Newbie's First Questions RCA TS 721 Restoration

[Penthode]

Yes it is ceramic because it dissipates a lot of heat.

And the tube,shield is in place? The fine tuning range is suspect... is the range sufficient to adjust the video extinguishing at one end of its range?

[Notimetolooz]

Originally Posted by Chris K

The Leader has a channel 3 or 4 option for output...not 5 or 6. Its LCG 396...not LGC 396. Maybe that's the issue

My typo.

The manual I found doesn't mention options. Perhaps yours is a later version.
http://bama.edebris.com/manuals/leader/lcg396/

You could use a sig-gen with AM modulation (1KHz) on 21.25 MHz to inject the signal at the output of the tuner. Trace it thorough the sound IF with a detector probe attached to a scope. You could not get the sound any further than the discriminator, however you could confirm the sound IF transformers were peaked correctly. You could check the 21.25MHz with a frequency counter if need be.

[Chris K]

Originally Posted by Penthode

Yes it is ceramic because it dissipates a lot of heat.

And the tube,shield is in place? The fine tuning range is suspect... is the range sufficient to adjust the video extinguishing at one end of its range?

I'll check the fine tuning tonight. Yes, I put the shield back in place each time I tried a different tube.

[Penthode]

You mention the fine tuning adjusts full range. On ch4 on the 721TS the full fine tuning range is only about 0.5MHz where each channel is 6MHz. So the fine tuning is very narrow.

So I switched on just now my 721TS on channel 4 and adjusted the fine tuning across its full range. The pictures attached below depict what you would normally see on a properly aligned set.

The first image is with the fine tuning fully clockwise. Note the picture is brightest because the video carrier is at the top of the response curve. As a result the picture will lack fine detail. And there is no sound.

The second image is with the fine tuning roughly center with the picture a bit dimmer but with full detail. This is the correct point where the video carrier is at the 50% point on the video bandpass slope or nyquist slope for vestigial sideband demodulation. As this is a spilt sound set, you must adjust for best sound which would be the discriminator zero position.

The third image is with the fine tuning control fully counter clockwise and the picture is very weak. It has trouble locking because the carrier is at the bottom of the slope. There is no sound.

So as you adjust the fine tuning control counter clockwise, you should see the picture grow gradually dimmer if the tuner's local oscillator is set correctly within range of the tv signal. Either end of the fine tuning control there will be little or no sound.

If the image brightness remains the same across the tuning range or if the image grows a bit dimmer when the fine tuning control is clockwise, then the local oscillator is off frequency and you will get no sound.

[Chris K]

Originally Posted by Penthode

You mention the fine tuning adjusts full range. On ch4 on the 721TS the full fine tuning range is only about 0.5MHz where each channel is 6MHz. So the fine tuning is very narrow.

So I switched on just now my 721TS on channel 4 and adjusted the fine tuning across its full range. The pictures attached below depict what you would normally see on a properly aligned set.

The first image is with the fine tuning fully clockwise. Note the picture is brightest because the video carrier is at the top of the response curve. As a result the picture will lack fine detail. And there is no sound.

The second image is with the fine tuning roughly center with the picture a bit dimmer but with full detail. This is the correct point where the video carrier is at the 50% point on the video bandpass slope or nyquist slope for vestigial sideband demodulation. As this is a spilt sound set, you must adjust for best sound which would be the discriminator zero position.

The third image is with the fine tuning control fully counter clockwise and the picture is very weak. It has trouble locking because the carrier is at the bottom of the slope. There is no sound.

So as you adjust the fine tuning control counter clockwise, you should see the picture grow gradually dimmer if the tuner's local oscillator is set correctly within range of the tv signal. Either end of the fine tuning control there will be little or no sound.

If the image brightness remains the same across the tuning range or if the image grows a bit dimmer when the fine tuning control is clockwise, then the local oscillator is off frequency and you will get no sound.

