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Old 22nd Sep 2020, 3:31 am   #1
Chris55000
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Default H.T. Line Voltages in 1950s T.V. Sets?

Hi!

I used to look at many, many old 1950s circuits in the dark red R & TV books when I was much younger, and it always puzzled me that even when silicon rectifiers arrived, this didn't automatically result in greater h.t. voltages quoted, strangely enough, it was common for some of these to have less unsmoothed h.t. (180–190V) simply as all the mains was dropped across more limiters!

There was one a.c./d.c. Pye set from the early 1950s where the maker quoted h.t. line voltages of "250V" without using a transformer, and that was a metal–rectifier equipped set! How did Pye get that much?

Nearly all the Murphy's, GEC,s, etc., using M.R.'s quoted "205V" or "215V" on the main smoothed h.t. line at the time, it was rare to get more than 200V from valve rectifiers, altho' the PY33 was more efficient (See "Valves & Their Habits", by Harold Peters, 1962 and 1965 P.T.), but the real waster of h.t./mains voltage I ever saw was the 1960 P.T. "Olympic" design, two XU604 silicon rectifiers and 175V on the main h.t. line, and the Front Cover actually said "Uses High Efficiency Silicon Rectifiers!"

Chris Williams
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Old 22nd Sep 2020, 10:14 am   #2
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Default Re: H.T. Line Voltages in 1950s T.V. Sets?

I suppose that what was presumably inevitably half-wave rectification needed plenty of filtering that involved series wirewounds as well as the biggest value electrolytics that the budget could stand? The drive for bigger and bigger screens with bright and contrasty pictures would make even slight hum obtrusive and not good PR amongst other brands in the shop window, so perhaps a maximum HT of around 200V was a knock-on of the need for good ripple filtering. Also, I would imagine that the new-fangled silicon rectifiers would need safe-guarding from their own virtues, i.e. low forward impedance and forward voltage, so there might even have been a need to pay more attention to series resistance than with thermionic rectifiers when there was a direct mains connection without a transformer to limit peak currents.

All finger-in-the-wind stuff from me I'm afraid!
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Old 22nd Sep 2020, 12:25 pm   #3
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Default Re: H.T. Line Voltages in 1950s T.V. Sets?

Hi!

I think that was probably the reasoning behind it, it wasn't until the mid–1960s that dual–standard operation and much larger wide–angle scanning–angle CRTs made designers realise that more h.t. line volts was the answer to the scan power needs – I remember the "KB Featherlight" portables used 235V, the Thorn 1500 a smidgin under 250V plus two lower h.t. lines for sound, frame and video, whilst P.T.'s "Constructor's 625 line Receiver" used two lines, one +250V and one +200V plus transistor L.T. of course!

I think the +285V that Mullard specified as the design figure for their 1967 hybrid D/S colour–set design was about the maximum you could reasonably get direct off the mains without a transformer, using the minimum amount of smoothing with one choke.

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Old 22nd Sep 2020, 12:37 pm   #4
Leon Crampin
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Default Re: H.T. Line Voltages in 1950s T.V. Sets?

In the '50s, 200 - 210V mains was the norm in many areas, and most sets were designed to accomodate this. In any set without a transformer or autotransformer (eg. Ekco T217), the rectifier could therefore see <200V on its anode after the surge limiting resistor, when used in some areas.

This constrained the designer to work with an HT voltage of around 190V after smoothing which, with the highish forward voltage drop of some of the available rectifiers, was the best that could be done.

There's no merit in having a good picture at 240V input, and low width and height at 200V, so the HT supply to the rectifier was ballasted in much the same way as the heater supply. Some sets offered the option to link out the rectifier for DC supplies - a risky option with 2 pin mains plugs....

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Old 22nd Sep 2020, 12:49 pm   #5
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Default Re: H.T. Line Voltages in 1950s T.V. Sets?

I do recall noticing from the days when valved tellies were piled high on the dumps and boiling them down for bits that a few mid-'sixties dual-standard types would actually have a choke of a henry or two and low resistance in the PSU arrangements- presumably as complexity and scanning power increased, manufacturers were pushed into a corner and found it difficult to avoid the extra cost of magnetic energy storage and minimal ohms combined with effective ripple reduction.
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Old 22nd Sep 2020, 1:06 pm   #6
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Default Re: H.T. Line Voltages in 1950s T.V. Sets?

