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Vintage Computers Any vintage computer systems, calculators, video games etc., but with an emphasis on 1980s and earlier equipment.

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Old 13th Nov 2004, 10:58 am   #21
ppppenguin
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Default Re: Thyratron pulse generator (for Sam)

When I studied Elec Eng at Imperial College we all had to do some work in Eric Laithwaite's " heavy " lab. This was an interesting place for us light current types. Sheets of metal used to fly down the lab corridor from Laithwaite's linear motor experiments and you learnt to keep out of their way

One of the experiments we did was to synchronise a small (5kW) alternator to the mains. It was driven by a DC motor and connected to an old fashioned 3 lamp synchroniser. You would up the DC motor gently and tried to hold everthing in phase with the 2 outer lamps equally lit. Then you closed the switch to bring the alternator on line. 10 degrees out and it would shudder and jump into lock. Somebody (not while I was there) got it 180 degrees out which took out 3x100A fuses.

Happy days!

Most modern plant is synchronised automatically. There is also a synchroscope which shows the phase angle between the alternator and the busbars on a clock face calibrated in degrees.
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Old 13th Nov 2004, 11:25 am   #22
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Default Re: Thyratron pulse generator (for Sam)

Less of the old-fashioned! We still do that! I did it about three weeks ago. Same set-up: DC motor, stiff rheostats, a synchronous generator, three flashing lights (one red, two green) of the synchroscope, and a switch. The synchroscope is quite mindbending to fugure out! 3-phase!

Nice to know the University of Durham is right up there with modern techology! Maybe it is just as well I came here!

Another thought for the pulse generator, could you take a radio-control unit from a clock, and amplify the pulse from the Rugby signal to control the thyratron?

Sam
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Old 13th Nov 2004, 11:53 am   #23
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Default Re: Thyratron pulse generator (for Sam)

Sam, your synchoniser is modern. It's got coloured lamps! Bback in 1977 ISTR ours had some very ancient looking pearl bulbs.

Just remember that in all 3 phase calculations your answer will be wrong by a factor of 3 or SQRT(3)

Maybe Durham bought some of Imperial's old kit when Imperial stopped doing heavy current stuff. There aren't many universities where you can still do heavy current Elec Eng degrees. But then you don't need engineers to run the grid any more. Just accountants
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Old 13th Nov 2004, 12:22 pm   #24
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Default Re: Thyratron pulse generator (for Sam)

Sam,

an MSF clock with a one pulse-per-second TTL ouput will synchronise the current circuit quite well (I tried it using a function generator), but there is still a little jitter on the output.

Jim.
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Old 13th Nov 2004, 5:51 pm   #25
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Updated the web page to include notes on possible alternative valve types.

Jim.
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Old 17th Nov 2004, 7:58 pm   #26
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Default Re: Thyratron pulse generator (for Sam)

Sam,

I've done a little work on the thyratron frequency divider today, and managed to get a divide-by-ten circuit working, with a 50Hz input (only uses 6 components!). It needs a lot of refinement, but again, I have the maths sorted. I doubt I'll get it on the website before Friday, but I'll keep you posted.

Jim.
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Old 23rd Nov 2004, 1:55 am   #27
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Default Re: Thyratron pulse generator (for Sam)

Sam,

I've posted the basic frequency divider circuit here:

www.g1jbg.co.uk/thyrdiv.htm

The next step is to cascade them, so I can get 1pps out of the end.

Jim.
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Old 23rd Nov 2004, 9:26 pm   #28
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Default Re: Thyratron pulse generator (for Sam)

Sam,

having done a little thinking, and considering that each EN91 draws 600mA at 6.3V, I have something here that you may need, a heater transformer with a 60A (no I haven't misplaced a decimal point) ouput. Let me know if you want it.

Jim.
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Old 23rd Nov 2004, 9:40 pm   #29
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Default Re: Thyratron pulse generator (for Sam)

That will be VERY useful when the clock is finalised. I only have a small 3A heater transformer. I was thinking I could use some kind of series/parallel arrangement for each ring/section, with capacitive droppers. I worked out 50 EN91s (round estimate of the number involved!) would need either 30A of heater current if they were in parallel, or would drop 315v if they were in series!

Looks lihe the heater power will be the main drain on the National Grid!

I will have a think about the transformer, and where it would be best sent.

