UK Vintage Radio Repair and Restoration Powered By Google Custom Search Vintage Radio and TV 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.

Closed Thread
 
Thread Tools
Old 20th Jan 2016, 12:04 am   #21
Hunts smoothing bomb
Octode
 
Hunts smoothing bomb's Avatar
 
Join Date: Oct 2005
Location: Wimborne, Dorset, UK.
Posts: 1,407
Default Re: Bush TV12B Restoration

Hi Mark,
The mask on my T105 is in very bad condition too and has cracked and hardened, it is also a pale green. I was going to try smoothing it over with decorators caulk with the "wet finger" and then try to paint it with matt pale green emulsion.

Cheers
__________________
Lee
Hunts smoothing bomb is offline  
Old 20th Jan 2016, 8:10 pm   #22
Lloyd 1985
Nonode
 
Lloyd 1985's Avatar
 
Join Date: Jun 2008
Location: Coningsby, Lincolnshire, UK.
Posts: 2,814
Default Re: Bush TV12B Restoration

Just a thought, if you go down the hammer route, you'll then have the task of picking very sharp shards of glass off the inside of the mask. I made use of an old bank card (or old mobile phone top-up card, plastic type) to shove between the CRT glass an the rubber on my TV12. Less likely to damage the mask or the tube (if it was any good!!). Maybe keep the dead tube bits, someone might be able to re-gun it one day!

The mask on my TV12 is all cracked and hardened like yours too. Whatever you decide to fill the craks with, make sure it's paintable! Some silicone sealants won't be painted.

Regards,
Lloyd.
Lloyd 1985 is offline  
Old 22nd Jan 2016, 2:46 pm   #23
mark pirate
Dekatron
 
mark pirate's Avatar
 
Join Date: Mar 2008
Location: Worthing, West Sussex, UK
Posts: 5,185
Default Re: Bush TV12B Restoration

It was certainly a difficult job to remove the old broken CRT, the knurled brass nuts that secure the strip round the mask refused to budge. Plenty of patience and WD40 finally got them free, but the CRT was stuck to the chassis rim by the mask.

I eventually freed it using an artists pallet knife. The scan coils also refused to budge, gentle prying with a small screwdriver broke away the hardened rubber round the clamp and they then slid off the neck.

The mask itself is in poorer condition than I feared, it has hardened and split where it was fused to the rear of the CRT.
I managed to free it from the CRT in the sink with hot water flowing over the cone of the CRT while I used the pallet knife to pry it away from the glass.

Having got it off in one piece, I am now soaking it in Flash kitchen spray with bleach. Hopefully this will get it as clean as possible.

The amount of black soot on the underside of the CRT had to bee seen to be believed

The chassis is by far and away the filthiest I have ever seen, I am having to wear latex gloves to keep the black sooty muck off my hands while I clean it.

My resistor order arrived this morning, so I will strip down the paxolin panel and replace the EHT bleeder resistors. A new EY51 will be fitted and the EHT wiring replaced.

The Visconal will be left in place for show, no EHT smoothing will be necessary with the replacement CRT. I will have to give it some thought how to connect the dag to the chassis though.

Mark
Attached Thumbnails
Click image for larger version

Name:	P1130176.jpg
Views:	246
Size:	76.1 KB
ID:	118750   Click image for larger version

Name:	P1130177.jpg
Views:	247
Size:	120.5 KB
ID:	118751   Click image for larger version

Name:	P1130181.jpg
Views:	247
Size:	63.0 KB
ID:	118752   Click image for larger version

Name:	P1130183.jpg
Views:	252
Size:	72.1 KB
ID:	118753   Click image for larger version

Name:	P1130186.jpg
Views:	265
Size:	131.9 KB
ID:	118754  

mark pirate is offline  
Old 22nd Jan 2016, 5:54 pm   #24
HamishBoxer
Dekatron
 
HamishBoxer's Avatar
 
Join Date: Aug 2007
Location: W.Butterwick, near Doncaster UK.
Posts: 8,923
Default Re: Bush TV12B Restoration

Dag is normally connected to chassis with a piece of thin springy copper.
__________________
G8JET BVWS Archivist and Member V.M.A.R.S
HamishBoxer is offline  
Old 22nd Jan 2016, 6:39 pm   #25
mark pirate
Dekatron
 
mark pirate's Avatar
 
Join Date: Mar 2008
Location: Worthing, West Sussex, UK
Posts: 5,185
Default Re: Bush TV12B Restoration

Indeed it can be, in fact I think I have just the thing on a scrap Pye chassis.
More modern sets used a length of braid tensioned by a spring across the bowl of the CRT.

The mask looks a lot better for a deep clean, I am sure I can save it...

