70's TV set parts

[ChrisA]

I took apart an OLD TV set last night. It was built in 1973. And appears to be built after the vacuum tube era but there is a lack of integrated circuits. I was looking for "interesting" parts. I found a few but have some questions about these...

1) An 9 pound power transformer with no less than 14 lead wires. The thing is huge, 4 inch square bass and 6" tall. eventually, I can figure out the windings on this but it is worth the effort? What voltages can I expect? Usable for a tube based amp? Or just toss it out.

2) a 60Hz choke (it was connected to the above.) I need to figure out how to measure the inductance. Is there a simple way? Put AC test signal across the leads and measure the voltage drop, use ohm's law to get reactance? Is it that easy?

3) A capacitor I don't know anything about. It is in a large 3 inch tall steel can with terminals on top. Marking reads 3.5 MFD, 200VAC. It seems large and over built. I think it's an oil filed cap. What are these good for?

[Geek]

That iron is very useable for a tube amp

What model/chassis is the TV? I have lots of TV data from that era.

The choke will likely be 5H and rated for a LOT of current.

There should be a vertical output transformer in there as well. They make OK chokes too by just using the primary and leaving the secondary open.

Cheers!

[Miles Prower]

Originally posted by ChrisA
I took apart an OLD TV set last night. It was built in 1973. And appears to be built after the vacuum tube era but there is a lack of integrated circuits. I was looking for "interesting" parts. I found a few but have some questions about these...

Parted out a few of those myself. It's almost always worth the effort.

1) An 9 pound power transformer with no less than 14 lead wires. The thing is huge, 4 inch square bass and 6" tall. eventually, I can figure out the windings on this but it is worth the effort? What voltages can I expect? Usable for a tube based amp? Or just toss it out.

Never toss something like that. Definitely measure the resistances to see which coils most likely do what, which leads are for independent coils, and which are coil taps. Expect to see some high current 6.3V coils, a HV winding (the one I salvaged had 200Vrms -- full wave voltage doubler and it'll power up many an audio VT design.) Perhaps some primary taps used for line voltage corrections.

Even if the thing is fried, you can always take it apart, and recycle the lams for either a new power xfmr, make a high current, low inductance choke for a SS parafeed design.

2) a 60Hz choke (it was connected to the above.) I need to figure out how to measure the inductance. Is there a simple way? Put AC test signal across the leads and measure the voltage drop, use ohm's law to get reactance? Is it that easy?

Not quite that easy. First, you'll need to know the DC resistance of the coil. Then you need to measure the AC voltage across the coil, and the AC current through it. Then:

Z= V / I

Z= sqrt(Xl^2 + Rdc^2) Rearrange that equation, solve for Xl, and determine the inductance from:

Xl= wL (Where w= 2piF)

Use a variac to keep the coil out of core saturation (loud humming, big currents, coil heats up quickly).

3) A capacitor I don't know anything about. It is in a large 3 inch tall steel can with terminals on top. Marking reads 3.5 MFD, 200VAC. It seems large and over built. I think it's an oil filed cap. What are these good for?

Sounds more like a motor run capacitor. If you found that in a TV set, then the power xfmr was obviously a constant voltage unit that used resonance to stabilize the voltage over wide line fluctuations. The power xfmr will likely burn out without it.

Also pull the vertical deflection xfmr (useful to make a quick and dirty OPT for a low power, SE VT amp) It can also be used as a source of lams for other xfmrs or chokes.

Don't forget to snag the horizontal deflection xfmr. Useful as is for HV experiments, or recycle the core for other high frequency power supply designs.

[keantoken]

I took one apart from 1979. This had some ICs. I don't know about the transistors though. I don't know if anything from 1979 would fit today's standards for audio, except maybe the UHF/VHF transistors.

I've been playing around with the flyback, of course. Managed to light up two small green neon lamps from the same TV, and sometimes by random chance I can light up one of those fluorescent spiral light bulbs. This is with a signal gen at the resonant frequency (40KHz), 15V max output with 50 ohm series resistance. The great thing about flybacks from this era is that there is no series diode in the output, so you have unconstricted output.

I had been using it as my main TV since it had a large screen and a flat top (whose drop-dead idea was it to make TVs with rounded tops? Now I can't stack anything). Looking back I wonder if I should have just replaced the burnt part and kept it for another 50 years...

- keantoken

[ChrisA]

Originally posted by Geek
That iron is very useable for a tube amp

What model/chassis is the TV? I have lots of TV data from that era.

The choke will likely be 5H and rated for a LOT of current.

There should be a vertical output transformer in there as well. They make OK chokes too by just using the primary and leaving the secondary open.

Cheers!

