We had a fairly scary situation the other day in our museum. An RCA 721 was one of several sets running in the display. After this particular set lost picture, we shut it off. But a minute or two later, we noticed that flames were coming out of the cabinet! Although it was a small fire, we had to use a fire extinguisher to put it out, and it was obviously an unsettling situation. We haven't done a full postmortem on the set yet, but according to the initial examination it appears that the filter caps shorted out and caused the power transformer to heat up. Possibly it heated enough to degrade the insulation on the wiring causing a massive increase in current, because the burnt primary leads seem to be the source of the fire. We're not sure yet, but we hope to figure out exactly what happened.

In all my decades monkeying with this stuff, I've never before heard of a case where an electrical fault, even in a 60+ year old piece of equipment, caused a fire. Smoke, sure. We all joke about the magic smoke. But fire?

These sets were made, of course, a long time ago, but I was under the impression that by that point in time things had been designed, especially by big companies like RCA, with safety during failure mode in mind. And I also seem to recall that in order to qualify for the Underwriter's Laboratory seal the equipment had to be designed to fail gracefully, i.e. smoke was acceptable but fire, if any, would be contained.

So I got to wondering, does anyone know how the design of this old equipment dealt with minimizing hazards during inevitable component failure? And has anyone else had the misfortune to actually experience an actual fire in an old piece of electronic equipment?

--Dave Sica

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Scary! I had a set with a resistor in the crt anode lead open and the arcing almost started the rectifier socket on fire. It was very close, the tv was running unattended at the time.
Now I NEVER leave old tvs or anything running unattended. If Im going to be out of the room for more than one minute I turn it off.

Since many of these sets were un-fused it's a miracle there weren't more fires, I guess they figured the 5U4 would blow and save the transformer, but if it's the transformer that's the problem I guess you're out of luck.

I too won't leave one unattended, I did accidentally leave a chassis and tube running on my workbench a few months ago while I ran an errand, luckily nothing happened and it was still playing when I returned.

Probably a fuse on the AC line before it enters the transformer would be a good idea, one big enough to run the set though is still big enough to cook the transformer though if it's not a dead short. A cheater cord arcing at the connector pins can also start a fire without drawing enough current to notice something amiss.

Reminds me of the time I fell asleep while watching Johnny Carson on my CTC-16 years ago and waking up to the smell of a burnt flyback and a blank screen. Fortunately, no fire started but it did melt the 3A3 socket cup a bit.

Maybe that was why those HV cages are so sealed up and unvented on RCAs.

And how many times have "you" fallen asleep in front of your set? Ok, at least don't fall asleep in front of something that's vintage!

My 5th grade teacher told me the story of her TV set catching fire back in the 50s. It was playing fine and she happened to wander away (as you do) for a moment or two. Next thing she knew flames were coming out of the back.

At least twice in years past the chassis of a set undergoing restoration at the Early Television Museum has caught fire. IIRC both were British prewar sets plugged into a 220 line, accidentally left on because the switch that killed 110 to the bench was a separate line. Good reminder not to get too casual with the old things.

I have noticed for old equipment that was designed for commercial/industrial use (jukeboxes, PA amps, broadcast equipment) and which was designed for 24 hr. a day use there is always fuse protection in the power line and usually additional protection such as a B+ fuse. The notable exception is Hammond organs.
However most consumer equipment seems to have no protection.

I always retrofit any old device I repair with a fuse, even table top plastic radios. The only ones I don't are series string radios with a tube rectifier as the rectifier cathode is designed to be fusible in case of a short and usually a portion of the rectifier filament acts as a fusible/surge resistor.

Also I don't let there be anything on the power line in the set before the fuse. If there are noise suppresion capacitors across the line I just remove them and have had no trouble.

I replace all electrolytic/paper capacitors and any old silicon rectifier diodes before using a piece of equipment. I have had too many failures of these old things from previous experience to trust them. One was a shorted capacitor or diode in a Harman Kardon A-300 amp which worked perfectly on original components for years but luckily had a fuse which blew when the short occurred to prevent serious damage to the power transformer.

I also have seen too many cases of burned/shorted wiring in places like Hammond organ tone cabinet connectors, and melted 5U4 tubes due to shorts where damage likely would have been minimized had a fuse been in the unit.

