Baird M702 - UK Vintage Radio Repair and Restoration Discussion Forum

EF80TVVALVE · 6th Feb 2023, 10:12 pm

Hi all,

So I saved this set from an auction this week, the poor thing had previously been unsold in the last one and had found its way in the next auction day when I discovered it. I left a bid without seeing it and to my surprise I became the new owner of what looks to be a nice untouched set.

Colour really isn't my thing let alone such an early colour set, a little out of the familiarity of 405 mono sets which I've come to know very well. As it's a fresh start for me is there anything I should be particularly weary of component wise before applying any power? Anything that is best replaced even before the first power up to avoid damage to other components?

If anybody has any data for the M702 I'd be interested to know, I'm sure it'll prove useful in getting this set back into working condition again. I'm looking forward to learning about these sets and familiarising myself with them, it's quite a beast!

PYE 405 · 6th Feb 2023, 11:09 pm

Hello and very well done for saving another example of this rather rare set.
Just briefly, I would suggest to proceed with great caution before thinking of powering up. There will be a number of capacitors to be reformed plus any actual fault that might have retired the set from use. The EHT stage is especially deadly as well as the X-RAY radiation. Forgive me if you know this already, but 25KV from a low source impedance will kill.
Avail yourself of the full service data and have a very good read before commencing any work on this beautiful piece of engineering.
This link below is a good example of a restoration of this model....
https://www.radios-tv.co.uk/communit...dual-standard/

EF80TVVALVE · 6th Feb 2023, 11:37 pm

Thanks for the pointers Andrew, yes I'll certainly be proceeding with caution and I wouldn't just plug the set in and hope for the best either. I'll be going over the chassis before applying any power at all just to be sure there are no obvious faults that will cause any problems for the initial power up. I will try and find the data for it as I know it will be useful and essential for both making repairs and setting up. It looks to have been stored extremely well over the years, no damp or anything untoward. In sure it's probably been in someone's house enjoying its retirement for many years.

G8KBG Tony · 6th Feb 2023, 11:46 pm

https://www.service-data.com/section.php/9145/1/702-t

Regards,

Tony

EF80TVVALVE · 6th Feb 2023, 11:54 pm

Thanks Tony! I Couldnt find it for some reason, maybe I searched M702 instead.

German Dalek · 7th Feb 2023, 7:41 am

Wow, thats a real beauty!

As a console it will have a great sound to watch music on it.
Color consoles of that style are really rare in Europe.

Regards,
German Dalek

Welsh Anorak · 7th Feb 2023, 1:18 pm

That was a lucky buy!

Besides being a bit difficult to access, most faults were quite traightforward, and despite the lack of a 'pudding bowl' on the back, yours looks pretty well untouched.

Hopefully the CRT is OK. As you're used to 405, then the basic approach is similar - snip out the mains filter capcitor for now and either use a lamp limiter or variac or else dive straight in. Before doing so I'd disconnect the tripler and the HT feed to the PL509 and see if it breathes. Hopefully you'll get sound the reconnect the PL and see if you get a nice spark at the top.

If good, then clean around the anode cap and give it a try!

This has an unusual decoder (think Philips G6 but weirder) but stock faults are rare other than the usual suspects.
There was a Television article on these in the mid Seventies which is also worth visiting.

As far as I remember these didn't have a PD500 shunt stabiliser so X-rays shouldn't be a problem. However I'm basing that on the later chassis so I could be wrong on thst one.

Panrock · 7th Feb 2023, 2:23 pm

What a lovely discovery! We had just such a set, supplied by Radio Rentals, in 1967. After delivery, the moment my dad was safely out of the house, I (a 17 year-old) had the back off, to be rewarded by the view in your third picture.

Steve

Petedox · 7th Feb 2023, 3:04 pm

I fixed a few of these at Radio Rentals and properly set up they were streets ahead of our every day 3000/3500 chassis. There was a subtlety to the colour rendition which I put down to the colour difference drive using the PFL200 for video, as opposed RGB.

