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Restoration of a possibly unique pre-war TV

 
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Re: Restoration of a possibly unique pre-war TV

Post by Briancuff » Fri Mar 21, 2014 9:53 pm

The chassis, in its original state had some really bad rust pitting, some vaguely rusted and some absolutely shiny surfaces (I thought that they were nickel plated but it turned out to be bright zinc) which had been under brackets etc. I know what you mean, Till, but I recon just of dusting with the acrylic aerosol will make that little bit of difference, especially on the back.

 
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Re: Restoration of a possibly unique pre-war TV

Post by peter scott » Sun Mar 23, 2014 1:00 pm

[quote="Brianc"] I just wonder whether a mist coat of acryllic "appliance" paint would help with the appearance of the main chassis!

Nah! Much better that it looks old and patinated.

Peter

 
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Re: Restoration of a possibly unique pre-war TV

Post by Briancuff » Tue Mar 25, 2014 5:10 pm

The owner of the set has decided that a mist coat of acrylic paint is the way to go and I must admit, it does look somewhat better!
A bit more progress - At last I have brought my ultra-sonic cleaner back into action. It holds 10L of solvent (I use "jewelery" grade) and what a difference it makes to the paxolin and Bakelite components. I have restored the two smoothing chokes (their clamps were zinc plated) and the picture shows these two components with a very unusual 2 wiper slider pot. The two sliders feed the RF and detector bias respectively. During dismantling, a three tags snapped off but fortunately, I have some eyelet tags which are almost identical to the originals so I was able to drill out the broken ones and replace them. Next is to rivet in the paxolin valve holders and bolt in the Bakelite ones - I don't want to risk cracking them.

Restored-Choke-assemblies.jpg
Spot the new tags (I've straightened the crooked one!!

 
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Re: Restoration of a possibly unique pre-war TV

Post by Briancuff » Sat Mar 29, 2014 10:11 pm

A bit more progress on the 12C today. After much searching for semi tubular rivets, I found some ideal tubular rivets so decided to use them. I turned a swaging tool out of silver steel to make a neat, rounded swage. I used silver steel as it can be hardened - but I didn't harden it as I had run out of Propane the last time I used the blow-torch and didn't replace the cylinder :bbd .
The pictures show all the valve bases and the screens dividing the grids from the anodes all riveted in place. The next step is to wait for some braided wire I have ordered so that I can start the wiring.

Chassis-top-1.jpg

Chassis-Under-1.jpg

RF-Strip-Mechanicals-1.jpg
The new RS bases are almost identical to the originals which had rotted!

 
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Re: Restoration of a possibly unique pre-war TV

Post by Briancuff » Fri Apr 04, 2014 10:47 am

The braided wire has arrived. I ordered some from 3 suppliers so that I can compare them. The only stuff that hasn't arrived is the push-back solid core wire from Radio Daze in the 'States. Using the tracking system, it says that my shipment has been "progressed through the office of exchange" whatever that means - probably that it's going to cost a lot in clearance fees :bbd .
I've started to wire the main chassis but am taking it very slowly as there are many opportunities to make mistakes and, as I like to make mechanical joints, there is a real risk of damage when trying to rectify errors.
One really annoying thing was that the field blocking oscillator transformer seems to have developed an O/C sync winding (I'm sure when I removed it, I chaecked it and it was OK!). Anyway, the sync winding is the outer of the three so I decided to use my new coil winder in anger. I de-lammed it and stuck it on the winder to unwind the faulty winding and count the turns at the same time - 600 in all. I had some 40swg enameled copper wire which was a fraction larger than the original but as it is the sync winding, I decided that it would be OK as long as there was enough room. As it turned out, I was 60t short of the 600 but as I said before, it's only a sync winding and I have bypassed these before and used a capacitor with success! At the same time as the rewind, I decided that I would change the appearance of the transformer which was obviously a replacement (see picture) and looked really out of place with its bright red PVC leadouts. I therefore made a tagboard which simply bolted onto the lugs which were present on the xfmr clamp frame - it looks so much better now (say)!
The other pictures show how the chassis looks so far. I know that most of the resistors are new but I have never met such a high percentage of resistors that are out of tolerance, most by at least 25% so they had to go!
As I write this, a parcel has just arrived from Radio Daze! No extra charges to pay so hooray for that and the wire is fantastic. It really looks the part and is so easy to use (thanks for the pointer, Cathy).