The only time I actually experienced a fire was a flyback fire in an RCA CTC-31 when I was a teenager. Everything inside the HV cage was burned and melted. Luckily there was no other damage to anything else but that was very scary.

Another potential problem can be (i am theorizing) when the enamel insulation on magnet wire degrades due to heat. I have had several motors in electric fans burn up and my theory on this is that the motors were overheating for some reason in use which led to the insulation breaking down to the point where a short finally occurred across the windings and burned them up. This sounds like the kind of failure which may have occurred on Dave's set.
If a motor has seized due to lack of lubrication and the windings look discolored, even if I can relubricate it and get it turning again I just replace it due to perhaps the increased possibility of a short.

God bless; you caught it!!! I hope you can save the set. As far as the cause, take a good look at the on-off switch. I had a '50 or '51 RCA (KCS49, IIRC), that had a B+ short, and the on-off switch began to arc at 20 amps, and set fire to the greasy wires. From there, it started up the inside of the wood cabinet front panel. I too got lucky and caught it, and saved the whole set only because the back was off, and the back of the switch is exposed in that chassis. I've also seen the on-off switch fail and flame up in CTC-16 non-remote sets.

Charles

Yikes! I used to intentionally over voltage caps scrounged from dead SS stuff to make them explode, and in addition to the mineral oil steam they would some times catch fire. I also once acidently cooked a DMM by measureing line voltage with the test lead connected to the(effectively shorted) 10A terminal and that almost caught fire(that scared the crud out of me).
Only time a TV ever smoked on me was when I variaced up my 9-t-246....No raster ,but all seemed well, and I wanted to test the sound as I was doing so I heared a sizzling sound and didn't make it to the switch before one of the papers let loose both wax and smoke.

You are lucky.

How many times have we seen sets brought back to life by replacing only what is wrong, NOW, and then having to deal with it again when something else dies?

I'm sorry the transformer cooked, but it should have had all of the electrolytics replaced, especially if it is being run regularly. I sure dont want a 5U4 to be acting as a fuse!

Almost none of my old electronics came with an inline fuse. Now, most of them do. I'd rather lose a fuse than lose a really hard to find transformer... like when I got my DuMont...
It's slowly being re-capped, and with each one, the sound becomes more clear, or, in the case of the last ones, I could hear the vertical sweep running... Still no HV, though...

I have had a few modern sets catch fire at work. One was an Akai plasma, and we taped it. It had a note on it "do not plug in, smokes". So we took the back off, whipped out the phone cam, and taped it. It was a mylar cap, had a nice white arc going, then caught fire.

I had a Philips LCD inverter with a bad solder joint arc bad enough to ignite the circuit board.

These were all burned under controlled circumstances. But it makes you think about the unfortunate times were these TVs burn when nobody is around to put them out.

I have noticed for old equipment that was designed for commercial/industrial use ... there is always fuse protection in the power line and usually additional protection such as a B+ fuse. The notable exception is Hammond organs.

I've heard this is because Hammond got sick of all the warrenty calls related to blown fuses. :sigh:

I have had a few modern sets catch fire at work. One was an Akai plasma, and we taped it. It had a note on it "do not plug in, smokes". So we took the back off, whipped out the phone cam, and taped it. It was a mylar cap, had a nice white arc going, then caught fire.

I had a Philips LCD inverter with a bad solder joint arc bad enough to ignite the circuit board.

These were all burned under controlled circumstances. But it makes you think about the unfortunate times were these TVs burn when nobody is around to put them out.

I wasn't even thinking about modern stuff... Switchmode supplies routinely fail and burst into flames, as there isn't often enough current load to blow any fuses. CFL light bulbs are major house fire causes, as are cellphone chargers. Cheap, thin plastic + high frequency power supplies = fire threat. Period. We have a 35-foot tall Christian cross on the hill just west of our house (a reproduction of a cross which was put there in the 1700s as a landmark for Catholics traveling from Los Angeles to Mission San Buenaventura). We maintain it, and I replaced the incandescent light string with LED. LumiHose. Guess what: I got home late last Monday night, noticed it was out, and found the power module all burned up beyond recognition. Luckily the fire was confined, and didn't take hold of the wooden cross itself. That could have, in addition to being dangerous, been incredibly embarrassing. We just happened to be having a friend over that night earlier, who is Black. He got a good laugh when we told about it, but it's not funny really.