Thanks,

On the front it says "Zenith Chromacolor II" and it's about 22 or 21 inches diagonal, depending on how you measure. There is no other model number anyplace. The TV was built like a tank and would be easy to service. Has a very heavy steel chassis that unfolds for service, every thing plugs together and can be swapped out with no tools. It must have been expensive when new. Made is USA too.

The choke is only about 1.5" tall by 2" wide. It does not look like something that can handle a lot of current. The other transformer is the same size but has four leads. I'm sure I'll find a use for these.

Near the power cord it reads "120VAC 1.6A 175 Watts" so that tells me something about the size of the power transformer.

The cap does look like a motor run cap. I was wrong about it's specs. The correct spec is "3.5 MF 440 AC".

[ChrisA]

Originally posted by keantoken
I took one apart from 1979. This had some ICs. I don't know about the transistors though. I don't know if anything from 1979 would fit today's standards for audio,....

There is a huge difference between 1973 and 1979. In 1979 I was a student at UCLA and in one of my classes we dissected the Zilog Z80 microprocessor. Micro computers were common in 79. But in 1973 a four function calculator was still an expensive device.

The use of ICs just exploded in the 70's

[keantoken]

You must be right about the explosion. I think convenient inventions such as the IC propagate faster than the speed of light. I wasn't there to see it happen, but I suspect that once anyone could make a functional complex circuit with little know-how and a few chips, the worth/demand for clever engineers began to drop quickly. I feel that we have gained so much, but have sacrificed much also in getting here. I myself am studying the old Tektronix scope schematics and trying to put together a functional triggering circuit in LTSpice that will work up to 10MHz. It's harder than it looks...

I have to apologize since my earlier post was all but useless and was not totally on-topic. I have been slipping on my ethics lately...

- keantoken

[Geek]

Originally posted by ChrisA

On the front it says "Zenith Chromacolor II" and it's about 22 or 21 inches diagonal, depending on how you measure. There is no other model number anyplace. The TV was built like a tank and would be easy to service. Has a very heavy steel chassis that unfolds for service, every thing plugs together and can be swapped out with no tools. It must have been expensive when new. Made is USA too.

Oh yeah, I remember those! Notorious for cooking VDR's and the HV shooting up to nearly 100KV

IIRC that was a 420-440VCT transformer at about 300 or so mA. I'll double check my data tomorrow.

Cheers!

[DigitalJunkie]

The choke is only about 1.5" tall by 2" wide. It does not look like something that can handle a lot of current. The other transformer is the same size but has four leads. I'm sure I'll find a use for these.

So there's the power trans,the choke,and another small transformer? The small transformer with 4 leads sounds like it could be an audio output transformer?

[tubelab.com]

The poster included those words. "And appears to be built after the vacuum tube era."

I left the TV repair business in 1971 (worked in a stereo shop until 1973) but even then the major manufacturers had abandoned vacuum tubes in their premium TV sets. As I remember the Chromacolor TV's had 4 tubes, and the Chromacolor II TV's had none.

The power supplies in the early SS TV's often used a large ferroresonant transformer which REQUIRES a matching AC cap (and sometimes an inductor) for operation. It will have several windings with the majority of the power favoring SS voltages (under 100 volts) there may be a low current winding to develop the high voltages needed for the CRT's screen grids.

I don't remember the specifics of the Zenith design, but the RCA XL100's of the day used dual SCR's in a multivibrator like arangement to drive a flyback transformer to generate horizontal sweep and CRT anode voltage. The big Zeniths likely used a similar circuit since the silicon of the day didn't handle the high flyback voltages needed in large TV's yet.

It is highly likely that there is no vertical output transformer. The SS TV's used a circuit not unlike the SS stereo output stages to drive the yoke directly.

The transformers and other parts are possible canidates for a SS amp. Zenith TV's had the biggest and best power transformers in the industry back then. In 1960's and 1970's south Florida many homes didn't have air conditioning. TV sets died often due to the heat and humidity. Replacing a power transformer was a weekly occurrence in the shop where I worked. I never changed the transformer in a Zenith.

I learned to make guitar amps from old TV sets as a teenager. The best TV's to use for tube amp parts are the ones from the late 1950's and early 60's, especially the color sets with the round 21 inch CRT's. Some of the later rectangular screen TV's still had power transformers, and they were good too. By the mid 60's many TV manufacturers had eliminated the power transformer from their designs.

As stated the vertical output transformer will work fine for the OPT in a small SE amp, but you need to find one with 4 wires on it (often blue, red, green, and black). Again in the mid 60's the TV manufacturers switched to an autotransformer to save money.

TV's sets from this era are getting very hard to find. I saw one old Zenith TV in the electronics recycling yard. The goon at the gate wouldn't let me touch it on premises, but I did manage to convince him to let me take it home. I returned it a few hours later weighing about 10 pounds less.