Early Flyback EHT

[Duke_Nukem]

I displayed my D18T at the last NVCF. After a couple of hours it was definitely not happy, being somewhat defocussed, and after five hours I switched it off as it looked very poor (a shame as it is capable of a very good picture). The fact that it was also very hot in the display area probably didn’t help too much either.

BTW, the D/B18T was not the first British set to derive EHT from the flyback – but it was the first to use the combination of flyback EHT plus a boost diode.


TTFN,
Jon

[Heatercathodeshort]

Originally Posted by Duke_Nukem

BTW, the D/B18T was not the first British set to derive EHT from the flyback – but it was the first to use the combination of flyback EHT plus a boost diode. TTFN,
Jon

Hello Jon,
Now that is very interesting. I always thought that the B18T was the first set to use flyback EHT [and an AC/DC circuit] as opposed to the separate R.F. system.
The post war Philips using 2 HVR2s in a very dated circuit was released after the B18T.
The Wireless World gives the release date for the B18T at 1948.
Who made the first one?

Regards
John.

[Heatercathodeshort]

Hello again Jon,
Since meeting you at Harpenden today and having a chat I realize that there are a couple of sets that predate the B18T, but use flyback EHT.

K.B.'s first post war set [1947?], the CV30 and that Philips I mentioned with the voltage doubler HVR2s.
I thought that set arrived after the Pye even with its very dated circuit and odd valve line up.
The K.B. is a very rare set and I have never seen one.
The PYE on the other hand was made in huge quantities and was Britain's first AC/DC set [I think!]

Nice meeting you today, I enjoyed the whole swapmeet.

Regards
John.

[ppppenguin]

Originally Posted by Heatercathodeshort

...I realize that there are a couple of sets that pre date the B18T but use flyback EHT.

Flyback EHT with energy recovery was invented by Blumlein in the 1930s. It wasn't used until after WW2. Perhaps because the efficiency diode was an awkward thing needing excellent HK insulation, perhaps because the benefits were not sufficient with narrow angle CRTs.

[Duke_Nukem]

Someone has just reminded me - the Bush TV1 pre-dates the Pye B18/D18 by some 4 months and that uses flyback EHT.

The B18T still remains a most important design as it was the first to utilise both flyback EHT and a boost diode which within a few years was used almost universally.
It was also the first true AC/DC design, but I think Pye didn't necessarily consider this, the circuit was designed purely on cost grounds. Pye very soon realised that the set was capable of operation on DC mains and soon modified the HT smoothing choke so that a section of it could be bypassed for DC mains, just to squeeze those extra few vital volts through to the HT rail.

Originally Posted by ppppenguin

Flyback EHT with energy recovery was invented by Blumlein in the 1930s.

His 1932 patent was only for the energy recovery circuit. The circuit topology looked like that of a transistor set ! The "diode" (well, triode) was simply connected in reverse across the line output valve. The circuit was unlike that used in British tv's as no additional supply voltage was generated - it was, as you say, energy recovery and not a boost circuit.

Originally Posted by ppppenguin

It wasn't used until after WW2.

I believe it was used in Germany prior to WWII. Can anyone confirm this ?

Perhaps because the efficiency diode was an awkward thing needing excellent HK insulation

It doesn't. In the Pye the cathode of the boost valve is grounded. The boost voltage is hence negative and its only use is for the line output stage itself (and extra -ve bias for the brightness control). Of course a +ve boost volts is far more useful.

Incidently if the LOP valve warms up quicker than the boost diode then the LOP valve's cathode bypass electrolytic gets reverse biased.

TTFN,
Jon

[ppppenguin]

Originally Posted by Duke_Nukem

His 1932 patent was only for the energy recovery circuit. The circuit topology looked like that of a transistor set ! The "diode" (well, triode) was simply connected in reverse across the line output valve. The circuit was unlike that used in British tv's as no additional supply voltage was generated - it was, as you say, energy recovery and not a boost circuit.

Agreed that Blumlein's patent was purely for energy recovery and is very much like a modern transistor energy recovery circuit. The later boost diode arrangement performed energy recovery but also gave a boosted HT rail which eased the design of the line output stage. A higher HT and resulting lower current were certainly better conditions for a valve.

It's worth remembering how much energy is being flung around when scanning a wide angle CRT. I can't lay my hands on the exact numbers but for a first generation delta gun shadowmask CRT I think the peak volt x amp product was around 3500VA. Whether you did it low voltage with transistors or high voltage with valves that's an awful lot of energy. Without energy recovery you would be dissipating over 3kW of heat to do the line scan. With energy recovery you only have to supply enough power to replace the energy lost on each stroke due to copper, iron and switching inefficiency.

It's safe to say that without energy recovery, the scanning of wide angle CRTs would not have been practical.

[FERNSEH]

Originally Posted by Duke_Nukem

I believe it was used in Germany prior to WWII. Can anyone confirm this ?

The E1 television receiver (Volksfernseher?) of 1939 was one of the most advanced TV sets of the time. It had flyback EHT and a special rectangular CRT with integral implosion protection.

The 1946 RCA 630 series of 1946 used a flyback EHT system.

DFWB

[mickjjo]

Details of the 1939 E1 here :-

http://bs.cyty.com/menschen/e-etzold...efunken/e1.htm

Regards, Mick.

[Duke_Nukem]

Originally Posted by Duke_Nukem

I believe it was used in Germany prior to WWII. Can anyone confirm this ?

Have just re-read my post - in my haste I seem to have missed out that I was referring to boost/energy recovery circuit. Ooops

TTFN,
Jon

[FERNSEH]

Originally Posted by Duke_Nukem

Have just re-read my post - in my haste I seem to have missed out that I was referring to boost/energy recovery circuit. Ooops

TTFN,
Jon

No pre-war British TV sets had flyback EHT and none of the HMV and Marconi TVs had boost or energy reclaim circuits.

However, the EMI studio monitors did have an energy reclaim diode, actually called a "resonant energy reclaim diode" (V8).

According to text in the Black Book the reclaim circuit permits the use of a less powerful line output valve. (V7). Also, there was a flyback damping diode across the scan coils (V9)

DFWB.

[ppppenguin]

Originally Posted by FERNSEH

According to text in the Black Book the reclaim circuit permits the use of a less powerful line output valve. (V7). Also, there was a flyback damping diode across the scan coils (V9)

Odd sort of arrangment, almost schizophrenic. The damping diode simply dumps stored energy into a resistor while there is also some attempt at energy recovery.