Mark
Attached Thumbnails
Click image for larger version

Name:	P1130188.jpg
Views:	266
Size:	108.3 KB
ID:	118766   Click image for larger version

Name:	P1130189.jpg
Views:	247
Size:	88.5 KB
ID:	118767   Click image for larger version

Name:	P1130190.jpg
Views:	227
Size:	97.4 KB
ID:	118768  
mark pirate is offline  
Old 22nd Jan 2016, 9:32 pm   #26
Lloyd 1985
Nonode
 
Lloyd 1985's Avatar
 
Join Date: Jun 2008
Location: Coningsby, Lincolnshire, UK.
Posts: 2,814
Default Re: Bush TV12B Restoration

I wrapped gaffer tape round the mask on mine! Probably wants something better really though...

Regards,
Lloyd
Lloyd 1985 is offline  
Old 22nd Jan 2016, 9:39 pm   #27
McMurdo
Dekatron
 
McMurdo's Avatar
 
Join Date: Jun 2009
Location: Staffordshire Moorlands, UK.
Posts: 5,263
Default Re: Bush TV12B Restoration

What a state the mask is in. That would probably defeat me.
An alternative to a dag spring, I've observed in industrial applications sometimes, is a self adhesive copper foil that can take a soldered wire. It can be applied discreetly, though I've no idea where to buy a reel.
__________________
Kevin
McMurdo is offline  
Old 22nd Jan 2016, 11:44 pm   #28
brianc
Rest in Peace
 
Join Date: Jun 2004
Location: Burghfield, Reading, Berkshire, UK,
Posts: 1,055
Default Re: Bush TV12B Restoration

Another way is to use a long spring such as curtain wire and loop it from the chassis up over the dag coating to another chassis anchor point such as the CRT clamping band.
brianc is offline  
Old 23rd Jan 2016, 10:06 am   #29
mark pirate
Dekatron
 
mark pirate's Avatar
 
Join Date: Mar 2008
Location: Worthing, West Sussex, UK
Posts: 5,185
Default Re: Bush TV12B Restoration

I have decided the best option is to use the copper spring strip from a scrap LV20 chassis. I should be able to mount it to the chassis under the bowl of the CRT using an existing hole.

My resistor order showed up yesterday, so I wasted no time in replacing the old ones.

It still has me wondering why the original resistors fitted were 22Mohm, I know my set is a late model that has the modifications listed in the Bush manual.
The EHT transformer is the 'Yellow spot' type (for increased EHT). The manual states that the EHT bleeder chain should have 27Mohm resistors fitted if the EHT transformer was changed for the later type.

Maybe the value was changed again after the manual was printed?
I certainly could not find any 27Mohm resistors anywhere, so went with the same value that was fitted.

I tested the old ones after removal, one was O/C and the rest had risen in value between 28.2 to 37Mohm.

I replaced C23 (CRT A1 decoupler), so just need to fit a NOS EY51 and replace the wiring to the PL38 top cap and fit a length of suitable wire for the CRT anode. The original is just a piece of standard rubber wire from the now redundant Visconal!

I have spent a fair bit of time cleaning the chassis, the amount of muck round the line output stage was incredible. The photos show the rather odd arrangement of the separate line output transformer with the EHT transformer sitting on top, the last photo shows the dag earthing strip I scavenged from the Pye chassis.

I hope to have the top of the chassis finished today, then move on to the underside. Unlike the TV22, this does not appear to have any components hiding under the tag strips.

Mark
Attached Thumbnails
Click image for larger version

Name:	P1130191.jpg
Views:	250
Size:	97.1 KB
ID:	118801   Click image for larger version

Name:	P1130193.jpg
Views:	232
Size:	84.8 KB
ID:	118802   Click image for larger version

Name:	P1130194.jpg
Views:	226
Size:	89.0 KB
ID:	118803   Click image for larger version

Name:	P1130197.jpg
Views:	198
Size:	21.0 KB
ID:	118804  
mark pirate is offline  
Old 23rd Jan 2016, 12:03 pm   #30
ukcol
Rest in Peace
 
ukcol's Avatar
 
Join Date: May 2003
Location: Harlaxton, Lincolnshire, UK.
Posts: 3,944
Default Re: Bush TV12B Restoration

In the original design using the 10M ohm resistors there will be almost 100uA flowing in the EHT bleeder chain and the current drawn by the CRT will have to be added to get the total EHT current.

The Mullard sheet for the EY51 EHT rectifier states the maximum anode current limit as 0.5mA for 50 to 150 c/s operation and 100uA for 1kc/s pulse operation.

They don't give a figure for 10kc/s operation but it would be much nearer the 100uA than the 500uA(I suspect ?).