FBOT-Before-Mods.jpg
The horrible FBOT

TB-Section-Top-2-web.jpg

Under-Chassis-2-web.jpg

 
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Re: Restoration of a possibly unique pre-war TV

Post by Briancuff » Sat Apr 19, 2014 7:42 pm

A bit more done! It's very slow work with the new braided wire as I have to superglue each cut end in order to stop the stuff fraying but it does look so much more in keeping with the age of the set. Even the push-back wire has a tendency to fray but I've found that if I use it as "pull-back" wire it's a lot better as the distortion of the sheath happens towards the middle of the connection being installed. The pictures show whats been done up to now - the time base section and smoothing/filtering are pretty well finished and I am now concentrating on the RF side. This is much more time consuming and is proving quite difficult but it is progressing. The front control panel with two rotary pots and nine slider controls is normally mounted on a separate metal assembly which bolts to the front of the main chassis. However, the mount for the CRT implosion guard is part of this assembly and, when in position, has two "sticky-up" things that prevent the chassis sitting upside down on the bench making it very difficult to wire. The panel had to be in position to get the wiring the right lengths when completed so I made a couple of cheeks for the rotary pots and stood the slider panel off the front of the chassis using 4BA studding. The pictures tell the story!

RF-Wiring-up-to-19-04a.jpg
The RF wiring - waiting for some systoflex!

Wiring-up-to-19-04a.jpg
A general view

Temp-Control-Panel-Mounting.jpg
The temporary mounting for the control panel

 
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Re: Restoration of a possibly unique pre-war TV

Post by IJK2008 » Sat Apr 19, 2014 8:11 pm

Brian

Looking wonderful. How did you re-stuff the cardboard cased caps? I have one if these to do on a set.

Cheers

Ian

 
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Re: Restoration of a possibly unique pre-war TV

Post by Briancuff » Sat Apr 19, 2014 9:16 pm

Hi Ian. One cardboard cap was missing and the other damaged so I had to make both complete assemblies. I sourced some card of the right thickness and used the old one, opened up, as a template. The metal fixing plate also had to be made. One of the things I did for these and the tubular caps was to buy a cheap (£14) mini deep fat fryer and some beeswax. The fryer is thermostatically controlled and can be set to under 100deg. so that the wax doesn't get too hot. One warning though: Don't buy the wax from a craft outlet but from an apiary supplier as it's much cheaper and available in 800g blocks.
After the caps were stuffed, I filled the "boxes" with wax and let them cool a bit and dipped them into the molten wax. The finish isn't perfect but looks the part. The LOPT was also filled with wax as I had to "decant" it to fit new lead-out wires.

 
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Re: Restoration of a possibly unique pre-war TV

Post by Michael Watterson » Sat Apr 19, 2014 10:06 pm

Beeswax?

It wasn't beeswax but Paraffin wax some place between candle and petroleum jelly. (You can mix the two actually to get it).

 
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Re: Restoration of a possibly unique pre-war TV

Post by peter scott » Sun Apr 20, 2014 11:26 am

Brianc wrote:Hi Ian. One cardboard cap was missing and the other damaged so I had to make both complete assemblies. I sourced some card of the right thickness and used the old one, opened up, as a template. The metal fixing plate also had to be made. One of the things I did for these and the tubular caps was to buy a cheap (£14) mini deep fat fryer and some beeswax. The fryer is thermostatically controlled and can be set to under 100deg. so that the wax doesn't get too hot.


Excellent! I love it! Must investigate a fryer for myself.