Charles

On the CFL note, I have one in a fixture in the house here. I have left it turned on for several years, and it finally died. When it did, it got the base so hot that it smoked, burning dust. It's inside of a metal casing, but it could have set my old wooden house on fire! I was home when it happened, and when I smelled the burning hair smell (I have 3 useless kitties here, so theres cat hair around) I ran and turned off the fixture.

The longer I have CFL's, the more nervous I am. I use them at work, too, and several have gotten hot enough to trip the overheat switch inside the light fixtures... and these fixtures were set up for incandescent lighting initially! One sent sparks down to the floor! They were "Lights Of America" branded. We use Sylvania's now.

Watching my CTC-4 right now. I left it unattended for a couple of hours once, then thought about what I did.:scratch2: Now I won't leave it for more than a couple of minutes, and even that seems too long.:nono: Great chassis, in super condition, with very low hours when I got it, but these precious old relics can't really be trusted the way they could have been when they were new. Same with the B/W sets in the collection. :yes:

On the CFL note, I have one in a fixture in the house here. I have left it turned on for several years, and it finally died. When it did, it got the base so hot that it smoked, burning dust. ...
The longer I have CFL's, the more nervous I am. I use them at work, too, and several have gotten hot enough to trip the overheat switch inside the light fixtures... ...

I've salvaged electrolytic caps from dead CFLs that did not fail so spectularly. Got 2 15uF at 250V 105C caps from one yesterday. Yes, I tested them, as I know these can lead hard lives. The bulb blew one of its filaments, and it looks like the electronics were fine. And got 4 1N4007 diodes out of it too, tested fine.

The CFLs have a fusable resistor that opens when it burns. When the bulb hits end of life the current increases till the switcher burns up, basically their failure mode is smoke.
We had a power surge here several years ago and all the CFLs that were on at the time basically exploded into sparks and flame.
CFLs are bad news, do not leave unattended unless they are contained in a fixture.

I worry reading this not so much as if I fall asleep with my old Magnavox on (which I do often-- oops (at least the converter box shuts off after two hours and the raster on the screen is usually loud enough to wake me up) but more because I have a collection of old electric clocks plugged in thru out the house, every once in a while I'll hear one running a little loudly as if it needs more oil, and they do get hot to the touch running continuously...

I do a lot of restorations for other people, and one modification I always do is to put in a line fuse. Stories like this one make me glad that I do. I also advise people never to leave antique sets running unattended.

I saw a newspaper article from Germany a few years ago where a house fire was caused by an antique radio. German radios usually had a line fuse, so even that will not provide 100% protection.

We had a traded-in record player in the shop one time, a cheapie 'portable' with crystal cartridge, 50C5, 35W4 and motor winding in series with the heaters, and no fuse. Filter cap was a typical cardboard tubular 50/30-150V, and it was overheating. Since the phono was basically junk anyhow, the decision was made to give it the run-to-destruct test. In 15-20 minutes or so the cap was bubbling and smoking, and then caught fire, the flame augmented by the waxed cardboard. The 'fusible' link in the 35W4 never let go.
And to think if that were in someone's house and left running unattended.

And there was that big flap with RCA CTC-25 color sets whose AC switches were catching fire and a few houses even got burned down. (Possibly some CTC-16s and 17s were involved, but much more rarely.) There was a big field refit program where the factory sent all service dealers refit switches that couldn't arc. We refitted a mess of 'em preemptively.

It can never be over-emphasized: Never, ever leave a vintage color set, B&W set, radio, or even a phono running unattended. Not even for a minute.

Some years ago (10?) I left my 1955 Magnavox Regency Phonograph (with all it's original caps) plugged in and turned on for a day or two, I finally realized it was on because it heard a little bit of static coming from it.
Fortunately nothing happened but it scared me a bit.

I've had a number of Zenith 9-160 modules where power supply connections caused severe scorching of the card board undereath and some cabinet damage. The flameouts I've seen where usually a fire gets going were big early, (200+ watt per channel) solid state amplifiers. The emitter resistors explode into flames when the output transistors short. I sat and watched one at a customers house burn on one channel and then the other channel after it burned a while. The customer was horrified.....
There was no real danger of catching the house on fire as it was on a custom stand that prevented anything under burning. It was weird entertainment.