Welsh Anorak · 8th Feb 2023, 12:29 pm

I'd agree - IMHO the only contemporary set to approach the G6's 'nice' colour, which, of course, also used a mainly valved decoder a PFL200 and CDA drive, this time using PCF200s
.

EF80TVVALVE · 8th Feb 2023, 12:39 pm

Thanks everyone for your advice and comments. It was a lucky buy indeed and incredible these things are still turning up undiscovered, the auction it came from is popular with collectors and antique dealers so I'm surprised it didn't get snapped up as most dealers know old tvs are quite collectable nowadays.

I have given the set a once over internally. It looks to have had the smoothing cans replaced in the past as these are both identical RS units. The 250mA fuse for the 405/625 solenoid has blown so I looked into this, probably more to do with the various switch linkage seizing a bit that has caused it as there's no obvious fault there.

Other than this the set looks quite untouched other than R508, a 5.6meg bleed resistor from the focus pot that has been shorted, its one of those horrible stick type resistors with crimped ends so no doubt it went intermittent and was just bodged with linking it over. The set is dated February 1968 and has a Mullard CRT, whether or not this is original I don't know, I have read the earlier ones had RCA CRT's fitted.

Cheers
Bren

Welsh Anorak · 8th Feb 2023, 1:27 pm

That's correct. The Mullard CRT was the A63-11X which has a rimband. Later Mullards were the A63-120X which catered for the 'push through' type of TV but was fully interchangeable with the earlier type.

If it's an -11X it's likely to be the original.

A tube rebuilder told me the 11X versions could implode in the oven so they wouldn't rebuild them. Not sure how true this was, though all rebuilds I've seen were 120X versions.

EF80TVVALVE · 9th Feb 2023, 1:47 pm

Thanks for the info Glyn, I'll check whether it is an 11X or 120X when I next have the back off. I'm going to make sure all of the switching is nice and free and sort out that bleed chain before I power the set up, the rest looks okay with no obvious faults so fingers crossed it will give some life.

dazzlevision · 9th Feb 2023, 1:55 pm

Quote:

Originally Posted by EF80TVVALVE

I have read the earlier ones had RCA CRT's fitted.

Yes, that is true, as Radio Rentals set up a colour CRT factory in Skelmersdale as a joint venture with RCA of the USA (in 1966) - RCA Colour Tubes Ltd.
Thorn acquired Radio Rentals interest in this plant when it took over Radio Rentals in 1968. The business was later known as Thorn Colour Tubes Ltd.
The factory closed in 1976

Cathovisor · 9th Feb 2023, 2:32 pm

I believe there have been write-ups of the restoration of these sets over at VRAT - I remember pointing one out to one of the members there (Pye625) and he got it for pennies at auction.

ctc15 · 9th Feb 2023, 3:27 pm

I was in a tube rebuilders workshop when a 11X tube was taken out of the oven after cooling. I could see that some the adhesive had melted and run down the tube towards the the base. This was removed with wire wool and the tube was repainted with Dag.
I looked at the adhesive in the shell on the tube and it was full of cracks.
How safe was that tube?
Keith

Welsh Anorak · 10th Feb 2023, 10:52 am

Oh I think it was safe in normal use - especially with the rimband. However when it was made I don't think rebuilding was in their mind and perhaps the rebuild ovens were hotter than it required?
So my rebuilder wasn't mistaken then.

EF80TVVALVE · 11th Feb 2023, 2:50 pm

I've had the back off again today to have a look into these 5m6 resistors on the convergence panel, as well as the bottom one to chassis that has been soldered over a couple more are OC so some replacements are on the way. The CRT is a 120X so looks like it's been replaced sometime in its life, fingers crossed it's a good one. I'll leave powering up until these replacement resistors are fitted and I've given everything a final check but so far so good.

EF80TVVALVE · 19th Feb 2023, 1:35 pm

I carried out some more pre-power up work on the set yesterday, I replaced the 5.6meg resistors that were all open circuit bar one which read 11megs. I had a look inside the EHT cage to see the condition of the LOPT, it all generally looks good but has definitely seen some serciving in the past. The set was obviously kept near to a coal fire as it's absolutely caked in soot and the EHT must have attracted much of that into the housing and all over the LOPT.

