ETRONIC HV203 10" console. [1949]

[TNC]

Thanks John for another fascinating restoration story, much more exciting than Poirot, with the added benefit that it manages to keep me quite awake, which at this time of the year is a real achievement!

Trevor

[Hunts smoothing bomb]

Originally Posted by Heatercathodeshort

I don't know, after all my efforts at enlightening you young lads to the delights of 405 television receivers. When did the PCF80 triode/pentode turn into a EF80 screened pentode? Answers on a post card please.

Ahh,

Why is this ingrained on my brain?!
I've just done a search and found this from Oct last year! Post #13

https://www.vintage-radio.net/forum/...orn+980&page=2



Right!

Thorn 980 = PCF80

[Heatercathodeshort]

Thanks for the compliment Steve but its amazing what you can do with a dozen leads with crocodile clips on each end and a handful of odd capacitors. Just sounds more professional and all round nicer when you write it down. Cheers! John.
P.S. It could also be a 30C1 Lee but I won't complicate things..

[murphyv310]

Hi John.
Great result as always! There is (was) one of these at Bobs in Sorn less the cabinet, Sadly he has been dumping stuff recently including some 405 line TV's which has caused a bit of a rift, so I wonder if it still is there?
I can never understand why people dump stuff especially when they have friends or know of people that would be over the moon to have the items!!

[murphyv310]

Originally Posted by Heatercathodeshort

P.S. It could also be a 30C1 Lee but I won't complicate things..

A PCF802 works too

[Heatercathodeshort]

Stop it Trevor. Lee is confused enough as it is..J.

[Hunts smoothing bomb]

[Tazman1966]

Hey that picture looks as smooth as silk John. Really nice work - of course. Any further developments with the LOPT?

[Heatercathodeshort]

I've left it switched on for an hour or so Tas and the width has reduced by about an inch. Looks like the LOPT is struggling. It is quite warm to touch and think it is not long for this world. Had a similar symptom with a PYE B18T but that transformer has very hard pitch and is difficult to remove. Soaking in Petrol for a few days usually does the trick but its a filthy job. If it does go down in the Etronic it will be a very good reason to get the wave winder back into service. It won't be untill the spring as I don't fancy making up the bits required in a gale or snow storm! If it is still OK by the weekend it should be OK. We will see. Regards, John.

[Hunts smoothing bomb]

Hi John,
As you have pointed out, it does seem like the LOPTS days are numbered, you say it is an odd LOPT and I must admit it does look something out of the ordinary in the pics.
Does it differ electrically from a normal run of the mill design?

Cheers.

[Heatercathodeshort]

The circuit is self oscillating using a feedback from the transformer to the 807 line output tetrode. The primary winding is similar to a conventional audio or frame output transformer other than it has the EHT 'extension' which is wound in layered sections in an attempt to reduce capacity at 10kc/s. No Ferroxcube back in 1949 so the core is probably constructed using the best magnetic materials they had at that time.
The primary is isolated from the secondary which comprises two windings in series. One winding supplies the scan coils through the width and linearity inductors and the other winding is connected to the grid of the 807 providing the feedback.
The slightly later circuit employs the more usual Mullard EL38 with what appears to be the same transformer with a very different circuit, still utilizing the self oscillating feature. I would like to obtain a circuit for this model with the 807 as it may be possible to use an alternative transformer. There appears to be nothing available for this exact HV203 model. Failing that I will have to trace it out. There are not many receivers that used the self oscillating circuit. None of the transformers I have are wound with the isolated winding. When it goes pop I will have a play around with transformers but I think it would be more sensible to have a go at rewinding the primary/EHT winding as it is a very simple affair. I do have the wave winder and to be honest I have no excuse!
I'll let you know when it breaks down..Regards, John.

[Heatercathodeshort]

Way back in 2011 I restored a rare Etronic 10" console TV manufactured by the Hale Electric Co. Talbot Road, West Ealing W13 in London.

The link to the original thread is here: http://www.vintage-radio.net/forum/s...ght=Etronic+tv

I eventually forwarded the LOPT to Mike Barker who carried out an excellent rewind. It sat on my to do pile for some considerable period and a few weeks ago decided to fit the LOPT and finish this unusual Etronic.

The transformer was soon wired up and a picture was displayed almost immediately. The line output stage is a real hotch potch with a self oscillating 807 as a line generator/output valve. I had to select a suitable valve that would work satisfactorily from around ten 807 candidates. Most examples were way off on frequency while others lacked width. I don't think any of the valves were actually faulty as such but they simply turned their noses up at being forced into line output duty.

The line linearity is poor but it probably always was. The picture is acceptable with plenty of solid EHT. Any attempt to modify the rather odd circuit results in the frequency shifting massively. I will have to live with it!

