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Old 11th Sep 2015, 9:22 pm   #21
ianm
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Default Re: HMV 905 Project

Andy, at this rate you'll have first light in no time.
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Old 14th Sep 2015, 11:19 pm   #22
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Default Re: HMV 905 Project

Thanks for the Encouragement Ian.
Could take a while to get first light. It needs a bulb first...

I'm still trying to track down loads of parts and making others.

I've made a start on the timebase tagboard. It is not quite the same as original I'm adding parts as I find them. So far it is just the low wattage EMI style resistors and a 230pF mica cap that I have fitted.

That's all for now.

Andy
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Old 16th Sep 2015, 11:55 am   #23
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Default Re: HMV 905 Project

Hi All,

The postman came this morning and delivered a bulb.

Kudos to the guy that sent it to me from the Ukraine, because he packed it really well, using expanding foam. The box had to be destroyed to get the tube out!

The Tube is a Russian 18ЛК5Б (18LK5B). It has a triode gun with an ion trap, a 6.3V heater, a 33mm neck, a 52 degree deflection angle and a face that is 1/4" undersize.
This particular tube has some very scary deep scratches on its face, but as it didn't break in the post I'm sure it will be ok.

I've no way of testing it at the moment (my CRT tester is elsewhere), but the getter is nice and bright and the filament is intact.

If this works then it will be a major boost and this type of CRT could help out others as well and it might also replace the Mazda CRM71.

With the 5 & 7" EMI sets the EHT is very low, only 2.5KV; this means that a weak focus field is required which in time leads to a very large ion burn, much larger than we are used to on post war tubes.
At such a low EHT aluminising is not an option, but a CRT with an ion trap is the best solution...

Cheers
Andy
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Old 16th Sep 2015, 12:07 pm   #24
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Default Re: HMV 905 Project

Do you think you'll get away with such a low EHT for the Soviet tube?
Was this the tube they used in the Russian KBN49 TV set, the world's first 625 line receiver.

DFWB.
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Old 16th Sep 2015, 2:11 pm   #25
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Default Re: HMV 905 Project

Hi David,
Yes indeed it is from the KBN49.
Will the 18LK5B work at 2.5KV? I guess it depends on the phosphor material.
It is rated at 3.2-6KV

Then again the 7BP4 is known to work and that is rated for a minimum of 4KV. Also the 5FP4 works as well and it is rated for a typical anode voltage of 7KV.

Another good thing about the 18LK5B is that it is extremely common in some parts of the world.

So as to whether it will actually work, I guess there is only one way to know and that is when the chassis is restored...

Andy
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Old 16th Sep 2015, 2:49 pm   #26
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Default Re: HMV 905 Project

Hi Andy,
I reckon we must buy as many of these tubes while we can.
Variants of the KBN49 were sold in many Eastern Bloc countries including the German Democratic Republic.
From the Radiomuseum: http://www.radiomuseum.org/r/aleksandro_kvnkw_49.html
The set is full of decadent Western type valves.

DFWB.
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Old 18th Sep 2015, 8:18 pm   #27
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Default Re: HMV 905 Project

The Russian CRT looks to be a bit shorter than the 3/2. Is the deflection angle greater and is there room on the neck for the deflection and focus assembly? It looks a bit short. I tried to find the deflection angle of the 3/2 but couldn't find it - who knows what it is?
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Old 19th Sep 2015, 11:02 am   #28
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Default Re: HMV 905 Project

Hi Brian,

The 3/2 must be somewhere between 45 and 50 degrees. You can measure it by measuring the distance from the centre of the scan coils to the front of the screen and then measuring the exact screen diameter, from that you can work out the deflection angle. It might be worth having a go at that some time to see what the figure is.

The 5" 5FP4 is reported to just about work and that has a deflection angle of 53 degrees.
The 7" 7BP4 has been used to and that also has a deflection angle of 53 degrees.

