Sound and video not tuning together with digital converter: 1956 philco 21"

[Tubejunke]

Before the loss of the perfectly fine analog TV signal my set worked fine. Now that I have to use a converter for the digital channels the sound is low for one thing and doesn't tune to the best picture. Another device like a VCR is better, but not much better. I haven't tried a DVD yet, but that's not the issue.

Channels 3 and 4 were never used around here, but now they are the only two choices. It is obliviously a matter of alignment which many of us are smart enough to stay away from. I am hoping that someone who does understand this condition and/or is familiar with these sets (one piece chassis) can point me to the right place to perhaps touch this up. It can't be off by much, so I assume that there is a coil somewhere that I can carefully adjust to bring the best sound over the best picture.

I have similar problems with all of my vintage sets when I use the converters. I have three, so it's not the box. Thanks folks!

[Electronic M]

I'd try a Blonder Tongue Agile Modulator. Most consumer grade RF modulators fall far short of broadcast standards.

[dieseljeep]

Originally Posted by Tubejunke

Before the loss of the perfectly fine analog TV signal my set worked fine. Now that I have to use a converter for the digital channels the sound is low for one thing and doesn't tune to the best picture. Another device like a VCR is better, but not much better. I haven't tried a DVD yet, but that's not the issue.

Channels 3 and 4 were never used around here, but now they are the only two choices. It is obliviously a matter of alignment which many of us are smart enough to stay away from. I am hoping that someone who does understand this condition and/or is familiar with these sets (one piece chassis) can point me to the right place to perhaps touch this up. It can't be off by much, so I assume that there is a coil somewhere that I can carefully adjust to bring the best sound over the best picture.

I have similar problems with all of my vintage sets when I use the converters. I have three, so it's not the box. Thanks folks!

What make of converter are you using?
Magnavox is one, that doesn't seem to work very well, on certain sets, even the newer, solid state sets. I generally use the audio-video outputs on them.
A strong possibility is the oscillator slug on the Philco set might need readjusting. It depends how well the fine tuning works.

[Kamakiri]

I run into the same issue on some sets. Some sets I can get tuned on frequency, but I can't seem to lose an audio hum with the converter. Agile modulator works fine on them though.

[Phil Nelson]

If "agile modulator" is a new concept for you, this article describes how I use one to broadcast TV throughout my house:

http://antiqueradio.org/HomeTVTransmitter.htm

Phil Nelson
Phil's Old Rados
http://antiqueradio.org/index.html

[old_tv_nut]

Broadcast analog signals had a stronger audio carrier relative to the video carrier [as high as -7 dB] than the channel 3/4 modulators used in VCRs, DVDs, or digital converter boxes. This is because these simple modulators first frequency modulated a 4.5 MHz audio intercarrier and added it to the baseband video before modulating on the channel 3 or 4 carrier. Lower level [typically -15 dB] prevents generation of chroma/sound beats, but makes the alignment of old sets more critical.

Professional agile modulators may have adjustable audio carrier level and be capable of the higher ratios.

[walterbeers]

I have a Zenith converter and it seems to work on the older retro B&W sets, but it does seem to produce a fine beat effect in the picture that sort of looks like a herringbone pattern - sort of like a screen effect. Looks like 4.5 Mhz beat, but tuning the 4.5 trap doesn't help it. It shows up on all the old B&W consoles and my RCA TS721 as well, however it isn't there on my RCA color CTC9. I wonder if it has to do with the 3.58 color burst signal.

[Electronic M]

If it is strongest on saturated primary colors and looks sort of like a checker board when viewed up close then you are seeing the 3.58Mhz color subcarrier.

[old_tv_nut]

Originally Posted by Electronic M

If it is strongest on saturated primary colors and looks sort of like a checker board when viewed up close then you are seeing the 3.58Mhz color subcarrier.

Correct - it should disappear if you are looking at monochrome material.

