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Old 03-07-2019, 06:38 PM
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Electronic M Electronic M is offline
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Join Date: Jan 2011
Location: Pewaukee/Delafield Wi
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Quote:
Originally Posted by Penthode View Post
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.
I don't own a 21MHz sweep generator (and many TV repair shops in 1948 didn't either thus why the service lit had a procedure to align the IFs WITHOUT a sweep gen).

Your talking to probably the biggest test gear cheapskate on VK. I haven't spent more than $6 a pop on the last 10 soldering irons I've used...And not much more on anything else I have...Also I have never done a sweeping alignment on anything, and never have needed it to get satisfactory operation. Also, every 21MHz sweep rig I've seen is tube thus needing a recap to even work, and obviously woefully out of cal. Show me a freshly calibrated 21MHz solid state TV sweep/marker generator with cables for under $40 and I'll show you a chicken with a full set of teeth.

My 8TS30 (I'm not sure why you think it was a 9t240) which I did that sound work on had a great picture and absolutely NO sound after recap, replacing off tolerance resistors, tube swaps, etc...Before I adjusted it I used my AM generator (the modulator on it is crude enough for the 400Hz audio mot to make some FM detectable modulation) to find the sound IF freq and it was WAY WAY off (so I had nothing to lose). Once my adaptation of service lit procedure got sound to pass I peaked the IF, set finetuning for best picture and repeaked the IF. I couldn't have done a better job with the equipment I had, and may even have been able to do worse with a sweep gen.

The coils were above chassis, but the set was an 8TS30. Those coils probably were the traps...I looked them up on the schematic and knew what they were/how I needed to deal with them when I was working on that set, but that was probably over 6 months ago, and memory has faded.

Someday when I have the money/gear and time I'll pickup sweep alignmet....I actually have been buying some dirt cheap 44MHz gear, but I haven't had time to use it...I have few enough 21MHz sets that it ain't worth gearing up for those.
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Last edited by Electronic M; 03-07-2019 at 07:55 PM.
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