Peter :aad

 
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Re: Restoration of a possibly unique pre-war TV

Post by Briancuff » Sat Apr 26, 2014 11:42 pm

I did some more work on the RF section over the last couple of days and have succeeded in getting RF through it! I had to rewinding all 9 coils to lower the frequency to 45MHz by adding a turn or two to the originals. I kept to the original layout by lots of reference to the many pictures I took during the dismantling.
The first picture shows the strip without the screening cans fitted. These slide in between the 6 vertical screens to form a completely enclosed section for each bandpass coupling arrangement of two coils, inductively coupled.
The last RF stage drives the anode bend detector via a bifilar wound transformer. I was able to make rewinding easier by sourcing some ready made bifilar wire from a company called The Scientific Wire Company (http://www.scientificwire.com). This is a useful source of all sorts of “magnet wire” as enameled copper wire seems to be called now! They will supply small quantities which keeps the prices down.
The second picture shows the sweep of the RF section from aerial to CRT cathode It starts at 45MHz and finishes at 48.5MHz so the results so far are not too bad. The 9 cores to be tweaked make for an interesting exercise in patience and memory (that’s a bit of a blow for me!) because every adjustment seems to affect the waveform in some way but, more annoyingly, seems to affect the effect that the previous core made before! Anyway, I’m looking forward to increasing the gain while keeping a respectable bandwidth (needs, in theory, to be only 2.5MHz which seems to be the bandwith of most pre-war sets.

Finished-RF-Strip-web1.jpg
The coil in the right hand section is an HF comp coil in the detector anode

RF-Sweep-1-web.jpg
Marker at 45MHz

 
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Re: Restoration of a possibly unique pre-war TV

Post by Cathovisor » Sun Apr 27, 2014 2:11 am

Brianc wrote:The last RF stage drives the anode bend detector via a bifilar wound transformer. I was able to make rewinding easier by sourcing some ready made bifilar wire from a company called The Scientific Wire Company (http://www.scientificwire.com). This is a useful source of all sorts of “magnet wire” as enameled copper wire seems to be called now!

I blame the Merkins for that one...

Brianc wrote:The second picture shows the sweep of the RF section from aerial to CRT cathode It starts at 45MHz and finishes at 48.5MHz so the results so far are not too bad. The 9 cores to be tweaked make for an interesting exercise in patience and memory (that’s a bit of a blow for me!) because every adjustment seems to affect the waveform in some way but, more annoyingly, seems to affect the effect that the previous core made before!

Fairy Fingers! That's what you need! (Old BBC in-joke there)

 
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Re: Restoration of a possibly unique pre-war TV

Post by Briancuff » Sun Apr 27, 2014 8:09 am

"Fairy Fingers"That's the term we used to use when setting up the afterglow panels on the old MK1 Cintel telecines. Stick a bit of destreak film in the gate and twiddle for hours. All controls interacted with all others - but not so many tweaks as for a delta-gun shadow mask tele!
The side racks of audio manipulation devices (flangers, graphic equalisers, echo devices etc. in editing and dubbing suites were called "Fairy Dust". It's a pity that fairy dust wasn't used during the editing of Jamaica Inn!

 
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Re: Restoration of a possibly unique pre-war TV

Post by Till Eulenspiegel » Sun Apr 27, 2014 9:19 pm

Hi Brian,
That's a really good response curve. So the set is aligned to the upper sideband which means that there is a wide trough between the 41.5Mc/s sound carrier and the vision passband. I assume for that reason there are no sound rejector traps in the vision channel. Evidently when the AP transmitter was replaced by the VSB Crystal Palace transmitter many sets aligned to the upper sideband would not work properly.

Till Eulenspiegel.

