UK Vintage Radio Repair and Restoration Powered By Google Custom Search Vintage Radio Service Data

Go Back   UK Vintage Radio Repair and Restoration Discussion Forum > Specific Vintage Equipment > Vintage Television and Video

Notices

Vintage Television and Video Vintage television and video equipment, programmes, VCRs etc.

Reply
 
Thread Tools
Old 16th Feb 2019, 11:38 am   #81
1100 man
Heptode
 
1100 man's Avatar
 
Join Date: Apr 2016
Location: Ventnor, Isle of Wight, & Great Dunmow, Essex, UK.
Posts: 986
Default Re: 1938 Murphy A56V television restoration

Hi Catkins,
Great restoration- many thanks for writing it up in such detail. It's always good to see such attention to detail. At least when everything is that rusty, the decision to restore a component or leave it alone is made much easier!

I've just been reading your detailed description of your re- plating methods. We bought several similar kits to plate small car components. We try, when doing a restoration, to send a batch of stuff to the platers in one go but there are often small items that get missed, so being able to plate them ourselves would be great.

So far, our results have been pretty poor: due, no doubt, to bad practice on our part.

Referring to the pot backs shown in post 74, firstly, how was the very rusty back cleaned up? We would have sand blasted it with very fine sand, but whatever method was used, it would have been very pitted. The re-plated item looks perfect- did you not have to go through the copper plating process outlined in your earlier post?

Some of your pictures show a very shiny finish- was that as it came out or have you polished those after plating?

Many thanks
All the best
Nick
1100 man is offline   Reply With Quote
Old 17th Feb 2019, 4:31 am   #82
Catkins
Tetrode
 
Catkins's Avatar
 
Join Date: Feb 2015
Location: Chepstow, Monmouthshire, UK.
Posts: 95
Default Re: 1938 Murphy A56V television restoration

Quote:
Originally Posted by 1100 man View Post
Hi Catkins,
Referring to the pot backs shown in post 74, firstly, how was the very rusty back cleaned up? We would have sand blasted it with very fine sand, but whatever method was used, it would have been very pitted. The re-plated item looks perfect- did you not have to go through the copper plating process outlined in your earlier post?
No, it was a single plate, as I said in my previous post.

As I said in my previous post, it is really a question of try and try again. If the plate doesn't look the way you want it to, put it into the acid pickle, burn off the previous plate, fix whatever the problem was, and do it again, perhaps experimenting with different approaches.

The pot backs were an interesting problem. The problem is that they have writing stamped into them (the ohmage as shown in the previous photo). Repeatedly plating with copper will "fill in" the writing leaving it indistinct (and certainly not keeping the crisp appearance).

The reason for that should be obvious, you're using repeated plating and polishing to smooth over imperfections, and the process doesn't distinguish between pitting and writing, it's all the same to it.

So the question was I want to do this with one plate, *and* I want to get a good finish too.

So the finish before plating had to be good, which required a lot of slow hand sanding, going down the grades to fine polishing paper. After a couple of test platings, and more sanding/polishing of the metal before plating, I finally got a finish I found acceptable. After plating, I then polished the result to produce the final finish. This is because for very fine polishing, it is easier to polish the zinc plating, than the steel, as it is softer. But obviously, because the plate is fairly thin, it will only stand a small amount of polishing, otherwise you polish through the plate.

In otherwords most of the polishing had to be on the steel, as I only wanted one plate. But I allowed a small amount of polishing on the zinc plate to perfect it where it was easier to do so.

Quote:
Originally Posted by 1100 man View Post
Some of your pictures show a very shiny finish- was that as it came out or have you polished those after plating?
As mentioned above, for the pot backs, I polished them up to a final appearance after plating, for the previous reasons.

For the other finishes, repeated plating and polishing was done to produce a mirror surface *before* the final plate. So the finishes are the final plate, without any extra polishing.

