09-01-2021, 07:34 PM
Good evening. Here's the alignment update. I pretty much followed the procedure in the 48-1270 service manual (similar if not the same as 48-482). Since I did the AM/SW alignment a couple of months back I decided to redo as I now have a frequency counter. That was all pretty straight forward. The FM alignment was straight forward also - just a bit tedious with the jumper, loading network and various places to hook up sig. generator. The IF alignment really woke up the radio. I can tune in a lot of FM stations now. Not as good as the modern digital radio in my car but pretty darn good. I can get several Raleigh-Durham stations now. I decide to go ahead with the oscillator also. The procedure aimed for a zero beat when turning the trimmers. I never was not able to obtain a zero beat so I put trimmers back where they were originally. After removing the jumpers I selected a strong station and tuned the trimmer for strong clear signal. A bit unorthodox but I am pretty satisfied with result. Oh yeah, the procedure also involves adjusting the spread of the FM coils (L406, L407, L408) for tuning the lower frequencies. I skipped that part. I did not want to risk damaging those old things.
Going to put it back in the cabinet tomorrow after I go over all the ground connections (got a tiny bit of hum that is only detectable when there is no audio signal like between record changes or untuned stations). If I don't find something obvious pretty quick I'm just going to ignore it.
There is one more oddity. On FM 103.7 there is a fairly loud hum when that station is tuned (only one that does this). I get the same hum on another vintage FM radio, !947 Zenith. I don't think I hear it on my car radios. You know of something I might be able to do to eliminate that? I've unplugged everything in my house to eliminate stuff like chargers, bug repellers etc. One thing in the back of my mind is that I replaced the old wave trap with just a capacitor. Wonder if that's the culprit. Of course the Zenith has same problem (I didn't restore that radio). I might start a separate thread on this issue.
I sure appreciate your help.
Going to put it back in the cabinet tomorrow after I go over all the ground connections (got a tiny bit of hum that is only detectable when there is no audio signal like between record changes or untuned stations). If I don't find something obvious pretty quick I'm just going to ignore it.
There is one more oddity. On FM 103.7 there is a fairly loud hum when that station is tuned (only one that does this). I get the same hum on another vintage FM radio, !947 Zenith. I don't think I hear it on my car radios. You know of something I might be able to do to eliminate that? I've unplugged everything in my house to eliminate stuff like chargers, bug repellers etc. One thing in the back of my mind is that I replaced the old wave trap with just a capacitor. Wonder if that's the culprit. Of course the Zenith has same problem (I didn't restore that radio). I might start a separate thread on this issue.
I sure appreciate your help.
