Ekco TS46 Excitement

[Hunts smoothing bomb]

Originally Posted by Heatercathodeshort

This is rather a nicely designed self contained EHT unit manufactured by 'HIVOLT Ltd. 34A Pottery lane, London S.W.11.
The valve employed is a Brimar 6BW6, the B9A based version of the 6V6GT with a similar circuit to the Ekco TS46.

That is a really nice piece of equipment John, such good condition too, out of interest what would be its upper limit on the HT supply?

Cheers

[dazzlevision]

Originally Posted by Heatercathodeshort

This is rather a nicely designed self contained EHT unit manufactured by 'HIVOLT Ltd. 34A Pottery lane, London S.W.11.
The valve employed is a Brimar 6BW6, the B9A based version of the 6V6GT with a similar circuit to the Ekco TS46.

The EHT output is dependent upon the H.T. available from the receiver chassis, typically 300/350v producing around 5/7kv.
The primary and grid coils can be seen at the bottom of the low loss Perspex former. The very small 1.2v two turn winding for the U37 filament are seen at the extreme base of the former.

No less than seven stacked windings for the EHT secondary. I have not powered this up but I bet the regulation is good.

How circumstances change. I expect that very small company thought they would be manufacturing these units for quite a few years not realizing that flyback was just around the corner. I wonder how long they lasted?

When I was a kid living in Wimbledon, many small industrial workshops existed. I was fascinated by the goings on along Beulah Road and to the rear of Merton High Street with the barn doors of small workshops open revealing men beavering away in small foundries, sparks flying and arc welding. All gone forever. Regards, John.

Maybe this thread related to the Hivolt Ltd that made your EHT supply unit: https://www.vintage-radio.net/forum/...ad.php?t=72631 Quote from thread "Originally F.G.Miles Engineering, using the trade name Hivolt. Became Wallis Hivolt, then became Hunting Hivolt, then became Farnell Hivolt."

Alternatively:Hivolt Ltd (successor to Hazlehurst Designs Ltd – the transition occurred in 1951), 34a Pottery Lane, London, W11 (in 1951). High voltage engineers (e.g. TV EHT units).

[Heatercathodeshort]

The aluminium plate states 5-7kv Lee. At 350v HT the EHT output is 7.5KV. The frequency of the oscillator will no doubt alter this slightly but I have left the ceramic trimmer alone as it is doing what it says on the tin. The output is entirely dependent on the HT supplies.

It's probable that they produced higher output units but this one is dated 1950 and flyback probably overtook them.

Mike and Tone are lucky with their example of the TS46. I believe Ekco experienced low 'Q' problems with their coil but it was wound on a Tuxite former and then dipped in wax.
Not a good start but they were only designed for a 10 year life and by 1958 many owners visiting their local Ekco dealer would have looked longingly at the T330 and decided to retire the old TS46. Regards, John.

[Mikey405]

Hi all and apologies for the delay in replying.

Thank you to everyone for their nice comments (and especially to John for offering to keep an eye out for a volume knob - Thanks John).

Things have been very busy of late and I have still yet to fit the new EHT cable but I might try and get that sorted out this weekend.

On the subject of those RF EHT oscillators - Invicta had a sort of half-way-house with their T102 and T103 sets. They used two PL38 output pentodes driven from the same 10.125KHz source - one to drive the line output and another to drive a separate EHT transformer which was then rectified in the normal way with an EY51. I don't think these suffered anywhere near as badly as the Ekco ones. I suppose those Mullard projection transformers were a similar thing too - and they always seemed to carry on working forever - or they'd suddenly fail.

[flyingtech55]

Things come a full circle...my B&O 5502 has separate mains powered EHT supply and line output stages. When running, the line oscillator provides the 'sync' to the power supply to avoid the possibility of BK appearing on the screen.

[julie_m]

You can almost see the evolution of the design there ..... From a dedicated mains transformer for the EHT, to a separate oscillator, to a common oscillator driving separate valves for the line scan and the EHT PSU, to the "modern" design -- which ended up lasting as long as the CRT itself.

What was the main reason for the setmakers dropping mains EHT? Were they really keen for their sets to be operable on DC (there can't have been many people who could afford to buy a brand new TV set, living in DC areas by the end of the war .....) or was it desirable to improve safety for service personnel (thereby implying that it might need to be opened up again sooner rather than later), by using an energy-limited EHT supply? Or was it simply a matter of cost, and the rest a happy accident?

[Heatercathodeshort]

Mains EHT required a large, heavy, expensive, cumbersome and unreliable transformer together with a large EHT rectifier and smoothing capacitor. The maximum that could be reliably obtained from a mains transformer is 6kv without voltage doubling. [more cost]
This limited the EHT to a 9" or 12" tube. There was also a small fire risk when the EHT transformer broke down. They were often dipped in pitch.

Added to this is the danger of lethal electric shock due to the low impedance source at 50c/s. A number of engineers were killed by chassis falling on them while working on them. Electrostatic deflection was even worse requiring more current from the mains derived EHT system to cater for the bleeder network. This is why most makers that had employed electrostatic tubes before the war, washed their hands of them in 1946. John.