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 27th Oct 2016, 11:19 pm   #1
lloydwells
Heptode
 
Join Date: Aug 2016
Location: Dumfries, Scotland, UK.
Posts: 549
Default GEC BT 302 no picture. (Now identified as a 318)

This set has apparently been stored since 1974 when its original owner bought a colour set. After gently warming it up over several hours I've got noise so the sound stage apparently works, nothing at all on the CRT. Tube heater is working, I have an audible clicking coming from the chassis not audible through the speaker and a nasty looking bodge under the chassis which seems to have replaced something. I could do with knowing what. I've had a little light smoke maybe coming from the bodge or possibly the LOPT may be getting warm.
Help needed please.
Attached Thumbnails
Click image for larger version

Name:	WP_20161027_22_23_18_Pro.jpg
Views:	242
Size:	54.1 KB
ID:	131866  
lloydwells is offline  
Old 27th Oct 2016, 11:37 pm   #2
MALC SCOTT
Octode
 
MALC SCOTT's Avatar
 
Join Date: Aug 2006
Location: Willington, County Durham, UK.
Posts: 1,498
Default Re: GEC BT 302 no picture help.

This is a BY100 diode and surge resistor. It is fitted in place of the old type metal rectifier. Not a bodge, many sets had these fitted. I would replace any wax caps in the set before running it any longer. Damage to the LOPTX could happen, Malc.
__________________
Malc Scott
MALC SCOTT is offline  
Old 27th Oct 2016, 11:38 pm   #3
petertheorgan
Hexode
 
petertheorgan's Avatar
 
Join Date: Dec 2006
Location: Bromley, Kent, UK.
Posts: 332
Default Re: GEC BT 302 no picture help.

The "bodge" is where the metal rectifier has been replaced by a diode and a limiting resistor, the resistor will get hot in normal use and if the set has not been used for a bit, may even emit the odd puff of smoke. Keep it clear of the bowl of the tube or you may have a story to tell like one of my friends!

A good set and you should get it going, but will probably need a massive capacitor change.

Good luck , Peter.

Sorry, Malc got there first.

Last edited by petertheorgan; 27th Oct 2016 at 11:38 pm. Reason: Malc got there first
petertheorgan is offline  
Old 27th Oct 2016, 11:51 pm   #4
lloydwells
Heptode
 
Join Date: Aug 2016
Location: Dumfries, Scotland, UK.
Posts: 549
Default Re: GEC BT 302 no picture help.

Yes I'm on with changing all the caps now. I've never tackled a valve TV before and I'm slightly concerned about the apparent lack of EHT. It has an EY80 in it which I think is an EHT rectifier? Should this glow or not as it isn't. Is the audible clicking most likely due to the smoothing cap (100-300uF) which I assume smooths the EHT supply? This is a bit on the bulgy side.
lloydwells is offline  
Old 28th Oct 2016, 10:29 am   #5
Edward Huggins
Dekatron
 
Join Date: Sep 2015
Location: Southwold, Suffolk, UK.
Posts: 8,302
Default Re: GEC BT 302 no picture help.

The EY80 is the EHT rectifier and it should certainly glow. Edward
Edward Huggins is offline  
Old 28th Oct 2016, 11:26 am   #6
AC/HL
Dekatron
 
AC/HL's Avatar
 
Join Date: Nov 2003
Location: Heckmondwike, West Yorkshire, UK.
Posts: 9,637
Default Re: GEC BT 302 no picture help.

The EHT rectifier should be a U25, a wire ended valve which will be on the LOPT. The EY80 seems out of place, the heater will not glow in a 300mA chain, could the lettering be indistinct?
AC/HL is online now  
Old 28th Oct 2016, 12:20 pm   #7
FERNSEH
Dekatron
 
FERNSEH's Avatar
 
Join Date: Mar 2005
Location: Gateshead, Tyne and Wear, UK.
Posts: 7,444
Default Re: GEC BT 302 no picture help.

Original EHT rectifier was a GEC U47, alias Mazda U25. Wire end valve, 2 volt 0.2amp heater. Some U25 valves marketed by Mullard were given the pro-electron code KY50.

