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?
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?
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!
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!
ChrisA said:
Parted out a few of those myself. It's almost always worth the effort.
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.
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).
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.
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
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
Geek said:
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".
keantoken said:
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
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
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
ChrisA said:
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!
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?
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.
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.
My first ham transmitter used the transformer, rectifier, filter caps, doorknob cap AND a 6DQ6 from a black and white TV.
The early color TV transformers were good for a few hundred watts.
The early color TV transformers were good for a few hundred watts.
Mine used an 807. 6DQ6's were saved for my guitar amps.
This is true. The later Zenith transformers had heat radiating fins (every 10th lamination was oversized) and they were dipped in some epoxy like substance. I have sucked some serious power through these without issue. One went into a guitar amp that used 6 KT88's. These were the cheap Chinese ones from 15 years ago that blew up a lot, so the whole deal made only 150 watts. B+ was 380 volts, about the limit for those tubes.
I know of two other excellent sources (but don't tell the collectors, they get really angry).
The old Hewlett Packard 200 series audio oscillators had some excellent power transformers in them.
The 200AB has a transformer with a 5 volt winding that used a 5AR4 rectifier. The original tube was an Amperex Bugle Boy in most of them. The B+ is about 360 to 370 volts and the power level is suitable for a 50 watt guitar amp using 6L6GC's or a small stereo amp. It will run a Simple SE forever.
The 200CD transformer has no 5 volt winding and used a solid state rectifier. B+ is a bit lower, maybe 350 to 360 volts.
The Textronix 500 series scopes have monster transformers in them. There are enough 6.3 volt windings to light up a small town, and there are usualy several high voltage windings. Every one is different, but with some digging the diagram can usually be found on the internet. Many are good for 500 watts or more.
Tube type test equipment still shows up at hamfests and often the seller just wants to get rid of it. Sometimes they can be bought for $5 or even free at the close of the show if the seller doesn't feel like dragging it home. Just don't tell him that you intend to part it out!
I prefer to think that I am at least diverting the tubes and transformers from the land fill, and I did snag 20 HP oscillators right off of the scrappers truck. I still have some transformers from that deal about 5 years ago.
tubelab.com said:
I did use an ARC-5 which had 1625's -- cousin to the 807 -- it was my first transmitter with a VFO! I still have the rotary tuning coil.
While the TEK-Group would want you burned in effigy, there are just so many used scopes and power supplies destined for the land-fill that's a pity not to reincarnate them.
Mine was an ARC-5 too. There was a Army Navy surplus shop near my house that sold them for something like $5. It was about 1965. My brain didn't remember the tube number, only the shape and the top cap, and the fact that I couldn't make anything cool with it because it didn't fit any of the sockets that I got from all of the dissected TV sets. I used a Hallicrafters S-38 for RX. I still have it. With the drift in the TX frequencies, and the drift and lack of selectivity of the old Hallicrafters RX, I didn't make many QSO's. I later got an S-46. It worked a little better.
I will admit to gutting about 20 HP oscillators, about 10 sweep generators, and several other pieces of tube type test equipment and military surplus. I have only relieved one TEK scope of its vital organs.
I have a friend that I went to high school with who has been in the surplus business all his life. He gets tons of old test equipment that no one wants. He lists the stuff on Ebay and his web site. If no one buys it after a while, it goes to the metal scrap dealer to be crushed and melted. He will set aside some of the tube stuff for me if I get there before the scrap man comes, since he is 200 miles away, I haven't been there in a while. I stopped in to visit him one day when he had about 20 of the HP oscillators headded for the crusher. I took all of the transformers out and paid for the metal value.
The scope was auctioned on Ebay. The winning bidder only wanted the tubes (lots of 6DJ8's). The carcass was in the scrap pile, so I took the transformer, a bunch of those shiny white terminal strips and some big resistors. Again for the scrap value.
If I see any tube type equipment being scrapped, I try to get the tubes and transformers. Unless I have plenty of time, I don't consider the other components worth grabbing.
I presume this is all because of your low mains voltage over there?, mains transformers were extremely rare in UK TV sets.
Set's normally used a live chassis with the incoming mains directly rectified to give 300V+ on the HT rail. Older sets used a halfwave rectifier (usually a metal one), with the chassis at neutral, or fully live, depending on the plug polarity (back when two pin plugs were still in use). Later ones used a bridge rectifier (new requirement from the electicity companies), so the chassis was half live, regardless of polarity.
