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Old 21st Aug 2015, 8:47 pm   #1
beery
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Default HMV 905 Project

Hi all,

After some rather drawn out negotiation, I have become the custodian of this thing...

It was not cheap, but, oh dear, I felt sorry for it!

All the TV components are missing, as second speaker and grille has been added and lots of external speaker sockets have been added. The brightness and contrast controls have been replaced by a selector switch that selects the different sepaker outputs.

The cabinet is quite good, but there are some deep scratches in the laquer on the top.

The first thing was to strip out the unwanted parts and measure the fixing centres of the missing parts.

I will be posting a list of parts required in the wanted section soon.

Cheers
Andy Beer
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Old 21st Aug 2015, 8:54 pm   #2
beery
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Default Re: HMV905 Project

I've now removed most of the unwanted parts and cleaned the dust off the chassis.

There was some good news. Behind the extra speaker grille was the original CRT mask

Now to collect parts...

Cheers

Andy
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Old 21st Aug 2015, 8:57 pm   #3
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Default Re: HMV905 Project

Hi Andy,

Looks like a good start to me!

I have the winding data for most of the transformers on this chassis if you need them made or rewound.

In fact I have just finished a LOPT for a 904 and sent it back to the customer.

I did the Mains / EHT transformer a while back and the frame/sound transformers.

I think there is every chance that you can get this back to a working TV/Radio again without too many problems. Just collect up several EMI radios of this period for donor parts that are missing.

Mike...
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Old 21st Aug 2015, 8:58 pm   #4
Nickthedentist
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Default Re: HMV905 Project

Good heavens!

Good luck with it,

Nick.
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Old 21st Aug 2015, 8:59 pm   #5
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Default Re: HMV905 Project

Andy,

Can you let me have the serial number of this set for the pre-war TV database please.

Mike...
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Old 21st Aug 2015, 9:03 pm   #6
dave walsh
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Default Re: HMV905 Project

Fascinating Andy. Do you know anything about the history from [1938?] onwards. Has it been reduced to a workplace or entertainment [club] radio feeding output to different rooms or something like that over the years? Do you anticipate difficulty finding a CRT to fit?
Dave W
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Old 21st Aug 2015, 9:55 pm   #7
mark pirate
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Default Re: HMV905 Project

I have seen this set before, used to sit a TV22 on
Glad to see it find a worthy custodian, good luck with your quest for the missing parts.

Mark
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Old 21st Aug 2015, 10:20 pm   #8
beery
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Default Re: HMV905 Project

Yes Mark, you spotted it correctly!
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Old 22nd Aug 2015, 1:48 pm   #9
brianc
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Default Re: HMV905 Project

So he sold it in the end! I chased after that set after it appeared as a coffee table! The negotiations didn't go very well - not an inch budged by the vendor! I hope you were able to move him, Andy.
You have a PM.
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Old 22nd Aug 2015, 2:10 pm   #10
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Default Re: HMV905 Project

As I mentioned in my PM, all the RF transformers etc. are present but I've just noticed there is one missing. However, it's a single winding 8MHz tuned circuit so very easy to replicate. I might even have a housing - I'll check.
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Old 26th Aug 2015, 10:20 pm   #11
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Default Re: HMV 905 Project

Hi all,

In reply to Dave's question. I don't know much about the history of the set.
The seller (an antiques dealer) told me that it had been in the possession of a collector for many years.

The set itself does reveal a few clues. The capacitor box on the top of the chassis has been replaced with a tag strip, this was part of the standard EMI post war overhaul that they did on all the sets that they could find at the time.

Most of the surviving paper capacitors are pre-war together with most of the resistors.

A look at the video amp shows a cardboard 1940s style electroyltic (C58) connected to a metal cased sprague cap (C59) from the 40s/50s. There is also a 50s style 47K resistor (R38). These parts must have been replaced when the set was still a complete TV and indeed they might suggest that all was not well with the tube by then.

If we look at the audio section we find some late 50s/early 60s style RS caps. These were fitted when the set was converted to being a radio only. I'm not sure why the tone control was removed...

Thats all for now. I will update once I have a few spare parts to show.

Regards
Andy
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Old 27th Aug 2015, 9:16 am   #12
brianc
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Default Re: HMV 905 Project

It looks a lot better with all that extraneous wiring removed, Andy. Apart from the tube assembly, the missing items should be fairly easy to find/replicate. Mike Barker made the main power transformer for my 706 which had (has!) a bodged-in foreigner. It really looks the part. Good luck with the set - I will be watching your progress keenly.
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Old 30th Aug 2015, 10:36 pm   #13
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Default Re: HMV 905 Project

Hi Brian,

Thanks for your interest. I need all the encouragement I can get as the project is quite intimidating.
I'm still collecting parts of course, but I aim to make a proper start soon.
I've been exploring CRT options and I've also been looking at how to replicate the missing IF coil.
I've got a replacement IF can and trimmer, but the coil formers for the video IF are unusual bakelite mouldings. I might have to adapt a cardboard HMV SW aerial tuning core instead. I'll post some pictures of the cores tomorrow.

