User talk:GoldenMeadows

Vacuum Tubes

Regarding your 'heater' failures as opposed to cathode failure: heaters are only used in indirectly heated valves (tubes). The heaters themselves although they did occasionally fail, it was comparitively rare for the heater of a valve to fail. The emissivity of the cathode dropped to a point were the valve would fail to amplify or oscillate long before the heater failed. Of course, in such a scenario the heater would never get to fail, as the valve would be replaced.

As for citation: I am an electronics engineer who has been in the business since the 1960's. My apprenticeship was based on valves, and I have been involved in building and maintaining many examples of valve equipment, some having output powers in the killowatt range and operating from many thousands of volts at many tens of amps. And some amplifying the tiniest of currents (< 10e-18 amps - that's pretty small). I therefore know a bit about the subject. In the 1980's, in conjunction with a colleage, we figured out a way of determining the grid crossover current of a valve. If you know what that is, you will know why it was previously impossible to measure. That colleague has now passed on, and AFAIAA, I am now the only person on the planet who knows how to determine the exact grid crossover current of a valve. There is a method of extrapolating it, but it only gives an approximation. Sadly the method has no commercial value as nobody uses valves any more. The only real application where this grid crossover current needs to be known has long ben taken over by MOS-FET devices.

Having said that, I have not encountered any valve where the heater has failed (other than due to being run from too high voltage). I am aware of plenty of filaments (directly heated) that have failed. I B Wright 21:01, 14 November 2006 (UTC)

More Vacuum Tubes

Thank you for you further comments. To answer some of your points.

The exact mechanism that shortened the life of valves was not fully understood at the time of the Second World War. Tommy Flowers (as you state) believed that the most harm was done during start up and shut down. Such was the lack of understanding that no one else believed him. Flowers nearly had it right: the most damage is done during start up. Whilst the cathode is warming up it was expected to start emitting electrons as soon as sufficient temperature was reached. This meant that the cathode was emitting at saturation until the temperature exceeded the point where the saturation current was greater than the required cathode current. This was a particular problem in Thyratrons where the the reverse flowing ion current would quickly strip the cathode under such conditions. Once Flowers demonstrated that he was correct in his belief, there followed greater understanding. Post war valve designs employed rectifier valves where the cathode was deliberately heated much more slowly than the rest of the valves. This minimised the wear (but didn't eliminate it completely) to the active valves at the expense of greater wear to the rectifier. However, the expense of replacement valves was considerably reduced especially as the rectifier was usually the cheapest valve.

I think Tony Sale's recollection of the powering of Colossus is faulty (remember he was not directly involved in the engineering side, being a codebreaker). Flowers, much like engineers today, didn't like to dirty their hands designing something as simple as a power supply. However, Flowers would have found a total lack of off the shelf power supplies for powering a 1500 valve project with capacity to spare for future expansion.

What he did was resort to the Westat power supplies that were actually designed for powering telephone exchanges (The UK used 50 volts then, rather than the more international standard of 48 volts in use today). They were rated at 50 volts at 20 Amps each. As you note, Flowers connected 5 of them in series to provide +200 and -150 HT rails for the valves. If you grab your calculator you will discover that each Westat unit is rated at 1kW each, the 5 of them accounting for the 5kW. But this was only the HT supply. The Westat units did not power the heaters of the valves (they wouldn't have provided enough power anyway). These were separately fed from a transformer. What I don't know is whether the heaters were parallel connected (as is the norm for 6.3 volt valves) or series parallel. My information on Colosus says that Mullard EF37s were used (which happens to be a close equivalent of the VR56). I don't have a data sheet for the VR56 (strangely), but the EF37's heater is rated at 200 mA (which may be why this particular valve was chosen). The thyratron valves would be about 800 to 1000 mA each (and there were 508 of those required to emulate the Lorenz rotors). The power required to heat those and 2000 odd EF37s as ever with valve equipment dwarfed the HT power requirements. The rebuild has had to sacrifice authenticity for availability and has been made using the post war improved EF37A (lower microphony and lower heater induced hum).

