The PHILCO Phorum
48-482 DISTORTED SOUND - Printable Version

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48-482 DISTORTED SOUND - rck46 - 10-08-2019

I posted earlier about this radio on the AR forum. See https://antiqueradios.com/forums/viewtopic.php?f=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

RE: 48-482 DISTORTED SOUND - mikethedruid - 10-09-2019

I restored a 48-482 some years ago. Here is a link to my thread about it here on the Phorum. You may get some ideas from it.
https://philcoradio.com/phorum/showthread.php?tid=10134
If you PM me your e-mail I'll send you what I have for service information on the set, the complete Rider's information which includes helpful
tr4oubleshooting guides. Another thing that occurs to me is you mentioned a 6SQ7. This is NOT the correct tube for this radio! The 7B6 is the correct tube. Double check all the wiring you did there. If you don't have a receiving tube manual to look at the pin outs, you can find the information online, just search the tube number and "data sheet."

RE: 48-482 DISTORTED SOUND - Jake Blake - 10-09-2019

It will be interesting to see if your problem is at all related to the "kick-back"  your discussion on ARF got buried in,  or a simple off-voltage from your tedious measuring.  I think you're on the right track.

RE: 48-482 DISTORTED SOUND - Bill Bacco - 10-09-2019

I would start by trying to isolate whether the distortion is in the audio section or in the RF section. You should be able to decouple the two and inject some sort of Audio signal to the amplifier section. If you still get distortion then you know it is in the audio section. I would then proceed to use a signal generator and scope to see where that distortion is occurring.