In otherwords if you polish after plating, that then becomes the input for the next plate. You stop when you have a finish *after* plating that doesn't need polishing.
Catkins is offline   Reply With Quote
Old 17th Feb 2019, 9:46 am   #83
bluepilot
Hexode
 
Join Date: Feb 2010
Location: Duffort, Gers, France
Posts: 424
Default Re: 1938 Murphy A56V television restoration

Quote:
Originally Posted by 1100 man View Post
We would have sand blasted it with very fine sand,
Electrolytic de-rusting with washing soda is better. Here's one example of how to do it:
Electrolytic-Rust-Removal-aka-Magic/
__________________
Stuart

The golden age is always yesterday - Asa Briggs
bluepilot is offline   Reply With Quote
Old 11th Mar 2019, 9:27 am   #84
Catkins
Tetrode
 
Catkins's Avatar
 
Join Date: Feb 2015
Location: Chepstow, Monmouthshire, UK.
Posts: 95
Default Re: 1938 Murphy A56V television restoration

Apologies for the two week delay in updates, I have been very busy in work, and this has left no time for anything else. As it is, it is now very late, and so I'm going to have to be very quick in this posting.

The last posting left me explaining all the things planned for my 2 week vacation over Christmas 2016 (and yes there's still almost two extra years of work still to detail).

As planned, I got the respraying of the top of the chassis done over late November and early December, leaving the paint work hard enough to start work on the underneath of of the chassis.

I had already had a good look at the paintwork underneath the chassis and decided it didn't need respraying, this was a very good bonus as it meant I didn't have to strip off all the components/tag-boards on the underside just for respraying, and it left them in place for the careful task of rewiring and component replacement (of the various restuffed waxies, electrolytics, and other repaired or replaced components).

There is a good reason why I wanted to keep the underside electronics in as undisturbed and original condition as possible. I didn't want to introduce issues/instability in the circuits. Pre-war televisions are notorious for pushing the available electronics to the limits due to the then high frequencies employed, and this often involved careful placement of components, wire routing and wire lengths. If you ever see something "unusual" in the placement or routing, this is usually the reason why, and you'd be stupid to loose this in any disassembly/reassembly and rewiring.

Photo 1 shows an obvious example of this, the frequency changer circuit. The entire frequency changer circuit is built on-top of the oscillator coil, and the whole assembly is immediately over the frequency changer valve socket. This makes an extremely dense and difficult to work with circuit, but, the obvious intent is to make the signal paths (wire-length etc) as short as possible. This is the reassembled and replaced circuit and pains were taken to match it exactly against photos taken before removal and disassembly. I replaced the connecting wires even though I knew I would eventually replace them, but, it is better to get everything right when replacing, and then follow that as a guide when replacing the wires, as it is less to concentrate on at that time.

My replacement of components and rewiring was pragmatic. I generally took one circuit at a time, and replaced components and rewired in "one go" to minimise the overall level of disruption. Rewiring was done one wire at a time, point to point, keeping each new wire the same length and preserving the routing. The components were replaced exactly using photographs.

The one exception to this was inter-circuit wiring, which I preferred to do separately, either before or after individual circuit rewiring, depending on circumstance. This is obviously because they relied on a global perspective to get the rewiring right. This mostly meant the filament wiring and the various HT feeds.

The filament wiring in the set was quite interesting. There are three separate circuits, with each one obviously connected to the same pins (on the power unit socket). The first circuit powers the valves on the lower side of the chassis (framebase, sync separator, and video detector/amplifier), the second circuit runs up the side powering the video IF valves, FC valve and HF valve. The third circuit powers the valves on the top side of the chassis, which are the linebase and the audio circuit valves. Additionally each circuit is wired the opposite way for negative and positive. The negative is daisy chained from one end of the circuit to the other end, and the positive is daisy chained from the other end. This I found quite unusual, and I can only assume it is an attempt to reduce inter-circuit interference.

There are separate three HT feeds in the circuit, and I again took pains to preserve the exact wiring between circuits. There were not many surprises here, but some circuits are daisy chained, and others are fed from a central HT point.