Has anyone got a copy of the original service data for the HV203? I have the later ECV1523/1527 but this has major differences including a completely redesigned line output stage incorporating an EL38 in place of the 807. I have an original manual for the much earlier ST12 of 1947 with mains EHT so if anyone ever comes across one you must donate it to me so that I can play with it.. Unfortunately I have nothing for the HV203.

At least it is showing a stable picture so for a 68 year old television receiver, that can't be bad.

Do you like the Cossor 108K tube with it's string knickers? It is BRILLIANT. An early ion trap tube. [Invented by Cossor I believe.]

Thanks Mike for the rewind. You made a grand job of it considering I presented the original to you in about ten pieces...

The Hale Electric Co went bust in 1952 I believe. Such a shame but it was a time of rapid television development and only the fit would survive. No sooner had you set up tooling and production of a model when great changes were required for the following seasons models. 14" 'wide angle' tubes, new valves and circuits, flywheel sync, AGC, Band 3, it never stopped.

A small firm like Etronic could never keep up and it would only take a problem such as the disastrous line output transformer fitted to the flyback models such as the HV203 and later to tip them over the edge.

Regards, John.
PS. Moderators, is it possible to open the original thread and link it to this one?

[1100 man]

Hi John,
I've just read the original thread- very interesting and entertaining It really does highlight the fact that there is little point in powering up a set without changing all the wax caps (and Hunts too). Granted, it's more entertaining to watch them fail one by one, and also allows one's fault finding skills to come into play: after all that's where the fun of it is
Remarkably good picture, I thought. Pity about the poor linearity- I guess that is an inherent problem with valve LOP stages and manufacturers have to make the best compromise. Do you think it would have been that bad when new?
That's a really strange LOPT- looks more like a metal rectifier in the picture! Any chance of some close up photo's of it?
Do you know why the tube has a string vest? I doubt it would help much in the event of implosion
Cheers Nick
PS, my cat used to like to sit on the workbench and help with TV repairs, pointing a paw at particularly difficult faults now and then! Reminded me of 'Spock', LLJ's cat from his very entertaining articles in TV mag!

[Argus25]

Heatercathodeshort,

The set you have is certainly a wonderful example. The self oscillating line output stage for electromagnetic deflection was ,it appears, unique to 405 line television sets. It did not feature in American textbooks. The first time I encountered this design was in a "Philco" branded tv (not American Philco but English). Just as there are "Motorola" branded car radios of all English design which contain AF117 transistors and Tropical Fish capacitors.

In any event, this particular Philco tv set, using an MW31-74 crt, had the lopty encased in a large aluminium cylinder, filled with oil, the EY51 mounted on the top. The line opt tube was a PL38, obviously suited to the application. The H linearity was excellent. Since a schematic was unobtainium at the time, I transcribed it from the set (a model BT1251L).. see attachment.

The oscillations are sustained by feedback from a coil on the line output transformer's core. (The negative going sync is injected at the screen grid of the PL38 which brings forward the time that cutoff of the PL38 occurs).

The frequency of oscillation is determined by the time it takes for the rate of change of current in the anode circuit to become non-linear, which in this circuit depends on the tube parameters, largely when the plate current slope flattens off, because as it does the feedback voltage (proportional to the rate of change of current) reduces, so a positive feedback effect results, and the tube is driven rapidly into cut-off for fly-back. Hence the operating frequency is controlled by the series resistor in the grid No1 circuit. This circuit draws substantial grid no.1 current so the 5K potentiometer in the grid circuit needs to be a wire wound type.

It would be interesting to document all the known tv models (and there won't be many) that used this unique self oscillating output stage. The only other self oscillating H scan output stage I know of was the design by Faudell & White for electrostatic H deflection, which was the topic of another thread.

On your circuit, to improve the linearity, if there is one try altering the cathode resistor value, if there isn't a cathode resistor, try adding one as shown in the attached schematic, or try an EL38 instead of the 807.

[Heatercathodeshort]

I have tried just about everything! Any attempt to include a cathode resistor results in crazy line speed followed by collapse.
It's a nasty circuit and noting that the next model had a complete line output stage redesign, I think it was working on the edge with everything in very close tolerance. I'm done with the nasty thing! Ha! ha!

The line output transformer is a very early flyback type. The core is made of 'Caslam' a Plessey product with a much higher Q at 10kc/s than conventional laminations.
The 807 primary and EHT overwindings are wave wound over the layer wound scan feed and feedback windings. The EHT is wound in several separate sections to reduce capacity. It is these sections that appear to resemble the cooling plates of the old Westinghouse metal rectifiers.

