Is anyone having trouble getting your Digital converter box to work with old sets?

[Tubejunke]

Originally Posted by Robert Grant

I'm not sure exactly what kind of "noise" or "distortion" you may be experiencing, so I'll make a couple of guesses about what the problem may be.

If your local analog signals had been weak, and your picture with the converter box is prone to very high contrast or "tears up", you may be able to fix this by backing up on the AGC control on your set (presuming it has one). When only weak analog stations were feeding the set, signal overload was never a problem. With your converter box, a strong analog signal (capable of overload) is fed to your tuner, whether the DTV signal the box is receiving is across the street or from the deep fringe.

When we had analog signals, the stations varied in strength but the set was always amazing in the fact that it would pull in the stronger channels with no antenna at all, and it would do the rest with only the built in antenna. Perhaps I will hook it up again tomorrow to give a better description of the noise and distortion that I have mentioned. In short, I was very disappointed that my set that always seemed invincible and strong suddenly became unviewable with all of this digital CRAP! I will say that I am not referring to digital reception. That is why I mentioned in my original post that I use the digital converters MENU as my signal source so I don't even have to think about reception. Again, even when I am in the menu there seemed to be a streaking or tearing in the video with a buzz in the sound which is generated somehow by this box or its associated connections. All symptoms go away when the box is removed. I tried two different converters and RF modulators, but not cabling. Again, tomorrow I will try it again for better description and I will swap the co-ax cable.

Thanks Robert and everyone else who has helped out here!

[Tubejunke]

Originally Posted by Findm-Keepm

I'm not assailing the OP's intelligence - just wondering what converter he's referring to, given there are "no 'over the air' channels.

Instead of trying to decipher all of the abbreviations, I will describe the "converter" as one of the 'boxes' they are pushing for those of us left who have no, or choose not to participate in, cable or satellite service and were watching over the air ANALOG signal TV. My abbreviation is A.B.O.F.S.! LOL! Go figure....

Also, I see now that I made a mistake in stating that there are no 'over the air' channels. It is STILL 'over the air', what has changed is the TYPE of signal from analog to digital. Sorry for the misinterpretation.

[Robert Grant]

@Tubejunke

Just a thought, have you tried unplugging the TV and plugging it back in the other way?

Perhaps you have a hot-chassis set, a cap has shorted somewhere, and you're putting 120VAC into the tuner when you hook the CECB up to it?

Just a thought.

[Tubejunke]

Good thinking, but my Philco is a transformer set....

[martyfreeman]

Originally Posted by Phil Nelson

What's in those attenutators, exactly, besides a potentiometer? I have a similar looking Radio Shack model. Got it at a garage sale for a nickel or something. Maybe it's defective. I tried it a couple of times, and it seemed to have a range between distorting the signal and really really really distorting the signal.

Phil

If it is properly designed, a "T-pad". This is similar to the "L-pad" used for speaker-level volume controls but it has three ganged potentiometers instead of two.

The stem of the T is a potentiometer to ground and the arms go to source and load.

An L-pad presents a constant impedance to the source and variable to the load (assuming that the source and load impedance are correct).

A T-pad presents a constant impedance to both the source and load (with the same underlying assumption).

Switched attenuators are really stepped T-pads.

[cbenham]

Thanks JR for the pointer to the rf attenuator sold by solid signal.

As to the Philco set, some of the early 1950 Philcos had several versions for urban or fringe reception. There were different parts in the AGC circuit for higher gain in fringe areas. If this is the case with your set it is being waaay overloaded by the signal from the converter box. Also it's video amp is narrowbanded to help hide snow in the pictures. If you can give me a model number and code number (something like 50T 1400 code 121), I may have the original Philco bulletin that details the resistors and caps you would change to lower the set's gain for urban use.

Cliff

[DaveWM]

well I am a believer now that indeed the converter boxes can cause issues. I was fighting a bad sync buzz on my motorola T-14, until I tried a transmission based on a blonder tongue modulator. NO BUZZ, I could not believe the difference, so to the OP yes indeed I was havving trouble with my digital converter box on my old set. It just seems to be certain old sets that can't deal with it. My 59 predicta and up have no problems.