By the way, can I ask for suggestions about the light surface rust on the chassis?
It is not so bad that I want to paint it, indeed I am tempted to leave it as it is because I want the set to look its age where possible. To give an idea of the general condition, the rust is not furry and is only found on some parts of top of the chassis. The valve sockets, switches and pots are all in very good condition. I don't really want to dismantle the set further...

Cheers
Andy
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Old 30th Aug 2015, 10:44 pm   #14
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Default Re: HMV 905 Project

Hi Andy,
tomorrow I'll take a look at my Marconi 707 which I understand uses all the same components as the HMV 905 version.

DFWB.
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Old 31st Aug 2015, 5:10 pm   #15
Leon Crampin
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Default Re: HMV 905 Project

For dealing with light chassis rust, I would suggest light mineral oil rubbed in with a green "Scotchbrite" scouring pad (best binned afterwards).

This will largely restore the surface if it is not too pitted and inhibit further rust. If you feel further measures are needed, you can degrease the treated area and apply further treatment to your choice.

Leon.
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Old 31st Aug 2015, 10:15 pm   #16
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Default Re: HMV 905 Project

The attachments show the triangular bracket that supports three pre-set controls.
I will make an accurate template to assist the reproduction of this part. The steel is 2mm thick. The video peaking coil is also attached to the bracket. The former for this component is a piece of 10mm diameter Tufnol type material and is 42mm long.

I'm sure I can get a piece of glass cut for the CRT window.

DFWB.
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Old 3rd Sep 2015, 12:16 am   #17
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Default Re: HMV 905 Project

Hi all,

Thanks David for your help.

Thanks also to Leon for your suggestion about what to do about the rust, I have just bought some scotchbrite pads...

When I restored my Cossor 54 it was just that little bit more rusty and I took the decision to paint it. To give an idea of the condition, the valve sockets were still good, indeed the EHT transformer was ok, but the chassis rust was furry and pitted.
The 905 is not nearly as bad as that thankfully.

I've opened up one of the IF "cans" to have a look at what I need to do to replace the missing final vision IF coil, L28. I have a replacement "can" and trimmer cap, but I can't find a coil former like this. The coil former is made of bakelite, it mounts with a large slotted round brass nut and has an adjustable brass core. Does anyone have one? I might have to use something else...

I've moved one of the smoothing inductors (CK2) back to its correct position and where there is another missing inductor to the right of it I found some extra holes. They happened to fit a monster inductor (CK1, clearly not original) that was also found in the wrong place. However since this inductor measures 500 ohms instead of the 160 ohms of the correct one, I can only think that the set can't have performed too well with it in place (it feeds the timebases).

The original style tag board is almost impossible to find and most newer stuff has completely the wrong pitch. I've some tag strip from Germany that has almost exactly the right pitch if I remove every other tag. The tags are much smaller, but they seem to be the best idea at present. I've attached a photo comparing the old style tags with the new.

That's all for now.

Regards
Andy
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Old 3rd Sep 2015, 7:02 am   #18
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Default Re: HMV 905 Project

Good progress Andy.

The coil former is not of bakelite, but EMI called it "trolitol".
Better known as "trolitul". It is in fact polystyrol/polystyrene.
You can easily check by touching it with a soldering iron. Bakelite would not melt, polystyrene very easily.

Hope this helps...

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Old 11th Sep 2015, 12:41 am   #19
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Default Re: HMV 905 Project

Hi folks,

still progressing slowly...

Thanks for the info Jac. It would make sense because looking at the coil former it had a grainy look, like wood, but then also a mould split line.

I've now rubbed down the chassis with an oily scouring pad as per Leon's suggestion and it looks much better.
I've replaced rubber grommets and fitted the octal valve sockets (proper EMI ones) in the timebase section. I've used M3 screws for the moment, but will be replacing them with domed 4BA screws.

I've also fitted a missing insulated tag next to the video amplifier valve and have replaced the bolt through HT caps (thanks to askjan).

Loads more parts waiting to arrive.
Thanks to everyone that is helping out with parts and info.

That's all for now.

Cheers
Andy Beer
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Old 11th Sep 2015, 7:59 am   #20
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Default Re: HMV 905 Project

Nice to hear that you have had such a good response to your request for the missing parts, it really deserves to be restored and see a picture once more.

Mark
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