Advanced Search

— Forum Scope —






— Match —





— Forum Options —





Minimum search word length is 3 characters - maximum search word length is 84 characters

sp_Feed Topic RSS sp_TopicIcon
The resoration of a Pre-war HMV 900 Mirror Lid.
Topic Rating: +1 Topic Rating: +1 (1 votes) 
August 14, 2017
7:47 pm
Avatar
Brian Cuff
Burghfield, Reading, UK
Member
Engineers
Level 11
Forum Posts: 199
Member Since:
March 2, 2015
sp_UserOfflineSmall Offline
1sp_Permalink sp_Print
+1

Well, Till. My project is not so exiting as yours and I shall be following it closely in order to glean some ideas on the art of challenging restorations. It will be, I’m sure, a very interesting thread, the first chapter being on paint stripping.

A few months ago, I bought an HMV 900 with a view to using the electronics from it to install into an empty Marconi 705 cabinet as the 900 is one of the most common mirror lids an the 705, one of the rarest and my collection is focused on Marconi sets anyway! However, on more careful examination, it turns out that the electronics are not identical – the radio chassis are different and require differing sizes of Bakelite escutcheons. This, I don’t want to get involved in so I decided that instead of transferring the “gubbins”, I will restore the 900 to full working order and wait a little longer for a 705. As a matter of interest, I now have the following Marconi sets, the 702, 703, 706, 707 and 709. That means that I need to find a 701 (unlikely), a 704 (even more unlikely) and a 705.

I have started the restoration at the picture end – the CRT unit. This is a very large, very heavy steel enclosure encasing the CRT and it’s power circuitry such as EHT smoothing (5kV on 2 off 0.1mfd caps electro_gif) and bleed resistor chain. The pictures show before and after states.

Old-Set-of-CRT-Unit-Components-1.jpgImage Enlarger

 Set-of-CRT-Unit-Components.jpgImage Enlarger
  Set-of-CRT-Unit-Components-CU.jpgImage Enlarger

The metal casing will be painted next while I make preparations for the TRF (TV Receiver) and sync chassis and, having looked at them, their condition is not that good – rather messy, to say the least! However, I will take plenty of pictures and notes before embarking on what could be a rather long process!

You may think that the EHT cable I am using is a bit flaky but it’s test cable rated at 10kV so with a 5kV EHT, that will be fine. I tested all the resistors in the bleed chain and 4 were O/C so not much of a bleed there!

Cheers

Brian

August 14, 2017
8:21 pm
Avatar
Chris
County Durham
Admin
Level 11
Forum Posts: 1558
Member Since:
February 15, 2015
sp_UserOfflineSmall Offline

Brian Cuff said
Well, Till. My project is not so exiting as yours

I beg to differ Brian.

Pre-war restoration threads are a real treat, there are very few folk tackling them now. Couple that with your technical and engineering skills, these threads always make for a rare (much like the sets themselves) treat and I’m sure highly entertaining to us all.

Great photos too Brian, all helps in documenting your processes for those that may follow in your footsteps.

Look forward to reading more.

thumb_gif

August 14, 2017
9:22 pm
Avatar
Till Eulenspiegel
Member
Engineers
Level 11
Forum Posts: 361
Member Since:
September 24, 2016
sp_UserOfflineSmall Offline

 Chris wrote:

“Pre-war restoration threads are a real treat, there are very few folk tackling them now.”

Don’t let me forget there’s still the final restoration of the GEC BT9121 to complete.  Acquired in 2003, cabinet remade in 2004 and some work on the electronics was done from time to time.  Brian kindly had the timebase transformers rewound last year.   Original CRT has an open circuit heater, the dual phosphor CV1085 will be used as a replacement. 

Till Eulenspiegel.

August 15, 2017
8:41 pm
Avatar
Brian Cuff
Burghfield, Reading, UK
Member
Engineers
Level 11
Forum Posts: 199
Member Since:
March 2, 2015
sp_UserOfflineSmall Offline

I won’t forget the BT9121, Till. Especially as you very kindly kept out of the ebay auction in order that Mike Izicky had a better chance of getting it for the BT8161 which he has taken over from me.