The 18ЛК5Б has a deflection angle of 52 degrees, so it will work, but yes it is a bit shorter. Here is where it gets interesting because we need to take advantege of the shorter cone by pushing the tube forward, but keeping the tube clamp where it is. So a spacer need to be made to enable the focusing and scanning coils to move forward of the clamp by about 1". It needs to be done this way because there needs to be space for the ion trap magnet.

The other point about the 18ЛК5Б is that unlike the 5FP4 and 7BP4 the heater-cathode insulation is not good enough to simply connect the CRT heater to the 6.3V timebase supply, so some kind of separate 6.3V supply is required. The minature 3VA 4V to 6.3V auto transformer hidden somewhere would do the trick.

Cheers
Andy
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Old 19th Sep 2015, 11:42 am   #29
brianc
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Default Re: HMV 905 Project

An autotransformer wouldn't work as it does not isolate - I'm sure you knew that. Perhaps Ed can wind a small 4/6.3 Xfmr for you.
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Old 19th Sep 2015, 11:54 am   #30
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Default Re: HMV 905 Project

Indeed it does not. But, there is already an isolated 4V heater supply for the original CRT, so no need to isolate the 4 to 6.3V transformer provided it has a fairly low capacity to its frame.

Btw, I said 3VA, but it needs to be nearer 4VA as the 6.3V heater is 0.6A.

Of course I could have the replacement TV heater supply/EHT transformer wound with a 6.3V CRT heater winding, but I'm a little reluctant to deviate from the original design if possible.

Regards
Andy
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Old 19th Sep 2015, 3:20 pm   #31
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Default Re: HMV 905 Project

If you're having a new transformer made, Andy, why don't you have a 6.3V winding tapped at 4V? At least then, there is no additional Xfmr and the same tag could carry either the 4V tap or the complete winding as required by the CRT for when you find a 3/2 with the other connection "hellermanned".!
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Old 19th Sep 2015, 4:40 pm   #32
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Default Re: HMV 905 Project

Ive done some measurements on the peaking coil as you asked and they are as follows:
resonance without tuning C 1.22MHz
resonance with 96pf tuning C 570kHz

I'm having trouble with my bridge on L measurements at the moment so no inductance - you can calculate it. Here's a picture:
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Old 29th Sep 2015, 2:06 pm   #33
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Hi all,

Not much progress on the 905 due to being busy with work at the moment. I hope to pop back to my parents' place soon to pick up some more vintage components. I'm not sure whether to bring back the RF generator or the CRT tester; I don't have room for both.

Thanks to Brian for your help. I've got loads more questions...
You've convinced me Brian that adding a 6.3V CRT heater tap to the EHT transformer is really the best way to go, I think I was just trying to make it difficult for myself

The info on the vision detector coil is great. I'm not quite sure how to replicate it yet.
I was hoping to use an EMI radio IF coil unwound till it reached the right inductance, however it turns out the two coils on an EMI IFT are not wound on the same former, but on separate bobbin sections that are then assembled between spacers on a steel rod. Great for mass production of radios, but not so useful for me
For those who don't know the circuit I'll explain the challenge (without winding data) that this particular coil presents. The 905 uses an anode bend detector that drives the CRT cathode (low impedance) directly via an RF choke. The output on the valve anode will be half wave rectified 7-8MHz IF pulses which are amplitude modulated with the video signal which in this set is expected to have a response of up to 2MHz. So the RF choke has to block 8MHz effectively, but also pass 2MHz reasonably well, with the capacitance of the CRT providing the smoothing. Not all that easy then...

That's all for now, not much else to report except that I am now slowly rebuilding caps in the radio section...

Cheers
Andy
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Old 30th Sep 2015, 11:03 am   #34
brianc
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I have a wave-winder, Andy, so I suppose I could have a go at winding such a beast - not a good example to cut my teeth on but worth a go. I'll see what I can do. I also want to remove L28 from my chassis so that I can give you the spec for it and perhaps make you a former!!
It won't be for a couple of weeks though as I am working on a presentation I have to give to the RTS Thames Valley Section - that should be fun.
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Old 27th Oct 2015, 1:46 am   #35
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Hi all,

Just a quick update on the 905.