I was not refering to directly heated valves when I said that I had never encountered an open circuit heater. I have encountered a few open circuit filaments in directly heated valves. I didn't say it didn't happen, just that I hadn't encountered them - not even when I serviced valve colour televisions, and I don't recall my colleages encountering one either (the frantic trial replacement of each valve in turn would have been a dead give away), so I do not accept that it was a common failure mode.

I am not convinced that thermistors were incorporated in the heater chain of AC/DC televisions for the purpose of slowing down valve failure. AC/DC radios got along quite happily without them. I believe that the thermistor was purely to limit the switch on surge (though the lowering of the stress to the heaters was a convenient side effect). The principle risk to the heater wasn't the bit of the heater that was actually inside the cathode tube, but the few milimetres that led from the cathode to the connection point. On applying power, this short length, in many valves, lit up like a light bulb and then dimed down as the heater reistance rose and the current fell. Parallel connected valves (E series) did this as well and they had no thermistor either.

Heater failure due to burn out is already mentioned in the Vacuum Tube article. It does not belong in the Colossus part of the article because that is not the failure mode that Flowers was trying to eliminate. The most common cause of a 'burnt out' valve as people incorrectly describe it, is emission failure of the cathode and it was this that Flowers was addressing.

I should perhaps end by observing that Mazda's AC/ series valves produced in the 1930's never failed. I never encountered a failed one (low emission or open circuit heater). Like many a service shop, we bought a full set of spares and never used a single one.

I B Wright 12:36, 18 November 2006 (UTC)

I just had a look at te VR56 page that you linked to and one or two other pages that reference this valve. The shape of the VR56 doesn't quite match the shape of the valves that can be seen in some of the very rare wartime photographs. However it is more than likely that in order not to attract undue attention to the size of the project (25,000 valves is bound to get noticed), that valves may have been multi sourced. I think the VR56 may be a Canadian device (Do you know where they came from?). I have not been able to locate a VR56 data sheet.

I was curious about the CV1056 on which someone has helpfully written 'EF36' in pencil. A quick trawl through my data sheets reveals that the EF36 was a forerunner of the EF37 (later improved to become the EF37A). The EF37A data sheet is actually headed EF36 and EF37A. the only qualification is the anti microphnic construction of the later valve.

I B Wright 23:12, 19 November 2006 (UTC)

Religous perspectives on dinosaurs (Rpod)

Thats a good point you raise there about species dying and Garden of Eden. Do you have a source for it? SmithBlue 02:18, 17 January 2007 (UTC) Hi -Orangemarlin is posting that "you have called us stupid twice". I can't find what he is refering to. Please point it out to me if you know. Your rewrite looks very interesting. One "bullet proof" way of including it is to put it forward as "Historical Christian Religous perspective on dinosaurs" - properly cited its then beyond dispute (by reasonable editors and we can find those if we have to.) I've never met fundamentalists before (scientific ones that is) - its not a pleasant experience. SmithBlue 00:10, 19 January 2007 (UTC)

Re-reading posts on the discusion page I begin to think of the story about BillyGoat Gruff and certain beings that lived under a bridge. The lack of contribution to article of material supporting claimed position, the slow revert war over "kinds", the stated belief that "there are no religous perspectives on dinosaurs", the "call us stupid" claim,

the avoidance of:

• questions asked about the editors own position,
• historical Rpods,
• nonUS and nonWest European Christianity Rpods,
• Rpod of fundamentalist Muslims and Jews and Hindus,

all give weight to your question of "serious contributor?". I wont be paying much further attention to editor posts unless material is contributed. SmithBlue 02:49, 19 January 2007 (UTC)

Goat-Gruff Theory didnt stand up - quick read of editors's talk pages shows apparent genuine editors. They been comming for a while - appear to dislike creationists. However editor is aware of many issues that the editor avoids at Rpod(as above). SmithBlue 03:14, 19 January 2007 (UTC)