So perhaps the increase in the value of the resistors in the EHT chain is to give the EY51 a better life?

It looks like the main (only?) purpose of the EHT resistor chain is to provide a potential divider for the CRT A1 voltage, so I suspect the bottom resistor in your set is changed in value from 1M ohm to 2.2 M ohms.
ukcol is offline  
Old 23rd Jan 2016, 3:05 pm   #31
mark pirate
Dekatron
 
mark pirate's Avatar
 
Join Date: Mar 2008
Location: Worthing, West Sussex, UK
Posts: 5,185
Default Re: Bush TV12B Restoration

Quote:
It looks like the main (only?) purpose of the EHT resistor chain is to provide a potential divider for the CRT A1 voltage, so I suspect the bottom resistor in your set is changed in value from 1M ohm to 2.2 M ohms.
According to the manual, it was 1.8Mohm originally. In the modified bleeder chain
it is reduced to 1Mohm, but my set has a 2.2Mohm fitted.

Going by the newest dates on the capacitors, my set must have been made in February 1950, only four months before the TV22 was released.

Mark
mark pirate is offline  
Old 24th Jan 2016, 11:39 pm   #32
mark pirate
Dekatron
 
mark pirate's Avatar
 
Join Date: Mar 2008
Location: Worthing, West Sussex, UK
Posts: 5,185
Default Re: Bush TV12B Restoration

More progress has been made today, the two main tagstrips under the chassis have been recapped and a couple of out of spec resistors have been replaced.
It has been a fiddly process to de-solder and unwrap the old component leads, but I want to do a thorough job on this set.

I am on my second box of cotton buds and have gone through most of a can of degreasing solvent to get the black sooty deposits off the chassis and tagstrips.

The physical state of some of the old caps is pretty poor, one of the electrolytic caps had split at the sides and badly corroded (see photos).

I am still amazed at the size difference between the old and new caps, especially the electrolytics, it certainly looks neater with the replacements in situ.

Hopefully I will finish of the underside tomorrow, and then make a start on the line and frame timebase tagstrips.

Mark
Attached Thumbnails
Click image for larger version

Name:	P1130204.jpg
Views:	246
Size:	120.4 KB
ID:	118897   Click image for larger version

Name:	P1130206.jpg
Views:	235
Size:	45.8 KB
ID:	118898   Click image for larger version

Name:	P1130207.jpg
Views:	229
Size:	48.0 KB
ID:	118899   Click image for larger version

Name:	P1130202.jpg
Views:	225
Size:	44.9 KB
ID:	118900   Click image for larger version

Name:	P1130203.jpg
Views:	215
Size:	51.7 KB
ID:	118901  

mark pirate is offline  
Old 25th Jan 2016, 6:36 am   #33
beery
Heptode
 
beery's Avatar
 
Join Date: Jun 2006
Location: Ware, Hertfordshire, UK.
Posts: 988
Default Re: Bush TV12B Restoration

Hi Mark,

I've never seen electrolytics split like that before. If connected backwards usually the ends pop out, but just to corrode all the way through is a new one to me.

I remember once my Invicta T102B attempted to send its 1st stage smoother (it has a voltage doubler) into orbit when the PZ30 had heater-cathode breakdown, but being firmly clamped it simply sprayed the cloth the chassis was sitting on with tar covered bits of paper and foil...

Btw. I always think it interesteing how we can track Bush's use of the tag board with the cut out for a blocking oscillator transformer. You can see it in both of the tagbaords in your photo and indeed it turned up in their sets for quite some time.
Does anyone know the last model to have this tagboard with the big rectangular hole in it?

Cheers
Andy
beery is offline  
Old 25th Jan 2016, 10:34 am   #34
mark pirate
Dekatron
 
mark pirate's Avatar
 
Join Date: Mar 2008
Location: Worthing, West Sussex, UK
Posts: 5,185
Default Re: Bush TV12B Restoration

Hi Andy, There are four tagstrips in this set, all four have the cutout. The two under the chassis are just cut down versions that are fitted to either side of the chassis for the frame and line timbase components.

One interesting comparison between this set and the TV22, is the blocking transformer is mounted on the opposite side of the chassis.
The TV22 has only one tagstrip, the other side of the chassis just contains one small capacitor.

It is interesting to see how this chassis evolved into the TV22, they share a few components such as transformers and chokes and their positions on the chassis.
The top chassis itself and wooden sides are identical to the TV22, but the later set has been stamped out for a quite different set of components.

This set appears to retain all it's original components and valves, the glass valves are very silvered and look well used, so it seems the set was very reliable in it's service life.
The only evidence of any work seems to be that someone had neatly added some wires to the output transformer going to two unused tags on top of the choke (L5) to add an external extension speaker, although there is no sign that this was actually used?

