1968 Zenith 20Y1C50 chassis - advice needed

[zeno]

Those controls used to get bad spots. Also the VDR was trouble.
All the NOS VDR's are bad now out of the package. Somewhere here
there is a post from Doug ( drh4683 ) he found the modern sub.
Nice work Doug !
Vert jitters may be the integrators, another common problem.

73 Zeno
LFOD !

[joe111671]

Thanks Zeno, I found the thread, here it is for anyone following along. Nice work by Doug indeed! I'm going to order a couple.

http://www.videokarma.org/showthread.php?t=261780

I'll still need to replace that burnt R44 1000 ohm resistor off the regulator tube. Is there anything special about it or can I just use any 1000 ohm resistor?

I recall seeing a youtube video by shango066 where he rebuilt a vertical integrator on some Zenith set. That didn't even cross my mind, so thanks for mentioning that as well.

[zeno]

Should be a regular carbon. Its a good idea to use whatever was in there.
In some apps using a wire wound will cause trouble because its not only
a resistor but also an inductor. Newer sets also use low value resistors as fuses
so stick to the original when you can.
Modern carbon film flameproofs are a good sub for carbons.
Sams manuals as a rule just list carbons by value. Other special resistors
they give specs & OEM part numbers.

73 Zeno
LFOD !

[Jeffhs]

Originally Posted by zeno

Should be a regular carbon. Its a good idea to use whatever was in there.
In some apps using a wire wound will cause trouble because its not only
a resistor but also an inductor. Newer sets also use low value resistors as fuses
so stick to the original when you can.
Modern carbon film flameproofs are a good sub for carbons.
Sams manuals as a rule just list carbons by value. Other special resistors
they give specs & OEM part numbers.

73 Zeno
LFOD !

I agree with your advice as to using the same component as was originally in the set. The manufacturer had a good reason for using the values originally installed in the chassis; the use of other parts can cause problems. In fact, it is very important to replace resistors, for example, with identical components; resistors are often used to drop voltages, and some, as you mentioned, are used as fuses, as they are designed to open under severe current overload conditions--not unlike fusible resistors in older, tube-type TVs. Replacing such a resistor with a standard carbon one could cause more damage than was originally done when the original part failed, particularly if the original resistor was meant to open in case of an overload or short.

[joe111671]

Originally Posted by zeno

Should be a regular carbon. Its a good idea to use whatever was in there.

73 Zeno
LFOD !

Originally Posted by Jeffhs

I agree with your advice as to using the same component as was originally in the set.

Thanks for your advice, guys. I added the correct resistor to my order.

I'm trying to make a list of as many components as know I'll be needing, to make the shipping cost lower than the parts cost, so I'm ordering the degaussing thermistor. Since all I do is ask questions, I'll share something I learned, that most people on here probably know but maybe some don't.

There are two types of thermistors. NTC and PTC. NTC means the resistance drops as it heats up, and PTC means the resistance increases as it heats up. So in my case, I need NTC since the degausser is in parallel with the thermistor, where I would need PTC if it was in series. I need a 120 ohm, but Mouser doesn't have it. They do have a 130 ohm, so I'll try that. It's only a buck, so if it doesn't work right, I'll jump it out again and go looking for a 120 ohm.

[zeno]

Me & Jeffhs are working at the same bench ! A few examples:

Hallicrafters SX 71 SW radio. I saw a toasted resistor in the front end.
We had a huge collection of Dale precision wire wound resistors thanks
to Raytheon & the American tax payers. I used one of them. The
radio went deaf. It was the new WW resistor acting as a coil.

1963 Zenith 19" tin can B&W. Found at the dump. It was in showroom condition so I fixed it up for the wife to be bedroom. 'lytic in cathode of vert out was opened. A common wham bam repair. Installed a seperate cap about 6 inches away & the set went into vert blink mode. Moved it back near the old can & it was fine.

Early 70's 12" B&W Panasonic. Fixed & was buttoning up. Noticed the best
text book case of jail bars I have ever seen. The cathode lead to the CRT had moved over by the FBT & was picking up the HV spikes.

enuf fer now
73 Zeno
LFOD !

[Electronic M]

Originally Posted by joe111671

There are two types of thermistors. NTC and PTC. NTC means the resistance drops as it heats up, and PTC means the resistance increases as it heats up. So in my case, I need NTC since the degausser is in parallel with the thermistor, where I would need PTC if it was in series. I need a 120 ohm, but Mouser doesn't have it. They do have a 130 ohm, so I'll try that. It's only a buck, so if it doesn't work right, I'll jump it out again and go looking for a 120 ohm.

Some sets have both PTC and NTC...RCA around the CTC16 would put the degauss in series with the B+ winding of the power transformer...they would put a PTC in series with the degauss and an NTC in parallel with the degauss and PTC to bypass them as the PTC got close to open circuit.