Live chassis.

[colly0410]

I know that British TV & wireless makers loved live chassis in days gone by, but did other countries makers love them so much? Did any country have an outright ban on live chassis?

[ppppenguin]

Widely used in the US, and with less attention to safety. Presumably due to the lower mains voltage.

I'm sure Synchrodyne with confirm the situation in the antipodes where I think that live chassis was rare and possibly illegal.

[Jayceebee]

I thought they were illegal in Australia but apparently not, definitely rare though. See the R2M chassis.

http://members.iinet.net.au/~cool386/baird/baird.html

John.

[ppppenguin]

That article says a lot about live chassis in Oz. For example:

Aside from that, live chassis radios and televisions are against the Australian culture of having an isolated and always safe chassis which can be earthed. Hence, they were intensely disliked by many servicemen. In fact, the R2M was the only live chassis Australian made television since the late 1950's, when even Ekco changed over to a transformer isolated design. Few live chassis sets existed in Australia. Ekco was the most popular and well known, but there were some early portables made by Admiral, Astor, and Pope Motorola.

To placate the conservative serviceman, the R2M is fitted with two neon lamps to indicate if the chassis is connected to the live or neutral. It's quite an ingenious idea which would have minimal increase to the cost. The mains earth is connected only to this warning circuit, and in the case of 17" portables, to the earphone socket as protection should the speaker transformer insulation fail. As a rental set, only the company technicians would be working on the sets, not servicemen at large. Thus, the live chassis work would be fairly confined to a few. For anyone with a phobia about live chassis equipment, the obvious solution is to use an isolating transformer.

[Terry]

I was fascinated by this:

... to adjust linearity a shorting sleeve is fitted to the neck of the CRT. ... This type of linearity control is apparently a Thorn invention.

I've never heard of this before and I've been trying to remember if I've ever come across a 110° tube without the shorting sleeve.

In my mind, the 110° CRT and the sleeve both arrived together - in which case, who did invent the idea as no other manufacturer would, initially, have been able to copy an idea which, I'm sure, appeared in every 110° set at the same time.

[pwdrive]

Some American receivers had one side of the mains connected to a busbar, the busbar being "isolated" from the chassis by a capacitor.

Lawrence.

[Terry]

In my mind, the 110° CRT and the sleeve both arrived together ...

Wrong!


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I've just glanced at the circuit diagrams of the Bush TV105/115 & 125 series sets and all three have a conventional Line Linearity control!

[Geordie McBoyne]

A 1953 Philips (Holland) publication describes the design and construction of a 625 CCIR television receiver in which we find all the familiar series heater chain valves are employed. The Philips "World Series" valves, EF80, ECL80, PY81, PY81 etc.
"Live" chassis technique TV receivers were commonplace in Continental Europe.
In fact 0.3amp heater versions of valves not used in UK made TVs were made. Examples are the PL95 and PLL80 audio output valves.
However, parallel heater supply television valves were available for use in high quality receivers. EL36, EL504, ECL85, EY88 etc.

Geordie McBoyne.

[ppppenguin]

The 6.3V valves were also used in professional video monitors where live chassis was not feasible. I think the EL509 colour LOP valve is rather liked by audiophools for transformerless amps.

[Geordie McBoyne]

I think the EL509 colour LOP valve is rather liked by audiophools for transformerless amps.

And also in single ended audio output stages. It was found when the audio signal is supplied to the screen grid of the EL509 a linear transfer characteristic is possible. The screen grid does however require the signal drive from a cathode follower which uses a high power valve such as an ECL82. Actually, the EL509 isn't a true pentode and is in fact a beam valve designed around the Philips "cavitrap" principle. Likewise the PL500/504.

Geordie McBoyne.