Anyway, back to the HMV 900 project and further progress on it:

I have painted the CRT enclosure and will post pictures tomorrow, hopefully! Secondly, I have taken a comprehensive set of pictures of the Sync/TRF chassis in it’s present tatty self and reduced a few of them for the thread. I have tweaked up the saturation a little over what it should be as it improves the detail which can be seen. My decision now is how to progress. Do I do a typical “Let’s strip the who;e chassis down” and drill out all the rivets to release the wiring assembly as a larger piece as possible or do I just tidy it up a bit? The former is the way I am tending to go as it does give a really good idea of how the set looked in 1936!

Here are a few of the pictures but let me draw your attention to the coaxial cables used at 45MHz. The picture shows two cable, one being the Aerial connection and the other the link, at 41.5MHz, to the sound receiver, tapped off stage 3 of the TRF vision RX.

900-RF-Coax-Cables.jpgImage Enlarger

  The longer one is the Aerial feeder and is 1800mm long. The other is 1200mm long.

Sync_TRF-Chassis-Over-3.jpgImage Enlarger

  This looks quite clean but it isn’t!

Sync_TRF-Chassis-Under-2.jpgImage Enlarger

  A few components hanging of  – “Not me, Guv”.

900-Sync_TRF-Under-1.jpgImage Enlarger

  A closer look – a fair bit of work to do – Hey ho, it’s into work we go!

And as a taster for things to come:

PSU-Chassis-Over-3.jpgImage Enlarger

The PSU Chassis – how dirty can you get?

The PSU is, as you can see, absolutely filthy with some fairly nasty rust but I will endeavor to clean it up without resorting to too many rust curative chemicals.

Save

Save

Cheers

Brian

August 16, 2017
8:07 pm
Avatar
nuvistor
Member
Engineers
Level 8
Forum Posts: 1026
Member Since:
March 23, 2015
sp_UserOfflineSmall Offline

I understand that BICC in Leigh Lancashire, OK, Greater Manchester now, did design work and manufacturing of coax cables used in early TV  and radar sets.

Frank

August 24, 2017
7:25 pm
Avatar
Brian Cuff
Burghfield, Reading, UK
Member
Engineers
Level 11
Forum Posts: 199
Member Since:
March 2, 2015
sp_UserOfflineSmall Offline

A bit more progress on the HMV 900 PSU front: The chassis has now been cleaned and primed & painted and looks half decent. I have returned the main power transformer to its rightful place together with the components that are connected to it (the EHT transformer had an O/C secondary winding so that has gone to Mike for a rewind).

900-PSU-Under-during-Restoration.jpgImage Enlarger

I removed these components together with the HT rectifier holder and transformer in the initial stages of the restoration so that they would go back together easily! However, I seem to have lost the pictures of the wiring which I took and have therefore will have to wing it a bit in order to get as close as I can to the original wiring.

I must admit that I have never been impressed with the standard of wiring for the EMI MKI TV sets! They all use Systoflex sleeving and they didn’t seem to take much care about the routing and lacing of the wiring and the result, as can be seen from the pictures, is not ideal.

I have painted the transformer and smoothing choke with mat black lacquer and this, in my opinion, makes a huge difference to the overall appearance of the chassis which always seems to be the settling point for the worst of the detritus that these mirror-lid sets can generate. Moisture seems to be the worst thing, causing rust pitting and plating damage and the transformer lamination stack seems to be a magnet (excuse the pun) to the moisture and ends up looking very tatty indeed.

900-PSU-through-Door-Custom.jpgImage Enlarger

I am now going into my mechanical workshop to make a couple of the electrolytic capacitor boxes out of tinplate. The boxes are almost always missing but I have made quite a few before for other restorers who like the chassis to look as closely like the originals as possible. This means, of course, that I have already done the ACAD drawings so I should have the two boxes finished today.

900-PSU-Under-during-Restoration-2.jpgImage Enlarger

  The cap boxes have been made and stuffed and are mounted properly on the underside of the PSU chassis.

