10-08-2018, 04:59 PM
Thanks for the tips, guys.
Terry: I disconnected the lead coming from C-15 to the wiper of the volume control as you said and when I touch the lead, there is no change in volume from what it was when it was connected to the volume control. Same faint buzz on the opposite end of the capacitor, where it is connected to the 12SQ7.
I took a few more voltage readings too:
on the 2nd (IF AMP) 12SK7:
Pin 8 (plate) reads 94 VDC (should be 74)
Pin 4 (grid) reads -2.0 VDC
Pin 6 reads 94 VDC (should be 74)
On the 12SA7:
Pin 3 (plate) reads 91.3 VDC (should be 74)
Pin 8 (grid) reads -1.8 VDC
on the 1st (RF AMP) 12SK7:
Pin 8 (Plate) reads 70.8 VDC (should be 40)
Pin 6 (Grid 2) reads 94 VDC (should be 70)
Pin 4 (Grid 1) reads -1.4 VDC
I have a long wire antenna connected directly to the lug on the top of the tuning capacitor. This set was missing the back cover, and also the loop antenna connected to it. I added a similar loop from another AA5 I parted out, connecting one end to the tuning cap and the other to ground as shown on the schematic. The sound is even quieter with just the loop antenna, so the only way to get any volume is to use the long wire at this point.
Terry: I disconnected the lead coming from C-15 to the wiper of the volume control as you said and when I touch the lead, there is no change in volume from what it was when it was connected to the volume control. Same faint buzz on the opposite end of the capacitor, where it is connected to the 12SQ7.
I took a few more voltage readings too:
on the 2nd (IF AMP) 12SK7:
Pin 8 (plate) reads 94 VDC (should be 74)
Pin 4 (grid) reads -2.0 VDC
Pin 6 reads 94 VDC (should be 74)
On the 12SA7:
Pin 3 (plate) reads 91.3 VDC (should be 74)
Pin 8 (grid) reads -1.8 VDC
on the 1st (RF AMP) 12SK7:
Pin 8 (Plate) reads 70.8 VDC (should be 40)
Pin 6 (Grid 2) reads 94 VDC (should be 70)
Pin 4 (Grid 1) reads -1.4 VDC
I have a long wire antenna connected directly to the lug on the top of the tuning capacitor. This set was missing the back cover, and also the loop antenna connected to it. I added a similar loop from another AA5 I parted out, connecting one end to the tuning cap and the other to ground as shown on the schematic. The sound is even quieter with just the loop antenna, so the only way to get any volume is to use the long wire at this point.
Greg V.
West Bend, WI
Member WARCI.org