Sam
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Old 23rd Nov 2004, 11:24 pm   #30
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Default Re: Thyratron pulse generator (for Sam)

Series heaters may give you H-K insulation worries.
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Old 24th Nov 2004, 12:19 am   #31
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Default Re: Thyratron pulse generator (for Sam)

I had been mindful of the HK resistance/voltage, but didn't realise exactly how much of a problem it could be - for an EN91, the heater can be 100v negative wrt cathode, but only 25v positive wrt cathode! Looks like a parallel arrangemet will have to be used. At least I can use AC heaters! The circuit I am working from is so old, it needs DC filaments (Wynn-Williams stated batteries or separate LT windings for each Thyratron!).

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Old 24th Nov 2004, 12:26 am   #32
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Default Re: Thyratron pulse generator (for Sam)

Yes,

for 2D21 / EN91

peak HK, heater -ve, 100V
peak HK, heater +ve, 25V

(From Brimar manual No8 )

Jim.
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Old 24th Nov 2004, 12:39 am   #33
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Default Re: Thyratron pulse generator (for Sam)

Sam,

you got to the data book first!

I have a circuit that uses SCRs (thyristors) as the switching device, which should easily adapt to the thyratron. It uses capacitors connected between the anodes of the SCRs to pass the reset pulse. However, it does require the use of steering diodes for the trigger pulse - are diodes allowable in the design? - bearing in mind the selenium diodes were used in the ring counter circuits of Sumlock Anita calculators of this era (along with cold cathode trigger tubes).

If you're interested, the circuit is in the G.E. (General Electric) SCR manual, fifth edition, 1972 - found in the works library last week.

I have scanning problems at the moment, so I'll try and make it available soon.

Jim.
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Old 24th Nov 2004, 12:45 am   #34
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Default Re: Thyratron pulse generator (for Sam)

I'm extremely pleased that what I thought were a load of junk components have generated this much interest. I still have maybe 10 EN91s or equivalents, so if anybody wants these, let me know (Sam?)

Best regards, Paul
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Old 24th Nov 2004, 12:50 am   #35
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Default Re: Thyratron pulse generator (for Sam)

I suppose the diode problem would be solved if anyone has a couple of hundred EB91s lying about..........

Jim.
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Old 24th Nov 2004, 9:17 am   #36
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Default Re: Thyratron pulse generator (for Sam)

Hi Jim, how many do you need, plenty of EB91's and equivs, NOS and pulls but can be tested easily. I'm also not located too far from Sam.
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Old 24th Nov 2004, 9:56 am   #37
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Default Re: Thyratron pulse generator (for Sam)

Another 10 EN91s will be useful! I think I am nearly to the number I will need for the counters now!

I was thinking of basing the clock on Wynn-Williams' counters, as this was the only circuit I had found! I had read about the ANITA calculators, and the selenium diodes in them. I suppose I can try both kinds when I start expertimenting. I have an EB91, and some 12/6H6s about somewhere!

This thing could end up REALLY big!

Sam

PS, what does SCR stand for? We have started to learn about thyristors, but I haven't come accross that term!
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Old 24th Nov 2004, 10:25 am   #38
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Default Re: Thyratron pulse generator (for Sam)

SCR=Silicon Controlled Rectifier=thyristor
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Old 24th Nov 2004, 10:45 am   #39
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Default Re: Thyratron pulse generator (for Sam)

If you are struggling with finding a big enough transformer then I suggest pairing up the heaters and running the whole lot off a car battery.

Now just add a vibratorary or rotary converter and the whole thing becomes portable! Make sure that the display is kept in a separate unit - then the main guts can go in a ruck sack with the display strapped to your arm.

This has got to beat a Rolex any day.


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Old 25th Nov 2004, 1:17 am   #40
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Default Re: Thyratron pulse generator (for Sam)

Sam,

I've created a small index page for these experiments, which is the best place to link to:

http://www.g1jbg.co.uk/thyratro.htm

I have also added the scans of the SCR ring counters to this index. The Anode coupled version looks to be the most promising.

If you want to stay all thermionic, it would be worth taking Ed up on his offer of the EB91s, but I intend to try it with some cold cathode trigger tubes I have, and some ordinary silicon diodes - I after I get a reasonable circuit for the pulse source.

I've checked the transformer tonight, and it has two 6.3V windings, one of 60A and one of 40A, so that should keep you going!

Jim.

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