[Tubejunke]

Originally Posted by dieseljeep

What make of converter are you using?
Magnavox is one, that doesn't seem to work very well, on certain sets, even the newer, solid state sets. I generally use the audio-video outputs on them.
A strong possibility is the oscillator slug on the Philco set might need readjusting. It depends how well the fine tuning works.

I have two converters. One is a Magnavox TB100MW9, and the other is a Digital Stream DTX 9950. The Stream is superior for a few reasons, but both do fine on solid state stuff. Now, I think you hit the nail on the head with the oscillator slug needing readjustment. The fine tuning works fine. I am hoping someone familiar with this chassis will direct me to the right slug. I don't want to mess the set up.

NOW, here is something interesting. Tonight I took the Digital Stream and hooked it to my 49ish RCA TC-127 which has had low volume issues since I restored it. I wasn't even getting decent video and almost no audio, so I started playing with the coaxial cable. I found that if I only touched the center conductor to the connector without letting the outer shell touch (which is hard) that I ended up with almost perfect video and audio. I believe I will disconnect one side of the RF adapter at the antenna terminal and let it ride. Very happy with that discovery, but I don't understand it.

Thanks everyone for the ideas. I am not familiar with "Blonde Tongue" or "Agile" converters.

[dtvmcdonald]

The pre-1950 RCA sets had a very very strange RF setup.
You should try using a standard 75 to 300 ohm balun, the cheap
ones from Radio Shack, and connect one side of the 300 ohm line output to
chassis ground and the other side to one of the RF terminals ...
try both, they are not equivalent. Note that this may require fairly long leads ...
this is immaterial on channels 3 or 4.

My such set (a 9T-246) has a plug-in
thing for the antenna lead which is supposed to support 75 Ohms
directly with a different plug, and that simply does not work.

Doug McDonald

[Phil Nelson]

Originally Posted by Tubejunke

Now, I think you hit the nail on the head with the oscillator slug needing readjustment. The fine tuning works fine. I am hoping someone familiar with this chassis will direct me to the right slug. I don't want to mess the set up.

I don't have a service manual for your TV, but on many sets the oscillator adjuster is inside a little hole on the front of the tuner, something like this diagram (labeled A14).



When you turn to a given channel, its adjuster appears through that little hole (labeled H). In your TV, everything would have different labels, of course. First, tune the TV into a signal and set the fine tuner to the middle of its range. Then, using a very thin, non-metallic screwdriver, you turn the adjuster until you have the best picture. Sometimes the adjuster is deep inside that hole, so it helps to use a strong flashlight.

Be careful not to screw the adjuster out too far. On some TVs, the screw will fall out and perhaps get stuck in an inaccessible place.

It's not clear to me that this is the root of your problem, but if you are careful, tweaking the oscillators for channels 3 and 4 can't hurt. If you can already use the fine tuner throughout its range to tune the signal completely in and out in both directions, then adjusting the oscillator won't improve anything. It is just a way to get the tuner (and fine tuner) centered on the correct frequency, if that makes any sense.

Phil Nelson
Phil's Old Radios
http://antiqueradio.org/index.html

[kramden66]

the adjustment for channel 3 or 4 tweaked in the front of the tuner should help align it closer

[Tubejunke]

OK Phil and Kramden66, I am familiar with this adjustment, but I lean toward the idea or fact that it would center the range of the fine tuner for that specific selection. My fine tuner is about dead center. My problem is that a good sound signal is just off 'to the side' if you will to the best (or worst) video signal; right on the edge.

I feel badly that I have forgotten just what lays the two in alignment. Thanks Phil for the graphic. That will help a lot of folks and me too as it is similar in nature to my tuner. We're getting there, and as for the RCA I feel that going with the one side to antenna input and the other to ground may be the thing to do.

[Phil Nelson]

Originally Posted by Tubejunke

a good sound signal is just off 'to the side' if you will to the best (or worst) video signal; right on the edge.

Sometimes you can fine-tune it for best picture and then carefully tweak the sound alignment adjusters to match, so to speak. Those will be identified in the Sams manual, if you have that.

Phil Nelson