[old_tv_nut]

I would be interested to know if these sets that have trouble with the converter boxes also have trouble with VCRs. Also, what does the BT modulator have in it for audio? Separate audio oscillator and modulator, or 4.5 Mhz added to the video like VCRs and converter boxes do?

[Tubejunke]

The 1956 Philco that started this thread has trouble with both digital converter and VCR. The VCR is way better than the digital converter. If I remember right the converter seemed to have some sort of interference, while the VCR signal seemed a little weak with low volume. I haven't checked the tuner and I.F strip tubes yet. Again, the set played fine when I had an analog signal. It seems like years ago I used a VCR with this set with no trouble. Channels 3 and 4 have seen little or no use for many years. Perhaps a good cleaning is in order. I just don't feel like dirt would be the whole problem here....

My 1949 RCA uses a digital converter, VCR/DVD combo with no trouble. Interesting......

[Phil Nelson]

Cleaning the tuner would be easier than realigning the RF/IF or rebuilding your AGC section to change its behavior. If that doesn't improve the situation, cross it off your list of possible causes and try something else. Sitting around and theorizing for weeks isn't getting you anywhere.

It's not surprising that one old TV will respond differently to a given source than another old TV. They have many differences, not only in original design but also in the degree to which they have been restored.

Phil

[Tubejunke]

I will clean the tuner as general purpose, but I still doubt that it is the cause, the dirt that is. As far as theorization goes, I just made this thread in hope to compile enough good ideas and theories to be able to attack the situation. No real hurry anyway. I only use the old sets a few times a year.

Last night I hooked up the digital box to an early 50's WELL MADE Sparton and it worked fine. The Philco has been a mainstay of mine for MANY years, but it is a very basic set in all respects. I do feel that the basic nature of it is why it has always played perfect beyond minimal repair like a tube or a resistor here and there over the course of over the 25+ years that i have owned it. Oh, I forgot, the original CRT finally got weak enough for a change out.......

[Phil Nelson]

If this TV works well on channel 3 & 4 with your VCR, then tuner cleaning probably won't work any miracles.

Can you borrow a DVD player (or even a different brand of converter or VCR) from a friend? Every source can be a little different, and it wouldn't be unusual to find that your TV "likes" some better than others.

If you discover that your converter has a stronger signal than other sources, then maybe a cheap attenuator will make it more usable on this TV.

Phil

[Tubejunke]

Originally Posted by Phil Nelson

If you discover that your converter has a stronger signal than other sources, then maybe a cheap attenuator will make it more usable on this TV.

What is this (attenuator) and where do you get them? I am familliar with signal boosting, but not signal reduction....

[Tubejunke]

OK, I finally did something with this. I removed the two tuner tubes and tested them; both are good. I always scrape the pins of tubes with my knife for good measure, especially if I see the needle on the tester jump around, and I did with one tube. Anyway, I replaced them and tried the set with and without the metal shields to see if that would make a difference. I forgot to say that cleaning the pins on the tubes must have done some good because the worst of the interference I mentioed was gone. However, the picture was still a bit snowier than I would like it to be. So, I connected ONE side of the built in VHF antenna to ONE side of the antenna terminal and MOST of the snow came out. The TV is now viewable! That's good, but I wish I could get the picture crystal clear like it used to be. Perhaps some more experimenting will work that out. Maybe there are other tubes involved.

[old_tv_nut]

Originally Posted by Tubejunke

However, the picture was still a bit snowier than I would like it to be. So, I connected ONE side of the built in VHF antenna to ONE side of the antenna terminal and MOST of the snow came out. The TV is now viewable!

Now, what you said sounds squirrelly to me. Could you state plainly how you have the converter hooked to the TV?
Should be:
Converter output 75 ohm coax --> balun transformer (75 coax to 300 ohm converter) --> 300 ohm twinlead (usually a short piece with spade lugs built into the 75-300 ohm balun) --> 300 ohm screw terminals of TV.

Are you saying that you hooked up the internal antenna on one side ALSO in addition to the 300 ohm twin lead from the balun? Or what, exactly?