"The Brute" takes form.

Forum for discussion of narrow-bandwidth mechanical television

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Postby AncientBrit » Sat Jan 31, 2009 12:20 am

Steve re schematics,

Tektronix manuals were always well produced.

I still have one for the 545B I think somewhere.

Regards,

Graham
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Postby Steve Anderson » Sat Jan 31, 2009 1:02 am

AncientBrit wrote:Tektronix manuals were always well produced. I still have one for the 545B I think somewhere. Graham


There are of course exceptions, and Tek is one of them. I too have the full set for the 545 which is what I cut my teeth on in the 70s. Large files though...just like the instrument itself! Turn it on and go and have a coffee..

The Tek 'scope I recently bought is more like a womans handbag and coloured to suit. It was in real terms about the same price as the Goldstar it replaced after some 15 years but does 100 things more and is certainly more accurate. Some 1500 quid, but worth every penny. A TDS2014B.

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Postby AncientBrit » Sat Jan 31, 2009 2:45 am

Nice if you have the money Steve.

Set it against business expenses?!

Regards,

Graham
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Postby Steve Anderson » Sat Jan 31, 2009 12:51 pm

AncientBrit wrote:Nice if you have the money Steve. Set it against business expenses?! Regards, Graham


In a way it is part of my operating expenses. In the UK one would set it off against tax, but as I don't pay tax I just see it as a vital expense. After all I simply wouldn't be able to do my work without it. A bit like a taxi driver without a taxi.

If it lasts five years (and I hope it lasts longer than that) that's about 80 pence a day which is far less than running an automobile (which I don't have).

I put aside an amount for equipment, tools and component stocks each month such that if a job comes along I can cope with it and purchase whatever is required. For example this laptop PC I'm using right now could do with being replaced, there's nothing wrong with it and does all I ask of it. But after nearly five years it's starting to look scruffy. Not very impressive to potential clients. If it were possible I would just replace the case and keyboard and hey! One new PC.

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Postby Steve Anderson » Sun Feb 15, 2009 5:48 pm

dominicbeesley wrote:Those little tubes really are sweet. Dom


Well they ain't that little. The EF91 pentode is the large tube in the centre. On the left is a 9002 single triode, to the right is a rather corroded 7586 single triode Nuvistor.

The tube at the front is a 6111WA...this is a twin triode ideal for the smallest of NBTV CRT-based displays. It's ratings are similar to those in the ECCxx range including a plate dissipation of over 1W.

I've changed my mind over which tubes to use in 'The Brute', I'll still be using EF91's for the 5" deflection but for the 1" tube I'll use the 9002's...just for the heck of it.

Steve A.

Sorry for the poor focus, that #@&! camera again!...and it was at its smallest aperture, f11.
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Postby Viewmaster » Sun Feb 15, 2009 7:22 pm

Steve Anderson wrote:[
I've changed my mind over which tubes to use in 'The Brute', I'll still be using EF91's for the 5" deflection but for the 1" tube I'll use the 9002's...just for the heck of it.

.


Why not use the valve that won World War 2 for us? .....The EF50. They come up for sale on eBay very often and are cheapy.
Albert.
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Postby Steve Anderson » Sun Feb 15, 2009 7:37 pm

AncientBrit wrote:..re Mini NBTV scope using ICP1...."Here's one I made earlier" Regards, Graham


Graham, I've just been studying the circuit diagram for your Mini 1CP1 NBTV monitor and notice you drove the vertical differentially where the datasheet I have (one and one only) mentions asymmetrical drive. Nothing wrong with doing that, I was wondering if there were any visible effects due to the anodes/grids being modulated? Like defocussing, intensity modulation or deflection sensitivity changes.

My example needs 130V p/p vertical drive at 600V on the tube, with an HT of 215V I was wondering why you did it? Not a criticism, I'm just quizzical. Using the datasheet values the nominal drive is 153V p/p so it seems I'm lucky and have a sensitive CRT, perhaps you were worried about getting a slightly 'deaf' tube where 215V might become marginal.

If anyone has a datasheet for the 1CP1 or the DH/DB3-91 (not the philips version which I already have) I sure would appreciate a copy.