Zenith26kc20 makes a good point...those early SS monster amps can cause many fires...one way they did it was to 'go DC' and set the woofers in the loudspeakers ablaze....NOT good! Thinking of Hafler, Phase Linear, Sansui, and others.

I make a point of never leaving my tube gear on when I'm out, but I have done it (modern hifi amp mostly, a Rogue Audio integrated EL34) but then again i retrofitted the stereo cabinet to have a 12v computer fan whenever the amp is lit... and the thing has 6 fuses total...one per output tube, a b pos fuse and a main fuse.

As far as the tv's, i never leave em on since my grandma used to tell a story of their tv going on fire as my grandpa was asleep in front of it one time..."hey why the hell are you making toast in the middle of the night?!" ---:sigh::thumbsdn: It was an un-identified early 70s color set...probably a hybrid

I do a lot of restorations for other people, and one modification I always do is to put in a line fuse. Stories like this one make me glad that I do. I also advise people never to leave antique sets running unattended.
I saw a newspaper article from Germany a few years ago where a house fire was caused by an antique radio. German radios usually had a line fuse, so even that will not provide 100% protection.

I always put in a line fuse. Also a three conductor grounded line cord. Some concessions to strict "originality" just seem obvious to me, especially when the set will be used by a non-technical person. One thing I *usually* do when restoring a vintage set (although sometimes I manage to forget) is to break the center tap connection to ground on the power transformer and install a small fuse in the circuit. The reasoning, as I was taught, is that an overcurrent in the B+ can damage the power transformer without drawing enough current to blow a fuse in the primary. I usually install a fractional amp fuse greater than or equal to about twice the maximum design current draw. I've never figured out how to account for the surge current as the filters charge, but I've never had a problem with that. Perhaps a timed relay that shorts out the fuse for a few seconds when first powered on then opens would be a good enhancement. But I've always been taught that a line fuse wasn't foolproof protection.

I've salvaged electrolytic caps from dead CFLs that did not fail so spectularly. Got 2 15uF at 250V 105C caps from one yesterday. Yes, I tested them, as I know these can lead hard lives. The bulb blew one of its filaments, and it looks like the electronics were fine. And got 4 1N4007 diodes out of it too, tested fine.

I wrote an article a while back about this for our club newsletter. People were surprised that they could get "free" restoration parts this way. The caps rarely seem to fail in a CFL circuit. They make great filters for AA5 receivers. The diodes are useful items too, if you can deal with the short leads.

But CFL fixtures have been sort of "exhibit A" for me in terms of contained danger. I've had any number fail (virtually all of them far sooner than the claimed life span!) but although some of them smoked, and most of them scorched the housing of the base, none of them failed with any external sparking or flames. Likewise with any previous vintage electronic equipment failures I've seen. Seeing how many stories you guys have about fires makes me realize I've just been lucky.

I "always" turn off vintage equipment when I'm done with it, but of course there've been times when I forgot and left a radio or record player, or worse yet a TV or a piece of test equipment (especially easy to forget) on overnight. Like I said, I guess I've been lucky. I guess we're gonna fuse all the working artifacts on display in the museum. Now just have to figure out how to account for human failure, the "forgetting" to turn it off part...

ive only watched 2 CFL lamps fail. one of them failed with open filament, watched the opposite filament start glowing, then quit. that was it..

the second one was working and POP, smell of carbon/sulfur and it went out. the ballast driver transistor had shorted/blown.

Then ive seen those cheap chinese flea market ones fail in short order, disassembly has revealed those capxon caps popped.

I just remembered an ammusing incident from a few years back.

I had bought a cool looking 60's GE toaster with a mini oven on the bottom at a garage sale a few months maybe a year back from this incident. It was around 8 years back, and I was about 12. We were running late for picking Dad up at the airport, and Mom gave me two options for fixing my self a snack (or was it breakfast), and the more apealing one involved draging out the toaster (which had been put away for some reason porbably related to trying to sell the house) well I set it up and ran it. The wireing in the kitchen buzzed ( granted this was an old house with very old wireing and I could hear the wireing buzz when every thing was turned off sometimes, but this was much louder than normal). The Toaster finished toasting while I waited impatiently (and somewhat nerviously) watching it, and as I was waiting for it to cool down enough for me to retrieve my meal the buzzing continued.....And suddenly POP! PFFSFSFSFSSFSSSSSSH! The cord exploded into a crimsion flame that was a dead ringer for the morning glory sparklers my friends and I would light on summer nights. Along with the flame there were sparks all of which came from the cord at the point that it entered the molded on plug. My first reaction after the I realized what was hapening (I feel was very brave) I grabed the cord and yanked it out of the outlet! It was a miracle the plug came with as one of the wires was completely evaporated from the plug to about 1/4" away, and the cord end of the melted lead had the conductor exposed. The strands at the exposed end had melted together and fused for about 2mm!

