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Old 7th Dec 2015, 6:29 pm   #61
beery
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Default Re: HMV 905 Project

Thanks Hamishboxer.

Here is a view of the top deck looking from the timebase section.

The scan coil socket has been fitted, as has the rear control bracket, the horizontal form bracket and the EHT capacitor.

I have roughly cut some capacitor cans to provide covers of the line output and oscillator transformers. These will be finished at a later date and fitted with mounting brackets.

I just need to re-mount one of the valve sockets as the orientation is not quite right.
Then it will be back to working under the chassis again, re-capping the radio section...


Cheers
Andy
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Old 23rd Dec 2015, 7:29 pm   #62
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Hi All,

Brian C has just sent me a parcel of goodies.
In the parcel were the new tag strips and the tagboard for the timebase as well as parts liberated from a scrap HMV 1804.

In the photo of the parts you can see a grey doughnut shape, this is the focus coil from an 1804. The 1804 has its coil in series with the HT and consequently measures about 100 ohms while the 905 has its focus coil in parallel with the HT and measures of few Kohms.

I have found out that the EMI 5" and 7" sets originally had a focus coil of about 10K ohms (as stated in the service manual), but when the 9" sets went into production, the smaller sets gained the same focus coil as the 9" models, having a large diameter hole and a resistance of about 6K ohms.
The coil from the 1804 has the same metalwork. I will to rewind it at some point, unless something more suitable turns up (it is held together with a massive 1 3/4" diameter hollow rivet/eylet), but for initial tests I shall hook it up to a bench PSU.
Also the colour of the coil is wrong. In the style of the Stones, all together now... I see a focus coil and I want to paint it black...

You can also see the scan coils from an 1804, though these can't be used exactly as they are, but might be a basis for winding new coils.

I have fixed a couple of the new tag stips in the EHT bleeder position, though these particular ones will be for the sync separator, I'm merely using the EHT brackets as a jig as you can't really solder the sync separator components on in situ. If you have one of these sets you will know what I mean, access for component replacement is really bad simply due to the component density.

I've also started to populate the timebase tagboard.

Many thanks to Brian for his excellent work on the tagboard and tag strips, as well as for all the 1804 bits

I hope to get back to the set on New Years day.

Regards and Merry Christmas to all.
Andy Beer
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Old 23rd Dec 2015, 10:14 pm   #63
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Default Re: HMV 905 Project

I doubt I'll ever work on a vintage TV, let alone a pre war one. I am enjoying reading this thread and watching your progress though.
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Old 24th Dec 2015, 10:36 am   #64
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Default Re: HMV 905 Project

And the same here too.
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Old 24th Dec 2015, 12:05 pm   #65
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Apropos adapting the 1804 scanning coils, it may be possible to dismantle them down to the individual coils and, with a little heat, mould them into a tighter radius round a mandrel of the diameter as the CRT neck (or the larger of the replacement and original necks). This would reduce the scanning power required for full scans. There is the slight danger that the insulation might be compromised but providing the coils are thoroughly warmed right through by passing a DC (I use 1A) through them for a while, there must be a good chance of it working. The outer wrapper/tag board can be made from a suitable fibre material and the appropriate mounting brackets added.
Here's the wrapper I made for my 707 - the original had disintegrated. The wrapper is tied onto the coil assembly using lacing twine through the four eyelets in the corners of the wrapper. The second picture shows the mechanical arrangement of the brackets supporting the CRT assembly. Should you wish, Andy, I can draw it for you - let me know.
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Old 28th Dec 2015, 12:45 pm   #66
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Default Re: HMV 905 Project

Hi Brian,

Hope you had a good Christmas.

Regarding the scan coils, I plan to use them as a basis for complete re-construction, because the coil resistance is wrong anyway.
Drawings, of anything, yes please.
But whilst you have the coils out you could measure the wire diameter with a micrometer (best to measure an enammeled part of the wire and then I will work out the nearest metric wire size from there allowing for the enamel thickness, also a vernier will tend to crush the wire and give an innacurate reading)?

Also can you measure the aproximate outer circumfernce of the line and field windings (along the direction of the actual coils - parallel to the CRT neck, not the circumference of the scan coil clamp) and also inner circumference of the coils (the length of the cardboard x the distance between the inner sides of the coils)?
It is also good if you can measure the aproximate diameter of the wire bunch of each coil (just wrap a bit of string around it to find the circumference).

I also need to know the bore diameter of the hole through the coil assembly for the tube neck.
Even the length of the flex to the scan coil plug would be useful as I need to make this as well.

Note: I'm not very good at explaining things, so I might have to draw a picture of the measurements I am after.
Anyway the idea is to be able to estimate the number of turns of wire needed to obtain the resistance values quoted in the manual.

Many thanks again for all your help.

