PYE 9" Television model B18T. - UK Vintage Radio Repair and Restoration Discussion Forum

Heatercathodeshort · 15th Oct 2008, 7:48 pm

Over the years I have collected a number of PYE B18T 9” receivers and passed the tatty ones on to fellow enthusiasts to either rob for parts, crt’s or maybe carry out restoration projects. This particular example has been in my safe keeping for well over 30 years and I thought it was about time its CRT displayed test card 'C' once again. I can’t remember ever having plugged it in so the results could have been interesting to say the least.
I removed the back and placed it under the bench as usual. Connecting the set to the mains resulted in nothing, a dead set. Removal of the chassis is a delight. Simply remove the two rear chassis retaining screws, unplug the speaker and remove the entire chassis complete with picture tube, Lovely!
A quick check with the meter quickly confirmed what I had forgotten after all these years. [I can hear you shouting the answer] The little Pye is fitted with a safety interlock that consists of two brass pins mounted in a small Paxolin panel that is riveted to the inside of the back panel. When the back is removed the pins disconnect the mains supply before it reaches the mains switch. The only way to get the supply to the mains switch is to insert two separate banana plugs in each socket in place of the interlock. I think they were nervous of the possible live chassis hazard.
That saga over and it was time to see if the old girl had any life in her. The valves lit after a while and to my amazement a faint line whistle could be heard. I switched off and turned the chassis over. First to get the snip was the mains filter capacitor. The smoothing block was in a shocking mess, bulging and very tired with dried puss around its connections. It is dated Feb 1950 so the set must have been one of the last produced having been first released in 1948. It was Britain’s first true AC/DC receiver with line flyback eht and of course a series heater chain of .3amp valves and CRT. Construction was to a high standard. I cannot see any replacement components so the set must have been reliable.
The bulging block was ignored for a while and the mains reconnected. The valves lit and after a short delay a faint line whistle could be detected. This slowly faded to a low level and continued in this state without any overheating. The front cover of the line output transformer was removed revealing the EY51 eht rectifier. The set was again powered up and the valve carefully observed. The line whistle built up and the EY51 heater began to glow. Once again the whistle subsided and a blue glow could be seen within the anode area. Snipping off the anode connection resulted in a good spark from the transformer connection but as soon as the rectifier was connected it died. Of course the rectifier could have been faulty but my suspicions were confirmed after substituting a brand new valve. The heater winding had broken down to the transformer core and the easy option was to fit a small stick rectifier in place of that little EY51 isolating the heater winding and connections. I have not examined the construction of the transformer itself. If the heater winding is a separate arrangement it might be possible to rewind it but these early flyback transformers did not have the benefits of ‘Ferroxcube’ and to maintain efficiency usually wound it on top of the underwind. I do not want to risk disturbance of the windings and will leave well alone.
Powering up again resulted in a very bright controllable raster with no ion burn despite the lack of an ion trap on the MW22-17 crt. Certainly out of shape but a raster for sure. I applied the output from the Aurora and low and behold a distorted picture appeared together with very good quality sound and plenty of it! The sync was somewhat weak and the edges of the raster ragged. This is usually caused by a leaky sync coupling capacitor connected between the video output stage anode and the control grid of the sync separator. Not so in this case, it is a SPRAGUE metal cased type of high quality and showed infinite resistance on the AVO 8 as did all the other Sprague condensers in the set! A glance at the circuit shows a 12uf electrolytic condenser decoupling the supply to the Video amplifier an EF50. I stabbed a test condenser across it and the picture immediately straightened up and increased in contrast. The quality really was very good and replacement of the TCC wax condensers in the frame stage sorted out the linearity problems. The line linearity is not 100% but is not noticed on a picture. I’m not certain that this was perfect on these early flyback models but considering I have not replaced any components in the output stage and this may account for this. Next to tackle was the incontinent main smoothing block. I replaced this with an identical size NOS can I discovered in my condenser stash and it performed as new. The scan coils are slightly twisted but stuck to the tube neck. The set will need to run for a few hours to soften the wax before attempting to move them. The cabinet is in very good condition with a solid back. I have posted pictures showing the ragged effect, some chassis shots and one working with the valves glowing. I like that one!
The chassis is a delight to work on and the circuit very simple. There are no less than eleven EF50’s three EB41’s A PZ30, PL33, PY31 and PL38. It was produced from late 1948 to be replaced in late 1950 by the LV30 that mostly using the new Mullard B9A television series.
How manufacturers committed to MAZDA must have looked on in despair having to struggle with 3 odd heater chains, [100ma/200ma/300ma] gas Thyratrons, hopeless H.T. rectifiers and a triode picture tube that went heater cathode short at the drop of a hat [unless the emission failed first] A real credit to Pye and Mullard in 1948 setting standards that others would have to follow. Regards, John.

