Help with a HMV TV
 

Hi All,

I have been hunting for a tube for a HMV TV for a while now. See the thread

https://www.vintage-radio.net/forum/...ad.php?t=63808

It is now in place after re-caping the waxies and the electrolytics. I brought it up slowly on the Variac and the HT supplies are fine. There is a healthy amount of static from the speaker and the line whistle is present. It is an Australian set, so although it is 1959 it is 625 line.
All tranformers/chokes measure reasonably including the LOPT.
I have a 2-3mm spark from the 1S2 (DY86) but no life from the tube.
The boost voltage shown in the circuit below is low at 375V instead of 650V.
All the valves in the EHT section are NOS. I haven't yet replaced the disc ceramic C86, 150pF across the LOPT.
Any thoughts on how to test\check if the tube is OK and the low boost voltage would be apprectiated.

regards
Craig

Re: Help with a HMV TV
 

You could try shorting the Grid and Cathode of the crt together very briefly you should see a bright raster.

Chris

Re: Help with a HMV TV
 

Are you drawing the spark from the top cap of the DY86? If so and you are using a decently sized screwdriver and only getting a 3mm spark, I would think the line stage is in distress!
Check the HT, the line drive preferably with a scope, one thing comes to mind. How old are you?
If like me you have a few grey hairs I would doubt you should hear a 625 line whistle so if its way low and sounding like 405 that will possibly be your problem!
Let us know your findings.
That 21 inch 110 degree tube will need about 16 kv EHT a spark of 10-12 mm is what I would be looking for.

Re: Help with a HMV TV
 

Hi whats the voltage on the line output valves grid and screen feed ? check the connections to the scan coils and asociated components. Danny

Re: Help with a HMV TV
 

As mentioned above, with a low boost voltage I would be concerned about the Line Output stage operating conditions.

Check that the screen, grid and cathode voltages are within spec for the 6CM5 output valve. If they are close to correct then you can safely leave the set running for more in depth troubleshooting on the CRT.
It is most important that the 0.14 volts on the cathode not be much above 0.18 or so volts (measured with an analogue multimeter) or the Line Output transformer will be overly stressed. If voltages are near correct, the Horizontal Oscillator may be running off frequency,causing boost voltage to drop a lot but the CRT should still light up.

If the Line Out stage conditions allow extended running, then check the CRT pin voltages. It may be biased off despite the low boost volts.

Re: Help with a HMV TV
 

Check the H.T. as Trevor suggests. Then check line coupling capacitor to grid of line output valve. Next capacitor is boost storage that usually has a value of around .25uf-.5uf. It is connected between the H.T. rail and boost rail. If line output valve is stressed, remove top cap from boost diode and see if stage livens up. If it does, this suggests the fault lies in the boost capacitor mentioned. The LOPT could be faulty and may have been the reason the receiver was set aside originally. The EHT rectifier should be lit if there is EHT present. It should be a noticable glow.
The CRT will be fine. The Philips/Mullard AW53-88 is indestructible and will give 100% emission when the set is sorted. John.

Re: Help with a HMV TV
 

Hi All,

Thanks for the comments, it is always encouraging to get advice.
I used the CRO on the oscillator. It was an interesting comment about my age, 44. The oscilator was working at 12kHz instead of 15.625kHz. I replaced C81 and the horizontal hold pot which was broken. It now oscilates at 15kHz and I can't hear the whistle!
The boost voltage is up to 530V and I can draw a spark to approx 5mm now. Still no life from the tube though.
There is no glow in the 1S2 (DY86) though.
I have replaced all the waxies and electros, so this includes the boost cap.

regards
Craig

Re: Help with a HMV TV
 

The DY86 heater is fed from usually a loop of EHT cable around the core of the LOPT, so check this is ok and there isnt an o/c resistor or choke in the valve base of the DY86.
530V boost is getting there and with that level of boost you really should have a lit up screen, have you tried another DY86? A DY87 or DY802 will do as well.