The tripler looks to have been rebuilt at some stage with REMO brand diodes and what look to be polystyrene capacitors in place of the original ceramic ones. I would have trusted the original ceramics but I'm questioning whether I should replace these ones as all of the casings are showing tiny splits too. There also looks like there has been some arcing from the join between the final diode and EHT cap to the chassis, it looks like the rubber boot which shields the join has suffered a bit and there is a tar like substance on the chassis of the set opposite this rubber boot so his will need some correcting, I wonder if a replacement rubber boot could be found if I find this one has failed?

Cheers
Bren

Ferguson 2000 · 20th Feb 2023, 12:12 am

Dear Bren,

Congratulations on your auction find, it looks in very good condition for it's age.

The repair that I disliked on these sets was replacing the sufflex / polystyrene capacitors around the PFL200, I cannot recall now if these failed due to a flash over in the valve or if their failure damaged the valve, all were replaced just in case.

I think that the M indicated that the set was sold through a dealer or ordered especially for sale rather than rental.

Best wishes, Geoffrey.

6th Feb 2023, 10:12 pm	#1
EF80TVVALVE Octode Join Date: Feb 2010 Location: Leicester, UK. Posts: 1,433	Baird M702 Hi all, So I saved this set from an auction this week, the poor thing had previously been unsold in the last one and had found its way in the next auction day when I discovered it. I left a bid without seeing it and to my surprise I became the new owner of what looks to be a nice untouched set. Colour really isn't my thing let alone such an early colour set, a little out of the familiarity of 405 mono sets which I've come to know very well. As it's a fresh start for me is there anything I should be particularly weary of component wise before applying any power? Anything that is best replaced even before the first power up to avoid damage to other components? If anybody has any data for the M702 I'd be interested to know, I'm sure it'll prove useful in getting this set back into working condition again. I'm looking forward to learning about these sets and familiarising myself with them, it's quite a beast! Attached Thumbnails

6th Feb 2023, 11:09 pm	#2
PYE 405 Pentode Join Date: Dec 2009 Location: Chatteris, Cambridgeshire, UK. Posts: 176	Re: Baird M702 Hello and very well done for saving another example of this rather rare set. Just briefly, I would suggest to proceed with great caution before thinking of powering up. There will be a number of capacitors to be reformed plus any actual fault that might have retired the set from use. The EHT stage is especially deadly as well as the X-RAY radiation. Forgive me if you know this already, but 25KV from a low source impedance will kill. Avail yourself of the full service data and have a very good read before commencing any work on this beautiful piece of engineering. This link below is a good example of a restoration of this model.... https://www.radios-tv.co.uk/communit...dual-standard/ __________________ Andrew

6th Feb 2023, 11:37 pm	#3
EF80TVVALVE Octode Join Date: Feb 2010 Location: Leicester, UK. Posts: 1,433	Re: Baird M702 Thanks for the pointers Andrew, yes I'll certainly be proceeding with caution and I wouldn't just plug the set in and hope for the best either. I'll be going over the chassis before applying any power at all just to be sure there are no obvious faults that will cause any problems for the initial power up. I will try and find the data for it as I know it will be useful and essential for both making repairs and setting up. It looks to have been stored extremely well over the years, no damp or anything untoward. In sure it's probably been in someone's house enjoying its retirement for many years.

6th Feb 2023, 11:46 pm	#4
G8KBG Tony Pentode Join Date: Sep 2006 Location: Wombourne, South Staffordshire, UK. Posts: 225	Re: Baird M702 https://www.service-data.com/section.php/9145/1/702-t Regards, Tony __________________ G8KBG - BVWS Member - BATC Member

6th Feb 2023, 11:54 pm	#5
EF80TVVALVE Octode Join Date: Feb 2010 Location: Leicester, UK. Posts: 1,433	Re: Baird M702 Thanks Tony! I Couldnt find it for some reason, maybe I searched M702 instead.

7th Feb 2023, 7:41 am	#6
German Dalek Hexode Join Date: Jan 2011 Location: Düsseldorf, Germany. Posts: 368	Re: Baird M702 Wow, thats a real beauty! As a console it will have a great sound to watch music on it. Color consoles of that style are really rare in Europe. Regards, German Dalek __________________ And now something completly different: MARC BOLAN, he was/is the real king of Pop Music!