My God...what a beautiful picture. Let me do a little more orienting. I have a digital to analog converter box and an over the air digital broadcast antenna that works OK on my other vintage TVs and I don't get anything approaching a picture on the 721 with this setup. The only picture I've gotten is with the pattern generator...crosshatch...dots etc...through the Leader 396. I did double check and it does not produce a tone. Maybe I should stop focusing so much on getting the sound and concentrate more on getting a broadcast picture. I don't know if my digital to analog converter box has enough "oomph" to get a picture on the 721. What are you pumping into your set to get that beautiful picture?

[Penthode]

To get the picture I am using a Zenith set top DTV box and rabbit ears. The station is TV Ontario from the Paris Ontario transmitter about 20 miles away.

[Chris K]

Originally Posted by Penthode

To get the picture I am using a Zenith set top DTV box and rabbit ears. The station is TV Ontario from the Paris Ontario transmitter about 20 miles away.

I'm right outside Philadelphia PA USA and we're pretty right with OTA digital stations. The unit I'm using as a converter was very inexpensive. Let me see if I can find something with more muscle

[Chris K]

Originally Posted by Penthode

To get the picture I am using a Zenith set top DTV box and rabbit ears. The station is TV Ontario from the Paris Ontario transmitter about 20 miles away.

Actually what I would like to do the most, and how I would use this TV most of the time, is to use my computer as a signal input source and play old movies and black and white TV shows from YouTube and other Internet based broadcasts. I've seen Bob Andersen and Buzz1151 do this without much trouble but I really don't know where to start with equipment etc.

[Penthode]

Originally Posted by Chris K

Actually what I would like to do the most, and how I would use this TV most of the time, is to use my computer as a signal input source and play old movies and black and white TV shows from YouTube and other Internet based broadcasts. I've seen Bob Andersen and Buzz1151 do this without much trouble but I really don't know where to start with equipment etc.

There is a lot of stuff available for video sources. Besides a DVD player, I also have a HDMI to composite video convertor. I also watch YouTube videos on my set via a Roku1.

I received an email from Roku yesterday telling me the Roku 1 has reached end of life and will no longer be furnished with software updates. Well it is 10 years old....

[Kevin Kuehn]

Originally Posted by Chris K

I have a digital to analog converter box and an over the air digital broadcast antenna that works OK on my other vintage TVs and I don't get anything approaching a picture on the 721 with this setup. The only picture I've gotten is with the pattern generator...crosshatch...dots etc...through the Leader 396. I did double check and it does not produce a tone. Maybe I should stop focusing so much on getting the sound and concentrate more on getting a broadcast picture. I don't know if my digital to analog converter box has enough "oomph" to get a picture on the 721. What are you pumping into your set to get that beautiful picture?

I would agree focus on getting a broadcast picture using the converter box. First verify everything is working correctly using another analog TV. Next verify you're set to the same channel and center the fine tuning control on your 721, then try adjusting the oscillator slug associated with that same channel. It is curious that the Leader produces a picture on ch 3 or 4 but not the converter box. I believe the Leader produces it's signal using digital logic, but it is possible it's master clock frequency has wondered slightly.

[Chris K]

Originally Posted by Kevin Kuehn

I would agree focus on getting a broadcast picture using the converter box. First verify everything is working correctly using another analog TV. Next verify you're set to the same channel and center the fine tuning control on your 721, then try adjusting the oscillator slug associated with that same channel. It is curious that the Leader produces a picture on ch 3 or 4 but not the converter box. I believe the Leader produces it's signal using digital logic, but it is possible it's master clock frequency has wondered slightly.

I'll take that route Kevin. Thanks very much.

[Penthode]

Yes I agree follow Kevin's route. However be aware of the process of adjustment of the local oscillator to bring the set in tune and yield a picture like my set.