DFWB.
FERNSEH is offline  
Old 28th Oct 2016, 12:31 pm   #8
Restoration73
Nonode
 
Restoration73's Avatar
 
Join Date: Jun 2013
Location: Surbiton, SW London, UK.
Posts: 2,801
Default Re: GEC BT 302 no picture help.

The lack of EHT will be down to HT or boost HT. C152 may short, so lift top cap of
U339, if EHT returns the cap is suspect. Is the line whistle audible ?
Restoration73 is offline  
Old 28th Oct 2016, 12:31 pm   #9
lloydwells
Heptode
 
Join Date: Aug 2016
Location: Dumfries, Scotland, UK.
Posts: 549
Default Re: GEC BT 302 no picture help.

Having given it a clean it appears to be an EY86
lloydwells is offline  
Old 28th Oct 2016, 12:35 pm   #10
lloydwells
Heptode
 
Join Date: Aug 2016
Location: Dumfries, Scotland, UK.
Posts: 549
Default Re: GEC BT 302 no picture help.

No line whistle but I've now disconnected the can and bunged a meter on it the 300uf side is measuring 656uf and the 100uf side doesn't read at all. I have ordered replacements.
lloydwells is offline  
Old 28th Oct 2016, 3:06 pm   #11
AC/HL
Dekatron
 
AC/HL's Avatar
 
Join Date: Nov 2003
Location: Heckmondwike, West Yorkshire, UK.
Posts: 9,637
Default Re: GEC BT 302 no picture help.

Possibly had a LOPT transplant then?
AC/HL is online now  
Old 29th Oct 2016, 8:04 pm   #12
lloydwells
Heptode
 
Join Date: Aug 2016
Location: Dumfries, Scotland, UK.
Posts: 549
Default Re: GEC BT 302 no picture help.

I'm not entirely sure it is a BT302 there's no model number on the back the mains voltage sticker has BT318 and 319 written on it.
lloydwells is offline  
Old 29th Oct 2016, 8:17 pm   #13
TonyDuell
Dekatron
 
Join Date: Jun 2015
Location: Biggin Hill, London, UK.
Posts: 5,188
Default Re: GEC BT 302 no picture help.

Quote:
Originally Posted by petertheorgan View Post
The "bodge" is where the metal rectifier has been replaced by a diode and a limiting resistor, the resistor will get hot in normal use and if the set has not been used for a bit, may even emit the odd puff of smoke. Keep it clear of the bowl of the tube or you may have a story to tell like one of my friends!
Do tell . I assume the heat from the resistor cracked the CRT glass or something equally unpleasant.
TonyDuell is offline  
Old 29th Oct 2016, 8:53 pm   #14
Restoration73
Nonode
 
Restoration73's Avatar
 
Join Date: Jun 2013
Location: Surbiton, SW London, UK.
Posts: 2,801
Default Re: GEC BT 302 no picture help.

318/319 is slightly later - the 319 is the fringe version and the IF panel will have 7 valves
instead of the 6 in the 318.
Restoration73 is offline  
Old 29th Oct 2016, 9:12 pm   #15
FERNSEH
Dekatron
 
FERNSEH's Avatar
 
Join Date: Mar 2005
Location: Gateshead, Tyne and Wear, UK.
Posts: 7,444
Default Re: GEC BT 302 no picture help.

If it is a BT318 the sound output valve will be a PCL82 triode-pentode.
The earlier BT302 series employed a beam tetrode, a GEC N369 or Mazda 30P12. Separate audio amplifier, DH77 or 6AT6.
Also, if the set is a BT318/9 the EHT rectifier will be a GEC U49 or Mazda U26, this is a plug in valve with B9A base. Has a 2 volt heater unlike the EY86 which has a 6.3volt heater. If the correct GEC line output transformer is fitted the EHT rectifier valve is positioned about the centre of the screening box.

DFWB.
FERNSEH is offline  
Old 30th Oct 2016, 3:26 pm   #16
lloydwells
Heptode
 
Join Date: Aug 2016
Location: Dumfries, Scotland, UK.
Posts: 549
Default Re: GEC BT 302 no picture. Help.