Ian B · 15th Oct 2008, 8:12 pm

Nice work John. It's a better picture than my D18T gives, although that has improved a lot with use. The focus still drifts a bit, but if you can put up with the first 10 minutes of a film being out of focus, it's perfectly watchable from then on.
Regards,
Ian Blackbourn

Heatercathodeshort · 15th Oct 2008, 9:22 pm

Hello Ian,
EHT drift during warm up can be a problem with these sets. Its probably due to saturation of the overwind caused by years of inactivity or a slightly gassy tube. No problem as the tubes go on for ever! Great to know there are a few of these sets that still give a good picture. Regards, John.

Brian R Pateman · 15th Oct 2008, 9:33 pm

The first T/V set I ever repaired was one of these.

Obtained from a jumble sale for 5/- (a week's pocket money) and it wasn't in the first flush of youth. I was 12 or 13 at the time and it gave me the bug for fixing things!

I ran it in my bedroom for a while with Wolsley adaptor for Band III.

I must get another one one of these days.

Thanks for bringing back a happy memory.

Regards,

peter_scott · 16th Oct 2008, 4:51 pm

Hi John,

Looks excellent! If you can't easily rotate the scan coils would it be easier just to rotate the tube?

Peter

Heatercathodeshort · 16th Oct 2008, 7:12 pm

Nice one Peter!
Yes you are correct of course. Problem is the Sorbo [?] rubber strip around the tube bowl is stuck to both the glass and the securing strap. I really don't fancy rolling it back like a sardine tin with the assistance of a pair of long nosed pliars! I think the scan coils will free up once I have warmed the set. I will have to find another repair job I can carry on with while the set warms...[Oh I see an HMV 1803 in the corner..]I don't want to leave it switched on unattended. Thanks for the interest. regards, John.

Aerodyne · 16th Oct 2008, 8:01 pm

What an amazing test card display, John. As you say, Pye built them well. A testament to the designers, too.
Very nice. Even I'm tempted, after swearing I'd never touch another TV after long years of working on them...
-Tony

Heatercathodeshort · 16th Oct 2008, 9:17 pm

Ooww. Come on Tony. The SMELL of rotting capacitors the ROAR of escaping EHT........
Get yer rubber gloves out of retirement! Seriously, thanks for the comments. Its 60 years old and as you say a great tribute to those PYE designers. Regards, John.

Heatercathodeshort · 18th Oct 2008, 6:22 pm

The final pictures of the Pye now boxed up and working. I have run the set for around 4 hours but the scan coils remain firmly stuck to the crt neck. Its only very slightly out and I'm going to leave them that way. Its not worth the risk having twisted the neck off one of these very models when I was a 14 year old....Dealers must have complained about the lack of model identification numbers on Pye receivers until the familiar blue anodized plate appeared on the LV30 and all subsequent models. The cabinet is nice and original and still has that 'Grannies front room' smell! Regards, John.

BGmidsUK · 19th Oct 2008, 5:24 am

Which of the controls is hidden by the back cover? I notice that 6 sliders are accessible with the cover removed and only 5 visible with it in place.

BG

Tazman1966 · 19th Oct 2008, 11:28 pm

Hi John.

What a great set and write up too

. One day I'll try something that old...

Heatercathodeshort · 22nd Oct 2008, 4:07 pm

Hello BG,
Ha Ha! I had not noticed that one of the sliders was covered by the back.. I set it up and simply slid the chassis back into place and screwed the back on. I was more involved getting the safety interlock pins into their sockets on the rear chasis wall. Very observant of you. It is the FRAME LINEARITY control that is covered. They probably thought it was just one too many for users to twiddle. Regards, John.

