RCA 9TC240 Alignment...The start of my education (I hope!) - Videokarma.org TV - Video

Chris K · #1 08-08-2024, 09:26 PM

Hi all. I wanna thank everyone for their help on the long thread that helped me sort out power, sound, re-wiring et al on this TV. I now have a good picture with very good resolution and sound coming out of a speaker. I'd like to learn something about alignments, fed signals, scope traces, sweep and the like. I thought I would start simple with the discriminator and sound IF alignment. Below is the instruction section in the Rider's service manual for this:

...and some traces and transformer location figures

For those who have participated in helpful discussions before, you probably know what my level of experience is. I can talk some of the talk but there are some significant gaps there. I usually get over my embarrassment fairly quickly but please, be gentle!!!

Over the next few days, I hope to move through the VTVM and scope trace steps in this protocol. Ten fifteen pm on the east coast so tomorrow evening I'll begin. I have done a couple of min/max adjustments using the VTVM before so hopefully, I'll get off to a good start! TIA for the help!

bandersen · #2 08-09-2024, 10:59 AM

Good luck. I suggest you also take a look at the Sams instructions. Thye often use language that makes more sense.

Penthode · #3 08-09-2024, 11:28 AM

Hi and happy aligning. I have had experience successfully aligning this chassis for more than 50 years. It can be a challenge if you do not keep various factors in mind.

First you must have accurate marker frequencies. This is a split sound set and to achieve optimum picture quality with best sound, the marker accuracy is utmost. I use an HP5245L frequency counter with an HP 606B signal generator. Plus my favorite alignment combo is the HP8601a Sweep generator with HP8600 Digital Marker. The total net cost for all of this equipment combined was $150 and it was top of the line. There are many solutions available and all are now pretty cheap. It would be wise to review what equipment you have before you begin. Remember this set has more trap circuits than any other set! Two adjacent sound, two adjacent video, two co-channel sound, a baseband trap and an RF trap, each if misadjusted can adversely affect the video quality.

Second as this is a split sound receiver, the fine tuning control is adjusted for best sound, not best picture. If the alignment is not correct, when fine tune for best sound, the video will not look good. So it is essential as the manual advises to first proceed with the sound IF and descriminator alignment before proceeding with the video alignment.

Third, be aware the quality of the video IF amplifier tubes will affect the end result. Make sure you have fresh tubes in place you can trust. Because changing a tube in the video IF will affect the response curve.

Lastly before you start, the set uses an over coupled transformer between the tuner and first video IF stage. This is a broadly coupled link and it is essential to sweep align it. You must follow the instructions in the manual to get the curve depicted. I found it pointless to proceed unless I can get the proper response at this point because the subsequent video IF sweep adjustment will not be right.

I would suggest following the step by step process to the letter and if/when you reach a stumbling block, simply post it on the forum.

Yamamaya42 · #4 08-09-2024, 11:46 AM

Yeah, you picked a very hard one as your first attempt for IF alignment, a real pain!

And as mentioned above, the way pointed out in the SAMS often makes more sense, it worked for me with the ARVIN, using a RF frequency generator and a meter to set the coils, I do not have a sweep marker generator, so I was not able to do the final overall IF alignment step, but as I said before, of all my BW sets, the ARVIN is the only one that gets snow W/O anything hooked to it, so I must have got it rather close to right!

Chris K · #5 08-09-2024, 12:47 PM

Quote:

Originally Posted by Penthode

Hi and happy aligning. I have had experience successfully aligning this chassis for more than 50 years. It can be a challenge if you do not keep various factors in mind.

First you must have accurate marker frequencies. This is a split sound set and to achieve optimum picture quality with best sound, the marker accuracy is utmost. I use an HP5245L frequency counter with an HP 606B signal generator. Plus my favorite alignment combo is the HP8601a Sweep generator with HP8600 Digital Marker. The total net cost for all of this equipment combined was $150 and it was top of the line. There are many solutions available and all are now pretty cheap. It would be wise to review what equipment you have before you begin. Remember this set has more trap circuits than any other set! Two adjacent sound, two adjacent video, two co-channel sound, a baseband trap and an RF trap, each if misadjusted can adversely affect the video quality.

Second as this is a split sound receiver, the fine tuning control is adjusted for best sound, not best picture. If the alignment is not correct, when fine tune for best sound, the video will not look good. So it is essential as the manual advises to first proceed with the sound IF and descriminator alignment before proceeding with the video alignment.

