Polarized AC plug on sets with a VRT

[Jon A.]

My Sylvania with the E48-2 chassis uses one. What's the point of this? I thought all sets with a VRT have a cold chassis.

[Electronic M]

Here in the states it seems like polarized plugs on TVs became mandatory in the early 70's. Some brands (Sears) seemed to pick it up across their TV line much earlier, others started with hot chassis sets, and later did all sets.

[zeno]

No point to it. Although they seemed to become standard in the
late 70's on almost anything. No point on one
with a hot bridge either as chassis is always hot. Probably laws.
On the service end if it came polarized it went out polarized.
What happened at home to it stayed at home.

BTW one of my favorite pass times is filing plugs, ripping off
safety tags and of course furniture tags. See feb 1972 cover here.

http://lampoon.rwinters.com/Lampoon1972.htm

73 Zeno
LFOD !

[dieseljeep]

Originally Posted by Electronic M

Here in the states it seems like polarized plugs on TVs became mandatory in the early 70's. Some brands (Sears) seemed to pick it up across their TV line much earlier, others started with hot chassis sets, and later did all sets.

It's all about U/L approval and purchasing-inventory issues. Instead ordering two different types of A/C cords and interlock connectors, they just ordered one type. Also minimized installing the wrong cord on the various models.
On a side note: I always wondered why Motorola used some 3 volt tubes connected in series on some of their sets, even though the set used a power transformer and 5U4.
It stated in the Motorola Service News that the purpose was quantity buying, as they built as many or more series-string, transformerless sets, than the transformer models.

[Ed in Tx]

When there's a high value like a 1 to 3 meg Ohm resistor or a capacitor from one side of the AC primary to the chassis for passing static electricity to "ground", you would want the side with the resistor or cap to the chassis on the neutral side.

[Electronic M]

Originally Posted by Ed in Tx

When there's a high value like a 1 to 3 meg Ohm resistor or a capacitor from one side of the AC primary to the chassis for passing static electricity to "ground", you would want the side with the resistor or cap to the chassis on the neutral side.

I've seen some Zenith product where they put that resistor on the transformer side of the switch so when the switch is on a different side is effectively connected to the resistor than when it is off.

[jr_tech]

For the purposes of bleeding off a static charge , wouldn't *either* side of the power line provide a nice low impedance path to ground?

jr

[Jon A.]

I noticed a 2.7 meg ohm resistor in my U-Matic player going from neutral to the chassis, and that uses a grounded plug.

[centralradio]

I remember back in 1980 when I hooked up a Sears 19 inch up to the cable and a huge spark came from the connector.More likely it did not have a polarized plug on it or it was mis-wired .I turned the plug and it was ok.I still have the set somewhere.I'll take it out and look and see if I rewired it with a new polarized plug.

[Findm-Keepm]

Originally Posted by centralradio

I remember back in 1980 when I hooked up a Sears 19 inch up to the cable and a huge spark came from the connector.More likely it did not have a polarized plug on it or it was mis-wired .I turned the plug and it was ok.I still have the set somewhere.I'll take it out and look and see if I rewired it with a new polarized plug.

Or the outlet was mis-wired. Talk to home inspectors - the DIY crowd is very ignorant to AC polarity. I've seen mis-wired sockets in homes, businesses, barracks, and even at a radio transmitter site - Every 7 hours or so, a breaker would trip, and a tech would be dispatched to reset the breaker. The tech got overtime, so troubleshooting wasn't to his benefit. Two installers (one is a good friend) got a fright when their equipment smoked, and they did the troubleshooting. Found three circuits with some sort of polarity or phasing difference. The techs' overtime dried up, and after some explaining, so did his job.

In the early days of hot chassis and grounded test equipment, I saw scopes get eaten, a CTC101 with a vertical problem become a non-economical repair, and two outlet covers get arc'ed to - the chassis was slid around, contacting the grounded cover.

[zeno]

The common reason antenna jacks went hot was there is
an isolation unit on them. There was a common one used
in Jap sets that would often get hit with lightning &
get blackened or blow apart. Almost always when on cable box.
That gave a solid path to ground. The newer the set the more
extensive the damage, often a total loss.

73 Zeno
LFOD !