7th Feb 2023, 1:18 pm	#7
Welsh Anorak Dekatron Join Date: Apr 2005 Location: North Wales, UK. Posts: 6,918	Re: Baird M702 That was a lucky buy! Besides being a bit difficult to access, most faults were quite traightforward, and despite the lack of a 'pudding bowl' on the back, yours looks pretty well untouched. Hopefully the CRT is OK. As you're used to 405, then the basic approach is similar - snip out the mains filter capcitor for now and either use a lamp limiter or variac or else dive straight in. Before doing so I'd disconnect the tripler and the HT feed to the PL509 and see if it breathes. Hopefully you'll get sound the reconnect the PL and see if you get a nice spark at the top. If good, then clean around the anode cap and give it a try! This has an unusual decoder (think Philips G6 but weirder) but stock faults are rare other than the usual suspects. There was a Television article on these in the mid Seventies which is also worth visiting. As far as I remember these didn't have a PD500 shunt stabiliser so X-rays shouldn't be a problem. However I'm basing that on the later chassis so I could be wrong on thst one. __________________ Glyn www.gdelectronics.wales

7th Feb 2023, 2:23 pm	#8
Panrock Nonode Join Date: Feb 2005 Location: Worcestershire, UK. Posts: 2,533	Re: Baird M702 What a lovely discovery! We had just such a set, supplied by Radio Rentals, in 1967. After delivery, the moment my dad was safely out of the house, I (a 17 year-old) had the back off, to be rewarded by the view in your third picture. Steve

7th Feb 2023, 3:04 pm	#9
Petedox Pentode Join Date: Feb 2020 Location: Waterlooville, Hampshire, UK. Posts: 200	Re: Baird M702 I fixed a few of these at Radio Rentals and properly set up they were streets ahead of our every day 3000/3500 chassis. There was a subtlety to the colour rendition which I put down to the colour difference drive using the PFL200 for video, as opposed RGB. __________________ Pete BVWS Member

8th Feb 2023, 12:29 pm	#10
Welsh Anorak Dekatron Join Date: Apr 2005 Location: North Wales, UK. Posts: 6,918	Re: Baird M702 I'd agree - IMHO the only contemporary set to approach the G6's 'nice' colour, which, of course, also used a mainly valved decoder a PFL200 and CDA drive, this time using PCF200s . __________________ Glyn www.gdelectronics.wales

8th Feb 2023, 12:39 pm	#11
EF80TVVALVE Octode Join Date: Feb 2010 Location: Leicester, UK. Posts: 1,433	Re: Baird M702 Thanks everyone for your advice and comments. It was a lucky buy indeed and incredible these things are still turning up undiscovered, the auction it came from is popular with collectors and antique dealers so I'm surprised it didn't get snapped up as most dealers know old tvs are quite collectable nowadays. I have given the set a once over internally. It looks to have had the smoothing cans replaced in the past as these are both identical RS units. The 250mA fuse for the 405/625 solenoid has blown so I looked into this, probably more to do with the various switch linkage seizing a bit that has caused it as there's no obvious fault there. Other than this the set looks quite untouched other than R508, a 5.6meg bleed resistor from the focus pot that has been shorted, its one of those horrible stick type resistors with crimped ends so no doubt it went intermittent and was just bodged with linking it over. The set is dated February 1968 and has a Mullard CRT, whether or not this is original I don't know, I have read the earlier ones had RCA CRT's fitted. Cheers Bren

8th Feb 2023, 1:27 pm	#12
Welsh Anorak Dekatron Join Date: Apr 2005 Location: North Wales, UK. Posts: 6,918	Re: Baird M702 That's correct. The Mullard CRT was the A63-11X which has a rimband. Later Mullards were the A63-120X which catered for the 'push through' type of TV but was fully interchangeable with the earlier type. If it's an -11X it's likely to be the original. A tube rebuilder told me the 11X versions could implode in the oven so they wouldn't rebuild them. Not sure how true this was, though all rebuilds I've seen were 120X versions. __________________ Glyn www.gdelectronics.wales

9th Feb 2023, 1:47 pm	#13
EF80TVVALVE Octode Join Date: Feb 2010 Location: Leicester, UK. Posts: 1,433	Re: Baird M702 Thanks for the info Glyn, I'll check whether it is an 11X or 120X when I next have the back off. I'm going to make sure all of the switching is nice and free and sort out that bleed chain before I power the set up, the rest looks okay with no obvious faults so fingers crossed it will give some life.