15th Oct 2008, 7:48 pm	#1
Heatercathodeshort Dekatron Join Date: Jun 2005 Location: Warnham, West Sussex. 10 miles south of DORKING. Posts: 9,147	PYE 9" Television model B18T. Over the years I have collected a number of PYE B18T 9” receivers and passed the tatty ones on to fellow enthusiasts to either rob for parts, crt’s or maybe carry out restoration projects. This particular example has been in my safe keeping for well over 30 years and I thought it was about time its CRT displayed test card 'C' once again. I can’t remember ever having plugged it in so the results could have been interesting to say the least. I removed the back and placed it under the bench as usual. Connecting the set to the mains resulted in nothing, a dead set. Removal of the chassis is a delight. Simply remove the two rear chassis retaining screws, unplug the speaker and remove the entire chassis complete with picture tube, Lovely! A quick check with the meter quickly confirmed what I had forgotten after all these years. [I can hear you shouting the answer] The little Pye is fitted with a safety interlock that consists of two brass pins mounted in a small Paxolin panel that is riveted to the inside of the back panel. When the back is removed the pins disconnect the mains supply before it reaches the mains switch. The only way to get the supply to the mains switch is to insert two separate banana plugs in each socket in place of the interlock. I think they were nervous of the possible live chassis hazard. That saga over and it was time to see if the old girl had any life in her. The valves lit after a while and to my amazement a faint line whistle could be heard. I switched off and turned the chassis over. First to get the snip was the mains filter capacitor. The smoothing block was in a shocking mess, bulging and very tired with dried puss around its connections. It is dated Feb 1950 so the set must have been one of the last produced having been first released in 1948. It was Britain’s first true AC/DC receiver with line flyback eht and of course a series heater chain of .3amp valves and CRT. Construction was to a high standard. I cannot see any replacement components so the set must have been reliable. The bulging block was ignored for a while and the mains reconnected. The valves lit and after a short delay a faint line whistle could be detected. This slowly faded to a low level and continued in this state without any overheating. The front cover of the line output transformer was removed revealing the EY51 eht rectifier. The set was again powered up and the valve carefully observed. The line whistle built up and the EY51 heater began to glow. Once again the whistle subsided and a blue glow could be seen within the anode area. Snipping off the anode connection resulted in a good spark from the transformer connection but as soon as the rectifier was connected it died. Of course the rectifier could have been faulty but my suspicions were confirmed after substituting a brand new valve. The heater winding had broken down to the transformer core and the easy option was to fit a small stick rectifier in place of that little EY51 isolating the heater winding and connections. I have not examined the construction of the transformer itself. If the heater winding is a separate arrangement it might be possible to rewind it but these early flyback transformers did not have the benefits of ‘Ferroxcube’ and to maintain efficiency usually wound it on top of the underwind. I do not want to risk disturbance of the windings and will leave well alone. Powering up again resulted in a very bright controllable raster with no ion burn despite the lack of an ion trap on the MW22-17 crt. Certainly out of shape but a raster for sure. I applied the output from the Aurora and low and behold a distorted picture appeared together with very good quality sound and plenty of it! The sync was somewhat weak and the edges of the raster ragged. This is usually caused by a leaky sync coupling capacitor connected between the video output stage anode and the control grid of the sync separator. Not so in this case, it is a SPRAGUE metal cased type of high quality and showed infinite resistance on the AVO 8 as did all the other Sprague condensers in the set! A glance at the circuit shows a 12uf electrolytic condenser decoupling the supply to the Video amplifier an EF50. I stabbed a test condenser across it and the picture immediately straightened up and increased in contrast. The quality really was very good and replacement of the TCC wax condensers in the frame stage sorted out the linearity problems. The line linearity is not 100% but is not noticed on a picture. I’m not certain that this was perfect on these early flyback models but considering I have not replaced any components in the output stage and this may account for this. Next to tackle was the incontinent main smoothing block. I replaced this with an identical size NOS can I discovered in my condenser stash and it performed as new. The scan coils are slightly twisted but stuck to the tube neck. The set will need to run for a few hours to soften the wax before attempting to move them. The cabinet is in very good condition with a solid back. I have posted pictures showing the ragged effect, some chassis shots and one working with the valves glowing. I like that one! The chassis is a delight to work on and the circuit very simple. There are no less than eleven EF50’s three EB41’s A PZ30, PL33, PY31 and PL38. It was produced from late 1948 to be replaced in late 1950 by the LV30 that mostly using the new Mullard B9A television series. How manufacturers committed to MAZDA must have looked on in despair having to struggle with 3 odd heater chains, [100ma/200ma/300ma] gas Thyratrons, hopeless H.T. rectifiers and a triode picture tube that went heater cathode short at the drop of a hat [unless the emission failed first] A real credit to Pye and Mullard in 1948 setting standards that others would have to follow. Regards, John. Attached Thumbnails Last edited by Heatercathodeshort; 15th Oct 2008 at 7:54 pm.

15th Oct 2008, 8:12 pm	#2
Ian B Hexode Join Date: May 2006 Location: Arlesey, Bedfordshire, UK. Posts: 401	Re: PYE 9" Television model B18T. Nice work John. It's a better picture than my D18T gives, although that has improved a lot with use. The focus still drifts a bit, but if you can put up with the first 10 minutes of a film being out of focus, it's perfectly watchable from then on. Regards, Ian Blackbourn

15th Oct 2008, 9:22 pm	#3
Heatercathodeshort Dekatron Join Date: Jun 2005 Location: Warnham, West Sussex. 10 miles south of DORKING. Posts: 9,147	Re: PYE 9" Television model B18T. Hello Ian, EHT drift during warm up can be a problem with these sets. Its probably due to saturation of the overwind caused by years of inactivity or a slightly gassy tube. No problem as the tubes go on for ever! Great to know there are a few of these sets that still give a good picture. Regards, John.