The PSU is now nearing completion but the main things that are missing are the EHT components including mains transformer, steel enclosure and safety interlock parts. The transformer will be some time yet but I will fit the enclosure etc. in the next few days.

900-PSU-Over-during-Restoration-3.jpgImage Enlarger

The large grey area is where the EHT enclosure and components fit, including the EHT rectifier valve.

Cheers

Brian

August 24, 2017
8:03 pm
Avatar
Lloyd
Member
Engineers
Level 4
Forum Posts: 247
Member Since:
October 30, 2016
sp_UserOfflineSmall Offline

Hi Brian,

That’s coming along nicely!

Regards,

Lloyd

August 28, 2017
5:15 pm
Avatar
Brian Cuff
Burghfield, Reading, UK
Member
Engineers
Level 11
Forum Posts: 199
Member Since:
March 2, 2015
sp_UserOfflineSmall Offline

I got a surprise when I decided to remove all the components from the Sync chassis in order to get he metalwork blast cleaned and plated. I drilled out all the copper rivets holding the valve holders in position but was going to leave the metal plate which covered the hole intended, originally, for V7 which re-inserted line sync pulses during the frame interval of the Baird 240 line system. This valve was, of course, unnecessary when the Baird system was dropped in favour of the Marconi-EMI 405 line system. It seems that almost all the MKI sets went back to Hayes to have the components removed or were modified by local authorised dealers. All my MKI sets have a blanking plate over the hole and the rest of the components have been removed. However, on my 900 chassis, there is a blanking plate over the V7 hole but the valve holder is still in place and wired to an extent – heater wiring for example – with the tagboard layout different to the layout given in the last technical data available (1953). One can also see where wiring has been cut but left in situ whereas the later units have their wiring changed.

The only conclusion that I can come to is that this chassis – serial number 0114 – is a very early one which was in production when the Baird decision was made and was hastily changed before it was installed into the TV.

Has anyone else seen this situation? It certainly is the only one that I have seen.

Cheers

Brian

August 28, 2017
7:56 pm
Avatar
Till Eulenspiegel
Member
Engineers
Level 11
Forum Posts: 361
Member Since:
September 24, 2016
sp_UserOfflineSmall Offline

Hi Brian,

               I’ll check my own 900, it is a very production model and it will have the dual standard timebase  cableforms.  It’s most likely the DS wiring continued well after the cessation of the Baird transmissions.  The cableforms  will be made at an assembly station and then passed to the next station where the 240/25 wiring would be clipped off leaving only the connections to the 405/50 TB components.

Till Eulenspiegel.

August 28, 2017
9:10 pm
Avatar
peterscott
Member
Engineers
Level 2
Forum Posts: 36
Member Since:
December 31, 2015
sp_UserOfflineSmall Offline
10sp_Permalink sp_Print
0

Brian Cuff said

The only conclusion that I can come to is that this chassis – serial number 0114 – is a very early one which was in production when the Baird decision was made and was hastily changed before it was installed into the TV.

Has anyone else seen this situation? It certainly is the only one that I have seen.  

Hi Brian,

I think it’s true to say that where the blanking plate is mounted on the top side then the valve base is normally still present on the underside.

Is this chassis from H 6149? 

I have the timebase chassis number as 614 for that set and also recorded as having top side blanking.

I suspect I’ve made a mistake with its number: http://www.nostalgiatech.co.uk…..age_31.htm

Peter

September 1, 2017
7:19 pm
Avatar
occiput
Member
Engineers
Level 6
Forum Posts: 52
Member Since:
November 21, 2015
sp_UserOfflineSmall Offline
11sp_Permalink sp_Print
0

Brian Cuff said
 It seems that almost all the MKI sets went back to Hayes to have the components removed or were modified by local authorised dealers. All my MKI sets have a blanking plate over the hole and the rest of the components have been removed. However, on my 900 chassis, there is a blanking plate over the V7 hole but the valve holder is still in place and wired to an extent – heater wiring for example – with the tagboard layout different to the layout given in the last technical data available (1953). One can also see where wiring has been cut but left in situ whereas the later units have their wiring changed.

