Quote:
Originally Posted by Electronic M
... Eventually, I started repeating peaking the system off freq at several KHz intervals and and below correct freq until I found a point where I could get a bit of audio from my agile modulator at some fine tuning setting. I then peaked the IF to the program audio by ear, tuned the generator to the freq I peaked the sound IF at and peaked the IF again...Those big unshielded coils on/near the tuner did need adjustment in the process.
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I was taken by your comments. Changing the if tuning to find the sound? That is certainly not what you are supposed to do!
To do the job properly, you must have a calibrated frequency generator. Then you must sweep the if. That is the only way to do the alignment properly. The equipment to do a proper job is cheap and is readily available on eBay.
These pre 1950 sets are of split sound design. You use your calibrated fixed 21.25MHz generator to initially get the sound if into the ballpark region and the sweep for proper bandwidth and discriminator symmetry.
You adjust the tuner local oscillator (fine tuning) setting to provide the correct audio if from the tuner. The fine tuning on these split sound sets are to always tune for best sound. This is the problem for if you do not coordinate the proper alignment of the video and audio ifs together, the best picture will not match best sound.
The alignment of the earlier RCAs can be quite a challenge. But when properly done, the RCA sets provide incredibly good pictures and sound.
Those big unshieided coils you mentioned, are they on the top? These are the traps. There are two adjacent channel sound, two adjacent channel video and two co-channel traps in the 9t240 video if. These must be properly aligned to achieve proper video and sound.
I have been aligning these sets for 50 years now and I believe with a bit of study with practise and perseverance anyone can be do it. It requires a bit of study and asking questions. And forget about using the Sams notes on these early sets. They are riddled with errors. Use the Riders as they are copied directly from the RCA Service notes. Just adhere to the step by step method in Riders and you will be fine. There are lots of other old publications on line which will provide some help.