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Old 29th Nov 2015, 1:40 pm   #41
brianc
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Default Re: HMV 905 Project

I am now in posession of 1000 special EMI tags . However, they forgot to plate them . Even the delivery note mentioned plating but they were just bare brass. I have found a platers in nearby Camberley who will barrel-plate small quantities so will be driving over next week. The tags do look the part though.
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Old 29th Nov 2015, 1:48 pm   #42
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Default Re: HMV 905 Project

Can't you get the firm that made the tags to plate them if that is what they were contracted to do?
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Old 30th Nov 2015, 11:31 am   #43
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Default Re: HMV 905 Project

That means shipping them back etc. Also it's a good opportunity to check out local services - a company who will plate small items is a very useful company to know about. I agree about contractual obligations but my money back will suffice this time!
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Old 30th Nov 2015, 6:00 pm   #44
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Default Re: HMV 905 Project

Hi Brian,
it is great that the contacts have been made. Strange they forgot to plate them.

I've obtained two quotes for the metalwork and chosen one to go ahead, but they are a bit slow with generating the pro forma...

I'm currently sorting out the EHT capacitor and will post an update when I've finished it.
After that it will be back to the overhaul of the radio section.

Cheers
Andy
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Old 30th Nov 2015, 7:13 pm   #45
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Default Re: HMV 905 Project

I am watching this thread in wonder and awe! I think I have done well when I resurrect a complete '30s radio never mind an incomplete '30s TV set.

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Old 2nd Dec 2015, 12:39 am   #46
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Default Re: HMV 905 Project

Thanks Paul for the encouragement. This is definitely a long game

I've just made te EHT capacitor.

I started off with a nice expensive looking Rifa screw terminal electrolytic which I opened up by working around the crimp with a screw driver.

I removed the contents. The original base insulator had a rubber seal as well which made a total thickness of about 6mm for the base assembly.

A new base was made from two circles of 3mm Tufnol. A large hole was drilled in each piece of Tufnol to produce two large insulated washers.

A threaded Bakelite capacitor base was recovered from a scrap Nicad shunt regulator removed from a Polyskop. The hole in the base was enlarged to 8mm to allow for two EHT cables to fit through it.

The threaded base was glued to the inner Tufnol washer with hot melt glue.

New capacitors were placed in the can and gluesticks were melted in with a hot air gun to secure the capacitors.

The leads were threaded through the Bakelite base and washer which were then pushed into the can. The other Tufnol washer was put on top and the aluminium can was crimed up again with a small hammer.

The overall effect seems to look about right.

That's all for now.

Cheers
Andy
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Old 2nd Dec 2015, 1:23 pm   #47
brianc
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Default Re: HMV 905 Project

That's an excellent Job, Andy.
I'll be sorting out the 1804 bits for you this week - sorry for the procrastination.
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Old 3rd Dec 2015, 4:32 pm   #48
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Default Re: HMV 905 Project

The local plating company did me proud - 1 day turnaround, fantastic.
I assembled a couple of trial strips and the picture shows the result which, in my opinion, is not half bad!
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Old 3rd Dec 2015, 4:35 pm   #49
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Looks absolutely fantastic Brian !

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Old 3rd Dec 2015, 6:11 pm   #50
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Default Re: HMV 905 Project

Brilliant Brian!
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Old 4th Dec 2015, 1:25 am   #51
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Hi Brian,

They look fantastic. Thanks for all your help.
1804 parts much apreaciated.

I visited Perlamsheetmetal (yes, it is one word apparently) today to pick up the replacement metalwork. I requested 2mm Zintec because it has the right look to it.
The results are spot on

Now I just need to experiment with enlarging the small pilot holes in the four new tag board brackets until the EMI self tapping screws start to bite.

Cheers
Andy
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Old 4th Dec 2015, 2:34 pm   #52
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Default Re: HMV 905 Project

They look good, Andy. Better than nickel or zinc plating. Shall I send you 4 finished strips? They are in the lighter Tufnel but the dark stuff is too brittle.
They can go in with the 1804 stuff. What about the shorter tag board. Shall I make one of those too - won't be expensive!?
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Old 4th Dec 2015, 3:55 pm   #53
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Hi Brian,
Yes please do send four finished strips
I do need the shorter tag board as well thanks. Remeber that the pitch is slightly different for the tag boards as opposed to the tag strips. I already have the rear insulator for the short tag board...
Do let me know what I owe you.
If you have the right thickness of Tufnol, I might ask you to have ago at the terminal strip for the audio op transformer (I have the terminals) or you could just take some measurements for me, they seem to be close together than on EMI mains tapping terminal strips. This is because it was fitted with a later RS replacement audio transformer.
Then there is the former and adjuster for the vision IFT... I do apreciate all the help, but don't want to hold up the restoration of your own set too much...

Can you tell me a couple of measurements?
1. Can you tell me the exact thickness of the lamination stack on the EHT transformer?

2. Can you tell me the length of visible shaft on the tone control (I think this is the same for all the presets, so a measurement of the synch control might be ok if the knob is hard to remove) i.e. from where it emerges from the mounting thread to the end as I need to cut the new control to length.

