The problem you face, if you are REALLY trying to make an "authentic" erzats replica of a Baird televisor is simply: HOW MUCH ARE YOU PREPARED TO PAY FOR IT? The valves I've specified will give you a good working model, and the beam pentode output stage, driven as a cathode follower, will probably draw enough anode current to drive LED's across the cathode resistor. These valves are typical of the 1950s, however, and by the strictest historical standards are not contemporary with the Baird transmissions of 1928 - 1935.
However, if you chose to use rarer, more expensive 1930s output tube like an American type '45 or type '50; or the British types used by Baird such as the DET1A, LS5 or LS5A you will run into several problems:
(1) much lower transconductance
(2) much greater Miller effect capacitance and potential high frequency rolloff.
(3) Lower dissipation ratings than the 807 or 6L6.
(4) Lower maximum standing current (generally around 50mA) which may not be enough to cathode-drive a bank of power LEDs to peak current, and which certainly will not be sufficient to drive a bank of Luxeons.
These could certainly drive neons but they may not have the reserve standing current to fully drive high-output LEDs. Incidentally, a bright emitter tube would also be inappropriate for use with most Baird equipment, as they were "on the way out" soon after Baird gave his first public demonstration in 1926. In the halcyon days of the BBC-Baird 30-line transmissions, September 1929 to September 1935, bright emitter receiving tubes were quite obsolete.
So then we're back to the original, main problem - how do we get something to either BE or LOOK LIKE an original television neon?
The original cathode-glow neon lamps specifically designed for television, with a flat nickel cathode plate about 3 cm square, are now, quite without exaggeration, as rare as proverbial "hen's teeth". They were not manufactured for more than a brief period (1927 - 1937 at the outside) and very few people bought them. In my 40 years of interest in this subject I have seen THREE in the whole of Australia, and I HAVE BEEN LOOKING! One was privately held, one was in the Sydney Powerhouse Museum's original 30-line Televisor, and one loose example was in the Powerhouse Museum's valve collection.
Melbourne's Science Museum of Victoria (now part of Museum Victoria) assembled a mechanical television exhibit in 1971-72. The veteran engineer Gilbert Miles (b1904 - d1981, former NBTVA President), in charge of Melbourne transmissions of Jenkins-style telecine over station 3UZ in 1929, teamed with the Museum's Curator David Turner to construct the combination Nipkow camera-monitor. This had two Nipkow discs assembled on a single shaft, driven by a double-ended washing machine motor - one disc as a camera-scanner and the other as a monitor. Scanning was from 35 mm transparency slides projected onto the "camera" disc.
Turner approached the neon sign manufacturers, Claude Neon, with the idea of making re-created flat plate neons for the exhibit. On the surface of it, this seemed like a simple proposition - or so they thought. As a 17 year old schoolboy, visiting the Museum's workshop on almost a weekly basis to watch these preparations, I saw how complicated the "simple" job of making a "television neon" could be.
Turner obtained a number of old VHF tetrode tubes, type QQVO6/40s, which had an envelope and plate mounting wires of approximately the right proportions to accommodate the 1 1/2 inch square nickel cathode plate. The valves, of all-glass construction, carefully had their bases cut off and were gutted of their original cathodes, heaters, plates and grids. The polished nickel cathode plate was then crimped to the former anode wires, and an "anode frame" or square of wire the same shape as the anode's periphery was set a short distance in front of the cathode plate and anchored to the former cathode, grid and heater wires/pins of the valve base.
The metal parts were then scrupulously cleaned, the parts were sent to Claude Neon's glassblowing shop, the glass base was worked back onto a seal with the original glass valve envelope and the tube was evacuated through the original exhaust pip. With some 200 volts applied to the neon lamp that they'd made in this way, the experimenters then slowly admitted enough neon to initiate a discharge, and then more gas to reduce the striking voltage to a minimum. That being done, the tube was sealed and Turner et al retired for some preliminary self-congratulation.
Somewhere here, I have a photo of Gil Miles examining the neon lamp before its failure.
The bad news was that while this tube initially worked exceptionally well, within an hour its light output was well down and its striking voltage had risen from 90 to 300 volts. To make matters worse, the cathode plate progressively became unevenly lit. The problem was that neither Turner nor the guys at Claude Neon had any means of rf-heating the metal parts while the tube was being exhausted. Without this precaution, gas (probably oxygen) occluded into the metal surfaces would slowly "poison" the discharge as the metal parts were warmed by the discharge's ionic bombardment. After a couple more tries, Miles and Turner gave up the approach. It would be OK if they had access to professional valve manufacturing gear, but there was nothing of that type then in Melbourne.
Instead, Miles eventually used much smaller indicator neons - of the type you suggested, Marcus - in association with a very short focal length condensor lens system to optically magnify their source area. This was not an ideal solution, as it greatly restricted the angle of view of the image. Only one person could view it at a time, and even then with his/her head carefully positioned - which many Museum visitors never managed to master. Nevertheless this display continued on exhibition at the Museum's Swanston Street site until about 1984, when after many neon and valve replacements it went into storage.
And there, I understand, the replica remains - sadly.
I really feel that the Museum did not keep faith with either Miles, Turner or myself in doing this, and in more recent years Museum Victoria has turned increasingly away from the history of technology. When the "official" 50th (actually 77th) anniversary of Australian TV occurred in 2006, the Miles replica was somewhat conveniently forgotten. How would it have looked for Australian TV networks sponsoring a commemorative exhibition if they had to acknowledge that they were NOT the first in the field? Am I cynical about all of this? Of course! I subsequently worked at Museum Victoria! SAY - NO - MORE !
Anyway the time may have come where there are a sufficient number of US to actually GET SOME TV NEONS MADE - possibly as a group purchase from a current valve manufacturer like Sovtek in Russia. I am sure that our Eurodollars, English pounds and American dollars would look good to them!
Just a thought, fellas! Any takers? Is this nuts, or does this have potential?
All the best,
Chris Long, VK3AML.