Surviving Baird circuitry in a first generation TV set.

[Ted Kendall]

Originally Posted by SteveCG

I hope this is not too silly a question but why would many TV sets be returned to EMI for renovation after the war? After all, wireless sets of that era ran for many years without needing 'renovation' and for TV there was no change to the broadcast standard.

The need for refurbishment after six years' inactivity is the cause for overhaul, but the television repair trade hardly existed at the time, so most of the required expertise would lie with the manufacturer, apart perhaps from demobbed radar technicians. Incidentally, much the same process had to take place at the originating end - although the AP transmitters had been used on war work, the studio equipment was at best on care-and-maintenance for the duration.

[Catkins]

Originally Posted by SteveCG

I hope this is not too silly a question but why would many TV sets be returned to EMI for renovation after the war? After all, wireless sets of that era ran for many years without needing 'renovation' and for TV there was no change to the broadcast standard.

I think the previously given explanations are correct, as mentioned electronics (especially electrolytic capacitors) deteriorate over time if not used. Televisions would not have been used for six years because there was no television transmitted during the war. On the other hand radios would have been in constant use during the war.

But, I think the poster may have been asking a slightly different question. That is many radios of that era could happily have been unused for six, ten or more years, but would then function perfectly after that time. So why wasn't that the case for televisions? Why did they "need" to be serviced after six years disuse, when a radio after a similar period of disuse probably wouldn't have done?

If that was the question the poster was asking, then the first answer is radio and television sets are obviously a combination of their parts, and televisions are much more complex than radios. A typical pre-war television would have had upwards of 20 valves or more and associated components, but a pre-war radio would typically have had 5 valves. Simply going on the laws of probability, a television is much more likely to require servicing after a period of disuse than a radio.

The second answer, in conjunction with the first, is pre-war televisions drove the available technology far harder than radios. Televisions operated at a far high frequency, and higher voltages than radios, and required components to be at their optimum to work. Radios due to their lower frequency and voltages would quite happily work with a level of component and/or insulation degeneration that would cause major problems for a television.

[Catkins]

Originally Posted by peter_scott

I think your H6181 is a very useful set for production dating and the factory fitted V8 top surface blanking plate places it very neatly in the January/February 1937 window. To preserve its history I hope that you will retain the plate with its original riveting over the socket.

Hi Peter,

You perhaps should know in my previous restorations of the HMV 904 and the Murphy A56V, preserving originality is one of the things I felt most important. I don't destroy originality for the sake of convenience.

As such, I feel removing the plate, and some of the dating to be off-limits.

Phillip

[peter_scott]

Hi Phillip,

I thought that was the case and I'm with you 100%. These sets are museum pieces and originality is of prime importance but I am also a supporter of them being operable and able to demonstrate their full capabilities.

Kind regards,

Peter

[SteveCG]

Quote: "But, I think the poster may have been asking a slightly different question. That is many radios of that era could happily have been unused for six, ten or more years, but would then function perfectly after that time. So why wasn't that the case for televisions? Why did they "need" to be serviced after six years disuse, when a radio after a similar period of disuse probably wouldn't have done?"

Thank you Catkins, yes, this was certainly in my mind as I posted the question.

I have great admiration for the forum members who spend a great deal of time and effort on these Pre-War TVs. And the chance to be dealing with an untouched dual-standard and get it going again must be exhilarating and daunting.

Certainly to be able to genuinely switch between 240 and 405 lines would make for a fascinating comparison 'in the flesh' compared to a theoretical appraisal of the relative merits of the systems.

[peter_scott]

Originally Posted by SteveCG

Certainly to be able to genuinely switch between 240 and 405 lines would make for a fascinating comparison 'in the flesh' compared to a theoretical appraisal of the relative merits of the systems.

When viewed from a distance the comparison of the two line standards is not as dramatic as the numbers suggest but the comparison of the interlaced versus non-interlaced is dramatic. Unfortunately it's not easy to capture the flicker and impossible to reproduce it via YouTube.

Peter

[SteveCG]

Peter,

Is it the case that in a dimly lit room - that is, typical evening viewing conditions - the flicker is not so obvious? C.F. viewing NTSC TV in daylight compared to European TV with their different field rates, where the flicker is quite noticeable.

