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CTV 1967 Baird M702: 700 Series Chassis: Dual Standard

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crustytv
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Well its here, the Baird M702 was a dream set that I thought would firmly remain that, a dream. However today it became a reality and now joins my early Rebuilt Baird 8724 & Baird 8749. Thanks to Steve for making it possible to purchase :cca and to Andy for looking after it. The 153 mile trip down was fairly innocuous and was done in three hours. The TV just fitted in the back of the car with a little room left for two boxes of 70's TV mags and a large box of TV odds n sods. The return journey was hideous, I left Andy's around 13:00 and didn't get home until 17:30. Well stressed out and feel like a zombie after 7 hours of driving, I'm not used to it as I hardly drive these days. However the couple of hours with Andy and Molly were a real treat and always great to put a real face to an avatar. As for Molly, what a sweetheart, when I was explaining what all the parts were whilst dad was making a brew, she proclaimed, " I think this is the most interesting day in my life" I love the way kids phrase things. I think she will be just glad toi see the back of the junk so the large shed can be returned to use as her den. Anyway will give it a thorough check over tomorrow and no doubt this thread will be filled with trials and tribulations.

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Posted : 24/07/2015 9:33 pm
colourmaster
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Hi Chris
Excellent news on getting a 700 . I'm sure that the set you have won a local newspaper award as being Macclesfield's oldest working tv afew years ago so I wouldn't be surprised if it doesn't work first time .
Gary.

 
Posted : 24/07/2015 9:40 pm
crustytv
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Hi Gary,

Had it been moved direct from one warm house to another I might expect that too, however the set has been stored in a shed since Dec 2013. Careful checking will be required and acclimatising to its new snug home, fingers crossed re the LOPT. Will check the system switching for corrosion too.

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Posted : 24/07/2015 11:49 pm
PYE625
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Well done Chris...it looks very nice !
A rare set indeed, I can hardly wait until you start work on her and read all about it here :aad

To understand the black art of electronics is to understand witchcraft. Andrew.

 
Posted : 24/07/2015 11:50 pm
Nuvistor
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To think that set is nearly 50 years old, I saw the first one during the winter 1966/67 or possibly spring 67 at the local technical college. I never repaired one but I do remember thinking the picture was good, the BBC were transmitting still photos the trade films came later. I presume the college got one of the first production or possibly a pre production model. It was the first CTV that I saw.
It looks in lovely condition with only a little dust inside, looking forward to see it back working again.
Frank

Frank

 
Posted : 25/07/2015 9:52 am
PYE625
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I found it interesting to see in the circuit that the EHT stage uses a tripler instead of a GY501 but makes use of a PD500 to stabilize the final EHT.
I guess the X-RAY emission is still very much something to be mindful of. :aao

To understand the black art of electronics is to understand witchcraft. Andrew.

 
Posted : 25/07/2015 11:06 am
Nuvistor
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I did not know it used a tripler, I saw the base of the PD500 and assumed it had a GY501. Does the line stage use 3rd or 5th harmonic tuning, the PD500/GY501 circuits I saw were 3rd (adjustable)but the later tripler circuits were 5th (fixed), this gave a more flat top to the EHT 15kc/s pulse for better regulation. I don't think the regulation was a good as the PD500 circuits though.

Frank

 
Posted : 25/07/2015 1:48 pm
PYE625
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It makes me think that the LOPT would be more reliable as there is no EHT over-wind as such.
Over-winds are scary enough in a mono set, let alone in a colour with 25kv EHT or the like. :bba

To understand the black art of electronics is to understand witchcraft. Andrew.

 
Posted : 28/07/2015 9:57 am
crustytv
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Initial inspection Time

Some free time this afternoon so thought I would start to give it the visuals. I like to spend a couple of days getting to know a sets layout, studying the cct and seeing what potential problems exist.

The cabinet has a Radio Rentals sticker with the printed date of 20th December 1967 and the large glass delay line Oct 67. Just imagine getting this installed 4 days before Christmas 67, I can appreciate the excitement that Mr & Mrs X might have experienced.