By the time colour started in the UK transistors were commonplace, and Thorn (Ferguson) produced the worlds first all transistor colour TV's (the 2000 series dual standard 405/625). This was foillowed a couple of years later with the worlds first domestic use of a switch-mode PSU, in the 3000 series (625 only).
The 2000 had a reasonably sized mains transformer (as far as I can remember), the 3000 had a small C-core one, feeding low consumption parts of the set, and powering the SMPSU drive circuits. Neither were very much use for other purposes though
Set's normally used a live chassis with the incoming mains directly rectified to give 300V+ on the HT rail. Older sets used a halfwave rectifier (usually a metal one), with the chassis at neutral, or fully live, depending on the plug polarity (back when two pin plugs were still in use). Later ones used a bridge rectifier (new requirement from the electicity companies), so the chassis was half live, regardless of polarity.
By the time colour started in the UK transistors were commonplace, and Thorn (Ferguson) produced the worlds first all transistor colour TV's (the 2000 series dual standard 405/625). This was foillowed a couple of years later with the worlds first domestic use of a switch-mode PSU, in the 3000 series (625 only).
The 2000 had a reasonably sized mains transformer (as far as I can remember), the 3000 had a small C-core one, feeding low consumption parts of the set, and powering the SMPSU drive circuits. Neither were very much use for other purposes though
We had directly rectified a.m. receivers with a hot chassis -- the output was almost always a 50C5.
Maybe, I don't know for sure. In my younger years I would spend the day at the trash dump just taking things apart to see how they worked. Much to my parents dismay I would often drag home whatever I could fit on a bicycle. I acquired a 1950's vintage color TV in the late 1960's and spent about 2 years rebuilding it. It was the only color TV in my neighborhood. I remember about 30 people in my bedroom during the first moon landing that was broadcast in color. (1970)
I may have the exact dates wrong but it goes something like this:
Radios from the late 30's and 40's had 6 volt octal tubes and used a power transformer for all voltages. The tube line up was often 6SK7 RF amp (if present), 6SA7 Mixer oscillator, 6SK7 IF amp, 6SQ7 detector and 1st AF AMP, 6V6 or 6K6 Audio output, 5Y3 or 6X5 rectifier.
High end radios from the 40's and early 50's used loctal or miniature tubes and had transformer based power supplies. 6BA6 RF amp, 6BE6 converter, 6BA6 IF amp, 6AV6 detector - 1st AF, 6AQ5 audio output, 6X4 rectifier. If it had an external antenna connection, it usually had a power transformer.
Cheap radios often used octal or miniature tubes with the filaments all wired in series and a half wave tube rectifier powered directly from the line voltage. Octal - 12SK7-12SA7-12SK7-12SQ7-50L6 (or 35L6) and 35Z5. Miniature - 12BA6-12BE6-12BA6-12AV6-50C5 (or 35C5) and 35W4. These were known as the AA5 or All American 5 (5 tubes). Most did not have an RF amp so they used a 50 volt audio output tube. If an RF amp was present then it was a 6 tube radio and used a 35 volt output tube. The antenna was usually a coil of wire on the back panel.
TV sets followed a similar progression but the tube type numbers changed every few years as the manufacturers made better tubes.
At first they all had power transformers.
Then the smaller black and white TV's went to a series filament string with a voltage doubler for B+.
Then smaller B&W TV's lost the doubler and went half wave while smaller color sets went series string with voltage doublers.
Then most TV's lost the transformer. The bigger color sets used voltage doublers. Low powered circuitry (often the IF) went solid state.
Later many TV sets used 3, 4 or 5 tubes for the horizontal sweep and HV while everything else was SS.
tubelab.com said:
Were you my long-lost twin brother? -- except I had a Plymouth Valiant as the electronic trashmobile -- and the TV repair shops would just give the stuff away.
What do you do with all the left-over 6AU6's? I always find a spot for a left-over 6BE6 in 1960's era ham receivers.
tubelab.com said:
As a kid we used to play at a small tip on the edge of a local moor, in fact I drove past it just today - long filled in though.
If I was building something I used to walk to the tip (about a mile up hill) armed with a pair of cutters and a screwdriver, and a piece of paper on which I'd written down what components I wanted, and the colour codes for all the resistors written out 😀
We also used to get old bikes and ride them down the hill (on the road), 1 in 6 hill, no brakes, sometimes no tyres - makes you wonder how we ever survived?. Luckily in those days, cars were few and far between - we used to be able to play a full game of football (soccer to you) on the main road, 45 minutes each way, and never have to stop for a car.
Looking back now from been a TV/Radio service engineer for 38 years, the historic radios we used to smash up for parts when we were kids, it makes you want to cry.
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