The EHT rectifier is near enough slap bang in the middle of the cage and it does have a pcl so must be a 318. Obviously whatever has been done to it it still worked while in use so I'm hoping recapping it will sort it and I can get it back together in time for the 2nd.
lloydwells is offline  
Old 31st Oct 2016, 7:41 pm   #17
lloydwells
Heptode
 
Join Date: Aug 2016
Location: Dumfries, Scotland, UK.
Posts: 549
Default Re: GEC BT 302 no picture. (Now identified as a 318)

Ok every cap.in the set replaced except the 16-32 can we have a picture of sorts and sound except the set is apparently emitting a very high pitched squeal I cant hear it bit the missus says its awful this seems to be related to the video side.as twiddling controls alters the pitch.

Picture... Slightly out of focus how is this adjusted ?? on test card C the left edge is off screen and the top is squashed up. The height pot has been replaced very badly with a 500k I'm assuming this should be 100k like the two other similar pots ?

Bearing in mind this set has been out of use longer than ive been alive ( unused since 1974 ) I'm quite please with progress so far. Should I leave the set to run for a while and see it it perks up a bit ?
lloydwells is offline  
Old 31st Oct 2016, 7:43 pm   #18
lloydwells
Heptode
 
Join Date: Aug 2016
Location: Dumfries, Scotland, UK.
Posts: 549
Default Re: GEC BT 302 no picture. (Now identified as a 318)

Arkwright
Attached Thumbnails
Click image for larger version

Name:	WP_20161031_18_09_52_Pro.jpg
Views:	168
Size:	56.8 KB
ID:	132068  
lloydwells is offline  
Old 31st Oct 2016, 8:26 pm   #19
Heatercathodeshort
Dekatron
 
Heatercathodeshort's Avatar
 
Join Date: Jun 2005
Location: Warnham, West Sussex. 10 miles south of DORKING.
Posts: 9,145
Default Re: GEC BT 302 no picture help.

Quote:
Originally Posted by TonyDuell View Post
I assume the heat from the resistor cracked the CRT glass or something equally unpleasant.
Yes you are spot on! In the late 1960's a customer brought in for overhaul a GEC BT302. It was very clean but required a replacement tube, a replacement HT rectifier [BY100 + 25 ohm] and a general clean.

The chassis was removed together with the original Mazda tube [badged GEC]
A silicon diode plus surge limiting resistor was wired in with care, sleeving the ends of the surge limiter resistor with fiberglass sleeving.

The chassis was cleaned, the new tube fitted, set up, soak tested and returned to the customer. He lived on Kingston Hill in what was to all intents and purposes a true mansion.

Two days later I had a phone call that I will never forget.

'Last night about 2am the family were awoken by a loud bang. We all got up to investigate the cause but discovering no apparent reason for the disturbance and returned to bed.
In the morning my wife examined the television and discovered she could 'see the works' through the front..
There was some fine shards of glass on the carpet so we knew something was very wrong so decided to give you a call.'

The gentleman suggested that he bring the TV along for examination. He did not seem at all concerned. He had been a customer for a few years so knew I would deal with it without a fuss.

His Jaguar MK10 pulled up outside and I opened the rear passenger door to discover the BT302 sitting on the red leather seat. I picked it up to discover fine glass all over the leather and advised that he employed the vacuum cleaner as soon as he returned home.

So what had happened? My fault entirely. With the tube removed I could not judge the clearance between the metal rectifier that is mounted directly underneath the tube bowl and the tube itself. I had wired the replacement components too high resulting in the hot resistor touching the edge of the 110 degree tube bowl where it meets the faceplate..Not a good idea.

This had created an incredibly hot local area on the glass that had cracked the tube as it cooled down after switch off. At 2am it could stand the strain no longer and imploded.

The only damage that had occurred to the chassis was a broken 30F5 valve.
After a massive clean up with the vacuum cleaner a new tube was again fitted, this time making sure there was adequate distance between the hot resistor and you know what!

I redelivered the GEC the following day to the complete satisfaction of the understanding customer. A mistake learned and never forgotten. Regards, John.
Heatercathodeshort is offline  
Closed Thread

Thread Tools



All times are GMT +1. The time now is 3:40 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.