I get strong motorboating when turning volume up past a certain point, maybe halfway point. Prior to that point I can hear a station coming in, but not clearly.

Also, hidden underneath the speaker is a metal box, 1" X 2" X 2", with three leads into the circuit and three leads that are cut. Is this the hum-buck coil?

Here are the plate and screen voltages:

6a7s pin 2 = 200V, pin 3 = 80V, pin 4 = 80V, top cap= 305mv, pin 5 = -3V

6z7 both plate pins 3, 4 flash -1.5V and 0V alternately.

41 pin 2 = 163V, pin 3 = 195V, pin 4 = 31V, pin 5 = 31V

6f7s pin 2 = 200V, pin 3 = 80V, pin 4 = 70V, top cap = 8.5V, pin 5 = .65V

Thanks!
-Chuck Potts

Hi,
There might be a few things worth checking. 1)Check the value of the grid loading resistor of the 41- see if the value has changed much from it's rated value, and that it's leads are soldered well. 2) Check to see if the output filter capacitor is open- this is the second filter capacitor in the power supply, thisone will have one lead to chassis ground,and the other to the B+ voltage. 3), Check the grid load resistors of each stage for shorting or open conditions, as well as general lead dress.

The output cap can be bypassed temporarily with one of similar ratings to see if that remedies it first.

It also sounds as if the radio needs some alignment in addition to the solving of the motorboating.

: I get strong motorboating when turning volume up past a certain point, maybe halfway point. Prior to that point I can hear a station coming in, but not clearly.

: Also, hidden underneath the speaker is a metal box, 1" X 2" X 2", with three leads into the circuit and three leads that are cut. Is this the hum-buck coil?

: Here are the plate and screen voltages:

: 6a7s pin 2 = 200V, pin 3 = 80V, pin 4 = 80V, top cap= 305mv, pin 5 = -3V

: 6z7 both plate pins 3, 4 flash -1.5V and 0V alternately.

: 41 pin 2 = 163V, pin 3 = 195V, pin 4 = 31V, pin 5 = 31V

: 6f7s pin 2 = 200V, pin 3 = 80V, pin 4 = 70V, top cap = 8.5V, pin 5 = .65V

: Thanks!
: -Chuck Potts