1950s or '60s vintage Zenith TVs, Need some info

[vortalexfan]

Originally Posted by Kevin Kuehn

Good you got that working.

Now before you go crazy trying to set linearity on the Zenith... do you have a known good somewhat modern TV you can hook the B&K to, something to verify it didn't get it's own linearity messed up during shipment? It does have linearity adjustments very similar to a TV. And don't mess with them unless you have a TV that you know is very near perfect picture. You can even use the B&K Video out to go into composite video in on a newer TV. Here again it doesn't need to be perfect, you just need a reference so you know what it normally looks like. Everything is relative.

Yes I have several newer CRT Sets all of them are color sets, one is a Zenith 9" Color TV from 1986, and then I have a Monkey Wards 5" Color TV from 1982, and then I have a 13" Magnavox Color TV from 1991, and then I have my GTE/Sylvania 25" Color TV from 1974 and all 4 of those TVs have darn near perfect linearity.

[Kevin Kuehn]

OK. After you get that squared away it would be great if you could provide us a picture of what you're currently looking at on the Bugs CRT. BTW did you actually check to see what you replaced the 60uf cathode bypass cap with on the video out tube? When you moved the ion trap, were you able to make the picture brighter, or was it best were it was previously?

[vortalexfan]

Originally Posted by Kevin Kuehn

OK. After you get that squared away it would be great if you could provide us a picture of what you're currently looking at on the Bugs CRT. BTW did you actually check to see what you replaced the 60uf cathode bypass cap with on the video out tube? When you moved the ion trap, were you able to make the picture brighter, or was it best were it was previously?

When I moved the ion trap the screen would get brighter. The bypass cap for the 6CM7 tube was replaced with a 47 MFD cap with a 39 MFD cap in parallel to make 78 MFD, both caps are rated for over 100v.

The weird thing is that I actually had a really good picture on the TV going through the Tuner using my NES as a good stable video source and when I went to switch over to a converter box the picture went haywire and I wasn't able to get the tuner to lock in on the converter box signal, but yet it locked in rock solid with the NES.

What's up with that?

[Kevin Kuehn]

Originally Posted by vortalexfan

When I moved the ion trap the screen would get brighter. The bypass cap for the 6CM7 tube was replaced with a 47 MFD cap with a 39 MFD cap in parallel to make 78 MFD, both caps are rated for over 100v.

The weird thing is that I actually had a really good picture on the TV going through the Tuner using my NES as a good stable video source and when I went to switch over to a converter box the picture went haywire and I wasn't able to get the tuner to lock in on the converter box signal, but yet it locked in rock solid with the NES.

What's up with that?

78uf may possibility be too much. That tube needs to be biased "just right" in order to get vertical linearity in it's sweet spot, so that it interfaces well with the height and linearity controls. I have a 47uf in parallel with 22uf on mine which seems OK. Has something to do with were the tube amplifies relative to it's characteristics load line.

Lot's of folks have reported very strange things a happening with converter box's. One thing we can be sure of , they were never designed for compatibility with older than dirt TV's.

[vortalexfan]

Originally Posted by Kevin Kuehn

78uf may possibility be too much. That tube needs to be biased "just right" in order to get vertical linearity in it's sweet spot, so that it interfaces well with the height and linearity controls. I have a 47uf in parallel with 22uf on mine which seems OK. Has something to do with were the tube amplifies relative to it's characteristics load line.

Lot's of folks have reported very strange things a happening with converter box's. One thing we can be sure of , they were never designed for compatibility with older than dirt TV's.

Well lets see here, I did previously have a 59 uF capacitor (a 20 and a 39 uF capacitor in parallel with each other) in place of the 60 uF capacitor but then you had said that the capacitor needed to be 60 or more so then that's when I upped it to the 39 and the 47 uF caps.

Should I go back to the 59 uF cap?

I wonder if the converter box issue has something to do with how sensitive the tuner and IF is to switchmode power supply noise? Because I know the converter box works fine with my Meck TV strangly enough but then it might be because that TV isn't overly sensitive to outside RF interference such as that put out by SMPS.

[Kevin Kuehn]

Originally Posted by vortalexfan

Should I go back to the 59 uF cap?.

I honestly don't know for sure. I was just suggesting it on a hunch because I struggled to get the vert linearity straightened out on my own set. It's not a straight forward linear amplifier.

Originally Posted by vortalexfan

I wonder if the converter box issue has something to do with how sensitive the tuner and IF is to switchmode power supply noise? Because I know the converter box works fine with my Meck TV strangly enough but then it might be because that TV isn't overly sensitive to outside RF interference such as that put out by SMPS.

If your tuner is so sensitive it's possible your TV's AGC circuit isn't working correctly. You could try measuring the AGC DC control voltage at point D on the Sams schematic. It should be around positive 1.5v with no input signal, around -4.5v with a strong signal. As a reference I've measured mine using an older DVD/VHS player with an RF output. The key being you should see some kind of AGC voltage swing dependent on signal strength. If that's not happening you could try forcing point D negative by putting some negative DC voltage across that point and ground(positive goes to ground). Maybe a couple 1.5v batteries in series. Just remember that going more negative reduces the gain of the TV's front end. In the end you really shouldn't expect these old set's to operate reliably in a noisy RF environment, such as switch mode supplies in their near vicinity.

[vortalexfan]

Here's what the TV looks like with my NES hooked up and running.

See picture below.