Fire!

[Dave S]

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

[M3-SRT8]

Originally Posted by Dave S

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.

[Penthode]

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.

[Dave S]

Originally Posted by M3-SRT8

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.

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" 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.

[Nuke]

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.

[Spinning Head]

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.

[jeyurkon]

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

Originally Posted by Dave S

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

.

[DavGoodlin]

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!

[dewdude]

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.


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[zenith2134]

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.!