Of course the kitchen fuse never blew. :roll:

I had just changed the original outlet when we made some minor renovations to the kitchen, and I had to change the damn thing again after that because of the char marks the fire (explosion?) left on the new plastic outlet! Grr.

I supose it could have been worse though.....

I have a vintage 1981 TV set in the back room, not as vintage as 40s, 50s, and 60s stuff, but it's running constantly 24/7 for over a year now, and has given no problems..

One thing I *usually* do when restoring a vintage set (although sometimes I manage to forget) is to break the center tap connection to ground on the power transformer and install a small fuse in the circuit. The reasoning, as I was taught, is that an overcurrent in the B+ can damage the power transformer without drawing enough current to blow a fuse in the primary. I usually install a fractional amp fuse greater than or equal to about twice the maximum design current draw. I've never figured out how to account for the surge current as the filters charge, but I've never had a problem with that. Perhaps a timed relay that shorts out the fuse for a few seconds when first powered on then opens would be a good enhancement. But I've always been taught that a line fuse wasn't foolproof protection.

Keep in mind Dave that unlike a solid state rectifier, the emissions on a tube rectifier will come up slowly, so there really is no power on surge to the filter caps. Going twice the rated current sounds just about right.

Darryl

Many years ago I had Sherwood tube type FM tuner that was on when I fell asleep.

The next morning I awoke and was dizzy and nauseous from the fumes from the burned out power transformer. The stench was awful !
Why it burned out was never determined.


BE CAREFUL OUT THERE !

Pallophotophone

The CFLs have a fusable resistor that opens when it burns. When the bulb hits end of life the current increases till the switcher burns up, basically their failure mode is smoke.
We had a power surge here several years ago and all the CFLs that were on at the time basically exploded into sparks and flame.
CFLs are bad news, do not leave unattended unless they are contained in a fixture.

I have a table lamp in which I installed a CFL about five years ago. The lamp still works. I usually leave it on from sundown until midnight or a bit later. The bulb hasn't caught fire yet. I had another CFL in my other table lamp, but it burned out (no smoke) after about five years (!). I know someone who had two CFLs in table lamps in her house; the bulbs simply burned out after several years or otherwise quietly failed.

BTW, I think the design of CFLs must be improved, and quickly, as the deadline for the phaseout of incandescent bulbs in the US is less than a year away. When CFLs are the only type of light bulb available will be no time for people to worry about these lamps setting their homes afire. I can only hope the CFLs made from 2012 forward are designed not to catch fire if they short or otherwise fail. I am surprised CFLs with the fusible resistor even smoke when they go bad -- I would think once the fuse resistor opens, the lamp would go out immediately, period, with no danger of fire, since once the resistor opens the lamp no longer receives power.

The only other thing I can figure is that the fuse resistors in these lamps are placed such that the lamps are still getting power when the fuse goes, which makes absolutely no sense. Also, I wonder why the house fuses do not blow (or circuit breakers do not trip off) when these CFLs fail for any reason. (I have a feeling that the fuse[s] on the kitchen circuits in Electronic M's residence must have been overrated if it or they didn't blow when the short occurred in his GE portable oven; after all, any short bad enough to cause the cord or plug to become red hot and burst into flames is extremely serious -- the fuse should have blown at once.) Again, the only thing that makes sense to me is that the bulbs do not draw enough power, even shorted, to open the breakers, even though a shorted CFL is like any other short in a light socket or anything else plugged into a wall socket; it should blow the fuse immediately, unless, of course, the short is very high resistance -- which I cannot see occurring in CFLs. Once one of these lamps shorts, it is, or at least should be, almost always a dead short across the AC line, which will trip any breaker on that circuit if such breaker is operating properly.

I grabed the cord and yanked it out of the outlet! It was a miracle the plug came with as one of the wires was completely evaporated from the plug to about 1/4" away, and the cord end of the melted lead had the conductor exposed. The strands at the exposed end had melted together and fused for about 2mm!

