Ferguson 246T-sound ok but no picture - Page 2 - UK Vintage Radio Repair and Restoration Discussion Forum

SGT.Pepper · 4th Jan 2010, 9:24 pm

There is now no EHT at the CRT or the AC connection of the EHT rectifier and the line whistle has been replaced with a hissing squealing sound. I'm not sure what is causing this but I have looked at the PY81 and it seems to be acting a bit weird. The valve warms up normally, but after about a minute a big part of the middle of the valve (not the heater) produces a soft orange glow for about five seconds, then goes back to normal. Could this just be a dodgy valve or something more drastic? I have changed some of the capacitors, but they are exact replacements and none of them are to do with this valve.

Steve_P · 4th Jan 2010, 9:30 pm

Check what you've changed, make sure it's right. It could be the valve, but try checking the grid of the PL81. Should be negative.

Try disconnecting the EHT winding and trying again.

Cheers,

Steve P.

Sideband · 5th Jan 2010, 12:36 am

The PY81 is the boost diode. As it's only a diode, the only other electrode that can glow is the anode and that is not good

. I'd check the boost capacitor if you haven't done so already. Try measuring (with the set off) the resistance between cathode (top cap) of the PY81 to chassis. It should be very high. If it low or s/c then it probably the boost cap. If the boost cap is faulty, you need a good quality 1000v component to replace it with.

Danny · 5th Jan 2010, 11:21 pm

Hi richard is prob right but also an over load in the frame can cause this as would any thing connected to the boost rail . check the caps you have replaced and make sure you havent done a blunder and either put one on a wrong tag or left a wire end touching deck ! weve all done it and bought the teashirt believe me. danny

chipp1968 · 6th Jan 2010, 12:07 am

It certainly is easy to fit a wire from a new cap to the wrong terminal even if you think you cant have done so . I have not repaired many sets yet myself all by myself .
I had read on here about avoiding changing caps on mass , that it is better to check after each change .I was working on a simple but cramped midget radio that was basically working somewhat . I did so checking on each change ,all except the last 3 which i changed together .The set then wouldnt work !!

I could have sworn i had put everything to the right terminals . Someone kindly looked at the set for me and after some bother and head scratching it turned out I had connected one cap to a wrong terminal.
Some people take pictures or areas they are working on , this may help for reference .

4th Jan 2010, 9:24 pm	#21
SGT.Pepper Retired Dormant Member Join Date: May 2008 Location: Bath, Somerset, UK. Posts: 37	Re: Ferguson 246T-sound ok but no picture There is now no EHT at the CRT or the AC connection of the EHT rectifier and the line whistle has been replaced with a hissing squealing sound. I'm not sure what is causing this but I have looked at the PY81 and it seems to be acting a bit weird. The valve warms up normally, but after about a minute a big part of the middle of the valve (not the heater) produces a soft orange glow for about five seconds, then goes back to normal. Could this just be a dodgy valve or something more drastic? I have changed some of the capacitors, but they are exact replacements and none of them are to do with this valve.

4th Jan 2010, 9:30 pm	#22
Steve_P Dekatron Join Date: Sep 2003 Location: Bolton, Greater Manchester, UK. Posts: 6,644	Re: Ferguson 246T-sound ok but no picture Check what you've changed, make sure it's right. It could be the valve, but try checking the grid of the PL81. Should be negative. Try disconnecting the EHT winding and trying again. Cheers, Steve P. __________________ If we've always had it, why is the Car Boot open? You're not sneaking another Old TV in are you...?

5th Jan 2010, 12:36 am	#23
Sideband Dekatron Join Date: Oct 2003 Location: Croydon, Surrey, UK. Posts: 7,578	Re: Ferguson 246T-sound ok but no picture The PY81 is the boost diode. As it's only a diode, the only other electrode that can glow is the anode and that is not good. I'd check the boost capacitor if you haven't done so already. Try measuring (with the set off) the resistance between cathode (top cap) of the PY81 to chassis. It should be very high. If it low or s/c then it probably the boost cap. If the boost cap is faulty, you need a good quality 1000v component to replace it with. __________________ There are lots of brilliant keyboard players and then there is Rick Wakeman.....

5th Jan 2010, 11:21 pm	#24
Danny Heptode Join Date: Jul 2003 Location: North Walsham, Norfolk, UK. Posts: 516	Re: Ferguson 246T-sound ok but no picture Hi richard is prob right but also an over load in the frame can cause this as would any thing connected to the boost rail . check the caps you have replaced and make sure you havent done a blunder and either put one on a wrong tag or left a wire end touching deck ! weve all done it and bought the teashirt believe me. danny

6th Jan 2010, 12:07 am	#25
chipp1968 Rest in Peace Join Date: Jul 2006 Location: Somerset, UK. Posts: 2,356	Re: Ferguson 246T-sound ok but no picture It certainly is easy to fit a wire from a new cap to the wrong terminal even if you think you cant have done so . I have not repaired many sets yet myself all by myself . I had read on here about avoiding changing caps on mass , that it is better to check after each change .I was working on a simple but cramped midget radio that was basically working somewhat . I did so checking on each change ,all except the last 3 which i changed together .The set then wouldnt work !! I could have sworn i had put everything to the right terminals . Someone kindly looked at the set for me and after some bother and head scratching it turned out I had connected one cap to a wrong terminal. Some people take pictures or areas they are working on , this may help for reference .