Third, be aware the quality of the video IF amplifier tubes will affect the end result. Make sure you have fresh tubes in place you can trust. Because changing a tube in the video IF will affect the response curve.

Lastly before you start, the set uses an over coupled transformer between the tuner and first video IF stage. This is a broadly coupled link and it is essential to sweep align it. You must follow the instructions in the manual to get the curve depicted. I found it pointless to proceed unless I can get the proper response at this point because the subsequent video IF sweep adjustment will not be right.

I would suggest following the step by step process to the letter and if/when you reach a stumbling block, simply post it on the forum.

Thank you so much for all of that information. I was looking at the HP606B generators on eBay but since they are analog, I thought they probably wouldn't be stable enough. At this stage, I'm probably going to need to purchase better equipment to do this right, at least from the generator/sweep end. I have a modern digital scope purchased last year and an HP scope that's about 30 years old both of which will do X-Y traces and are very accurate. I might try the Eico 369 I have just for practice until I can get better equipment. I'd be thrilled just to see a trace similar to the sound IF curve depicted. I have all NOS tubes in the TV

I'd like to treat this as an education journey and not a means to an end to get this particular TV perfectly aligned. How to feed in signals...set up scopes...interpret what changes in response curves mean etc... Other than adjusting coils for peak or minimum response on a VTVM is about all I have done in this realm! Believe me, I will ask questions but some of them may elicit an initial reaction of "He said what?...You're kidding me?"!!!!!

Chris K · #6 08-09-2024, 12:48 PM

Quote:

Originally Posted by bandersen

Good luck. I suggest you also take a look at the Sams instructions. Thye often use language that makes more sense.

Thanks Bob...I do have both.

Chris K · #7 08-09-2024, 01:07 PM

Does anyone have a suggestion for an accurate but affordable frequency generator? A working HP 606B generator goes for more than $300 on eBay. Sweep generators used during this TV's era, like the Hickock I had that was electromechanical (and had a destroyed speaker cone inside)...were they accurate like these modern digital equivalents? I thought getting and meticulously restoring the Eico, which is early 1980s technology, and getting new, custom built cables for RF out, demod in and scope out would have been more than accurate enough to align a TV from 1948. Am I missing something here? Like I posted in the other thread, I measured the RF frequency out of the Eico using the HP oscilloscope. It varied about 0.08 megacycles plus/minus around the intended frequency. Is using an oscilloscope in this manner an acceptable way to check the accuracy and stability of an RF generator?

old_tv_nut · #8 08-09-2024, 01:07 PM

Extremely accurate test gear is not so important in alignment EXCEPT for accurate frequency marks. Most of the alignment steps will be to peak or null the response at a certain frequency, or make two peaks of a double-peaked curve the same height, or make a particular marker 50% of the peak, for example. So accurate actual height of the curve is mostly irrelevant as long as you get the specified shape vs. frequency.

The touchiest part of the procedure often involves the signal injection cable/circuit, the ground point, length of leads, etc.

Chris K · #9 08-09-2024, 01:20 PM

Quote:

Originally Posted by old_tv_nut

Extremely accurate test gear is not so important in alignment EXCEPT for accurate frequency marks. Most of the alignment steps will be to peak or null the response at a certain frequency, or make two peaks of a double-peaked curve the same height, or make a particular marker 50% of the peak, for example. So accurate actual height of the curve is mostly irrelevant as long as you get the specified shape vs. frequency.

The touchiest part of the procedure often involves the signal injection cable/circuit, the ground point, length of leads, etc.

The Eico does have a variable marker frequency dial with adjustable amplitude but, I can't possibly know if a marker frequency selected on a crudely numbered dial scale is correct. My B&K alignment generator has all of the markers pre set and ready to go...for TVs aligned using frequencies around 20 mc higher.

bandersen · #10 08-09-2024, 02:06 PM

Are referring to the B&K 415? It only has markers for 44MHz IFs.

jr_tech · #11 08-09-2024, 02:08 PM

Quote:

Originally Posted by Chris K

The Eico does have a variable marker frequency dial with adjustable amplitude but, I can't possibly know if a marker frequency selected on a crudely numbered dial scale is correct. My B&K alignment generator has all of the markers pre set and ready to go...for TVs aligned using frequencies around 20 mc higher.

Does your digital oscilloscope have a frequency read out?

jr