[peter_scott]

Hi Steve,

I understand that flicker is more obvious with brighter screens and with bigger screens where your peripheral vision sees the outer parts of the picture. That said my HMV901 is the only set that I have that will display 240/25 and the CRT has no aluminising and only 5kV EHT so I have only been viewing on a small not very bright picture and the flicker is very noticable but you do get used to it. It's possible that Baird CRTs had a longer persistence phosphor in their early sets but I don't know to what degree.

Peter

[peter_scott]

I have now updated the EMI Dating table.

If there are other alterations, errors or omissions that anyone spots then please let me know.

Peter

[stevehertz]

Originally Posted by Ted Kendall

The need for refurbishment after six years' inactivity is the cause for overhaul, but the television repair trade hardly existed at the time, so most of the required expertise would lie with the manufacturer, apart perhaps from demobbed radar technicians. Incidentally, much the same process had to take place at the originating end - although the AP transmitters had been used on war work, the studio equipment was at best on care-and-maintenance for the duration.

Yes and no Ted. I mean, I reckon quite a few radio repairmen - without knowledge of TV technology as such - could fix most faults by using their experience and skills gained repairing radios, ie swapping bottles, checking caps etc, generally looking for faults. When I started collecting and restoring pre and post war TV sets in the 70s I knew very little about TV theory (and still don't to a great degree) yet I was able to - for instance - restore an Ekco TA201 vision only pre war set to full working order, do a write up and it was published in 'Television'. That's me, knowing 'nothing'.

[Ted Kendall]

1976 was so different from 1946 that I don't know where to start. In the seventies, television was a commonplace, not an expensive cutting-edge innovation; there was a ready supply of suitable components; the economy, though challenged, was not in the mess created by the the abrupt cessation of Lease-Lend at the end of the war. Furthermore, television sets themselves were, in 1946, scarce, not easily replaceable as the economy was geared towards export as a priority, and owned by higher-income households. In all likelihood, none of them had been switched on since 1939, whilst any serviceable radio would have been in regular use. In those circumstances, would you risk entrusting a carefully preserved pre-war set to anybody but the manufacturer, given the choice? Catkins' point about complexity is well made - after all, the difficulty of fault tracing tends to increase faster than linearly with component count.

I also think that to claim you knew nothing about television is irrelevant to the post-war situation - at the very least, you had extensive experience of the medium as a user, which most people didn't then, even, I'd suggest, most radio repairmen. Survival of pre-war sets was in the hundreds, concentrated in London, so Hayes factory refurbishment would have been a practical solution.

[Catkins]

Originally Posted by peter_scott

When viewed from a distance the comparison of the two line standards is not as dramatic as the numbers suggest but the comparison of the interlaced versus non-interlaced is dramatic. Unfortunately it's not easy to capture the flicker and impossible to reproduce it via YouTube.

Hi Peter,

Unlike most people you have seen the difference between the Baird system and the EMI system. Which puts you in a fairly unique position.

From what you said, I gather from your experience the major failure of the Baird system is the lack of interlacing, rather than the lack of definition? In other words on the small screens at the time, viewed from a distance the lower definition isn't apparent, but the flicker doesn't get any better

That would seem to chime with the contemporary reports I've read from the time. They don't complain about the definition, and in fact state filmed material looked better on the Baird system, than the EMI system!

One perhaps has to wonder, what might have happened if Baird had adopted 240-lines interlaced. Does anyone know what prevented the Baird system from using interlacing? Was there a patent on it?

Phillip

[Catkins]

Originally Posted by peter_scott

I thought that was the case and I'm with you 100%. These sets are museum pieces and originality is of prime importance but I am also a supporter of them being operable and able to demonstrate their full capabilities.

Re-reading my reply, it may have come over a bit "sharp", but no offence was intended.

As you know the question of keeping originality versus restoration is a difficult one and can get quite emotive. There are some people who think any restoration to get a television to work is "destroying it". On the other hand there are some people who think people who worry about originality are a bit obsessive.

I suppose I was worried about this becoming "one of those threads", and gave a terse reply.

