10-08-2019, 10:07 PM
I posted earlier about this radio on the AR forum. See https://antiqueradios.com/forums/viewtop...6&t=365314
Circuit diagram for this radio is here: http://www.nostalgiaair.org/Resources/637/M0013637.htm
I have finished replacement of all the electrolytics, paper caps and out of spec resistors.
I did an AM alignment but did not touch FM.
I am getting AM and FM reception across the dial but the speaker output sounds somewhat distorted - not bad but not right. I would describe the sound as gravelly or slightly garbled. Also, it seems that the distortion worsens as the station is tuned in. At first I thought it was a bad speaker but substituting in two different known good speakers did not change the distortion.
My radio has a 7B6 tube in place of the 6SQ7G tube shown on the circuit diagram.
I substituted for the 6V6 and 7B6 tubes to see if there was any improvement but got no change.
I checked voltages at the locations where voltages were given on the circuit diagram. They are as follows.
Location Voltage on circuit diagram Measured voltage
Section 1
C102A 200 203
C102B 187 187
C102C 250 243
C103 250 243
C104 250 243
-C104 -50 -54
Junction R102 -1.3 or -13? -16
&R103
Junction R103 -1.1 or -11? -1.2
&R104
Section 2
Plate 7B6, pin 2 132 126
Plate 6V6, pin 3 230 216
Grid 6V6, pin 4 250 242
Section 3
PL. FM1000, pin 4 200 157
Gr. FM1000, pin 5 40 54
Section 4
Plate 7H7, pin 2 240 235 1st IF
Grid 7H7, pin 3 75 110 "
K, 7H7, pin 7 .8 .6 "
Plate 7B7, pin 3 240 236
Grid 7B7, pin 3 100 103
K 7B7, pin 7 7 4.2
Plate 7H7, pin 2 225 221 2nd IF
Grid 7H7, pin 3 95 88 "
K 7H7, pin 7 1.? 1.4 "
Section 5
Plate 2, 7F8, pin 3 112 134
Plate 1, 7F8, pin 6 90 101
K2, 7F8, pin 4 4.5 4.3
K1, 7F8, pin 5 1.5 .6
Plate 7W7, pin 2 90 86
Grid, 7W7, pin 3 55 35
I need some help on this and am looking for ideas.
Thanks, Bob
Circuit diagram for this radio is here: http://www.nostalgiaair.org/Resources/637/M0013637.htm
I have finished replacement of all the electrolytics, paper caps and out of spec resistors.
I did an AM alignment but did not touch FM.
I am getting AM and FM reception across the dial but the speaker output sounds somewhat distorted - not bad but not right. I would describe the sound as gravelly or slightly garbled. Also, it seems that the distortion worsens as the station is tuned in. At first I thought it was a bad speaker but substituting in two different known good speakers did not change the distortion.
My radio has a 7B6 tube in place of the 6SQ7G tube shown on the circuit diagram.
I substituted for the 6V6 and 7B6 tubes to see if there was any improvement but got no change.
I checked voltages at the locations where voltages were given on the circuit diagram. They are as follows.
Location Voltage on circuit diagram Measured voltage
Section 1
C102A 200 203
C102B 187 187
C102C 250 243
C103 250 243
C104 250 243
-C104 -50 -54
Junction R102 -1.3 or -13? -16
&R103
Junction R103 -1.1 or -11? -1.2
&R104
Section 2
Plate 7B6, pin 2 132 126
Plate 6V6, pin 3 230 216
Grid 6V6, pin 4 250 242
Section 3
PL. FM1000, pin 4 200 157
Gr. FM1000, pin 5 40 54
Section 4
Plate 7H7, pin 2 240 235 1st IF
Grid 7H7, pin 3 75 110 "
K, 7H7, pin 7 .8 .6 "
Plate 7B7, pin 3 240 236
Grid 7B7, pin 3 100 103
K 7B7, pin 7 7 4.2
Plate 7H7, pin 2 225 221 2nd IF
Grid 7H7, pin 3 95 88 "
K 7H7, pin 7 1.? 1.4 "
Section 5
Plate 2, 7F8, pin 3 112 134
Plate 1, 7F8, pin 6 90 101
K2, 7F8, pin 4 4.5 4.3
K1, 7F8, pin 5 1.5 .6
Plate 7W7, pin 2 90 86
Grid, 7W7, pin 3 55 35
I need some help on this and am looking for ideas.
Thanks, Bob