UK Vintage Radio Repair and Restoration Powered By Google Custom Search Vintage Radio 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.

Reply
 
Thread Tools
Old 3rd Feb 2020, 6:40 pm   #1
FERNSEH
Dekatron
 
FERNSEH's Avatar
 
Join Date: Mar 2005
Location: Gateshead, Tyne and Wear, UK.
Posts: 5,975
Default Another Bush TV12.

My "Birmingham" Bush TV12 had a no sync fault. Tried another EF50 sync separator valve but no improvement. The 'scope confirmed that the full video vaveform was present at the grid pin of the sync valve but closer observation showed that the sync tips weren't clamped to chassis potential.
As a quick test a silicon diode was connected between the grid of the EF50 and chassis, sure enough the sync tips are now at chassis potential. Turned out the control grid contact on the valveholder is broken. A replacement has been fitted and now the set displays a steady picture, but there are still a number of other faults to sort out.
The first picture shows the high quality ceramic B9G valveholder. Seems a pity to use it for such a mundane task as in the sync separator.

DFWB.
Attached Thumbnails
Click image for larger version

Name:	BushTV12B_B9G.jpg
Views:	135
Size:	36.4 KB
ID:	198325   Click image for larger version

Name:	BushTV12B_2.jpg
Views:	134
Size:	52.7 KB
ID:	198326   Click image for larger version

Name:	BushTV12B_3.jpg
Views:	124
Size:	81.1 KB
ID:	198327  
FERNSEH is offline   Reply With Quote
Old 3rd Feb 2020, 9:12 pm   #2
high_vacuum_house
Octode
 
high_vacuum_house's Avatar
 
Join Date: May 2003
Location: Rugby (home) and all over the country for work
Posts: 1,153
Default Re: Another Bush TV12.

I am wandering if the unusually high quality valve holder and the EF50 were war surplus Components that were to hand rather than producing new valveholders from scratch.

Christopher Capener
__________________
A proper radio is one that needs to be moved with a wheelbarrow !!
high_vacuum_house is offline   Reply With Quote
Old 4th Feb 2020, 8:07 am   #3
mark pirate
Dekatron
 
mark pirate's Avatar
 
Join Date: Mar 2008
Location: Worthing, West Sussex, UK
Posts: 4,818
Default Re: Another Bush TV12.

Those paxolin valve holders can be troublesome, not had any problems with them on my TV12, but replaced a few on an LV20 due to corrosion.

I do like the spring clips fitted on Pye sets, they really get a firm hold on those EF50's

Pye obviously learned a few things when using EF50's in radar during the war.
I think the pin length was a design flaw on an otherwise excellent valve.

Mark
mark pirate is offline   Reply With Quote
Old 4th Feb 2020, 10:20 am   #4
Jac
Hexode
 
Jac's Avatar
 
Join Date: Jun 2006
Location: Eindhoven, Netherlands.
Posts: 498
Default Re: Another Bush TV12.

Very expert fault finding David!

Jac
Jac is offline   Reply With Quote
Old 5th Feb 2020, 11:22 am   #5
FERNSEH
Dekatron
 
FERNSEH's Avatar
 
Join Date: Mar 2005
Location: Gateshead, Tyne and Wear, UK.
Posts: 5,975
Default Re: Another Bush TV12.

Hello Jac,
the TV12B has two other faults to correct. As the attachment shows the vertical linearity could be better and the vision alignment needs attending to. Sound on vision and over emphasis of the vision HF component.

I'm considering replacing the MW22-14 CRT with the ion trap MW22-16. The original tube has evidence of ion burn and as this set has almost 7KV EHT available I'm certain there will be a worthwhile improvement in picture quality by fitting the later tube.

DFWB.
Attached Thumbnails
Click image for larger version

Name:	BushTV12_4.jpg
Views:	78
Size:	86.9 KB
ID:	198435  
FERNSEH is offline   Reply With Quote
Old 5th Feb 2020, 5:01 pm   #6
FERNSEH
Dekatron
 
FERNSEH's Avatar
 
Join Date: Mar 2005
Location: Gateshead, Tyne and Wear, UK.
Posts: 5,975
Default Re: Another Bush TV12.

Circuit diagram of the frame timebase. V3 (EF50) functions as a Miller transiton oscillator.

From r-type.org: http://www.r-type.org/articles/art-135.htm

The foldover might be caused by the changes in the values of the components associated with C2. Flyback time too long.

DFWB.
Attached Thumbnails
Click image for larger version

Name:	BushTV12B_5.jpg
Views:	31
Size:	91.7 KB
ID:	198467  
FERNSEH is offline   Reply With Quote
Reply

Thread Tools



All times are GMT +1. The time now is 7:25 am.


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 - 2020, vBulletin Solutions, Inc.
Copyright ©2002 - 2020, Paul Stenning.