 
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Re: Restoration of a possibly unique pre-war TV

Post by Briancuff » Sun Apr 27, 2014 10:49 pm

You are correct (as usual) Till. There is a sound trap but not in the vision strip. The aerial plugs into a small metal box with two coaxes coming out of it, one to the vision RX and the other to the sound RX. There are two parallel tuned circuits in the box, one tuned to 41.5MHz and the other to 45MHz (now!) and these are used as traps as they are in series with the appropriate receivers' feeders. I'm surprised that that is enough rejection but it seems to be - the proof of the pudding is when I see a picture but I can see no sound on the video signal when I null it out. Normally, if there is any breakthrough, it can most easily bee seen on the sync bottoms!
I have just converted the sound receiver to 41.5MHz and will probably mount the re-wound mains transformer over the next few days so the rest of the metalwork and CRT can be mounted. Then comes the moment of truth :ccf :ccf .

 
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Re: Restoration of a possibly unique pre-war TV

Post by Till Eulenspiegel » Sun Apr 27, 2014 11:44 pm

Hi Brian,
When I sort out the problems with the Marconi 702 I'll turn my attention to the Pye 838 TV-radiogram. This set uses a modified 815 TV chassis. The sound output is moved to the radio chassis which is similar to the model 802 table set. In the 815 the sound output valve is an EL3N, in the 838 the EL3N takes on a different role, as the focus stabiliser. the EL3N is a special slim bulb version of the ST shape EL3.
There are some similarities between the 815 and 838 and the 1939 915 chassis, the same special frame output valve for example but in practise the two chassis are as different as the D16 of 1946 is to the 915.
I read somewhere that the D16/B16 was really to be the 1940/41 successor to the 915 series. Although highly regarded by collectors the D16 isn't all that different in design concept from it's predecessors. There is nothing really special about the design at all. The strange triode-tetrode frame valve in the earlier 815 and 915 sets gave way to an octal double triode.

Till Eulenspiegel.

 
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Re: Restoration of a possibly unique pre-war TV

Post by Briancuff » Sat May 03, 2014 6:48 pm

The sound receiver unit is now finished (and will be delivered at NVFC). I spent rather a long time masking the mains energised loudspeaker prior to painting but when done, it was well worth the effort - no overspray and good clean edges!
When first tested, it was a bit deaf so I knew that I had to do a bit more work on it - there was a very low audio output with the signal generator output set to -30dB. There seemed to be a problem. However, a bigger problem was the fact that it was tuned to CH2 which, for a pre-war TRF TV did not ring true. I re-wound the three RF transformers, adding a couple of turns to each (the ratios were 1:1 so no problem there). They aligned to 41.6MHz but still low gain so I checked the circuit I had traced against the circuit in the IEE presentation paper and found a discrepancy around the detector stage (EBL3). Now I could have traced the circuit wrongly but I don't think so. The error could have been built in while changing the sound frequency to CH2! Anyway, I corrected the error and switched on the receiver. At that point the 'phone in the workshop rang and I answered it only to be deafened by 1kHz tone blasting out of the loudspeaker - I seemed to have found the cause of the deafness! It now responds to -70dB and the Aurora needs about 15dB attenuation!
Here are a couple of pictures of the finished unit:

Pye-12C-Restore-Side.jpg

Pye-12C-RestoreUnder.jpg


The connector hanging on screened cable is a three pin socket which mates with a plug carrying the three connections to the volume control on the vision unit - why didn't I plate the body when it was off? Too late now as the tiny tongues would almost certainly break off.
Another interesting departure from what became normal practice is the complete lack of sound/vision rejector circuitry in either chassis. Instead, there is a small metal box which has the aerial input connector (old car radio/EKco type) and contains two parallel tuned circuits , one in each of the feeds to the two chassis. These are used to reject the unwanted signal - and it works! Without it, the vision signal blasts through the sound receiver but with the rejector connected, there is not a trace of vision on sound, even at high input levels.
It's now time to return to the vision unit.

 
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Re: Restoration of a possibly unique pre-war TV

Post by Till Eulenspiegel » Sat May 03, 2014 8:25 pm

Hi Brian,
Looks like it just came off the production line. Absolutely superb. It is interesting to note that the predecessor chassis, the 815 is actually more compact than the two part 12C (915) chassis.
When I return to the shop later today I'll take some pictures of the TV chassis of the Pye 838.