Of course the kitchen fuse never blew.
Did you check the fuse box to see if someone mighta put over rated fuses in? Or coins to bypass the fuses? That's been done more times than one might think.

most of the fuses were newer (I tended to do stuff that would blow them when I was younger than that. No coins, slugs, or tokens were ever used to replace a fuse by my folks, and none were ever found to my knowledge.

I was told a story by my folks that when they first moved in the lights were dim, and would flicker, and after a tornado which took out a large tree in the back yard which in turn took down the over head utility wires, a utility worker came in to inspect the fuse box, and discovered that the main cartridge fuses had been replaced by the previous owners with UNDER rated replacements that were limiting the power supplied to the place.

I have used CFLs for over 10 years and have not seen a failure that involved more than a small amount of burned resistor smell in the room. By last count, I have about 30 of these devices in my house.

For grins, today I cut open 3 failed units (I save them for recycle because of the tiny amount of mercury in each tube).

In the oldest unit (which had been in service since 4/28/01), a small fuse (marked 4A) was the first component in the circuit before a cap and the diode bridge. In two newer units, a small 1/4 watt 4.7 ohm resistor and a coil wound with very small wire preceded the cap and diode bridge. In one unit, the resistor was open, in the other (which was replaced because it had started to flicker somewhat, when cold) the "fuse" resistor was ok. Nothing that I found in the units that I autopsied gave me any cause for concern.

I also did a "flame test" (using a match) on small piece of plastic from one of the bases and found that it only melted, and did not appear to support combustion after the match was removed.

Perhaps some earlier units or obscure brands were not fused, I don't know! Mine were marked "GE" , "N:Vision" and "Commercial Electric".

jr

Just found a Sylvania and took it apart... it had a 3 Amp glass fuse covered with shrink fit between the board and the center contact of the screw-in socket. I like this design, as it possibly could provide somewhat better protection in the case of a over-voltage line spike, which might create a charred path if the fuse or fuse resistor were mounted on the circuit board.
jr

I have noticed for old equipment that was designed for commercial/industrial use (jukeboxes, PA amps, broadcast equipment) and which was designed for 24 hr. a day use there is always fuse protection in the power line and usually additional protection such as a B+ fuse.

During the 6PM News I ran camera at an ABC TV affiliate in Florida. I saw an orange flicker down to my left which turned out to be the flyback in an RCA B&W Studio Picture Monitor burning brightly.

I dragged the beast by the power cord out of the studio and hit it with the fire extinguisher. The important point I made in my report was that the monitor had a 0.25 amp fuse in the B+ line to the flyback and a 2.5 primary line fuse. Both were the right value and NEITHER FUSE BLEW during the excitement.

So much for fuse safety.

Cliff

the main cartridge fuses had been replaced by the previous owners with UNDER rated replacements that were limiting the power supplied to the place.

Fuses "limit the power supplied" in one way and one way only: they blow. A fuse is an all or nothing proposition. Something else must have caused the flickering.

A fuse is an all or nothing proposition. Something else must have caused the flickering. Agree. In an old house, there are lots of mechanical splices that oxidize and cause intermittent circuits. In one old house I lived in, one day a table lamp slowly went out, then flickered low. I went in the basement and traced the knob-and-tube wiring from that outlet to a friction-taped splice where I could see a blue glow through the loose tape! That got taken apart and soldered.

Or coins to bypass the fuses? That's been done more times than one might think.

Reminds me of the dorm I lived in back at Syracuse U. No, no fuse panels, they used circuit breakers. But they had in the stairways wall fixtures that held light bulbs upwards. And the students would often steal the bulbs to replace burnt out ones in their dorm rooms, leaving empty sockets. Then some rocket scientists thought it'd be fun to drop a penny into the live but empty light bulb sockets to make some sparks. ZZZAAPPPPPP!. THe college eventually replaced the fixtures with vandal proof enclosed plastic fixtures.

I have used CFLs for over 10 years and have not seen a failure that involved more than a small amount of burned resistor smell in the room. By last count, I have about 30 of these devices in my house.

For grins, today I cut open 3 failed units (I save them for recycle because of the tiny amount of mercury in each tube).

