"The Brute" takes form.

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Re: "The Brute" takes form.

Postby Viewmaster » Sat Oct 18, 2008 7:55 pm

Steve Anderson wrote:At the top-left is the 'transformer farm' Steve A.


Is that a 'step down' from an animal farm or a 'step up'?

OK I'll go quietly! :)
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Postby Klaas Robers » Sun Oct 19, 2008 7:11 pm

Steve, don't you fear any hum caused by the magnetic stray fields of the transformers in the deflection of your CRTs? And that without a magnetic screening of the tube?

I had this problem once many years ago when I tried to build an oscilloscope with a 3BP1. Although the tube had a mu-metal screening I had hum of about 1/2 cm on the spot. I hadn't positioned the transformer aligned with the center of the tube and behind the tube. Too much mechanical work was done at that moment to change the lay-out. The oscilloscope never ran.
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Postby Steve Anderson » Sun Oct 19, 2008 8:39 pm

Klaas Robers wrote:Steve, don't you fear any hum caused by the magnetic stray fields of the transformers in the deflection of your CRTs?


Yes I am, that's why I squeezed them into the furthest corner of the chassis from the CRTs. If the previous 3" version is anything to go by then this distance (hopefully) will be enough. If not there's two things I can do, 1) to remove the transformers from the chassis and put them in a separate transformer box, which I did with the 3" display, however those transformers were much closer, around 100mm, these are some 350mm away from the closest point of either CRT. Or 2) find a source of sheet Mu-Metal and get a shield made up for the CRTs. Or even both!

Plus I'm hoping (perhaps foolishly) the rather random alignment of the transformers axis will help to an extent in canceling each others magnetic field.

Toroidal transformers are much better in this respect, but they've only just hit the retail stores here but not with 500V secondaries.

Time will tell...

Steve A.
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Postby Panrock » Sun Oct 19, 2008 9:34 pm

Klaas makes a good point. It's highly likely, I'm afraid, that you'll get some effect from the transformers without a mu-metal screen. In general the transformer(s) should at the insensitive end of the tube, far away behind the socket end if possible. This arrangement on my 'Argus' (built in 1990) was found to work satisfactorily. The mu-metal screen though was crucial.

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Postby Steve Anderson » Sun Oct 19, 2008 9:58 pm

Panrock wrote:It's highly likely, I'm afraid, that you'll get some effect from the transformers without a mu-metal screen. Steve O.


Yes it was a good point from Klaas and one I had thought about as I laid out the basic form of the chassis for "The Brute". It's not easy to judge the dimensions of your "Argus" but the single big transformer looks somewhat closer to the CRT than the cluster of smaller ones I'm using. However you do have a Mu-Metal screen.

I'm prepared to re-house the transformers if needed, it's been at the back of my mind since I started on this project so I'm ready should it be necessary.

I've dug out the 3" display and initially there were two transformers actually within 80mm of the CRT, they caused about 1mm of hum modulation, annoying enough for me to relocate them. I guess it's a case of wait and see.

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Postby AncientBrit » Tue Oct 21, 2008 5:18 pm

>Steve O,

Very nice construction. I bet the innards are just as neat,

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"The Brute"

Postby Steve Anderson » Fri Oct 24, 2008 1:20 pm

I've decided to turn this thread into a 'construction diary', much as Andrew did a while ago with his mechanical televisor, I'll update it when pertinent.

The current status is that the boards completed in Initial 1.jpg are tested and work as planned. But the transformer that supplies the heaters for all the tubes isn't up to the task (the one with the brown winding insulation in the same photo). So I'm going to have to add yet another one...there goes my baggage allowance.

The reason is that I'm feeding the heaters with regulated DC which has a slow rise to 12.6V (around ten seconds) at switch-on thus requiring beefier transformers than usual. Ho hum.

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Slow progress.

Postby Steve Anderson » Mon Oct 27, 2008 7:37 pm

Gents,

The current status of "The Brute" is the boards in the photos are all hooked up and working, a waveform display of it working in 36-line non-interlaced mode is attached. The yellow trace is the AC coupled video input, the green one after DC clamping. The cyan is the decoder frame pulse from the 24kHz burst in the video waveform and the magenta is the line drive for the timebase.

