11-07-2017, 04:59 AM
(10-07-2017, 07:53 PM)ppppenguin Wrote: In some countries, such as Australia, live chassis was rare. Was it illegal there? In the UK at least it was absolutely standard in TVs for several decades. A TV would need a big mains transformer and the magentic field could affect the picture. The Thorn 2000 I'm working on is a rare exception. It has a hefty mains transformer carefully designed to have low external magnetic field. Heavy and expensive but the only viable way in 1967 for a solid state colour set.
The same was true of New Zealand. Radio and TV receivers for the most part had double-wound power transformers. I am not sure if the live chassis approach was actually illegal. But I did hear once or twice that some of the electricity supply authorities prohibited or at least strongly discouraged such equipment because it put DC on the power supply system. But for whatever reasons, the Australian and New Zealand setmakers chose the “high road” where power supplies were concerned.
That power transformers might be deleterious to TV receiver performance was I think one of those potential but not actual problems that the UK setmakers (or their supporters) made more of than was warranted in an effort to justify their use of corner-cutting implied by live-chassis power supply arrangements. NZ TV receivers seems to work just fine despite their inclusion of power transformers. And this applied to derivatives of European models, such as the Philips K9, whose original versions lacked this feature.
Also, as far as I know some of the UK setmakers offered industrial receiver/monitor versions of their domestic models that did include double-wound power transformers, and presumably these were to some extent sold into markets where picture quality was more critically analysed than in most of the domestic market. So, there were obviously no insurmountable difficulties. Occasionally that good practice spilled back over into the domestic market, as with the Decca Professional 23. (Which also had line-gated AGC on both systems, something that some of the lazier setmakers would have argued was too complex/too difficult for the domestic market.)
From there it is not a major leap to suggest that in perpetuating the live chassis technique for receivers that were only for operation on AC power supplies, the setmakers were to some extent treating their customers with contempt in respect of safety. One may of course invoke caveat emptor, but then the typical customer for a domestic TV receiver would not have known enough to ask about power supply safety. Perhaps had one or two setmakers used isolated power supplies and extolled their virtues, things would have been different. And were the “consumer” groups mute on the topic? For example, a good write-up in “Which” that in conclusion came out against live-chassis receivers might have stirred things up a bit!
Some of the UK setmakers offered both AC-only (with isolated power suppliers) and AC-DC (live chassis) versions of their domestic radio receivers, rather than issuing the latter type for all situations. That implies that the AC-only type was thought to be a better choice where it could be used - which must have been the majority situation by the later 1950s. If not, why do it?
Cheers,
Steve
