Homebrew TV's in New Zealand.

[Argus25]

Split from this thread:-

https://www.vintage-radio.net/forum/...d.php?t=146228

Originally Posted by kurtm--

The Argos Tv project was most likely the one used by New Zealand radio ameatures to home build Tvs in 1958/9 when test transmissions started in Auckland.

Hi Kurt,

I think this was probably unlikely. The fixed channel nature, the reverse video modulation and the AM sound of the Argus would have put most constructors in NZ off the project.

I do not know of any Argus set being constructed in NZ around the early 60's, in Auckland at least. (there may have been one of course but it would have required extensive mods to work with the frequency of the VHF TV signals, 625 line and FM sound transmitted then in NZ). I was around in the '60's and knew people who constructed home grown TV sets though, but not the Argus.

The most popular small hobby set made in NZ in that era was the one from 1957 Radio,Television and Hobbies. (Image of front cover attached) that had an RF tuner and the correct scanning frequencies & FM sound system to suit the NZ transmissions & the 5BP1 crt. Some of these sets in NZ may have used the VCR97, but I never actually saw one.

(I recently built an Argus TV with VCR97 in Australia, but I had a 625/405 standards converter and RF modulators to replicate the UK's TV transmissions before I started the project)

There is a very good construction article on the 5BP1 TV set here:

http://members.iinet.net.au/~cool386...0receiver.html

Hugo.

[Argus25]

Looking back over the data, one way to have got the Argus to work with the NZ TV transmissions back then could have been to use a VHF tuner on its front end. The NZ transmissions had (like the American ones) the sound carrier frequencies above the vision carrier , by 5.5MHz in the NZ case, rather than the American 4.5 MHz.

The Argus was designed a 45MHz vision channels and a 41.5 sound channel (AM) So if that was widened to 5.5 MHz gap, say with a 40 MHz sound and 45.5MHz vision frequency and a VHF tuner used on the Argus TV input, this reflects the down converted carriers with vision frequencies higher than sound (because the oscillator in the tuner runs above the received carriers). Then it still would require the AM detector to be re-configured into an FM detector too, but it would have worked. So perhaps there were some heavily modified Argus sets able to receive the NZ Ch2 or 3 transmissions.

I think what I know as the "Bell Box" is a TV1.

[kurtm--]

My father's 1957 Argus (or very very similar) project was unaltered with fixed single rf tuner coil 405 line AM sound. No multi-channel tuner.

It used a 9" (or 10") P4 electrostatic deflection radar scope bought from Army Surplus in Newmarket. The 3x4" image was negative when it first came on but switching a diode took care of that.

It was never put in a cabinet and stayed on the basement workbench as an interesting project. In 1958 I started my apprenticeship at Bell and worked in the factory where the studio used to be. It had been converted to a radio assembly line.

Oh! the memories. Have fun!

Kurt

[Argus25]

Originally Posted by kurtm--

My father's 1957 Argus (or very very similar) project was unaltered with fixed single rf tuner coil 405 line AM sound. No multi-channel tuner.

Kurt,

Your father must have had some other VHF signal source to drive it, not the VHF 625 line FM NZ transmissions with carriers that had sound higher than vision and both with frequencies out of range for the Argus's TRF RF circuits. Of course the set might have been something loosely based on an Argus with a similar look to it.

However, the deflection amplifiers in the Argus can only just manage to deflect a 5.5 inch electrostatic image (the deflection stages running off 400 to 450V HT) with a 2.4kV EHT. Using a 9 or 10" CRT requires nearly double that EHT and would have also required very special deflection amplifiers running off an HT supply of at least, 800v to 1000V, not part of the Argus design, but if it was limited to a 3x4" image would help a lot.

So it is interesting from your description of the set what one can deduce; it cannot have been exactly like the Argus, electrically at least. So it sounds to me like he must have made quite a unique TV for himself at the time, and it would have been quite a challenge with the larger electrostatic CRT.

The primary reason electrostatic CRT's for TV work got abandoned in favor of eletromagnetic CRT's, is that the deflection voltage required for an electrostatic CRT is directly proportional to the EHT, but in electromagnetic deflection, the deflection current required is proportional to the square root of the EHT. So electrostatic CRT's over 10 to 12 inches in diameter required very high impractical sawtooth deflection voltages, especially if they had an EHT high enough for a reasonable brightness picture.

The Americans though stuck with a 7" electrostatic CRT in many of their small TV's (the 7JP4), it had a 6kV anode voltage and required +/450V pp (900v) total sawtooth drive for the line deflection.

[Synchrodyne]

Was it not the case that the original Bell experimental TV transmissions were to the 405-line standard? And that a change was made to the 625-line (CCIR) standard following the Government decision in 1958 that this would be the NZ standard. So the Argus unmodified would have worked in NZ for the initial period of experimental transmissions.


Cheers,

[paulsherwin]

It must have been an option to use the UK 405 standard in NZ and even in Australia given the British heritage, but the UK itself had pretty much decided to move to 625 by the late 50s, though it would take a decade to implement there.

[Synchrodyne]

I don't think that there was any real doubt that 625 lines would be selected for New Zealand. But until the time came to make a decision, all possibilities were on the table, at least in a nominal sense.

Cheers,

[Argus25]

Originally Posted by Synchrodyne

Was it not the case that the original Bell experimental TV transmissions were to the 405-line standard? And that a change was made to the 625-line (CCIR) standard following the Government decision in 1958 that this would be the NZ standard. So the Argus unmodified would have worked in NZ for the initial period of experimental transmissions.

Yes, but probably the only people that would have build an Argus like set then, in 1957 in NZ, would have been the initial experimenters themselves at Bell, not hobbyists in the community. They would have made home made TV sets only after the 625 transmissions were on the air for a while and therefore not built Argus like sets, but the one from Radio Television & Hobbies that had 625 line scan and FM sound, which is the point I was trying to make.