The CRT in this is an RCA tube, not sure what model as the ident label is right under the degauss shield but clearly an early import, were Mazda and Mullards not readily available yet trusted when this set was launched. I will be testing the CRT later this evening and reporting back the findings.

The chassis withdraws on runners then tilts forward to a locked position. To achieve this two retaining screws left and right need to be removed. Once pulled and tilted it gives great access, I'm struck by the similarity to the G6 with regards to all the hard-wires....... Crusty drops to knees and utters the following incantation, "Oh TV spirit of the great ozone, protect me from the pinged wire gremlins".

Immediately my beady eye is off to a start, I'm sure there will be more but for now :-

On the decoder coil L230 which feeds into the luminance delay line, was hanging off and will need fixing. Then there's the main smoothers, C603+C604, C607+C608 both pair are 2x400uF they look shot, one more than the other.

The quest continues, for now some more pics as we all like pics don't we.

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Posted : 29/07/2015 4:49 pm
crustytv
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Looks like the RCA picture bulb :qq1 will give a good account of itself once up and running.

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Posted : 29/07/2015 6:09 pm
Terrykc
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...The CRT in this is an RCA tube, not sure what model as the ident label is right under the degauss shield but clearly an early import, were Mazda and Mullards not readily available yet trusted when this set was launched ...]

There was a UK RCA Colour tube plant at Skelmersdale which was 33% owned by Radio Rentals.

Either they hadn't got up to speed when your set was made or a Christmas rush meant that that they had to import some ...

When all else fails, read the instructions

 
Posted : 29/07/2015 6:20 pm
crustytv
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There was a UK RCA Colour tube plant at Skelmersdale which was 33% owned by Radio Rentals.

Thanks for the info, I didn't know that. I assumed all RCA's were imported ready built. I have a NOS RCA 19" in its original box which is destined for another set, I will go check out of interest to see if that might be from Skelmersdale.

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Posted : 29/07/2015 6:30 pm
Katie Bush
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Hi Chris,

Eeh... Uncannily G6-esque.. I wish I had a 700 now!

I was wondering if those smoothing cans are totally kaput, or would they reform - I have seen worse - much worse!

Marion

 
Posted : 29/07/2015 9:08 pm
slidertogrid
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That must be a very early set Chris. (he says, stating the bleedin obvious !) :cch I have never seen an RCA tube in a British set before.
I have an article in Television magazine entitled first colour set rented by Radio Rentals, it was a Baird 700 in a Regency cabinet ISTR.
I will see if I can find it.
Lovely set !
:thumb
Rich.

 
Posted : 29/07/2015 9:22 pm
Terrykc
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... I have never seen an RCA tube in a British set before ....

We were Baird dealers when colour started and all of their colour sets were fitted with RCA tubes!

When all else fails, read the instructions

 
Posted : 29/07/2015 9:45 pm
Nuvistor
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This is a good write up of the problems faced by the Skelmerdale CRT factory. It seems that RCA were only a junior partner and provided the patents and start up experience. Thorn was the major shareholder and that was the sign on the factory wall and CRT's were labelled Mazda. It had a very short life of 5 years, 1971-76.

http://hansard.millbanksystems.com/comm ... on-factory

Frank

Frank

 
Posted : 29/07/2015 10:28 pm
Nuvistor
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I think, but not sure, that the early Baird dual standard followed the USA type design in quite a few of its circuits.

Frank

Frank

 
Posted : 29/07/2015 10:34 pm
Cathovisor
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Thanks for posting that Frank - absolutely fascinating and seemingly, intelligent discourse in the House. Compare that to PMQs nowadays...

 
Posted : 29/07/2015 10:47 pm
crustytv
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The Baird service manual states this tube is either an R.C.A. A63-13X or A63-16X and further research suggests the first released sets for the 67 colour launch all had R.C.A. fitted

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Posted : 30/07/2015 12:11 am
malcscott
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RCA tubes were used in the first Thorn 9000 chassis (1975)

 
Posted : 30/07/2015 1:19 am
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