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Vintage Television and Video Vintage television and video equipment, programmes, VCRs etc. |
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20th Jan 2016, 12:04 am | #21 |
Octode
Join Date: Oct 2005
Location: Wimborne, Dorset, UK.
Posts: 1,407
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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
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Lee |
20th Jan 2016, 8:10 pm | #22 |
Nonode
Join Date: Jun 2008
Location: Coningsby, Lincolnshire, UK.
Posts: 2,814
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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. |
22nd Jan 2016, 2:46 pm | #23 |
Dekatron
Join Date: Mar 2008
Location: Worthing, West Sussex, UK
Posts: 5,185
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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 |
22nd Jan 2016, 5:54 pm | #24 |
Dekatron
Join Date: Aug 2007
Location: W.Butterwick, near Doncaster UK.
Posts: 8,923
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Re: Bush TV12B Restoration
Dag is normally connected to chassis with a piece of thin springy copper.
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22nd Jan 2016, 6:39 pm | #25 |
Dekatron
Join Date: Mar 2008
Location: Worthing, West Sussex, UK
Posts: 5,185
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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 |
22nd Jan 2016, 9:32 pm | #26 |
Nonode
Join Date: Jun 2008
Location: Coningsby, Lincolnshire, UK.
Posts: 2,814
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Re: Bush TV12B Restoration
I wrapped gaffer tape round the mask on mine! Probably wants something better really though...
Regards, Lloyd |
22nd Jan 2016, 9:39 pm | #27 |
Dekatron
Join Date: Jun 2009
Location: Staffordshire Moorlands, UK.
Posts: 5,263
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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.
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Kevin |
22nd Jan 2016, 11:44 pm | #28 |
Rest in Peace
Join Date: Jun 2004
Location: Burghfield, Reading, Berkshire, UK,
Posts: 1,055
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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.
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23rd Jan 2016, 10:06 am | #29 |
Dekatron
Join Date: Mar 2008
Location: Worthing, West Sussex, UK
Posts: 5,185
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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 |
23rd Jan 2016, 12:03 pm | #30 |
Rest in Peace
Join Date: May 2003
Location: Harlaxton, Lincolnshire, UK.
Posts: 3,944
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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. |
23rd Jan 2016, 3:05 pm | #31 | |
Dekatron
Join Date: Mar 2008
Location: Worthing, West Sussex, UK
Posts: 5,185
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Re: Bush TV12B Restoration
Quote:
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 |
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24th Jan 2016, 11:39 pm | #32 |
Dekatron
Join Date: Mar 2008
Location: Worthing, West Sussex, UK
Posts: 5,185
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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 |
25th Jan 2016, 6:36 am | #33 |
Heptode
Join Date: Jun 2006
Location: Ware, Hertfordshire, UK.
Posts: 988
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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
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25th Jan 2016, 10:34 am | #34 |
Dekatron
Join Date: Mar 2008
Location: Worthing, West Sussex, UK
Posts: 5,185
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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 |
25th Jan 2016, 1:19 pm | #35 |
Octode
Join Date: Oct 2005
Location: Wimborne, Dorset, UK.
Posts: 1,407
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Re: Bush TV12B Restoration
Excellent,
I can't wait to see some light on the CRT! Cheers
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Lee |
25th Jan 2016, 11:18 pm | #36 |
Dekatron
Join Date: Mar 2008
Location: Worthing, West Sussex, UK
Posts: 5,185
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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 |
25th Jan 2016, 11:36 pm | #37 |
Heptode
Join Date: Sep 2013
Location: Manchester, UK.
Posts: 860
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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
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26th Jan 2016, 7:27 pm | #38 | |
Dekatron
Join Date: Mar 2008
Location: Worthing, West Sussex, UK
Posts: 5,185
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Re: Bush TV12B Restoration
Quote:
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 |
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26th Jan 2016, 7:48 pm | #39 |
Nonode
Join Date: Jun 2008
Location: Coningsby, Lincolnshire, UK.
Posts: 2,814
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Re: Bush TV12B Restoration
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26th Jan 2016, 7:54 pm | #40 |
Octode
Join Date: Jan 2009
Location: Falmouth, Cornwall, UK.
Posts: 1,987
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Re: Bush TV12B Restoration
CRT oh no, don't keep us in suspense
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