9th Feb 2023, 2:32 pm	#15
Cathovisor Banned Join Date: Dec 2022 Location: Peterborough, Cambridgeshire, UK. Posts: 418	Re: Baird M702 I believe there have been write-ups of the restoration of these sets over at VRAT - I remember pointing one out to one of the members there (Pye625) and he got it for pennies at auction.

9th Feb 2023, 3:27 pm	#16
ctc15 Pentode Join Date: Oct 2005 Location: Barnet, London, UK. Posts: 167	Re: Baird M702 I was in a tube rebuilders workshop when a 11X tube was taken out of the oven after cooling. I could see that some the adhesive had melted and run down the tube towards the the base. This was removed with wire wool and the tube was repainted with Dag. I looked at the adhesive in the shell on the tube and it was full of cracks. How safe was that tube? Keith

10th Feb 2023, 10:52 am	#17
Welsh Anorak Dekatron Join Date: Apr 2005 Location: North Wales, UK. Posts: 6,918	Re: Baird M702 Oh I think it was safe in normal use - especially with the rimband. However when it was made I don't think rebuilding was in their mind and perhaps the rebuild ovens were hotter than it required? So my rebuilder wasn't mistaken then. __________________ Glyn www.gdelectronics.wales

11th Feb 2023, 2:50 pm	#18
EF80TVVALVE Octode Join Date: Feb 2010 Location: Leicester, UK. Posts: 1,433	Re: Baird M702 I've had the back off again today to have a look into these 5m6 resistors on the convergence panel, as well as the bottom one to chassis that has been soldered over a couple more are OC so some replacements are on the way. The CRT is a 120X so looks like it's been replaced sometime in its life, fingers crossed it's a good one. I'll leave powering up until these replacement resistors are fitted and I've given everything a final check but so far so good.

19th Feb 2023, 1:35 pm	#19
EF80TVVALVE Octode Join Date: Feb 2010 Location: Leicester, UK. Posts: 1,433	Re: Baird M702 I carried out some more pre-power up work on the set yesterday, I replaced the 5.6meg resistors that were all open circuit bar one which read 11megs. I had a look inside the EHT cage to see the condition of the LOPT, it all generally looks good but has definitely seen some serciving in the past. The set was obviously kept near to a coal fire as it's absolutely caked in soot and the EHT must have attracted much of that into the housing and all over the LOPT. The tripler looks to have been rebuilt at some stage with REMO brand diodes and what look to be polystyrene capacitors in place of the original ceramic ones. I would have trusted the original ceramics but I'm questioning whether I should replace these ones as all of the casings are showing tiny splits too. There also looks like there has been some arcing from the join between the final diode and EHT cap to the chassis, it looks like the rubber boot which shields the join has suffered a bit and there is a tar like substance on the chassis of the set opposite this rubber boot so his will need some correcting, I wonder if a replacement rubber boot could be found if I find this one has failed? Cheers Bren Attached Thumbnails

20th Feb 2023, 12:12 am	#20
Ferguson 2000 Tetrode Join Date: Jun 2008 Location: Stratford upon Avon, Warwickshire, UK. Posts: 80	Re: Baird M702 Dear Bren, Congratulations on your auction find, it looks in very good condition for it's age. The repair that I disliked on these sets was replacing the sufflex / polystyrene capacitors around the PFL200, I cannot recall now if these failed due to a flash over in the valve or if their failure damaged the valve, all were replaced just in case. I think that the M indicated that the set was sold through a dealer or ordered especially for sale rather than rental. Best wishes, Geoffrey.