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Thermionic standards converter......?

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Nuvistor
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Surprising how many inventions are made in isolation, good read.

M.O.S.I in Castle gate Manchester have a reproduction of Baby, the machine used to develop the Williams-Kilburn tube.

Well worth a visit if in that area, certain days of the week it’s working.

https://www.msimanchester.org.uk/whats-on/meet-baby

From memory there are some 807 valves in the machine to sink all the current from the thermionic diode gates.

Frank

 
Posted : 02/11/2017 4:37 pm
peterscott
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Till Eulenspiegel said
The core part of the converter will have to employ RAM memory ICs but rest assured as much of the back up circuits will employ valves.  
Till Eulenspiegel.  

Mention of "core" makes me think the delay elements could actually be core memories. Surely they would be permissible as part of a thermionic converter? Just bits of ferrite and wire. If we can create a simple D/A we can also make an A/D.

Peter

www.nostalgiatech.co.uk

 
Posted : 02/11/2017 7:29 pm
Nuvistor
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Core memory, that  takes me back, you would be able to remove power and Test Card C would still be in memory. Used that dodge to get a recalcitrant computer to boot diagnostics by loading the core an one machine and putting the core memory board in the duff meachine, got me out of trouble a few times.

Frank

 
Posted : 02/11/2017 7:41 pm
Till Eulenspiegel
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A matrix of ferrite rings?    Sounds a good idea but the minimum number of samples during the active video period has to be 512. It's all to do with rows and columns.   This a fun project but I reckon there'll be some useful spin offs from it.

Till Eulenspiegel.

 
Posted : 02/11/2017 7:52 pm
peterscott
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nuvistor said Core memory, that  takes me back, you would be able to remove power and Test Card C would still be in memory.

Well you could....but I was thinking in much simpler terms of a couple of line stores (forget the interpolation). I'm sure Darius wouldn't mind us stealing his structure. Just need to make a couple of D/As and A/Ds and a PLL. Peter

www.nostalgiatech.co.uk

 
Posted : 02/11/2017 8:04 pm
Katie Bush
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Till Eulenspiegel said
A matrix of ferrite rings?    Sounds a good idea but the minimum number of samples during the active video period has to be 512. It's all to do with rows and columns.   This a fun project but I reckon there'll be some useful spin offs from it.

Till Eulenspiegel.  

Have a word with NASA! They used ferrite core matrices for the computers aboard the Apollo missions. The matrices were reputedly "Hand Knitted" by grandmas - a NASA euphemism, because they were literally manufactured by hand by teams of 'older' ladies with a lot of experience with crafts including knitting, crochet and macramé. Just imagine hand making a large lace curtain where one flaw, a dropped thread, or a wrong 'stitch' would render the whole thing useless.

Those 'grandmas' made a grand job of getting those astronauts to the moon and back again - no room for errors there!

 
Posted : 04/11/2017 10:38 pm
Nuvistor
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First core memory developed at MIT, 2048x16 bit words, valve driven.

http://museum.mit.edu/150/21

I was fixing computers with core memory in the 1980’s and no doubt somewhere they were in use much later, perhaps still are.

Frank

 
Posted : 05/11/2017 8:47 am
Katie Bush
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Wow, Frank,

That rack just shouts out 'Thermionic Standards Converter' in waiting!

 
Posted : 05/11/2017 7:28 pm
Till Eulenspiegel
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Extract from the text of "A Murphy Special"

Also on show was the TV transmitter being constructed by the Society for the 420Mc/s amateur band. Murphy Radio, in the person of H.A.Fairhurst and H. de L. Banting were responsible for the waveform generator and pulse gear which have been modelled on the famous Murphy T.P.G.11 pattern generator.  

Till Eulenspiegel.

 
Posted : 14/11/2017 10:07 am
freya
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The TPG11 sold for £140 net trade in 1951, I must say yours looks very clean compared to mine. Mine has the ECC34`s fitted with only one 6SN7GT the chassis is quite smoke stained from years in the workshop no doubt.

It has been modified to accommodate flywheel sync sets at some point, this is selectable using a wander plug which is connected to the front chassis earth post, the plug inserted into the redundant vid - monitoring point. obviously this looses the negative going video signal.

A test report in 1951 also mentions removing the test pattern, and using as a TV transmitter.

 
Posted : 17/11/2017 7:54 pm
Till Eulenspiegel
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That's why my TPG11 must be restored to it's former glory. The more I look at the circuit diagram I begin to appreciate the what a clever design this instrument is.  Sure to some observers it might seem to have a lot of valves in it but in reality Murphy engineers have created a sync pulse generator made to almost broadcast standards at a keen price.  £140 might seem a lot of money but if you think about it some so called deluxe TV sets were being sold for the same money and those TV sets didn't have twenty-six valves in them. 