I have even more work than last time I posted (the pre-Christmas rush), so hardly any time for hobbies.

I'm still gathering parts and information whilst at the same time trying to overhaul the remaining parts of the set.

The first picture shows all the valve holders in place and indeed filled with valves. The IF cans have also been polished.
This exercise was mainly to give myself some inspiration, but it also highlighted that I didn't have the video amp valve (V9, MS4B) in stock. I've obtained one now.
The missing IF can has been replaced, though it is currently empty and the missing grid leads for the video IF valves have been replaced, but not yet soldered to the top cap clips, so that I can still easily open the IF cans up.

The second picture shows one of the typical problems faced. Here the HT feed to the local oscillator can't be routed correctly due to a damaged solder tag. I drilled out the rivet from the old tag and fitted a replacement held in place by an 8BA screw and nut (see the third picture). New yellow sleeving on the heater feed from the 'radio' transformer can also be seen in this photo.

The forth picture shows evidence of a small fire in the HT supply to the RF and oscillator stages. R73 is toast as is R67. The heat had also damaged the solder tag for R73 which promptly fell off. I've now replaced the broken solder tag. Maybe C53 went leaky and caused this, then again V2 (X41) seems to have been a bit overheated...

The fith picture shows the remains of R73 mmm toasty...

Also thanks to brianc for sending me an original external speaker socket and bracket.

That's all for now.

Cheers
Andy
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Old 27th Oct 2015, 5:24 pm   #36
brianc
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Default Re: HMV 905 Project

Hold all the temporary tags, Andy
I have ordered 1000 off custom tags made to be identical to the tags in the 905/707 TVs. They are quite expensive (33p each) but it means that I can completely rebuild my 707 properly and it is worth the investment. If you need some, just let me know. Delivery promised is 4 weeks.

The price of 33p excludes the tooling charge so I will have to charge £10 for 25 pcs. I hope that that's not too expensive for the real thing!
Mods: If this is a bit too commercial for this section, I will post in the appropriate section.

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Old 28th Oct 2015, 8:58 am   #37
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Default Re: HMV 905 Project

Hi Brian,
Yes the right tags would be great, however, I need to find a way of punching the square holes in the paxolin.
I wonder if I can get a PCB manufacturer to use a tiny router to do this on some 1.6m paxolin if I create a gerber file??

Regards
Andy
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Old 28th Oct 2015, 11:24 am   #38
brianc
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Don't worry about the Gerber file, Andy. I am ordering a 3.5mm square punch and die for my bench press so I will be able to make the complete strips and boards. I'll do them for you at a nominal (material) charge .
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Old 30th Oct 2015, 9:51 am   #39
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Default Re: HMV 905 Project

Thanks Brian, that's great.
That's what I love about groups like this, when people help each other out

I've taken the trouble to track down as many vintage components as I can, so with the correct tag strips it will look just right.
So in that case I will hold off on the rebuilding of the missing TV parts until the new tag boards are made. That's no worry as there are plenty of other things that need to be sorted in the set...

Can I get the radio working before the new year? A challenge as I'm very busy with work and also away over Christmas...

Cheers
Andy
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Old 21st Nov 2015, 8:26 pm   #40
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Hi All,

just a quick update. After a busy period of work, finally some time to work on the HMV.
I've rebuilt a couple of waxies in the IF section and replaced some of the cracked insulation.
I've also replaced R73 and its missing solder tag. R67 has been removed for replacement as it was toast, just like R73 that was next to it.

That's all I've had time for at the moment. Hopefully I will have some free time in the next week.

I've sent off for some quotes for manufacturing the missing metalwork, asking for prices to make it from 2mm Zintec or from 2mm steel and have it nickel plated.

I have also consulted with a local machine shop to make up some concentric shafts for the missing Brightness and Contrast controls. I've been unable to source Morganite potentiometer tracks of the right value (1K and 5K), so I have decided for the moment to use 1970's 24mm pots as a basis for the missing controls.

That's all for now.

Cheers
Andy
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