Low HT and EHT on Philips 1768U - UK Vintage Radio Repair and Restoration Discussion Forum

Racalfanatic · 2nd Sep 2007, 1:27 pm

Hi All,
I'm really struggling with this. The HT should be about 200V but I'm struggling at around 150V. The boosted HT should be aroung 500V and I'm getting just 260V.
I've tried different PY82s and the LOPTy is running, I can hear, it and I can drag a spark off the PL36 anode.
The heater supply is fine and the Line oscillator has been traeted to new capacitors and resistors.
Any ideas?

Cheers,
Ian G1DRP

Steve_P · 2nd Sep 2007, 1:32 pm

Try the Smoothing Blocks and the Rectifier valve. If the HT is low, check the Power Supply.

Cheers,

Steve P

Racalfanatic · 2nd Sep 2007, 1:45 pm

Quote:

Originally Posted by Steve_P

Try the Smoothing Blocks and the Rectifier valve. If the HT is low, check the Power Supply.

Cheers,

Steve P

Hi Steve,
I've already tried the PSU. I am wondering if the rectifier valves are knackered. I have tried a couple more used ones but I get the same results.
I am really at a loss with this one. It did work for a while, but the following day it didn't.
I've checked everything I can think of.
Cheers,
Ian

Steve_P · 2nd Sep 2007, 2:04 pm

OK, well if they are old valves, then maybe there's not enough oomph left in them I suppose. Have you tried another ECL80? Also, change every other part in the LOPT enclosure. Also, can you get a spark off the EY86 Anode.

Have you got a circuit by the way?

Cheers,

Steve P

Racalfanatic · 2nd Sep 2007, 2:15 pm

Hi Steve,

Thanks for your input by the way!
I can get a spart of the EY86 anode.
I'll see if I can find another ECL80. I'm a bit low on them and haven't got any new ones.
The resistors in the LOPTY enclosure are all OK and the LOPTY checks out OK on my DMM.I did replace one capacitor in there actually, now I've been thinking about it.
I'll have another play in a bit.
Thanks again,
Ian

Steve_P · 2nd Sep 2007, 2:30 pm

One more quick question. Is the EY86 lit up?

Cheers,

Steve P

Racalfanatic · 2nd Sep 2007, 2:48 pm

I haven't looked at it when it's switched on as it's inside the LOPTY unit.
The cap is rubber as usual. I haven't seen a heater in it to be honest but I suppose it must have one.
I'm really a radio man and am learning about tellys.
Cheers,
Ian

Steve_P · 2nd Sep 2007, 2:58 pm

OK - Well start by a little reading. Go to http://www.oldtellys.co.uk/otindex.html and pick the section on Line Timebase and EHT.

Also, a DMM won't tell you if you have shorted turns in the LOPT. It only takes 1 turn to be shorted and the EHT will either not be there or lowered a great deal. Unrectified EHT should spark off about an Inch or so. This is why you use a WELL INSULATED screwdriver.

This valve heater is driven from the LOPT itself, so if it goes out then there's little or no Line Drive.

Cheers,

Steve P

Racalfanatic · 2nd Sep 2007, 5:09 pm

Right,
The heater in the EY86 is O/C.
I'll have to see if I can get one from somewhere.
Cheers,
Ian

Steve_P · 2nd Sep 2007, 5:37 pm

Are you sure it's Open Circuit? It's a common myth! The heater on these is between 2,5 and 8. Not 4 and 5! Check it!!

Cheers,

Steve P

Racalfanatic · 2nd Sep 2007, 5:50 pm

Just double checked it and it is definitely duff.
I should still have my 500V boosted HT rail though surely?

Steve_P · 2nd Sep 2007, 5:59 pm

I would expect so. Where are you measuring it? And try new PY82's and that the Anode Resistors haven't gone high.

Cheers,

Steve P

Racalfanatic · 2nd Sep 2007, 6:15 pm

Hi Steve,
I am measuring it off R119,if memory serves! The Anode resistors are OK.
Cheers,
Ian

Racalfanatic · 6th Sep 2007, 9:47 pm

Thanks to the help of this forum and its members,I now have a working telly!
The EY86 was fitted and up she came

The tuner is miles out, could even be the IFs. I have set my Aurora to CH2. I can get sound on ch2 but the picture is on ch3 with the fine tune right at one end.
I have not changed any components in the tuner or IF stages yet.
Perhaps I should check the IF stages first. I won't make any adjustments unless I have to though.
Cheers,
Ian

2nd Sep 2007, 1:27 pm	#1
Racalfanatic Retired Dormant Member Join Date: Aug 2007 Location: Stoke-on-Trent, Staffordshire, UK. Posts: 105	Low HT and EHT on Philips 1768U Hi All, I'm really struggling with this. The HT should be about 200V but I'm struggling at around 150V. The boosted HT should be aroung 500V and I'm getting just 260V. I've tried different PY82s and the LOPTy is running, I can hear, it and I can drag a spark off the PL36 anode. The heater supply is fine and the Line oscillator has been traeted to new capacitors and resistors. Any ideas? Cheers, Ian G1DRP

2nd Sep 2007, 1:32 pm	#2
Steve_P Dekatron Join Date: Sep 2003 Location: Bolton, Greater Manchester, UK. Posts: 6,644	Re: Low HT and EHT on Philips 1768U Try the Smoothing Blocks and the Rectifier valve. If the HT is low, check the Power Supply. 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...?

