UK Vintage Radio Repair and Restoration Discussion Forum - View Single Post - Baird T18

TNC · 13th Feb 2007, 1:50 am

I have been replacing the this tv's original tube (completely dead) with a Brimar C12B kindly provided through the kindness of another Forum member.
After fixing the leaky EHT and also a slight re-design of the tube-locating arrangements (basically to stop its tendancy to fall forwards..and out!) I was able to fire it up.
Plenty of contrast/brilliance but a distinct lack of focus. Adjustment of the focus coil to its optimum fails to fully resolve the image. (It's as if the coil could do with a bit more oomph). Lowering the brilliance/contrast/attenuating the input signal (aurora) helps a little but not to a watchable (that is comfortable) standard.
So I would be grateful for any thoughts on the matter. The tube is a simple triode so could it produce plenty of contrast and still be failing - isn't that unlikely??...could it be because its preferred EHT is 10k.ish and the T18 only produces 5kv...but there is no blooming of the picture.
The T18 has a common heater/cathode...would the tube be sensitive about which side of the heater this common connection is made to?
Thanks,
Trevor.

13th Feb 2007, 1:50 am	#1
TNC Hexode Join Date: Apr 2003 Location: Westcliff-on-Sea, Essex, UK. Posts: 386	Baird T18 - swapped Brimar C12B gave focus problem. I have been replacing the this tv's original tube (completely dead) with a Brimar C12B kindly provided through the kindness of another Forum member. After fixing the leaky EHT and also a slight re-design of the tube-locating arrangements (basically to stop its tendancy to fall forwards..and out!) I was able to fire it up. Plenty of contrast/brilliance but a distinct lack of focus. Adjustment of the focus coil to its optimum fails to fully resolve the image. (It's as if the coil could do with a bit more oomph). Lowering the brilliance/contrast/attenuating the input signal (aurora) helps a little but not to a watchable (that is comfortable) standard. So I would be grateful for any thoughts on the matter. The tube is a simple triode so could it produce plenty of contrast and still be failing - isn't that unlikely??...could it be because its preferred EHT is 10k.ish and the T18 only produces 5kv...but there is no blooming of the picture. The T18 has a common heater/cathode...would the tube be sensitive about which side of the heater this common connection is made to? Thanks, Trevor.