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Postby Steve Anderson » Sun Feb 15, 2009 7:48 pm

Viewmaster wrote:Why not use the valve that won World War 2 for us? .....The EF50. They come up for sale on eBay very often and are cheapy. Albert.


They are striking looking devices and perhaps for the next project using tubes/valves I'll consider them. The downside is you can't see that lovely glow.

The guy I buy most of my tubes/valves from lists them at three quid, or 20 at 2.40 each. The sockets/bases would you believe are a fiver! More than the tube!!

Sometime in the future I would like to use some space-charge tubes, those sort used in car radios that only needed 12V on the anode/plate. Also some of those 'battery' tubes for portable radios that ran with a 50-90V supply (from a battery) and 1.4/2.8V filaments. Trouble is I can't yet find a use for them!

Steve A.
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Postby Steve Anderson » Wed Feb 18, 2009 7:17 pm

A small update on "The Brute". The timebases are all done and work correctly in all four modes. The PWM drive for the main 5" CRT is done.

I did mention a little while back that it was the 1" waveform monitor CRT that was to be next but due to mechanical issues I have had to do the EM84 indicator first, the 1" CRT will be next.

Below shows the EM84 under test with zero signal and with nominal frame burst level, the two bars will be calibrated later to just meet at the correct level of burst. Photos were taken before I put it in its rightful place on the chassis.

One thing I might add is that the driver circuit worked flawlessly on its own yesterday but when I glued on the tube today the thing was unstable giving a fuzzy display at certain levels. I tried decoupling the supply and putting in a grid-stopper resistor, neither worked. So I put a 100k resistor is series with the grid then a 100n cap to ground...all OK now.

I looked through all the radio circuits I have that use a EM84 and they all have a cap to ground at the grid. Seems the tube is unstable without one.

It looks a bit fuzzy in the photos, it's just the thing is quite bright. I might have to put a neutral-density filter on it to match the CRTs.

Steve A.
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Postby AncientBrit » Wed Feb 18, 2009 11:47 pm

Steve, re symmetrical drive to 1 inch scope.

I was worried that I would run into the rails with single ended drive so I opted for push-pull.

You are correct that the tube is designed for single ended drive on the Y plates, and yes, there is some slight defocusing and geometric error when driving Y push-pull.

It's a pity that a few more pins were not available for Y2, and for manual setting of the focus.
Having said that, the focus is sharp and amazing for something 40years old.


Regards,


Graham
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Postby Steve Anderson » Thu Feb 19, 2009 12:36 am

AncientBrit wrote:Steve, re symmetrical drive to 1 inch scope. I was worried that I would run into the rails with single ended drive so I opted for push-pull.


I had a feeling that might be the case. I'm using it as designed with a deflection stage fed with 330V and the deflection tube is incorporated in the DC-coupled feedback loop of an op-amp, the combination can output over 200V p/p and is still very linear. Traces attached at 160V p/p, I only need around 110V for the example I have.

AncientBrit wrote:You are correct that the tube is designed for single ended drive on the Y plates, and yes, there is some slight defocusing and geometric error when driving Y push-pull. It's a pity that a few more pins were not available for Y2, and for manual setting of the focus. Having said that, the focus is sharp and amazing for something 40years old. Regards, Graham


Agreed, I would have made one end of the heater common with the cathode freeing up a pin for Y2, also many Loctal tubes used the spigot/keyway as a ninth pin. The sockets I have here support that. But as you say the focus is amazingly good as is.

Steve A.
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Postby Steve Anderson » Mon Feb 23, 2009 12:57 am

...further update...WaveForm Monitor is done, complete with very simple cursors just showing 0V and peak white (+3.5V in my case)...don't you just love things that glow in the dark...

Steve A.
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Postby Viewmaster » Mon Feb 23, 2009 1:40 am

Steve Anderson wrote:......don't you just love things that glow in the dark...
Steve A.


Perhaps glow worms could be modulated to replace LED's. ?
It's years since I've seen a glow worm.
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Postby Panrock » Mon Feb 23, 2009 8:49 am

Looks great Steve! I can understand the kick you're getting from this.

Steve O
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Postby dominicbeesley » Mon Feb 23, 2009 7:30 pm

Wow Steve, that looks pretty impressive with the cursors and all. In the end up did you go single ended for the Y-plate?

Dom
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