Re: Help with a HMV TV
 

Hi All,
So, I'm making some progress now. I have my first raster. There was a wiring mistake around the T7. Also the capacitor on the LOPT was between pins 2 and 8 not pin 3 and 7. With a new DY86 I now have something to work with on the screen. The boost volts are up to 570V now, not quite the required 650V.
Also pin 3 on the picture tube is 300V instead of 400V.
There is an anying "pip" in the speaker once every 1-2seconds which I need to trace too.

regards
Craig

Re: Help with a HMV TV
 

I'm a little stuck again and would appreciate your thoughts.
After making some good progress with the line oscilator which was running at 3/4 speed, I now have a stable picture.
But the boost volts are still low.
If I adjust the contrast, the picture rapidly expands and distorts.
The boot volts are at 450V, not 650V. There is practically no smoothing on this line with almost 100V ripple. The boost capacitor has been replaced.
I turned all the lights off in the room and there is not even a faint glow form the DY86.
I replaced the single loop for the heater for the DY86 which was open circuit originally. I used an EHT lead form another TV. This lead had a center core and an outer sheild. I didn't connect the sheild braid, but I wonder if that is limiting the effect of the loop around the LOPT.
Also, the aqudag on the new tube is in a really bad state of repair. If this is the smoothing cap for the EHT ot the tube, then this might effect the EHT level?

Re: Help with a HMV TV
 

That looks like the HT is still too low

Re: Help with a HMV TV
 

Poor coating on the crt would cause a kink in the picture not what you have at present.
David

Re: Help with a HMV TV
 

Certainly worth checking those high meg reses in the linestage as well as coupling cap from Line Osc.

Re: Help with a HMV TV
 

It would make sense to measure the HT before going any further.

Re: Help with a HMV TV
 

Hi,
I don't have an EHT meter. so apart from drawing a spark, I'm not sure how to measure it.
I do assume you are talking about the EHT, 16kV. The two HT rails are fine 210V and 234V, compared with 215V and 240V.

regards
Craig

Re: Help with a HMV TV
 

No I meant the HT rail itself. I'd have thought the HT was near enough then and that the problems lie with the boost HT circuit. High value resistors going higher are a favorite.

Re: Help with a HMV TV
 

As i stated earlier ,high meg reses in line stage also any waxy caps excluding small silver mica.

Re: Help with a HMV TV
 

Hi All,

Thanks for the comments.
Still no luck. All high value resistors are within 5%.
All wax caps have been replaced.
I fixed some wiring and resistors around the vertical height section which is now working.
But its still low on EHT I fear and the boost volts are quite low at around 450V.
I did have them up to 530V and brighter picture, but that was before I moved C86 on the LOPT from pins 4/8 to pins 3/7 as it says on the circuit diagram.
The small spark I can draw from the DY86, the low boost volts and the picture brightness, seem to imply low EHT, but I still haven't found the cause.
I'm going to try another cable loop for the DY86 heater. One without a sheilding braid.
Any other comments are welcome.

regards
Craig

Re: Help with a HMV TV
 

I've nothing much to add but perhaps an observation, I thought that if there was low EHT this would result in a overly large raster and that you do not have. Your raster is reduced in both directions, perhaps voltage checks throughout the circuit should be made and verifed against service data. Most likely one of those misleading faults that provide so much frustration.

Do you have a copy of the whole circuit you could post, it may help us all to visualise the problem better.

Chris

Re: Help with a HMV TV
 

Hi Chris,

Here is the circuit.
I moved the C86 back to where it was on the LOPT and boost volts are up a little to 480Vand the picture is more stable as I adjust the contrast.
I'm just trying another heater loop for the DY86 - 1S2 now.
Hope the circuit quality is OK.

regards
Craig

Re: Help with a HMV TV
 

Hi Chris,

So I replaced the heater loop with no change.
I will take your suggestion of hunting through the circuit until I find something.

regards
Craig

Re: Help with a HMV TV
 

The E.H.T. rectifier valve? it maybe low emission, I know you replaced it but was it a good one?