Cheers
Andy
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Old 28th Dec 2015, 1:38 pm   #67
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It may be best if I were to ship the assembly over to you for you to copy. In that way, you won't be wasting your time overe a possible incorrect measurement of mine (it will be yours ).
They are presently mounted in the cabinet with the CRT but I can get the assembly out and ship it without the CRT. I can't see me needing them for a few months so there would be no onus on you to hurry your coil manufacture!
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Old 28th Dec 2015, 2:47 pm   #68
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That's very kind of you Brian.

That will also help me to know how to mount the CRT.
Partly because the new CRT has a higher deflection angle and even more because its cone only reaches 6 3/4" diameter at the face, the scan and focus coils need to be pushed forward.
The neck clamp can't move much as it screws into a wooden block in the cabinet (I think it might even end up only clamping the CRT base), so extension pieces for the side arms are probably the way to go and this would of course create space for the ion trap magnet. However I might end up having to make the neck clamp out of brass to avoid messing up the ion trap magnetic field.

Cheers
Andy
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Old 1st Jan 2016, 9:18 pm   #69
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Default Re: HMV 905 Project

Happy New Year to all.

I've just tested the 18ЛК5Б CRT that I plan to use in the HMV and the results are good

Cheers
Andy
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Old 12th Jan 2016, 6:15 pm   #70
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Hi All,

After a freezing time last week working in Bremerhaven, where it was -6 degrees, I'm now back home and back on the HMV.

The first picture shows a set of scan coils for a 907/709 that were kindly supplied by Mick Kay. The focus coil is correct for later production 5" and 7" sets, and the focus coil clamp is correct. The scan coils are too big however and have the wrong resistance, but the basic construction can be re-used to build up a new scanning assembly with newly wound coils. The multi way cable and the 7 pin plug are also correct of course

The second picture shows the frame timbase tag strips. These are the tag strips that were made for me by Brian Cuff. I have fitted EMI components where possible, otherwise I have fitted the oldest suitable components I have. All the capacitors except the mica ones have been rebuilt and all the resistors are in tolerance.
I won't be fitting the frame timbase tagstips to the set until I really have too. This is because they actually poke out beyond the bottom of the chassis. It is rather odd that EMI did it this way. They added four rubber feet with spikey threaded inserts to raise the chassis up clear of the tagstrips, but they don't help when it is lying across a narrow bench. I will have to mount the chassis on wooden skids I think.
Despite the high volume of these sets that were manufactured, they do look a bit home made in places.

The third picture shows the line timebase tag board, that was also made by Brian Cuff. This also has all its components and is ready to fit.


That's all for now.

Regards
Andy
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Old 12th Jan 2016, 6:20 pm   #71
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Default Re: HMV 905 Project

I think it looks very authentic Andy, I don't envy your task of winding the scan coils though, it would have me running for the hills!
Great to see that you are making good progress.

Mark
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Old 23rd Jan 2016, 3:44 am   #72
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Hi all,

I'm still recapping the remaining bits of the set. It is very slow work as access is difficult.
I've just rebuilt four capacitors (C81, C2, C3 ,C4) and replaced a resistor (R33) in the RF amp.
In order to get to them I first had to remove the TV aerial tuning coil. I can't really describe how fiddly this is.
I decided to use a 50's resistor to replace R33 as my pre-war ones are a bit on the high side, so as this particular resistor is so hard to get to I decided to play it safe. It is worth noting that whilst most of the resistors in the set measure ok, all three 35K resistors in the set were high at around 50K.

The aerial tuning coil will remain out of the set for now so that I can get the coil former copied to replace the missing vision IFT.

I've now removed the decoupling caps from the local oscillator, so that they can be rebuilt.

I also used my trusty Weir PSU set to 0-30V @ 1A to clean the contacts on the TV mode toggle switch. One set of contacts on the switch connects the mains to the input of the EHT transformer, the other contact shorts across a resistor in the HT negative return to boost the HT in TV mode. The switch is operated via a cam attached to the front of the wavechange switch.
With the switch closed I wound up the PSU and I found that dirt on both sets of contacts broke down at around 20V, so the switch now works properly.

I've attached a photo of the Aerial tuning coil, also a picture showing the replaced components and a picture of the TV mode toggle switch.

Cheers
Andy
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Old 19th Feb 2016, 12:51 am   #73
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Hi all,

after some time back at my parents' place (which is when I had the chance to look at the Cossor 54), I'm now back in London and working on the HMV in my spare time.

All but one of the paper capacitors used for radio operation have all been rebuilt, but they have not all been put back yet. Once I've put them back in I can start rebuilding the HT circuit, so hopefully it's not too long before I can test the radio.

C6 is pictured, it wins the prize for the hardest to get to component. The second picture shows it in context, underneath the wavechange switch. At first is seems easy to get to, but end under the switch is conected to a tag on the switch which is almost impossible to get to. Grrr...
Still, at least I've sorted it out now.

Cheers
Andy
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Old 19th Feb 2016, 10:13 am   #74
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Default Re: HMV 905 Project

You are making good progress andy, at least the cardboard caps are quite an easy job to restuff.
I have restored HMV radios from the same period that also have caps buried in the most inaccessible places

It will be a great moral booster to have the radio up and running, I think I have some HMV caps in the workshop if you need any.

