Tube brighteners.

[kalee20]

It's made me think. A small low-voltage auto transformer (1:1.2) would certainly work for AC heater supplies. But:

If heaters were parallel-connected, it would need to be connected one way round.

If series-connected, it would need to be the other way round.

And if operated from a 'stiff' voltage source of twice the nominal heater voltage but in series with another heater (an unlikely but not impossible scenario), then either connection of the autotransformer would result in a slight drop in power to the CRT.

[Argus25]

The output of the autotransformer only runs one heater, that of the CRT's gun. Looking into the auotransformer "primary" the voltage there is still 6.3V, but off the extension tap say 9v and a higher than usual current there. So all that happens is the "primary" current of the autotransformer is higher than the CRT heater current would normally have loaded it.

This is one reason why its more awkward to use one in a series heater chain on an AC DC set, rather than the typical American set with a power transformer with 6.3V heater supplies derived from a mains power transformer.

In the series heater chain case, the current is set to some value to suit all the valves, and at that current, the CRT heater would drop its correct voltage, say 6.3V. So if an autotransformer is dropped into that series chain, the only way to get more power is to have its "primary" drop more voltage at the usual current, which means the load has to look like a higher resistance than the original CRT heater, but that implies the transformer would have to have a step down ratio, not step up ratio.

So what you gain on the roundabout you lose on the swing by trying to use a booster transformer in a series heater chain. Simply because the series heater chain is effectively powered by a current source. For example shorting out the heater of one signal valve alone only slightly changes the current.

As I mentioned previously, its more awkward which probably explains, given the predominance of AC/DC series heater chain sets in the UK, why the brighteners were not so common.

[TowerRadio]

Radio Constructor May 1960 " Is that tube really finished!" Les.

[Hartley118]

Originally Posted by TowerRadio

I have a RS 4 volt CRT booster transformer,I can certainly remember my father getting a bit more life out of a Bush TV tube with one of these boosters,possibly made by Elstone. Les

I recall using a CRT booster transformer when I was experimenting with old TVs in the 1950s and 60s. My memory of its appearance suggests it may well have been an Elstone which ISTR had +10% and +20% taps for different degreees of boost. The clear symptom of a low emission CRT was the way that, as contrast was advanced, the picture highlights would turn negative instead of getting brighter.

The transformer ran directly from the mains and had a special low capacitance secondary for use with a CRT that had suffered a heater-cathode short. That secondary isolated the heater from the cathode and enabled the video drive to be restored to the cathode. I suspect that video bandwidth must have suffered somewhat, but it saved buying a new tube.

Martin

[Craig Sawyers]

Originally Posted by Argus25

Not unlikely at all, the autotransformer booster at this point in history was 10 year old American technology and if he was well traveled "Uncle Clive" would have seen these on trips to America along with many other TV and Audio innovations. In those days it took about 10 years for new tech to get from the USA to the UK and about 15 to 20 years to get to the Antipodes.

Apart from that he was working as the editor of Practical Wireless, then Brabani and then a pro-audio magazine until his mid 20's at least. He always had his sights set to miniature stuff he could pile high and sell in volume. CRT rejuvinators were so not Clive Sinclair's thing.

[Craig Sawyers]

The earliest reference I can find to real products that Clive Sinclair supplied via the Sinclair Radionics name seem to date from late 62 into 63, so he seems to have been doing a bit of moonlighting. Usually miniature novel audio and radio stuff. Like audio power amps that would fit on a half crown, or integrated pre/power amp capable of supplying 1/2W.

[kalee20]

Originally Posted by Argus25

In the series heater chain case, the current is set to some value to suit all the valves, and at that current, the CRT heater would drop its correct voltage, say 6.3V. So if an autotransformer is dropped into that series chain, the only way to get more power is to have its "primary" drop more voltage at the usual current, which means the load has to look like a higher resistance than the original CRT heater, but that implies the transformer would have to have a step down ratio, not step up ratio.

...its more awkward which probably explains, given the predominance of AC/DC series heater chain sets in the UK, why the brighteners were not so common.

