody cruiser that has a loud ocsillating chirping sound that is ser off by wigglling the volune control. Schematic is in rider vol 14 page 2, model is a majestic 1S49. Originally the radio would not work at other than squeal and osccilate. Tubes check out ok. replaced filter caps and it seems to work fine except when oscillation occurs. Volume ocntrol is grounded to chassis on one lead, in parrell with a 250 pico mica cap, center tap of winding islinked to 2nd det grid via a .002mfd elec and to ground via a 15 mg resistor. this unit is very compact and has a roughly a 5 X 7 planform s i suspect it is subject to interference oscillation. inside of cruiser cabinet is lined with coper sheet that looks original. Due to the pitch I would suspect the 12q7GT. Any clues as to how to debug this thing would be greatly appreciated. I hate to take out the mica caps if I don't need to. Thanks, DWG