Mark
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Old 25th Feb 2016, 12:29 am   #75
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Hi all,

I have had some life from the radio!

Having rebuilt all the waxies in the radio section I set about re-building the HT smoothing arrangement.

The first photo shows the HT section. The connections to the audio output transformer at temporary as I'm awaiting details of the transformer's terminal board. Smoothing choke CK3 is still missing at this stage.

I went on to put in 3 temporary 50uF caps (2 for cathode bypass and one for vision gain).
Then I powered it up. The HT was rather high, but I put this down to the lack of supply to the focus coil and vision IF etc. Thankfully nothing went bang though.
There was no sound of any sort from the speaker and voltage checks led me to suspect the KT41 sound output valve. I didn't have any 4V Tetrodes to hand, so I wired up a 6F6G with croc clips. Amazingly this worked just about on 4V and Premier Radio came through very faintly.
I found that the aerial socket had no effect, but clipping a lead to the aerial tuning capacitor did work - I'll have to check C1 etc.
The radio was very deaf. Putting my hand near the mixer section made it liven up and I found that hanging a croc lead on C5 helped it stay that way. It now received Radio 5 and Absolute Radio as well. However Longwave and Shortwave were both dead.
I can only imagine it has been re-aligned to work with loads of wires running diagonally across the underside of the chassis (see picture in post #1).

Anyway, I now have a KT41 on order, so best to wait till then to go further. Actually the KT41 was a bit of a surprise as it lights up, has a nice clean getter and generally looks like new, but is has 0% emission. It is branded Bently Acoustic

Whilst I wait for the new valve I will rebuilt the 2nd IF stage so that I can test the TV sound. I will also do something with those new 50F caps that I have just tacked in.

Thanks to everyone for your encouragement to help me get this far. There is still a long way to go...

Cheers
Andy
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Old 5th Mar 2016, 2:36 am   #76
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Hi all,

some progress on the 905.

A new audio output valve enabled the radio to function - a bit...

After re-instating the second IF stage I decided to have a quick go at aligning it by ear, to see how it would respond.
I croc clipped the heater connection of the second IF valve to the 4V supply from the radio section.

After aligning the IF stages I tried the radio again. MW was now much more lively and LW now started to work a bit. SW was totally dead, as was the TV sound.
I replaced a very tired looking local oscillator (X41C). I cound not get an X41C, so I fitted an X41 (this does not have a ceramic base), but it was fine at VHF. After this, SW started to work and the TV sound stage showed some signs of life.
I tried aligning the Oscillator and aerial stages, but it was a real pain. The capacitor screws are quite damaged and the aerial side of things was not responding too well either.
I tried to get some sound from the Aurora, but the set was too deaf.
I replaced the first IF valve (KTZ41) and the RF amp (MSP4). The set was much more lively after this. I quickly went over the alignment again and tried the Aurora. By tweeking the local osc I was able to get TV sound

The only original valves left in the set are the sound detector and the HT rectifier

That will do for now. I will have to look at some of the smaller mica capacitors as they seem a bit out. The set is still lacking the TV aerial matching coil (taken out to copy the coil former) and the last vision IF coil.

The first picture shows an EHT PSU that I've just got hold of. Perfect for testing a set without an EHT transformer.

The second picture shows the second IF stage with the grid wire just tacked on for now (I need to be able to get into the IF can again).

The third picture shows the set being tested after some initial re-alignment, with the cover off the 2nd IF valve to check it was not in any distress.

The fourth picture shows a very dead looking X41C.

Cheers
Andy
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Old 5th Mar 2016, 9:33 am   #77
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Quote:
The only original valves left in the set are the sound detector and the HT rectifier
It sounds like it has seen plenty of use over the years, good to hear that you are now getting the TV sound through it

That EHT power supply looks to be a very useful bit of kit, I am sure it will be used in anger pretty soon...

Mark
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Old 5th Mar 2016, 10:02 am   #78
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Quote:
That EHT power supply looks to be a very useful bit of kit, I am sure it will be used in anger pretty soon
That EHT unit looks similar to a Radford 'LabPack', I wonder if it was manufactured by them for Harris?


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Old 5th Mar 2016, 10:07 am   #79
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Good progress Andy!

And a very nice EHT power supply you've got. How much current can it supply?

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Old 5th Mar 2016, 10:42 am   #80
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Hi Simon and Jac,

This unit works by using a potentiometer across the mains, which feeds an EHT transformer. After the transformer is a multipler made using silicon diodes and lovely rectangular chassis mounted oil caps. Together with a separate heater transformer, it is quite heavy. However it is still smaller and lighter than the Griffin version which uses a variac to feed a transformer that just has a doubler on the end of it.

The current is 3mA for the EHT and 4A total for the 6V and 12V AC outputs combined.

I will make a heater transformer with 4V and 6V windings for testing the TV section...

Cheers
Andy
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