It shouldn't be the least awkward, you just reverse the autotransformer for a series chain. Instead of, say, 300mA into the CRT heater, you want 20% more or 360mA, so you use (say) 36 turns on the autotransformer connected in the series chain, and connect the CRT at a 30 turn tap. The voltages adjust themselves largely to suit - the transformer will absorb 20% more voltage in the heater chain (so 7.56V rather than 6.3V), but as you point out, that will make hardly any difference.

What may have spoiled the use of a booster transformer in series heater chains is the use of a diode as a partial dropper. Though, by the time silicon diodes were coming available, CRT's were getting longer-lived, and cheaper too. (Someone correct me if I'm wrong!)

[G6Tanuki]

Part of me wonders if the sorts of TVs/tubes a 1960 booster would have been aimed at - the older models - would have been the first-generation types which still used a mains transformer for the heaters/HT.

When did series-heaters and flyback-derived-EHT become the norm for TVs in the UK?

[ms660]

This was the most common setup when I was in the trade, sometimes R wasn't included, the old tube heater feed simply being shorted out:

http://www.oldtellys.co.uk/otmonotube.html

Also used the boost tranny as part of a DIY tube bopper, +ve volts on the grid and tap away, posh DIY workshop boppers had an ammeter in series with the grid....Happy days:

https://www.thevalvepage.com/teletec...ej/crt_rej.htm

Lawrence.

[Argus25]

Originally Posted by kalee20

It shouldn't be the least awkward, you just reverse the autotransformer for a series chain. Instead of, say, 300mA into the CRT heater, you want 20% more or 360mA, so you use (say) 36 turns on the autotransformer connected in the series chain, and connect the CRT at a 30 turn tap. The voltages adjust themselves largely to suit - the transformer will absorb 20% more voltage in the heater chain (so 7.56V rather than 6.3V), but as you point out, that will make hardly any difference.

I agree and there would need to be about 9V dropped across the autotransformer primary to get the 7.5v about for the heater at the raised current of 360mA. But there is the nature of awkward, you have to have a reverse autotransformer for the case of a series heater chain set, compared to one with 6.3 heaters supplied by a power transformer. The Brighteners sold in the USA were all step up types and universal for most sets. Probably none were for series heater chain sets (at least I have never seen one or any labels suggesting they could be used in a series heater chain set). They were all sealed units.

[Nuvistor]

USA series heater chain brightners. Interestingly the crt heaters are very low voltage compared to UK ones.

[Argus25]

Originally Posted by Nuvistor

USA series heater chain brightners. Interestingly the crt heaters are very low voltage compared to UK ones.

Maybe the "Universal" ones had a way of reversing the autotransformer, or some taps that could be user altered.

[Nuvistor]

Perma-Bright advert, perhaps it’s an auto transformer but I don’t know, the advert states if the base is correct the boost will be, series or parallel. It’s possible the USA CRT’s used a range of heater voltages depending on its base type.
Looking at the photo that looks like a switch on the top.

The only CRT boosters I saw were the Radio Spares type that required finding a suitable place to mount the transformer and wire it in. I didn’t see many, regunned and new CRT’s had become much more affordable in the 60’s.

[Heatercathodeshort]

A selection of Radiospares low capacity isolation and boost transformers. The 2volt version used to boost and isolate Mazda triode tubes that were notorious for developing heater cathode shorts.
Almost every Mazda triode ended up with one of these transformers wired to it's sensitive bit and was without doubt the most popular.The 6.3v version probably ended up coming in second place due to the popularity of 6.3v tubes.
The 4volt version was much rarer being limited to mainly GEC and Ferranti tubes. They also marketed a 10.5volt version for EMI tubes but they didn't last long after boosting and the transformer was soon withdrawn, 'available until stocks are exhausted'.

The 6.3 version reappeared in the Radiospares catalogue during the early colour era for boosting very expensive colour tubes.

The 5.6K resistor method wired to the live heater pin of series connected tubes and valves was a nasty way of boosting the tube but the only way with DC mains and of course would not provide isolation and during the 1950's there were still many areas on a DC supply. Regards, John.