Photo 2 is a photo of the top left hand corner of the chassis in the middle of rewiring, with the waxies replaced. This shows the HF, Audio IF and Audio detector stages.

Photo 3 shows some rewired aerial/IF coils and Photo 4 shows one of them before rewiring.

One thing which perhaps needs to be mentioned here is the replacement wire. For this set I wanted to use wire that preserved the original vintage appearance. The cotton wire in the set was very dirty and very faded, but, one thing which was clear was that it was two-tone striped, with a darker colour and a lighter colour. This seems to me to be a particularly 1930s style, as I've never seen it in post war sets (but as usual there's always a first time which disproves this).

I looked for a long time for someone selling vintage NOS striped wire, and after a couple of months I finally found someone who had come across about 10 or so unused reels of different coloured striped wire. This wire was made in the early 1950s to a vintage colour coding. This was offered by the metre and it is easily the most expensive wire I have ever bought. But, I think it was worth it to preserve the original appearance.

Photo 5 is a view of the top of the resprayed chassis, showing the replaced coils and cans. At this point the rewiring was complete (except for the controls on long looms of wire, which would come much later).

Finally it looked to me, as if this might one day be a functioning TV again, rather than a lost hope.

But I'm out of time. This is mostly a pure brain dump due to lack of time, and I don't have time to edit it. As Pascal famously said, I would have written a shorter letter, but I did not have the time.
Attached Thumbnails
Click image for larger version

Name:	20161224_005254.jpg
Views:	152
Size:	52.8 KB
ID:	179731   Click image for larger version

Name:	20161228_231059.jpg
Views:	144
Size:	125.6 KB
ID:	179732   Click image for larger version

Name:	20161227_060706.jpg
Views:	151
Size:	127.3 KB
ID:	179733   Click image for larger version

Name:	20161228_011340.jpg
Views:	141
Size:	190.1 KB
ID:	179734   Click image for larger version

Name:	20170117_015900.jpg
Views:	136
Size:	172.6 KB
ID:	179735  


Last edited by Catkins; 11th Mar 2019 at 9:35 am.
Catkins is offline   Reply With Quote
Old 11th Mar 2019, 11:42 am   #85
Argus25
Nonode
 
Argus25's Avatar
 
Join Date: Oct 2016
Location: Maroochydore, Queensland, Australia.
Posts: 2,106
Default Re: 1938 Murphy A56V television restoration

Quote:
Originally Posted by Catkins View Post

I looked for a long time for someone selling vintage NOS striped wire, and after a couple of months I finally found someone who had come across about 10 or so unused reels of different coloured striped wire. This wire was made in the early 1950s to a vintage colour coding.
That was well done.

The only vintage TV I have restored and re-wired with fabric replacement wire is the Andrea KTE-5. The wire was available new (reproduction) from Antique Electronics in the USA.

I found when I stripped the ends, using a scalpel, the fabric weave would start to un-twine. So, for about 5 mm , I painted it with clear varnish that stuck the fabric threads together. (Photo attached of under chassis of KTE-5 Television set, 1939)

After that experience, for all my restorations, both radio & TV, I went to silicone rubber covered wire. The reason is it looks exactly like vintage rubber hookup wire, but is totally heat resistant and it does not burn or retract regardless of the soldering temperature (unlike PVC). It comes from RS components.

PS: Your restoration/s set a very high standard for the forum, it is eye candy to see the the work.
Attached Thumbnails
Click image for larger version

Name:	cotton.jpg
Views:	141
Size:	98.7 KB
ID:	179741  
Argus25 is offline   Reply With Quote
Old 8th May 2019, 7:52 am   #86
Catkins
Tetrode
 
Catkins's Avatar
 
Join Date: Feb 2015
Location: Chepstow, Monmouthshire, UK.
Posts: 95
Default Re: 1938 Murphy A56V television restoration

It was a while ago since I managed to make an update on this thread. Usual reasons apply, too much work and too little time.