In the oldest unit (which had been in service since 4/28/01), a small fuse (marked 4A) was the first component in the circuit before a cap and the diode bridge. In two newer units, a small 1/4 watt 4.7 ohm resistor and a coil wound with very small wire preceded the cap and diode bridge. In one unit, the resistor was open, in the other (which was replaced because it had started to flicker somewhat, when cold) the "fuse" resistor was ok. Nothing that I found in the units that I autopsied gave me any cause for concern.

I also did a "flame test" (using a match) on small piece of plastic from one of the bases and found that it only melted, and did not appear to support combustion after the match was removed.

Perhaps some earlier units or obscure brands were not fused, I don't know! Mine were marked "GE" , "N:Vision" and "Commercial Electric".

jr

I wish I had the same experience, and I'm glad yours haven't acted this way, but PLEASE be mindful that this can happen. These pics are of the one which falied in our barn, and had it not been for the fact that the barn is built of asbestos siding and a steel roof on a concrete floor, we'd have lost it, and since this happened during a Santa Ana Wind, it likely would have taken out other buildings and a few hundred acres of wildlands. The County of Ventura, CA fire marshal put out a public warning about CFL bulbs, and stated that they should never be used in lamps with paper or cloth shades, and never in recessed ceiling "can" lights.

Charles

http://i104.photobucket.com/albums/m174/kx250racer/BurntBulb3.jpghttp://i104.photobucket.com/albums/m174/kx250racer/BurntBulb2.jpg

The only place I have these is in the lamps outside the front door - the kids inevitably slam the door and CFLs don't have weak filaments to break. After reading this thread, I think I'll use rough-service shop light bulbs when replacement time comes, and paint them amber myself.

I wish I had the same experience, and I'm glad yours haven't acted this way, but PLEASE be mindful that this can happen. These pics are of the one which falied in our barn, and had it not been for the fact that the barn is built of asbestos siding and a steel roof on a concrete floor, we'd have lost it, and since this happened during a Santa Ana Wind, it likely would have taken out other buildings and a few hundred acres of wildlands. The County of Ventura, CA fire marshal put out a public warning about CFL bulbs, and stated that they should never be used in lamps with paper or cloth shades, and never in recessed ceiling "can" lights.

Charles


Yikes! :eek:
Thanks for the heads up! interesting comment about the fire marshal as well. Could you tell from the charred remains if the lamp was indeed fused?
jr

I know a fuse is either a short or an open, and what my folks told me did not make sence to me either. It is possible that the fuse was mechanically too small and was making poor contact, or there was another issue the guy corrected and did not tell them about.

Wow that CFL is really toasted.
There is an office in my school that is usually left open that has a desk with a CFL that burned at the points the tube enters the base. I think it is on permanent display as it has sat there for over 1 year now.

Reminds me of the dorm I lived in back at Syracuse U. No, no fuse panels, they used circuit breakers. But they had in the stairways wall fixtures that held light bulbs upwards. And the students would often steal the bulbs to replace burnt out ones in their dorm rooms, leaving empty sockets. Then some rocket scientists thought it'd be fun to drop a penny into the live but empty light bulb sockets to make some sparks. ZZZAAPPPPPP!. THe college eventually replaced the fixtures with vandal proof enclosed plastic fixtures.
That's no fun! I used to use a small bit of steel wool, stuffed in the sockets. It would produce a shower of sparks when it was energized.

Guess you shouldn't leave your Sony Brevia playing unattended, either. Sony just recalled 1.6 million of them due to fire risk:

http://www.bloomberg.com/news/2011-10-12/sony-starts-recall-of-1-6-million-bravia-televisions.html

Phil Nelson
Phil's Old Radios
http://antiqueradio.org/index.html

Dave, which 721 went up in smoke? The TS or the TCS?

Lee:smoke:

Lee,

It was a TS that a collector had loaned to the museum. We don't have a TCS. My own 721TS which had previously been on display had been sidelined with a vexing audio problem.

--Dave

Lee,

It was a TS that a collector had loaned to the museum. We don't have a TCS. My own 721TS which had previously been on display had been sidelined with a vexing audio problem.

--Dave

Aren't you at the ETF? Yeah you do:

http://www.earlytelevision.org/rca_721tcs.html

"Audio Problems" seem to be the norm with early RCA post war TVs. Especially output levels. My 630TS has good output, 721TS fair, 721TCS fair to good.:smoke:

I have repaired over the years a number of post war RCAs from the 630TS onwards. The problem of low audio on the post war RCAs I believe stems from audio alignment: when properly aligned, the sound is fine.