Till Eulenspiegel.

 
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Re: Restoration of a possibly unique pre-war TV

Post by Niall » Sat May 03, 2014 9:13 pm

Looks great. I like stuff like this because you can see how it would have looked. So many TV history programmes and museum room sets /shop windows are jarring and unrealistic when you realise that the stuff is clearly old and worn, which it wouldn't have been.

 
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Re: Restoration of a possibly unique pre-war TV

Post by Briancuff » Sat May 03, 2014 11:21 pm

Thanks Niall.
Till - do we know that the 815/915 came before the 12C? The drawing for the 815 is dated 1939 and it uses EF50s which means that it wasn't necessarily released before the 12C. All the circuit features described in the paper are incorporated in the 12C (verified by inspection) and the circuit of the 915 vision chassis also complies with the design. I have asked a couple of guys who worked at Pye before the war but unfortunately, neither of them remembers the 12C or 815/915 - possibly because the research labs were fairly secretive at that stage of TV design!

 
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Re: Restoration of a possibly unique pre-war TV

Post by Till Eulenspiegel » Sun May 04, 2014 12:10 am

Hi Brian,
The TV chassis of my Pye 838 is in an inaccessable corner of the workshop, however, I've managed to to take a picture of it. The other picture is of the 838 TVradiogram.

I don't think that Pye marketed a TV set as the 915. According to the Wireless World Radio show review of August or September 1939 the models that were on display were the 9C and 12C, 9 and 12 inch CRT console cabinet models. Also the 12RG, a TV radiogram combination. So with the introduction of these hi-spec models was the compact 9" 815 table still available in 1939?

Till Eulenspiegel.
Attachments
815_0122.jpg
815_0123.jpg

 
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Re: Restoration of a possibly unique pre-war TV

Post by Briancuff » Sun May 04, 2014 8:50 am

It could be that 915 (this number used in July 1939) was the project number for the development of the EF50 TV, later to become the 9C and 12C and that that project was the stimulus for Edwards' paper.
Your 838 chassis looks to be identical to the 815 and uses the EF6s in alternate vertical orientations. The interesting thing is that you can see the similarities between it and the 12C metalwork in the form of the CRT mask supports. The main difference being, because of the 9" tube, the front extension used in the 12C is not there. The 12C also moves the Austrian wire-wound variable resistors (11 off) to a panel at the front of the set and I assume that as there is a suitable hole in the front of the basic chassis (not used due to the front extension in the 12C), the 9C also used the slider control panel. Has anyone seen a 9C?
Can you show us "under the lid" of the 838 please, Till. I would like to compare it with my 703!

 
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Re: Restoration of a possibly unique pre-war TV

Post by Refugee » Sun May 04, 2014 11:56 am

It looks lovely now.
I can see all those pre-production features too. I bet they did not make many TVs before the war.

 
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Re: Restoration of a possibly unique pre-war TV

Post by Till Eulenspiegel » Sun May 04, 2014 12:10 pm

Hi Brian,
the only difference between the 838 TV radiogram TV chassis and the standard 815 table top set is the sound output stage. In the 838 the EL3N audio valve is retained and serves as a focus coil stabiliser only. The radio unit employs three Mullard "Amerty" American valves, 6A8G, 6K8G, 6Q7G and the HT rectifier which is on a separate chassis is a 5Y3G. The curious thing about this radio chassis is the choice of output valve, it's an European EL3.
When I found the set way back in 1988 the gramophone deck had been replaced with a BSR UA8 autochanger. It had to go. I believe the original was a Garrard RC1. I couldn't find one so a post-war RC60 was installed instead. It looks fairly convincing but I'm still on the look out for the correct record deck.

DFWB.

 
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Re: Restoration of a possibly unique pre-war TV

Post by Briancuff » Sun May 04, 2014 1:08 pm

Pictures???

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