I left off after starting to put the television back together after rewiring. Over the next month or so I concentrated on putting the audio section back together, with the aim I could then do an audio only test of the set. This would be a good intermediate check that hopefully everything so far was correct and functioning (power supply, wiring, HF/FC, audio IF and output stages). In fact I also put the video IF stages back together (leaving timebase/scanning/focus etc.), with the idea I could then also check video IF amplification was working. This was done by March 2017 (picture 1).

Happilly with one exception it worked first time on turn-on. That is on the first initial turn on I got a cloud of smoke emanating from the FC IF can. This proved to be an over-heating resistor caused by a HT short to one of the secondaries. As can be seen in picture 2, some of the wiring is bare, and the bare-wire HT feed was touching one of the secondary windings. Luckily this was caught in the first few seconds with the set on a variac slowly turning up the voltage, and so no damage was caused.

Once that was fixed, it perhaps "boringly" worked first time, with no days of fault tracing and fixing. This was on one hand gratifying and on the other hand a bit of an anticlimax. I spent a couple of hours in a soak test listening to 60s vidoes off ytube, checking the quality of reproduction (which was very good, the huge mains energised loudspeaker has very good reproduction). Then it was back to work.

The next thing to do was to address the CRT mounting, and check the differences between the CRM91 and the CRM92 CRTs.

Perhaps a recap (no pun intended) is needed here. The Murphy A56V was designed to use a 9 inch CRM91 CRT, but the CRM91 CRT in the set was broken, and getting replacement CRM91 CRTs is all but impossible. But, all is not lost. The slightly later 9 inch CRM92 CRT (introduced in 1939) is electrically identical to the CRM91 and can be used as a replacement. In fact FERNSEH on this forum had previously succesfully used a CRM92 CRT in his A58V.

But the CRM92 has a lower deflection angle (surprising for a later tube). and so it is differently dimensioned. The task was to work out how this affected the existing mounting arrangements.

If you look at photograph 3, you can see the mounting arrangement. The CRT is positioned vertically in the middle of the chassis in a large hole. The shoulder (where the gun joins the bulb) lies at the level of the chassis, where the scan coils are attached. The focus coil lies below the level of the chassis, within a sub-assembly bolted to the bottom of the chassis. The CRT sits in a sub-assembly mounted on top of the chassis, this consists of a flat plate with a (larger) hole where the CRT sits, and two support brackets which hold the plate above the level of the chassis.

So how does the different dimensions of the CRM92 affect the mounting? Well the CRM92 is longer due to the lower deflection angle, but the bulb widens out more rapidly than the CRM91. The result is the CRT sits higher within the hole on the mounting plate. So the extra length of the CRT is shared, the CRT sticks out higher above the mounting plate, and sticks out further below the chassis.

Can this extra height and depth be accommodated within the existing arrangements? The answer is sadly no.

The major problem is the CRT sticks out about half an inch too far even with the lowest height settings (see later). There is not enough clearance bwtween the CRT and the safety glass in "presentation mode" (where the chassis is swivelled at a 45 degree angle to place the CRT against the safety glass). There is also the problem that the shoulder is too high in respect to the scan coils, but, this is a secondary issue as in practice it will be fixed as a side-effect of fixing the height problem.

How to fix the height problem? The mounting brackets are slotted, but the maximum depth of the slots only brings the plate to the top of the mounting brackets. The plate needs to adjusted to about half an inch, or 1 inch (to give adjustment leeway) below the height of the mounting brackets.

FERNSEH solved this by basically bolting an extra set of brackets onto the plate, which sit above the plate. These brackets are then bolted to the existing mounting brackets, which allow the plate to sit about an inch below the top of the mounting brackets. You can think of these extra brackets as basically spacers. The spacers are bolted to the mounting brackets, not the plate itself.

I wanted to try something different, because I didn't like the idea of drilling holes in the existing plate to add the extra spacer brackets. If I ever got a CRM91 CRT I would never be able to put the set back to exactly how it was, because the drilled holes will still be there.