I recall that the mains adjustment range of our first TV (bought for the 1953 coronation) was 200 - 250VAC and only 230-250VDC. The same limited DC range is specified for a number of sets in several early 1950's manufacturers' TV leaflets. Our mains at the time was 200VAC. We were converted to 240VAC circa 1960.

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Old 22nd Sep 2020, 1:11 pm   #7
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Default Re: H.T. Line Voltages in 1950s T.V. Sets?

Over the pond they get away with a voltage doubler on 110 volts AC.

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Old 23rd Sep 2020, 8:43 am   #8
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Default Re: H.T. Line Voltages in 1950s T.V. Sets?

I think Leon has the answer here. An AC/DC chassis had to be capable of operating on 200V mains that might drop below this during periods of heavy load.
Valves such as the Mullard PL81 line output valve were deigned to give full scan with 200V H.T.
I would be interested to know which early PYE [AC/DC] that had a 250V H.T. line. The very rare and highly unusual Pye V54C from what I can remember used a mains transformer and a pair of PZ30 rectifiers with two pairs of anodes strapped and fed from the mains transformer H.T. winding. David has more experience with these 1952 models as they were quite popular in the NE than London, probably due to their very high gain, receiving the signal from Holme Moss back then. John.
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Old 24th Sep 2020, 5:09 pm   #9
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Default Re: H.T. Line Voltages in 1950s T.V. Sets?

Quote:
Originally Posted by peter_scott View Post
Over the pond they get away with a voltage doubler on 110 volts AC.
With our low voltage mains the only sets that would work well were the small CRT's with the narrower deflection angle. The larger screen sets had to use a voltage doubler. Most of our LOP valves required over 200 volts for screen and anode.
In the early 60's, Motorola started using a "P" range of valves in their sets. PL500, PL84's and the like, normally found in British and European sets. Those valves operated on 140V HT. The even used 23" CRT's and 110 degree deflection. They were very well performing sets.
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Old 24th Sep 2020, 5:29 pm   #10
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Default Re: H.T. Line Voltages in 1950s T.V. Sets?

In the mid-60s I remember visiting rellies who lived in the Nottingham coalfields [relative was their geologist/explosives-licensed guy] where the 'mains' was something like 210VDC, supplied 'free' from generators at t'pit; watching their old "Baird" Radio-Rentals 405-line telly, periodically it would lose line/frame-hold for 30 seconds - and the lights in the house would pulsate.

This was when the pit started-up its big conveyer to load the latest 1000 tons of coal into waiting railway-wagons so it could be wheeled-off to fuel the numerous generating-stations along the Trent. My rellies called it "cogging' and didn't mind because the more-often it happened the greater their productivity-bonus.

[When they were transitioned to proper National Grid power - with electricity-meters - and bills - there was some discontent]
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Old 29th Sep 2020, 4:12 am   #11
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Default Re: H.T. Line Voltages in 1950s T.V. Sets?

Quote:
Originally Posted by G6Tanuki View Post
In the mid-60s I remember visiting rellies who lived in the Nottingham coalfields [relative was their geologist/explosives-licensed guy] where the 'mains' was something like 210VDC, supplied 'free' from generators at t'pit; watching their old "Baird" Radio-Rentals 405-line telly, periodically it would lose line/frame-hold for 30 seconds - and the lights in the house would pulsate.

This was when the pit started-up its big conveyer to load the latest 1000 tons of coal into waiting railway-wagons so it could be wheeled-off to fuel the numerous generating-stations along the Trent. My rellies called it "cogging' and didn't mind because the more-often it happened the greater their productivity-bonus.

[When they were transitioned to proper National Grid power - with electricity-meters - and bills - there was some discontent]
This reminds me of trying to "dip" the anodes & "peak the grids" on an ATE VHF transmitter which was part of a link from Koolan Island to the mainland, in the far North of Western Australia.

Every time I started to "tweak" the thing, the big electrically operated excavator would bite into the ore face, the Mains would dip, & I would lose my anode dip.

Back on topic, in Oz, we never realised how fortunate we were using transformers in our BW TV sets, allowing us to have HTs of around 300v

By that time, there were very few 110v or 220v DC systems still in use, & they could be catered for by using inverters.

The standard "Van Ruyten" inverter my old work sold was the one to run 240v TVs off 32v farm power supplies, but we sold a few of the 110v units, too.
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