Bletchley Park

[trem]

A bit off topic...sorry.
So "back in the day"...like at Bletchley Park for example...when you had big machines that used A LOT of tubes...sometimes several hundred...
What kind of power supply did they use for the heaters.?
If you had 300 tubes that drew 20mA-3 Amps...how did they deal with that.?
To run them straight off a power supply...like we do with a guitar amp...they would have needed a service of several hundred to a few thousand amps...just for the tubes.
Thank You

[The Dude]

ENIAC

On a similar note, here's an interesting read on the ENIAC. Not great detail on power supply, but if you're into that sort of thing..... I remember seeing pictures of it and reading about it in my tech school books and being amazed at what it took just to keep things running and imagining how much heat was produced by all of the tubes.

The truly amazing thing to me is how far things have come in such a short time. Just imagine what that entire building full of tubes (approximately 19,000 of 'em) could accomplish compared to a modern smart phone that you hold in your hand.

[Enzo]

I won't assume they had ONE machine with 300 tubes. They might have a tube test setup that did 25 tubes at a time or something. But this is Marshall, so look at what they used. They liked EL34s a lot, at 1.5A heater. So 300 tubes at 1.5A means 450 amps of 6v. But at the 240v mains they use that is only 22.5A.

COnsidering the exponential increase in cost as transformers grown, I'd have to vote against a 450A 6v transformer. Probably a lot cheaper and cleaner to just use 20 transformers rated for 25A each.


Or were you speaking in general? Like early Eniac computers or some such that worked on rooms full of triodes? Again I'd think they didn't have one master 400 amp heater supply, they'd more likely just have mains powered subsections all over.

But that's just me thinking, i could be wrong.

[trem]

Enzo...as usual...you make a good point.
In my head, I had imagined 300 tubes all in one machine...from one power supply.
You are right...doubt they did it that way.
I would think any big business...Phone Company...CBS Radio...places like that must have used A LOT of tubes. That must have required a lot of amps to be run into a building...just to run the heaters I would think.
I remember that giant analog computer that Turing, Tommy Flowers, Bill Tutte...or whoever it was built it...guess they called it Colossus... they used hundreds and hundreds of tubes.
I cannot get out of my head that big companies must have needed a lot of service (amp wise) back in those days.
I guess...if you needed 1,000 amps at 6 volts...you could bring in 100 amps at 60 volts.?
Thanks

[g1]

I'd think they didn't have one master 400 amp heater supply, they'd more likely just have mains powered subsections all over.

I'd think using mains power for series heater strings would be the way they would have done it. Ten 12V heaters in series across 120V (or twenty 6V heaters).

That being said, I have an old Cordovox CG-1 unit somewhere. It has about 70 tubes, mostly preamp tubes for the tone generators. One unit has the power amp and power supply, the other unit the tone generators, connected by a long umbilical cord. I hadn't ever thought about the issue of powering all those heaters. Turns out they have a 6V heater winding in the PT for the power amp section, and a 14V winding to run all those preamp tubes. The run through the umbilical cord drops it down to around 12V at the tone generator tubes. I remember it being heavy, but never paid attention to the size of the PT. That would be around 120 watts just to run the heaters in the tone generator unit.

[Merlinb]

In this photo of Colossus you can see several LT transformers on the floor, which are surely for the heaters. They were rated for about 6V 100A each as I recall, or something like that (it was written on the side).
I suppose they may have used multiple sources for different banks of heaters, although I wouldn't expect them to use many series strings, due to the reliability problems that would introduce in such a big machine (finding the dead one in a batch might take a while!)


Here you can see eight of them stacked up during the construction:


You can see the originals in this photo quite clearly:

[R.G.]

I think I typed into the forum here at some point my thumbnail estimate of what it would take to do an *all tube* digital delay. The power and cooling were daunting. You need to have inherited a power generation station.

Ah: found it.

Once I did a thumbnail design for a tube based digital delay.

Lemme see...

it takes one duotriode per flipflop, 16 flops per word, and, say, 16K words for a reasonable delay. That's 16*16*1024 = 262144 duotriodes, not counting glue logic.

Assume we could do the glue for 10% of the memory array, so we have, in rough numbers, 288,000 duotriodes. That's 6.3*0.3 = 1.89W of heater power per triode, and assuming B+ of 250V and 1ma of plate current, 0.25W of active current per flop, so the power is 288,000*(1.89+0.25) = 616.3kWatt. Power supply efficiency is probably less than 80%, but let's be generous, so AC power input to the machine is 770kW.

If you can air condition for a net efficiency of 5, you'd spend 154kW to keep it cool, and we're up to 924kW, or just a hair under a megawatt.

And we haven't even touched on the issue of roadies to carry and set it up.

[trem]

Merlin...RG -
Thanks for the info.
Staggering is what I kind of thought.
I guess it highlights one more reason tubes were a fading technology...in the general scheme of things.
Thanks Again

[Randall]

I worked at a television station a long time ago. The old timers would tell of the days of tubes when if something went amiss on a broadcast, they would pull like, 20 - 30 tubes at a time and replace them just to shotgun the situation to get back on air. Time = money. Then they would spend the time with 2 -3 guys testing them in the shop to try to find the bad one. Said they would scrap any tube they didn't trust because of the heat they would get from the higher ups, (marketing, management) to keep it looking good.

[trem]

Those were the days huh.....