Now the basic problem is the mounting brackets are simply too high to accommodate the CRM92 tube. If the mounting brackets were lower, then the problem wouldn't exist.

So my decision was to fabricate new mounting brackets, these being otherwise identical to the originals but an inch lower.

I choose to fabricate them from fibre glass, as fibre glass has the necessary strength, but is easier to work with than metal.

Photograph 4 shows the frabricated mounting plates, with the slots cut, but before final sanding, mounting hole drilling and painting.

Photograph 3 is actually a photograph of the newly finished and painted mounting plates in place. I doubt anyone would easily differentiate them from the originals.

There are some more things which needed to be done, but, that will have to wait till next time.
Attached Thumbnails
Click image for larger version

Name:	IMG_20170307_230118867.jpg
Views:	115
Size:	176.1 KB
ID:	182672   Click image for larger version

Name:	IMG_20170326_073413621.jpg
Views:	107
Size:	33.5 KB
ID:	182673   Click image for larger version

Name:	IMG_0277.JPG
Views:	105
Size:	150.8 KB
ID:	182674   Click image for larger version

Name:	IMG_20170716_214441840.jpg
Views:	99
Size:	39.7 KB
ID:	182675  
Catkins is offline   Reply With Quote
Old 10th May 2019, 3:36 am   #87
Catkins
Tetrode
 
Catkins's Avatar
 
Join Date: Feb 2015
Location: Chepstow, Monmouthshire, UK.
Posts: 95
Default Re: 1938 Murphy A56V television restoration

To continue from my previous post.

I mentioned previously that the extra length of the CRM92 CRT with the original arrangement is shared, with the bulb sticking out a bit more above the chassis, and the CRT gun sticking out a little more below the chassis.

Obviously, once you fix the extra bit sticking out above the chassis by lowering the CRT mount brackets, all the extra length of the CRT now sticks out below the chassis.

As mentioned previously, below the chassis is bolted a sub-assembly which holds the focus coil, focus coil adjustment mechanism, and the CRT clamp.

The focus coil adjustment mechanism can move the focus coil up and down the CRT neck by about an inch. With the extra length of the CRT tube that means everything fits at the lowest setting, but it obviously leaves no room for focus adjustment.

To get that back, the sub-assembly has to be spaced about half an inch below the chassis. Obviously, this can be done with long bolts, and adding some spacing nuts.

Pictures 1 and 2 show the inside of the sub-assembly with the focus coil, and the outside of the sub-assembly with the CRT clamp. Both are obviously pre-restoration. These are there to illustrate the above text.

Picture 3 shows the under-side of the chassis with the long bolts in place, which the sub-assembly will be bolted to, with spacer nuts.

Picture 4 shows the sub-assembly and focus coil housing cleaned just before respraying.

Photo 5 shows the resprayed outside of the sub-assembly with the cleaned and restored CRT clamp arrangement.
Attached Thumbnails
Click image for larger version

Name:	20160221_005717.jpg
Views:	70
Size:	59.0 KB
ID:	182798   Click image for larger version

Name:	20160221_005706_1.jpg
Views:	64
Size:	73.4 KB
ID:	182799   Click image for larger version

Name:	IMG_0179.jpg
Views:	71
Size:	89.7 KB
ID:	182800   Click image for larger version

Name:	IMG_20170924_183002636.jpg
Views:	73
Size:	199.3 KB
ID:	182801   Click image for larger version

Name:	IMG_20171023_004727899.jpg
Views:	65
Size:	135.1 KB
ID:	182802  

Catkins is offline   Reply With Quote
Reply

Thread Tools



All times are GMT +1. The time now is 3:52 am.


All information and advice on this forum is subject to the WARNING AND DISCLAIMER located at https://www.vintage-radio.net/rules.html.
Failure to heed this warning may result in death or serious injury to yourself and/or others.


Powered by vBulletin®
Copyright ©2000 - 2019, vBulletin Solutions, Inc.
Copyright ©2002 - 2019, Paul Stenning.