I have found the video alignment generally poses less of a problem than the sound. This may be due to the the narrower bandwidth for the split sound audio IF which diminishes level when the alignment drifts over the years.

Aren't you at the ETF? Yeah you do:

http://www.earlytelevision.org/rca_721tcs.html

"Audio Problems" seem to be the norm with early RCA post war TVs. Especially output levels. My 630TS has good output, 721TS fair, 721TCS fair to good.:smoke:

No, Lee. I do get to the Early Television Convention every year, but only as a visitor. The temperamental 721 I was referring to was at our local museum, the New Jersey Antique Radio Club's "Radio Technology Museum (http://infoage.org/rtm.html)" at InfoAge. Sorry that wasn't clearer about that before. I know that several of Steve's sets have smoked over the years, including some of the prewar ones. I was there the day the TT5's power transformer bit the dust, but thankfully he's had only smoke as far as I know.

Dave - To answer your original question. I have a 721TS on the bench right now and underneath the chassis I can see inside the bottom of the transformer housing what looks like asbestos. So I am assuming that inside the metal transformer shell the whole unit is likely wrapped in it. It could be the field coil in the speaker is wrapped in it also. (I noticed that on an Admiral 20x1 I am working on - likely I will replace it with a PM speaker anyway - speaker vibration and asbestos - NOT perfect together - but I digress.) So RCA did build some fire protection into this tv. BTW be careful ripping into those things for a post mortem.

I once heard from an engineer that once worked at Zenith, that Zenith kept statistics on house fires started by TVs and what brand the TV was. I believe he said that GE was the most common and Zenith the least. Probably a lot to due with Zenith's metal chassis construction.

I don't have any good answers but my '49 Sylvania console had an unusually high number of fuses. It was pretty well protected that way. However, the UL sticker on the cabinet was inked out. The same is true for a '49 tabletop Sylvania that I have. It seems that they were expecting UL approval but never got it.

I remember my mother noticing the UL sticker being inked out and being concerned about it. It never caught fire, but it went through a couple of seleniums in its early life.

John

We had a fairly scary situation the other day in our museum. An RCA 721 was one of several sets running in the display. After ...

big companies like RCA, with safety during failure mode in mind. And I also seem to recall that in order to qualify for the Underwriter's Laboratory seal the equipment had to be designed to fail gracefully, i.e. smoke was acceptable but fire, if any, would be contained.

So I got to wondering, does anyone know how the design of this old equipment dealt with minimizing hazards during inevitable component failure? And has anyone else had the misfortune to actually experience an actual fire in an old piece of electronic equipment?

--Dave Sica

.

Leaving a tube TV on is a risk with today's line voltages running 120-125. Before the power company replaced our pre-war pole transformer, I had 114-117 volts and my old stuff did not mind. Now I need a variac or 10-15 ohm, 10W series resistor to buck the voltage. I had a RCA CTC38XAH set w/a switch for "high line" on the power transformer primary.

When I was 12, I had a Fisher HiFi receiver chassis (mono 2xEL85/6BQ5 outputs) that I used for sleepy time FM listening. I woke up one morning to smell of toasted power transformer. I plugged sets into a clock radio sleep timer after that!

This was a concern I had with my tube amps. Dating from the late 50's, I assume the transformer is wound for 115 vac. I should also mention whoever rebuilt them didn't add a fuse to the chasis...so they literally have 0 protection.

I run them on a power strip I equipped with a 5amp circuit breaker. But I will say I've put a good number of hours on them (one day last week they were on and running for about 11 hours) with no ill effect.

Maybe its because the transformer is pretty beefy. But its got me wondering if I should look in to a way of dropping the line voltage a little. Luckly, my mains supply stays steady at 120vac so I don't have to worry about it spiking any higher.


Sent from my Samsung Intercept with Tapatalk

Funny, I used to get 114-115VAC at my outlets and I complained to the utility. New pole-transfo and I see 118-121 now.

For my audio/hifi gear I need at least 115 at all times. To keep the output stage of my EL34B's biased properly. And because it's a drag to set-up a tube color tv at 114 and then come back when it's at 119 and have to re-check all the user controls.
Needed some powerline-stability.!