2nd Sep 2007, 2:04 pm	#4
Steve_P Dekatron Join Date: Sep 2003 Location: Bolton, Greater Manchester, UK. Posts: 6,644	Re: Low HT and EHT on Philips 1768U OK, well if they are old valves, then maybe there's not enough oomph left in them I suppose. Have you tried another ECL80? Also, change every other part in the LOPT enclosure. Also, can you get a spark off the EY86 Anode. Have you got a circuit by the way? 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...?

2nd Sep 2007, 2:15 pm	#5
Racalfanatic Retired Dormant Member Join Date: Aug 2007 Location: Stoke-on-Trent, Staffordshire, UK. Posts: 105	Re: Low HT and EHT on Philips 1768U Hi Steve, Thanks for your input by the way! I can get a spart of the EY86 anode. I'll see if I can find another ECL80. I'm a bit low on them and haven't got any new ones. The resistors in the LOPTY enclosure are all OK and the LOPTY checks out OK on my DMM.I did replace one capacitor in there actually, now I've been thinking about it. I'll have another play in a bit. Thanks again, Ian

2nd Sep 2007, 2:30 pm	#6
Steve_P Dekatron Join Date: Sep 2003 Location: Bolton, Greater Manchester, UK. Posts: 6,644	Re: Low HT and EHT on Philips 1768U One more quick question. Is the EY86 lit up? 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...?

2nd Sep 2007, 2:48 pm	#7
Racalfanatic Retired Dormant Member Join Date: Aug 2007 Location: Stoke-on-Trent, Staffordshire, UK. Posts: 105	Re: Low HT and EHT on Philips 1768U I haven't looked at it when it's switched on as it's inside the LOPTY unit. The cap is rubber as usual. I haven't seen a heater in it to be honest but I suppose it must have one. I'm really a radio man and am learning about tellys. Cheers, Ian

2nd Sep 2007, 2:58 pm	#8
Steve_P Dekatron Join Date: Sep 2003 Location: Bolton, Greater Manchester, UK. Posts: 6,644	Re: Low HT and EHT on Philips 1768U OK - Well start by a little reading. Go to http://www.oldtellys.co.uk/otindex.html and pick the section on Line Timebase and EHT. Also, a DMM won't tell you if you have shorted turns in the LOPT. It only takes 1 turn to be shorted and the EHT will either not be there or lowered a great deal. Unrectified EHT should spark off about an Inch or so. This is why you use a WELL INSULATED screwdriver. This valve heater is driven from the LOPT itself, so if it goes out then there's little or no Line Drive. 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...?

2nd Sep 2007, 5:09 pm	#9
Racalfanatic Retired Dormant Member Join Date: Aug 2007 Location: Stoke-on-Trent, Staffordshire, UK. Posts: 105	Re: Low HT and EHT on Philips 1768U Right, The heater in the EY86 is O/C. I'll have to see if I can get one from somewhere. Cheers, Ian

2nd Sep 2007, 5:37 pm	#10
Steve_P Dekatron Join Date: Sep 2003 Location: Bolton, Greater Manchester, UK. Posts: 6,644	Re: Low HT and EHT on Philips 1768U Are you sure it's Open Circuit? It's a common myth! The heater on these is between 2,5 and 8. Not 4 and 5! Check it!! 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...?

2nd Sep 2007, 5:50 pm	#11
Racalfanatic Retired Dormant Member Join Date: Aug 2007 Location: Stoke-on-Trent, Staffordshire, UK. Posts: 105	Re: Low HT and EHT on Philips 1768U Just double checked it and it is definitely duff. I should still have my 500V boosted HT rail though surely?

2nd Sep 2007, 5:59 pm	#12
Steve_P Dekatron Join Date: Sep 2003 Location: Bolton, Greater Manchester, UK. Posts: 6,644	Re: Low HT and EHT on Philips 1768U I would expect so. Where are you measuring it? And try new PY82's and that the Anode Resistors haven't gone high. 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...?

2nd Sep 2007, 6:15 pm	#13
Racalfanatic Retired Dormant Member Join Date: Aug 2007 Location: Stoke-on-Trent, Staffordshire, UK. Posts: 105	Re: Low HT and EHT on Philips 1768U Hi Steve, I am measuring it off R119,if memory serves! The Anode resistors are OK. Cheers, Ian

6th Sep 2007, 9:47 pm	#14
Racalfanatic Retired Dormant Member Join Date: Aug 2007 Location: Stoke-on-Trent, Staffordshire, UK. Posts: 105	Re: Low HT and EHT on Philips 1768U Thanks to the help of this forum and its members,I now have a working telly! The EY86 was fitted and up she came The tuner is miles out, could even be the IFs. I have set my Aurora to CH2. I can get sound on ch2 but the picture is on ch3 with the fine tune right at one end. I have not changed any components in the tuner or IF stages yet. Perhaps I should check the IF stages first. I won't make any adjustments unless I have to though. Cheers, Ian