Cheers
Andy
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Old 4th Dec 2015, 6:27 pm   #54
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Mike Barker has the exact spec for the EHT transformer. Are you going to measure it yourself or have it made? I will measure the stack and let you know as I have one of Mikes which I have not yet fitted to my 706. The length of the smaller board is 241.3 and the pitch is 15.5mm (14 pairs) with the fixing holes 4.4mm from the ends. I'll make a board for you.
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Old 4th Dec 2015, 8:06 pm   #55
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Hi Brian,

if you look back at post 22 you will see my attempt at making the small tagboard. It has most of its components on it at this stage, but I did not go any further when you anounced that you would get the correct tags made.
Hopefully the components can be easily transfered to the board that you make.

Regarding the EHT transformer. It would be nice if Mike can make me one. However it would be also be fun to try and work out the spec from first principles (then perhaps compare it with the original spec).
It turns out that the transformer uses the same sized laminations that EMI used in their radios at the time, it just uses more of them. So with the lamination tongue width (which I know already) and stack height I should be able to work out the turns per volt and the approximate VA rating etc.

I'm currently re-stuffing the HT decouplers that were fitted by HMV in the 50s to replace the original condenser box. I'll post some photos when I have completed them.

Cheers
Andy
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Old 4th Dec 2015, 9:33 pm   #56
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Default Re: HMV 905 Project

Hi Andy, if you post a picture of the lam with dimensions it should be possible to to identify its type. Some of these old imperial types are still available, if not it is possible to select a metric type that is pretty close.
It would be worthwhile seeing if you can get the lams in M6 Unisil material. This is grain orientated material the will either allow you to wind at a lower turns/ volt figure (less wire, more insulation) or a lower flux density and less external field.

Ed
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Old 5th Dec 2015, 8:10 pm   #57
brianc
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Hi Andy
I have completed the tagboard, The attached pictures show the result and it seems to be quite accurate as far as pitch etc. is concerned. You may have to fettle the 4 fixing holes but not more than 0.5mm.
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Old 6th Dec 2015, 2:07 am   #58
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Wow Brian,
It looks amazing

Cheers
Andy
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Old 7th Dec 2015, 10:36 am   #59
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Hi all,

I've just rebuilt the HT decoupling 'capacitor box' caps.

When these sets were made they were fitted with the same metal capacitor box as the HMV 565 radio, which contained 3 x 4uF and 1 x 8uF electrolytics, all with a common negative and a separate 4uF cap.

After the war EMI recalled many of their sets and fitted them with service kits of new electrolytics and new EHT capacitors. The early (and most expensive) sets seem to have been overhauled first and had their capacitor boxes replaced by tag strips fitted with lovely tubular cardboard capacitors.

The 5" and 7" sets seem to have been overhauled a bit later and are fitted with a tag board to which are attached aluminium axial electrolytics with an insulating strip wrapped round (to stop the cans from shorting to the solder tag rivets). The tag boards were wired with all the capacitors commoned at the negative end, since an isolated 4uF cap was only really needed in the 565 radio.
Quite a few 5" and 7" sets exist still with their original capacitor boxes in place. Mine had the tag board fitted, so I decided to re-build the capacitors fitted as they are part of the sets history with EMI.

When rebuilding electrolytic capacitors the problem faced is that all the internal metal parts are made of the same grade of aluminium to prevent it from becoming a battery. Hence there is nothing to solder to, so either we need to crimp the new leads to the ends of the original foil (can't be done in small electrolytics due to the risk of shorting to the case) or the new leads need to pass through to the outside of the capacitor to its solder terminals.

Here is the method I used to rebuild each of the capacitors:-

1. Each capacitor had celulose tape around it which was very brittle, so it was removed and discarded for each 4uF cap (not needed for insulation due to the paper insulator threaded between all the capacitors originally). However the tape on the 8uF cap was very carefully removed and kept, because on that one it contained the label. I then drilled a small hole at each end just below the solder tag.

2. I cut the capacitor length ways and opened it up enough to remove the end insulators with the terminal and then pulled out the old innards. The end insulators and the capacitor body were then soaked in water and scrubbed with a toothbrush to removed any remaining electrolite. Then the parts were dried overnight.

3. A new capacitor was then fitted with the negative wire threaded through the hole that was drilled and pulled right through. The positive wire was extended, fitted with a short length of sleeve and then pulled the through the hole in the positive insulator.

4. The the grooves in the capacitor body that hold the end insulators in place were filled with UHU glue. The new innards with the end insulators were fitted in. The capacitor body was closed up as tightly as possible (it will never go back exactly as it was). A tourniquet was fitted at each end, made of stiff wire to hold the assembly tight whilst the glue dried overnight. The next day the wires were threaded through the solder tags at each end and soldered. Then the original sleeving was fitted on the leads.

5. The capacitors were soldered back on to the tag board with the paper insulator back in place. The cut part of each capacitor faces the surface of the tag board to try to hide the work as best as possible.

Cheers
Andy
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Old 7th Dec 2015, 12:01 pm   #60
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Default Re: HMV 905 Project

Great job and write up.
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