15th Oct 2008, 9:33 pm	#4
Brian R Pateman Nonode Join Date: Jun 2005 Location: Western Lake District, Cumbria (CA20) - UK Posts: 2,136	Re: PYE 9" Television model B18T. The first T/V set I ever repaired was one of these. Obtained from a jumble sale for 5/- (a week's pocket money) and it wasn't in the first flush of youth. I was 12 or 13 at the time and it gave me the bug for fixing things! I ran it in my bedroom for a while with Wolsley adaptor for Band III. I must get another one one of these days. Thanks for bringing back a happy memory. Regards, __________________ Brian

16th Oct 2008, 4:51 pm	#5
peter_scott Dekatron Join Date: May 2003 Location: Edinburgh, UK. Posts: 3,274	Re: PYE 9" Television model B18T. Hi John, Looks excellent! If you can't easily rotate the scan coils would it be easier just to rotate the tube? Peter __________________ http://www.nostalgiatech.co.uk https://www.youtube.com/c/PeterScott/videos

16th Oct 2008, 7:12 pm	#6
Heatercathodeshort Dekatron Join Date: Jun 2005 Location: Warnham, West Sussex. 10 miles south of DORKING. Posts: 9,147	Re: PYE 9" Television model B18T. Nice one Peter! Yes you are correct of course. Problem is the Sorbo [?] rubber strip around the tube bowl is stuck to both the glass and the securing strap. I really don't fancy rolling it back like a sardine tin with the assistance of a pair of long nosed pliars! I think the scan coils will free up once I have warmed the set. I will have to find another repair job I can carry on with while the set warms...[Oh I see an HMV 1803 in the corner..]I don't want to leave it switched on unattended. Thanks for the interest. regards, John.

16th Oct 2008, 8:01 pm	#7
Aerodyne Octode Join Date: Jun 2004 Location: Hampton Vale, Peterborough, UK. Posts: 1,698	Re: PYE 9" Television model B18T. What an amazing test card display, John. As you say, Pye built them well. A testament to the designers, too. Very nice. Even I'm tempted, after swearing I'd never touch another TV after long years of working on them... -Tony

16th Oct 2008, 9:17 pm	#8
Heatercathodeshort Dekatron Join Date: Jun 2005 Location: Warnham, West Sussex. 10 miles south of DORKING. Posts: 9,147	Re: PYE 9" Television model B18T. Ooww. Come on Tony. The SMELL of rotting capacitors the ROAR of escaping EHT........ Get yer rubber gloves out of retirement! Seriously, thanks for the comments. Its 60 years old and as you say a great tribute to those PYE designers. Regards, John.

18th Oct 2008, 6:22 pm	#9
Heatercathodeshort Dekatron Join Date: Jun 2005 Location: Warnham, West Sussex. 10 miles south of DORKING. Posts: 9,147	Re: PYE 9" Television model B18T. The final pictures of the Pye now boxed up and working. I have run the set for around 4 hours but the scan coils remain firmly stuck to the crt neck. Its only very slightly out and I'm going to leave them that way. Its not worth the risk having twisted the neck off one of these very models when I was a 14 year old....Dealers must have complained about the lack of model identification numbers on Pye receivers until the familiar blue anodized plate appeared on the LV30 and all subsequent models. The cabinet is nice and original and still has that 'Grannies front room' smell! Regards, John. Attached Thumbnails

19th Oct 2008, 5:24 am	#10
BGmidsUK Retired Dormant Member Join Date: Oct 2007 Location: Leicester, UK. Posts: 809	Re: PYE 9" Television model B18T. Which of the controls is hidden by the back cover? I notice that 6 sliders are accessible with the cover removed and only 5 visible with it in place. BG

19th Oct 2008, 11:28 pm	#11
Tazman1966 Nonode Join Date: May 2006 Location: St Albans, Herts, UK. Posts: 2,193	Re: PYE 9" Television model B18T. Hi John. What a great set and write up too. One day I'll try something that old... __________________ All the very best, Tas

22nd Oct 2008, 4:07 pm	#12
Heatercathodeshort Dekatron Join Date: Jun 2005 Location: Warnham, West Sussex. 10 miles south of DORKING. Posts: 9,147	Re: PYE 9" Television model B18T. Hello BG, Ha Ha! I had not noticed that one of the sliders was covered by the back.. I set it up and simply slid the chassis back into place and screwed the back on. I was more involved getting the safety interlock pins into their sockets on the rear chasis wall. Very observant of you. It is the FRAME LINEARITY control that is covered. They probably thought it was just one too many for users to twiddle. Regards, John.