The symptoms sound familiar to a fault condition I read with regards to low emission E.H.T. rectifier

As soon as the brightness level of the picture is increased instead of becoming brighter the picture will increase in size and eventually disappear, I think you satisfied that criteria earlier in your posts. A test will prove that whilst a pulse potential exists at the anode of the e.h.t. rectifier little or no e.h.t. is present at the heater of cathode, I think you have also satisfied that one, have you another good spare?

Might be nothing but worth a go, I would still also verify voltages to know data and look for discrpancies

Chris

A test you can perform for the rectifier heater, is the scale lamp test. it can be temporarily to the heater supply legs to check that winding is getting what it should negligible voltage between the two leads to the lamp and any wire will do run an ordinary MES lamp holder but the whole affair must be supported to avoid touching chassis. It can be attached with removing the rectifier

Re: Help with a HMV TV
 

It seems that someone has been there before you which might well be why the cap' was in the wrong place. Such bodges in a desperate attempt to cure a problem were common. Why diagnose a fault when you can change the circuit?

As the HT is more or less correct and there is no EHT 'blooming' which as OTT says would not cause lack of width I'd say you are getting very near suspect the LOPT time.

Re: Help with a HMV TV
 

Excuse my poor wording in the bottom of the last post, I was editing but ran out of time.

Chris

Re: Help with a HMV TV
 

Reading over this thread again a few thoughts come to mind.
The Line Out stage is trying to operate but seems to have issues with its operating conditions.
As a start, confirm the voltage on the 6CM5 cathode and screen. These will establish that at least this area is operating correctly and the valve isn't overloaded.
Next, have you tried a replacement 6AL3 damper diode?
Check all connections are correct around the width coil and horizontal linearity coils, someone may have messed about with this area. Ensure all components connected to the boost volts supply are tested or confirmed as working. A leaky capacitor or resistor thats gone high can cause issues here.

Re: Help with a HMV TV
 

Hi All,

I had the picture below and decided to check the width. The internal slug was stuck, so I pulled it apart and fixed it and replaced it. Unfortunatley, I can't get back to picture below after my repairs!!! I've carfully checked and and it all seems in place. So now I have just barely 1mm of spark form the DY86 (1S2).

Re: Help with a HMV TV
 

I pushed the send button too early!!!

I have tried three NOS DY86's (1S2) and three EL36's (6CM5). All high value resistors are within 12% of values. All waxies and electrolytics have ben replaced. Externally, I put 1.4V to the DY86 and it does glow with a similar amount as the one in the set. The "boost" vlotage which says it sould be 650V is 450VDC with 150VAC superiposed on it. The 400V line that goes to pin 3 is 280VDC and quite well smoothed with a 0.22uF cap (new), but low of course.

The EL36 (6CM5) has the following voltages:
Screen is 165V, circuit syas 150V
Grid is -33V, circuit says -32V
Cathode says 0.13V, circuit says 0.14V.
This valve gets really really hot!

HT1, HT1A annd HT2 rails are quite close as stated earlier.

All the wiring around the LOPT has been checked and put back the same as the circuit diagram.

I haven't tried another EY88 (6AL3) yet, but this was NOS.

The cathode of V8 ECF82 (6U8), in the AGC\contrast section is 60V and the circuit says 48V. I didn't think this was related to the low EHT and boost though.

The LOPT does not get warm at all. Someone mentioned it might be time to suspect the LOPT. Is there anyway to test it. Its not getting warm, and does work to soem extent.

Any other suggestions on how to proceed from here would be great.

regards
Craig

Re: Help with a HMV TV
 

I have NOS boxed EL36 and EY88 if these are needed.

Re: Help with a HMV TV
 

Is the Horizontal Oscillator (their term) OK. There are two caps in the link to the output valve, one to earth and one in series. Swap them both. Check the anode resistances and the valve itself.

Cheers,

Steve P.