First, the way the tuner is designed is the inductances are cascaded. That is when you adjust, it was originally suggested that you start with channel 13 and move downward. If you do not need the other channels you need not really need to worry except to be aware the reason you may not be able to tune channels 6 , 5, 4 and 3 is that there is something wrong with the tuner oscillator coils above these channels. Or there may be a bad tuning capacitor in the tuner.

I have found with each of my late 40's sets which had sat unused for decades that the whole chain was off and I needed to adjust the higher channels in order to bring channel 4 correctly within range. Study the service notes as they will infer the same adjustment process.

Be aware that if you adjust the screw slugs initially counter clockwise, you have the danger of adjusting them so they will drop out from where they are threaded. Inspecting the tuner, you may find someone has been there before you and some of the slugs are missing for some of the higher channels. That may be why you are not able to fine tune properly. It is always worthwhile inspecting the holes where the screws are to see if any are missing.

I always begin by adjusting clockwise until snug and the back off the screws. Follow my suggestion in my previous comment to find the correct response slope to place the carrier at 50% which is proper tune for best picture detail and where you will find the audio. If you cannot adjust the fine tuning to where the image begins to fade, means the local oscillator frequency is too high. Brass slugs are used which means in screwing the slugs lowers frequency.

To fix the video to make it sharp as well as retrieve the audio, you must get the local oscillator tuning right.

[Kevin Kuehn]

Originally Posted by Penthode

Yes I agree follow Kevin's route. However be aware of the process of adjustment of the local oscillator to bring the set in tune and yield a picture like my set.

First, the way the tuner is designed is the inductances are cascaded. That is when you adjust, it was originally suggested that you start with channel 13 and move downward. If you do not need the other channels you need not really need to worry except to be aware the reason you may not be able to tune channels 6 , 5, 4 and 3 is that there is something wrong with the tuner oscillator coils above these channels. Or there may be a bad tuning capacitor in the tuner.

I have found with each of my late 40's sets which had sat unused for decades that the whole chain was off and I needed to adjust the higher channels in order to bring channel 4 correctly within range. Study the service notes as they will infer the same adjustment process.

Be aware that if you adjust the screw slugs initially counter clockwise, you have the danger of adjusting them so they will drop out from where they are threaded. Inspecting the tuner, you may find someone has been there before you and some of the slugs are missing for some of the higher channels. That may be why you are not able to fine tune properly. It is always worthwhile inspecting the holes where the screws are to see if any are missing.

I always begin by adjusting clockwise until snug and the back off the screws. Follow my suggestion in my previous comment to find the correct response slope to place the carrier at 50% which is proper tune for best picture detail and where you will find the audio. If you cannot adjust the fine tuning to where the image begins to fade, means the local oscillator frequency is too high. Brass slugs are used which means in screwing the slugs lowers frequency.

To fix the video to make it sharp as well as retrieve the audio, you must get the local oscillator tuning right.

All good info above. I realize it will make the purists cringe, but I often wonder if some novice collecting folks would not be happier simply adding a composite video and audio inputs to their vintage TV. That ultimately eliminates all this tuner and IF alignment confusion along with the specialized test gear, knowledge base, and frustration. Basically it turns the vintage TV into a video and sound monitor. Bottom line is you need to become borderline obsessed with this hobby to endure doing this the hard way, when possibly all the individual really wished for was to enjoy watching their old TV.

[Chris K]

Originally Posted by Kevin Kuehn

All good info above. I realize it will make the purists cringe, but I often wonder if some novice collecting folks would not be happier simply adding a composite video and audio inputs to their vintage TV. That ultimately eliminates all this tuner and IF alignment confusion along with the specialized test gear, knowledge base, and frustration. Basically it turns the vintage TV into a video and sound monitor. Bottom line is you need to become borderline obsessed with this hobby to endure doing this the hard way, when possibly all the individual really wished for was to enjoy watching their old TV.

Ill give it the old fashioned way try but I hadn't thought of injecting composite video. Hmmmmmmm

[Chris K]

Probably won't be able to use the suggestions here until tomorrow night. Busy weekend. I'll post with my progress.