The best self oscillating line output stage was without doubt the Plessey Mk1/2 of 1950 vintage. The whole chassis was incredibly reliable and as solid as a rock.
Many other chassis incorporated SOLOPT stages with varying success. Most had oscillator drift problems as the valves and LOPT itself warmed up.
Murphy had serious problems with the early versions of the V310. Philips examples as one would expect from such a quality company were very good.

It saved a valve but was it worth it? NO!

The Etronic is back in it's case ready for another poor wretch in 2085 to attempt to make it linear..
John.

[thermionic]

Great to see this rare set finally back to full health. 2011 seems an awfully long time ago.....

Small companies like Hale Electric are especially fascinating. As you've mentioned John, they had to attempt to keep up with the rapidly developing technology. I'm sure they may have been at a disadvantage as they probably did not have close ties to the likes of Mullard and Ediswan like many of the mainstream manufacturers, so did not have easy access to the latest valve & circuit developments.

Thanks for an interesting read.


SimonT

[Argus25]

Originally Posted by Heatercathodeshort

I have tried just about everything! Any attempt to include a cathode resistor results in crazy line speed followed by collapse.

It seems from looking at the test pattern that the main problem is compression of the raster on the right when the 807 is responsible for the scan current. A very small resistor in the cathode say a few ohms can be used as a current sense resistor to look at the scan current generated by the 807 with the scope connected across it.

One interesting thing about valve H output stages, vs transistor ones, is that the valve's grid drive voltage wave-shape will affect the H scan linearity. But in a transistor set it can't and the transistor is in a saturated switch mode. The linearity in this case depends on a constant rate of current rise in the inductance of the yoke and line output transformer. However in the valve stage the grid drive & plate current profile contribute along with the inductance of the transformer & yoke. In all cases though any additional resistance is detrimental to the linearity resulting in compression of the right side of the raster.

It might be that the output transformer has too little inductance or too high dc resistance, but most likely it is the 807 that is causing it. Off hand I think the 807 has a higher plate resistance than the EL38 pentode and would be less suited to this H scan application, but I haven't looked at the specs but it may still be worth a try one day using the EL38. An 807 seems like an unusual choice, maybe it was originally the EL38 and somebody changed it ?

The nasty part about this type of circuit is the poor frequency stability, but I guess it saved having either a double triode for a multi-vibrator circuit or a single triode and a blocking osc transformer. Sometimes though the drive for economy goes too far.

[Heatercathodeshort]

I may try an EL38 with a base adaptor. The 807 is definitely original with the valve holder riveted to the chassis. I believe that some HV203 chassis also employed the big fat Cossor 61SPT as the line output valve. I did try a 2.2 ohm resistor in the cathode circuit but even this caused the line stage to virtually collapse.
The circuit is far too tight for comfort with critical adjustment required to the line hold control but once set remains drift free. I may have another go at it when sanity returns if it ever does. Thanks for all your comments and yes 2011 was a good while back. Oh dear I'll be 69 in July. Regards, John.

[FERNSEH]

Hi John,
Link to the HV203 I repaired in 2012.

https://www.vintage-radio.net/forum/...=Etronic+HV203
The set was fitted with the Cossor 61SPT line output valve, I remember an EL38 was tried in the set with good results.
Some thoughts about the operation of the line output stage. When the valve is in conduction the forward scanning stroke is a result of the sawtooth waveform generated in the primary of the line output transformer. At the instant of the flyback the high amplitude negative going pulse present at the grid will hold the valve in a non conduction state.
The EV203 does not have a flyback damper diode. To damp the "ring" produced in the scanning coils during the flyback the set uses the simple arrangement of a variable resistor in series with a capacitor. All fine and well in a set without flyback EHT but when the EHT is produced by the flyback pulse as it is in the EV203 adjustment of the damping control will alter the amplitude of the EHT.
The 807 was used as a line output valve in only a few UK made TVs, the Pilot CV34 comes to mind. An alternative line output valve is the 6BG6G which is a further development of the 807 which in turn owes it's origins to the 6L6.
Info from the Radiomuseum: http://www.radiomuseum.org/tubes/tube_6bg6g.html

The attachment shows the circuit of the self oscillating line timebase. Note the damping components across the scanning coils.

DFWB.

[usradcoll1]

An interesting read, to be sure!
There was two US makes that used the self oscillating line output circuit. One was a Bendix and the other a Muntz. The Muntz was a knock-off of the Bendix, both smaller screen, magnetically deflected sets. The earlier models, didn't use a damper valve, the later models did, even though the LOP stage remained the same.
I was also amazed to find that some of the British sets used a TRF circuit, which was unknown here.
All of the sets built here were Superhet design. Even the inexpensive models and the foreign imports.