I still have yet to get the beefier transformer for the tube/valve heaters but at this stage it's not urgent.

Next is to move onto the timebases and the interlacing arrangement (the logic for interlacing is done). Then the CRT PWM drive.

This all might come to a temporary halt later this week as 'real' work has surfaced.

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Postby dominicbeesley » Tue Oct 28, 2008 7:23 am

Hi Steve,

I've noticed on some of your other pictures (including your Avatar) that you have a little dot train at the bottom left of each frame - I'm guessing from the scope traces above that this means you scan bottom left to top-right.

What's the dot train/frame pulse for is it just a frame pulse, or is it more clever and some sort of interlace/eq. pulses/colour burst? Would your circuits still work with a lower frequency burst?

Have you a spec for your "standard", I'd like to collect as many standards as possible before I embark on the next version of my encoder software.

Cheers

Dom
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Postby Steve Anderson » Tue Oct 28, 2008 11:41 am

dominicbeesley wrote:Hi Steve, I've noticed on some of your other pictures (including your Avatar) that you have a little dot train at the bottom left of each frame - I'm guessing from the scope traces above that this means you scan bottom left to top-right.


I scan left-to-right for the lines, top-to-bottom for the frame. The row of 16 dots at the bottom of the frame are what I've dubbed 'frame reference', to replace the usual frame (non) sync arrangement. It's 16 cycles of full-amplitude video at 24kHz (I'm sampling at 48kHz). The circuits and a simple explanation are in the thread 'HD NBTV?'. Download the pdf called PWM CRTmon3.pdf, it's two or three pages back in the listing of posts.

dominicbeesley wrote:Have you a spec for your "standard", I'd like to collect as many standards as possible before I embark on the next version of my encoder software. Cheers Dom


Well it is a 'standard' but it's totally unique to me, no-one else uses it as far as I know. It's sync-less, not a sync pulse in sight and has been used at 36, 48 and 72 lines, interlaced and non-interlaced. The 'frame reference' is in the last line of the picture, you lose one line but one day I'll get around to recovering it. After the burst there's a period of black where clamping is done to get correct luminance levels.

I've modified the timing slightly for "The Brute" due to the fact that it's multi-standard, but the principle is the same...so yet another standard! I really wouldn't bother creating software to deal with it unless you really really wanted to.

My avatar is an off-screen shot at 48 lines, I removed the green colour of the CRT.

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Postby dominicbeesley » Tue Oct 28, 2008 8:57 pm

Thanks Steve,

I'm just interested in collecting as many standards as possible and hope to make a "standard" designer that can set up various parameters in the software and then make a video wav file as specified.

Thanks for the link to the article, I'd been through the original thread a while ago but missed the actual article.

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Lack of progress...

Postby Steve Anderson » Wed Dec 10, 2008 9:33 pm

Dear All,

There's been no further progress on 'The Brute' as real work has taken up all my time recently. I'm hoping to get back to it in a week or ten days or so. But I don't see it being finished before the end of this year now, possibly late January.

I'll keep you updated as and when.

I do log on to the forum almost every day just to see that things are OK.

...and welcome to the new members...

Steve A.
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Postby AncientBrit » Wed Dec 10, 2008 11:32 pm

Good to see you are still around Steve, ("Local" situation and all that).

That's the trouble with paid work, it gets in the way of more interesting things,

Kind regards,

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Postby Steve Anderson » Thu Dec 18, 2008 10:39 pm

A small update...

Interspersed between real work and other matters I've been able to fit a suitable transformer to 'The Brute' for the heaters and +/-12V supplies. It hardly even runs warm. The two LM317 regulators which are bolted to what is quite a large chassis run very cool too.

I'm going to have to rearrange some of the other transformers to fit the new larger one in. More concerns regarding stray magnetic fields. Time will tell on this.

The design work for the cursor display on the 1" CRT is done, it was simpler than I thought it was going to be.

I'm still aiming for the end of January for completion, but who knows what might happen.

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Postby Viewmaster » Thu Dec 18, 2008 11:31 pm

Steve Anderson wrote:I'm still aiming for the end of January for completion, but who knows what might happen.
Steve A.


It might become, Feb or March.
But the 'Brute' marches ever onwards. We await the tryout when in its cage. :-)
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