EMI are known to have issued a number of field service bulletins for the first-generation television sets in the period 1936 – 39.  One of these was to remove the 240/25 timebase components once the Baird transmissions had ceased, as a reliability mod.  Whilst some sets will have gone back to the factory for service attention, it is also likely that many will have had the work done at a dealership.  I believe EMI issued a mod kit consisting of the domed cover for the control panel and the plate to cover the valveholder.

At the factory, I would expect the mod to have been applied in full.  At a dealership, it’s not that difficult to imagine a range of results from full implementation to “jumper the set into 405 mode, and sort the cosmetics”.  One factor which might have a bearing on how thoroughly the work was done might, for instance, be whether EMI paid the dealers to do it, or whether it was regarded as warranty work.

One question I have never seen answered for certain is whether EMI first-generation TV was flow- or batch-produced.

709379

September 1, 2017
8:22 pm
Avatar
peterscott
Member
Engineers
Level 2
Forum Posts: 36
Member Since:
December 31, 2015
sp_UserOfflineSmall Offline
12sp_Permalink sp_Print
0

Occiput said

One question I have never seen answered for certain is whether EMI first-generation TV was flow- or batch-produced.  

The chassis serial numbers appear to be in a simple incrementing with time sequence but the overall set serial numbers appear to partitioned into batches. http://www.nostalgiatech.co.uk…..age_31.htm

Peter

September 10, 2017
8:02 pm
Avatar
Brian Cuff
Burghfield, Reading, UK
Member
Engineers
Level 11
Forum Posts: 199
Member Since:
March 2, 2015
sp_UserOfflineSmall Offline

Occiput mentioned the EMI instructions to remove the 240 line switch and components in their omnibus service data release. This has given me an idea!  I would like to re-instate the 240 line circuitry as it was originally issued. However, I cannot find any layout info for the dual standard set. My 900 has, what I believe, are the original tag boards as fitted during its dual standard life. The more recent boards have no capacitors fitted at right angles to the normal orientation but one of the boards in my set has positions for three horizontal caps about one third of the way from the left.

This post was going to ask if anyone had an early version of the service data which includes the old tad board layout – I have the “obsolete” sync chassis circuit which includes the systems switch but nothing further – can anyone hep?

i have now decided that I will try to reconcile the EMI removal instructions with the tag boards I have to see whether I can get anywhere using the info I have to hand. 

To show you how much confidence I have, I have ordered a 240 line Aurora from Gerry!!!

Cheers

Brian

September 15, 2017
8:56 pm
Avatar
Brian Cuff
Burghfield, Reading, UK
Member
Engineers
Level 11
Forum Posts: 199
Member Since:
March 2, 2015
sp_UserOfflineSmall Offline
14sp_Permalink sp_Print
0

occiput said

EMI are known to have issued a number of field service bulletins for the first-generation television sets in the period 1936 – 39.  One of these was to remove the 240/25 timebase components once the Baird transmissions had ceased, as a reliability mod.  Whilst some sets will have gone back to the factory for service attention, it is also likely that many will have had the work done at a dealership.  I believe EMI issued a mod kit consisting of the domed cover for the control panel and the plate to cover the valveholder.

At the factory, I would expect the mod to have been applied in full.  At a dealership, it’s not that difficult to imagine a range of results from full implementation to “jumper the set into 405 mode, and sort the cosmetics”.  One factor which might have a bearing on how thoroughly the work was done might, for instance, be whether EMI paid the dealers to do it, or whether it was regarded as warranty work.

On reflection, it seems to me that the removal of the 240 line components was done, in my set’s case, at Hayes, as the blanking plate covering the V8 valve holder was riveted in using exactly the same technique (and rivets) as the other holders on the chassis!

I have now started work on the sync chassis and the pictures show my approach to this job. I made, for a previous set I restored, some brass “legs” to stand the chassis on an even keel during the restoration work. The legs comprise 8 bits of brass with 2BA tapped holes in their ends into which 4 lengths of studding is screwed to form 4 pairs of asymmetric legs – please see picture – using any available holes on which the chassis can stand .