Sync up the 405 master oscillator to the 625 frame sync pulses.  We know that the frequency of the 20,250c/s oscillator is controlled by a discriminator network which uses the 50c/s mains sine wave as the reference. What I have to do is process the 625 frame sync pulse to produce something similar.  The repetition rate is the same as the mains, that is 20mS, but the mark space is way out. Remember the rules of the game are that valves must be used.  The frame sync pulse must be stretched to 10mS in order to produce a 1:1 mark space ratio. Having generated the square wave control waveform we must find out if the Murphy discriminator will accept square waves or will have to be converted into some sort of sinewave?   Whole load of engineering fun coming up!

Till Eulenspiegel. 

 
Posted : 18/11/2017 12:22 pm
freya
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It does also mention a 625  line version for continental standards is currently being produced !

 
Posted : 18/11/2017 1:14 pm
Katie Bush
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Hi David,

I'm glad you're on the case, and look forward to seeing the converter completed, somewhere in the future.

 
Posted : 18/11/2017 7:10 pm
Till Eulenspiegel
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Hi Marion, Suggested block diagram of the 625 frame sync derived  symmetrical 14 volt P -P waveform to serve as the 50c/s reference for the TPG11 20125 Hz oscillator.

Valve sync separator is easy and so is the 10millisecond monostable "one shot" 10mS frame sync pulse stretcher.  The resultant square 14 volt 1 : 1 20mS waveform will be AC coupled to produce a waveform which is symmetrical about zero.  

After the TPG11 is restored to working order the 6.3volt 50c/s AC reference waveform will be disconnected and substituted with the output from a square wave test pulse generator. If the discriminator functions correctly with this shape of reference signal then so be it. But if it has to be a sign wave signal some type of low pass filter will have to made to extract the fundamental 50Hz from the square wave signal.

Till Eulenspiegel.

MurphyTPG11Fsync
 
Posted : 19/11/2017 4:28 pm
Katie Bush
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Hi David,

You're obviously putting some thought into this project, I just wish I could take it all in. I can follow some of it, but for the most part you're operating outside of anything I've ever dealt with, so I can't really pass comment or add anything of value, but I intend to follow this project and see what I can learn (I hope).

Marion

 
Posted : 19/11/2017 5:40 pm
Till Eulenspiegel
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"but for the most part you're operating outside of anything I've ever dealt with, so I can't really pass comment"   Hi Marion, there'll be a fair bit of spin off from my earlier attempts at constructing a standards converter, that was in the 1980s.  TTL and CMOS devices were used for those projects and now we're going further back in the technology timeline and using valves to create a converter.  The Murphy TPG11 uses loads of 6SN7GT or ECC34 double triodes, the 625 line part of the converter more modern B7G and B9A all glass valves will be employed.   I'll take a look in my valve stock to find some really odd-ball types.  How about those low HT types?  

Till Eulenspiegel.

 
Posted : 19/11/2017 10:39 pm
Till Eulenspiegel
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Circuit of a "one shot" monostable.    Pulse width = 1.5CR.

OneShotTubeMultiVib
 
Posted : 20/11/2017 12:38 am
Till Eulenspiegel
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A 625 line Murphy TPG:   This pattern generator will be a much more complicated unit to construct if compared the 405 line TPG11, assuming that is the Murphy designers built the 625 line version to full CCIR standards.   The master oscillator will operate at 2H = 31,250cs. Four divide by 5 circuits, so far , so good. But if a full specification CCIR pattern generator is to be realised equalising pulses will have to be introduced before and after the five broad frame sync pulses.  Not so easy to do with all valve circuits.

A 819 version could have been made.  Master oscillator 40,950c/s.  Three dividers: 13, 9 and 7.    Single broad frame pulse = 2H. In fact in some respects a much easier instrument to make compared with the 405 line version.   

I have a Philips 819 line pattern generator, a beautifully made instrument. In due course I will introduce a topic about the restoration of it.   It does use a lot of black tar capacitors. 

Till Eulenspiegel.

 
Posted : 20/11/2017 9:14 pm
freya
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The Taylor 94A pattern generator does 625 and 405 line, providing equalising pulses in British, FCC and CCIR. the manuals are in the library I believe as Chris used to have one.

Untitled
 
Posted : 20/11/2017 9:35 pm
Katie Bush
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Posted by: Till Eulenspiegel

[..] I'll take a look in my valve stock to find some really odd-ball types.  How about those low HT types?  

Hi David

Odd ball types! - Now that's what I call enthusiasm. Or are you just a glutton for punishment?

Admittedly, low HT sounds intriguing, and on the face of it, not a bad thing if there's to be a lot of HT to barbecue one's fingers whilst working on the converter.

I guess I could have gone a bit silly and suggest you use nothing but EF80 all the way - Why? because there's no shortage of them, but I think that would be pushing things to silly and potentially unattainable goals.

Yeah... Let's say "exotic" rather than odd ball?

Marion

 
Posted : 20/11/2017 9:37 pm
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