[Catkins]

Originally Posted by SteveCG

Thank you Catkins, yes, this was certainly in my mind as I posted the question.

I have great admiration for the forum members who spend a great deal of time and effort on these Pre-War TVs. And the chance to be dealing with an untouched dual-standard and get it going again must be exhilarating and daunting.

Thanks SteveCG for your response. As you said, having by chance got a 1st gen television with most of the dual-standard circuitry surviving, it does make the restoration more daunting, especially whether I should try to restore dual-standard operation.

Fortunately, there is a long way to go to get the set restored to 405-line operation. As such that is main task at the moment. But, opinions are always welcome.

[Catkins]

Originally Posted by peter_scott

I have now updated the EMI Dating table.

If there are other alterations, errors or omissions that anyone spots then please let me know.

Peter

Thank-you Peter.

You have updated the Mike Parsons entry to reflect the new ownership and extra information perfectly.

You did ask "If there are other alterations, errors or omissions that anyone spots then please let me know"

One thing I notice when I read the table is such entries as "< May 1937" and "< 26th Nov 1936".

This raises my curiosity as how do you know this? From where does this dating come? I suppose it is because the set has some irrefutable dating evidence such as a surviving sales invoice?

Would it be possible to add a footnote explaining where this dating comes from? If I wonder about this when reading the table, perhaps others do too?

Also it has been mentioned in this thread, that the survival of Baird circuitry dates the television to Jan/Feb 1937 and before. Do you think there's now sufficient evidence to state that in the table, such as "< Feb 1937", on such sets?

Obviously this depends on where your dating comes from, and how definitive it has to be to be included.

Thanks

Phillip

[peter_scott]

Thanks Phillip,

Any little dating notes are as you say from sets with sales or other documentary evidence.

I suspect that sets with top mounted V8 blanking plates probably can be categorised as having been shipped in the Jan/Feb 1937 period and possibly slightly early or later. I have tried to order the table top to bottom in earlier to later shipment order based partially on white label number, chassis numbers and internal metalwork.

I think, to reduce turn-around time, there must have been some chassis swapping at the time when EMI recalled the sets after the war.

I have probably not placed the three HMV900s at the bottom of the list correctly and the three 702s Y223, 224 and 241 should probably move up the list a few notches. I will aim for a better placement at the next table revision.

Peter

[peter_scott]

Originally Posted by Catkins

Would it be possible to add a footnote explaining where this dating comes from?
Thanks

Phillip

Hi Phillip,

I have changed the dating notes into hyperlinks. Unfortunately I can't actually remember the exact evidence that caused me to add all the notes.

Peter

[peter_scott]

Originally Posted by peter_scott

I have probably not placed the three HMV900s at the bottom of the list correctly and the three 702s Y223, 224 and 241 should probably move up the list a few notches. I will aim for a better placement at the next table revision.
Peter

Dating Table now revised.

[Catkins]

Hi,

Earlier in this thread I posted about the Baird circuitry in the yellow and green circles on the circuit diagram shown in Photo 1. This post will deal with the frame timebase circuitry shown in the yellow circle.

Unfortunately, this has been removed, but this is similar to the other photos I seen of sets with the Baird circuitry. Photo 2 shows where the "Baird C3 capacitor" would have been (C4 is also missing because it has been removed for restuffing).

The C3 capacitor would have been connected to the standards switch (tag 3), via a wire in the cableform (top of Photo 2), you should be able to see the cut-off wire in the cableform, and where it has been cut-off the capacitor tag too (Photo 3 shows this more clearly from a different angle).

The wire at the other end of the cableform which would have gone to the switch has also been cut-off, as can be seen in Photo 4.

Looking at the circuit diagram you should see that there is a connection from the standards switch (tag 4), to the bottom of C4. This wire does not need to be explicitly in the cableform for the switch, as there is already a wire from the bottom of C4 to VR4 (on the front panel) in the cableform. As such the circuit can be made by taking a wire from VR4 to the standards switch.

Photo 5 shows VR4, with evidence that this was how it was done, as it clearly shows a cut-off wire, which would have gone to the standards switch.

[Heatercathodeshort]

Interesting to see the pots are manufactured in the U.S.A. I wonder if they originated from their RCA family? John.