When I first got the set, I noticed that the back of the CRT appeared to have been broken by being hit from the bottom, maybe when removing it from a loft it took a hit on the hatch?
I think the fact the CRT was obviously broken put people off bidding on it, but this did not bother me as this was high on my list of sets I wanted to own.

The donor CRT tests good, and indeed gives a nice bright picture when tried out on an LV20 chassis.

Mark
mark pirate is offline  
Old 25th Jan 2016, 1:19 pm   #35
Hunts smoothing bomb
Octode
 
Hunts smoothing bomb's Avatar
 
Join Date: Oct 2005
Location: Wimborne, Dorset, UK.
Posts: 1,407
Default Re: Bush TV12B Restoration

Excellent,
I can't wait to see some light on the CRT!

Cheers
__________________
Lee
Hunts smoothing bomb is offline  
Old 25th Jan 2016, 11:18 pm   #36
mark pirate
Dekatron
 
mark pirate's Avatar
 
Join Date: Mar 2008
Location: Worthing, West Sussex, UK
Posts: 5,185
Default Re: Bush TV12B Restoration

Despite other distractions, I managed to make more headway with the set today.
I replaced the remaining three caps under the chassis, one of which was hiding away behind a small tagstrip at the rear, two more resistors were also replaced and a bit more cleaning saw the completion of the underside.

I have also finished one of the side mounted tagstrips. Working left to right, I replaced all the caps one at a time, cleaning the board of waxy grime behind the old components before fitting the new ones.
It is a very tedious job to desolder and unwrap the old leads. but to replicate the way the originals were fitted, the tags need to be clear to insert the new leads.

Three out of the five resistors also needed replacement, one had doubled in value!
Having finished this board, I turned the chassis round and started on the other one. I have got half way through this, but starting to feel tired I called it a day. It is not worth the potential risk of making mistakes, tomorrow is another day

I hope to get the chassis finished tomorrow, and hopefully install the replacement CRT and test the valves.

Mark
Attached Thumbnails
Click image for larger version

Name:	Hidden Capacitor.jpg
Views:	181
Size:	112.0 KB
ID:	118950   Click image for larger version

Name:	Recap finished.jpg
Views:	177
Size:	100.1 KB
ID:	118951   Click image for larger version

Name:	Before recap.jpg
Views:	184
Size:	102.3 KB
ID:	118952   Click image for larger version

Name:	Half way there!.jpg
Views:	185
Size:	102.6 KB
ID:	118953  
mark pirate is offline  
Old 25th Jan 2016, 11:36 pm   #37
unitaudio
Heptode
 
Join Date: Sep 2013
Location: Manchester, UK.
Posts: 860
Default Re: Bush TV12B Restoration

At this rate you'll have this one boxed off by weekend. You put me to shame. I've got a Rogers Ravensbrook receiver I bought in 2010. Still haven't got around to replacing the pots. The speed with which some people on this forum work astonishes me!

Regards,
Paul
__________________
...No, it's not supposed to pick up the World Service, it's not a radio!
unitaudio is offline  
Old 26th Jan 2016, 7:27 pm   #38
mark pirate
Dekatron
 
mark pirate's Avatar
 
Join Date: Mar 2008
Location: Worthing, West Sussex, UK
Posts: 5,185
Default Re: Bush TV12B Restoration

Quote:
At this rate you'll have this one boxed off by weekend
If all goes well, I just might!

I have finished the main chassis, and thought I would have a look at the receiver. There are only three wax caps and two electrolitics to replace, the rest are Mica caps.

I will post later about the CRT disaster later....

Mark
mark pirate is offline  
Old 26th Jan 2016, 7:48 pm   #39
Lloyd 1985
Nonode
 
Lloyd 1985's Avatar
 
Join Date: Jun 2008
Location: Coningsby, Lincolnshire, UK.
Posts: 2,814
Default Re: Bush TV12B Restoration

Quote:
Originally Posted by mark pirate View Post
I will post later about the CRT disaster later....
Oh no, this doesn't sound good!
Lloyd 1985 is offline  
Old 26th Jan 2016, 7:54 pm   #40
Freya
Octode
 
Freya's Avatar
 
Join Date: Jan 2009
Location: Falmouth, Cornwall, UK.
Posts: 1,987
Default Re: Bush TV12B Restoration

CRT oh no, don't keep us in suspense
__________________
Stephen
_________"It`s only an old telly" ___
Freya is offline  
Closed Thread

Thread Tools



All times are GMT +1. The time now is 11:16 pm.


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 - 2024, vBulletin Solutions, Inc.
Copyright ©2002 - 2023, Paul Stenning.