The second picture is the chassis so presented with the tag board assembly shown in its final position.

900-Sync-Chassis-with-legs-2.jpgImage Enlarger

900-Sync-Chassis-with-legs-and-Tag-Boards.jpgImage Enlarger

Cheers

Brian

September 16, 2017
10:20 pm
Avatar
Till Eulenspiegel
Member
Engineers
Level 11
Forum Posts: 361
Member Since:
September 24, 2016
sp_UserOfflineSmall Offline
15sp_Permalink sp_Print
0

Hi Brian,

             for starters we’ll examine the timebase unit in the HMV 902 followed by the early version of the HMV 900. The attachment shows that the socket for the Baird valve is present and so is the wiring associated with it although the 240/25 and 405/50 switch was not fitted in this receiver which was possibly made in 1937.                                  HMV902_5-1.jpgImage Enlarger

 

Till Eulenspiegel.

September 17, 2017
7:00 pm
Avatar
Brian Cuff
Burghfield, Reading, UK
Member
Engineers
Level 11
Forum Posts: 199
Member Since:
March 2, 2015
sp_UserOfflineSmall Offline
16sp_Permalink sp_Print
0

Thanks Till

I see that the V8 blanking plate is riveted in position suggesting your theory of a factory mod/build. Was there no plate over the V8 holder? The wiring to V8 holder on my 900 has been cut away but at on time was complete as there are still short interconnect wires existing which originally connected the holder to components on the tag boards. My problem is to determine to which tags/components these originally went.

A picture of the sync chassis through the side panel would be very useful – could you take a few for me please, Till?

Cheers

Brian

September 17, 2017
10:24 pm
Avatar
Till Eulenspiegel
Member
Engineers
Level 11
Forum Posts: 361
Member Since:
September 24, 2016
sp_UserOfflineSmall Offline

Hi Brian,

             the best plan is to remove the timebase and TRF unit from the 902 cabinet as it can be removed from this set without any difficulty.  I’ll take pictures and trace out the wiring around the Baird valve. It’s possible that the Baird timebase capacitors are still present on the chassis.                                                                                                                The attachment shows the timebase unit in the HMV 900.  Like the 902 the Baird valve socket is fully wired.

Till Eulenspiegel.   HMV900TB-1.jpgImage Enlarger

September 18, 2017
9:07 pm
Avatar
Till Eulenspiegel
Member
Engineers
Level 11
Forum Posts: 361
Member Since:
September 24, 2016
sp_UserOfflineSmall Offline

Hi Brian,  the timebase and TRF unit has been removed from the cabinet of the HMV 902.   All the components and wiring associated with the Baird valve are present on the group board including the 22Kohm cathode bias resistor and the 0.5mfd bypass capacitor.   However, there is no evidence of any timebase frequency switching wiring in the cableforms.  There is no standards switch wires present on the preset controls panel.   I will examine the HMV 900 next.  It is believed to be a very early production model.

Till Eulenspiegel. 

HMV902BairdValve-1.jpgImage Enlarger

HMV902TB1.jpgImage Enlarger
HMV902TB2.jpgImage Enlarger

Forum Timezone: Europe/London

Most Users Ever Online: 49

Currently Online:
3 Guest(s)

Currently Browsing this Page:
1 Guest(s)

Members Birthdays
sp_BirthdayIcon
Today None
Upcoming None

Top Posters:

PYE625: 1500

nuvistor: 1026

marc: 668

FordAnglia: 369

Till Eulenspiegel: 361

Lloyd: 247

Jayceebee: 246

ntscuser: 214

Brian Cuff: 199

Red_to_Black: 142

Member Stats:

Guest Posters: 6

Members: 106

Moderators: 3

Admins: 1

Forum Stats:

Groups: 4

Forums: 19

Topics: 779

Posts: 9770

Newest Members:

6.3volts, audioantique, Jon, mr_mog, Elektrofix, Tim.norris

Moderators: sideband: 295, Katie_Bush: 682, Cathovisor: 1031

Administrators: Chris: 1558