Re: Help with a HMV TV
 

Hi Steve,

The drive to EL36 (6CM5) does looks fine. See post #10 (this was shown at the cathode of the 12AU7). The waveform shape looks good into R106, the grid resistor. C87 4.7nF was a waxy and has been replaced. I haven't replaced or checked C86 a 180pF to ground. I will just check the drive into the grid resistor does go to -170V as in the circuit. This I have not yet checked.

regards
Craig

Re: Help with a HMV TV
 

Hi
An overheating PL36 with correct control grid drive (assuming you've changed the caps Steve mentions) means excessive damping in the output stage. That might well mean a shorted turn in the LOPT primary, I'm afraid. The width coil could possibly have a shorted turn, and if so might well be getting warm.
Unfortunately a cool LOPT doesn't necessarily mean it's OK, and the only real test is replacement (yes, I know).
Glyn
P.S. C86 will certainly affect the tuning and hence the width so that's the next logical step.

Re: Help with a HMV TV
 

Hi All,
So the story continues...
I obtained a replacement LOPT.
The chap who sent it to me had to bake his in the oven to remove moisture to retore his set.
So I also baked mine slowly for 2 hours in the oven. Although I haven't re-coated mine with anything else just yet and I'm not sure if this is the cause of any of the problems described below.
But at least things are now getting much better.

regards
Craig

Re: Help with a HMV TV
 

The previous issue with the EL36 overheating is not present anymore and the HT1 and HT2 lines are stable within a few volts of their correct values.
The current problem is that the boost volts take over an hour to rise from 450V to 650V.
This has now happened three times.
The pictures below show the TV picture with boost volts at 450V, 550V and 650V, and then the test pattern at 670V. The boost volts then remain at 670V after that. The correct value is 650V.
Pin 3 volts to the tube are a little low at 360V instead of 400V.
I thought I might try another slow baking session. The reason I haven't coated the EHT winding yet, is that I didn't want to do something permament just at the moment.
I'd like to ask people's opinion to see how to resolve this slow rising boost volts issue.

regards
Craig

Re: Help with a HMV TV
 

Hi,
So I took some more measurements whilst the set was in its "warm up phase". It takes 1 hour 5 minutes to get the boost volts up from 450V to 650V. This is consistent over serveral times watching the TV. I'm having great fun watching the original Pink Panther series again! :D
The grid drive to the EL36 (6CM5) shown in post #1 is rock steady at -150V instead of -170V. Sheild volts are 171V instead of 150V but don't change during the one hour.
Cathode volts should be 0.14V and are 0.15V and don't change.
HT1 should be 240V and is 244V.
HT2 should be 215V and is 221V.
Neither of these change during the hour.
So I assume the drive to the LOPT is OK.
The pin 3 volts to the picture tube should be 400V and does vary from 290V to 350V, but since this is derived from the boost volts this is not surprising.
It is interesting that whilst measuring this, the contrast on the picture significanlty improves.
Since the LOPT was tried and was working previously, although not out of suspission, is unlikely to be the culprit.
I may try a different selection of valves.
I'm also wondering if there is something loading the boost volts, causing this issue.
regards
Craig

Re: Help with a HMV TV
 

Hello all,
Thanks to everyone who has contributed. I have appreciated the feedback. I was reading back through all the comments to find the problem.
I re-baked the LOPT. I tried yet another set of EHT valves with no change.
Then I finally found the issue. A dry joint on one of the high meg resistors in the boost section driving the picture tube.
I also increased smooting on the boost volts to reduce the ripple.
Now, I have 550V on start up and within 10 minute its settles to 630V. It is very pleasing to turn on the set and be greeted by a full screen picture which is bright and with good contrast.
On this last point, I added a 6.8M resister from pin 3 of the picture tube to gound. I did this since I noticed the contrast got significanlty better each time I used my DMM to measure the pin 3 volts.
I am using direct video input to the video amplifier and the contrast is used to drive the RF section which I am bypassing and so the contrast controls have no effect.
The next issue to move onto is that the vertical hold keeps losing lock. Hopefully not as difficult as the boost volts.

regards
Craig

Re: Help with a HMV TV
 

Hi Craig, frame TB lock, usually high value resistors gone higher and leaky (even slightly) caps.
Poor linearity is cathode cap (if used) or tired valve.

Ed

Re: Help with a HMV TV
 

Hi Ed,
Thanks for the advice.
It turned out to be an easy fix. I was AC coupling the video directly into the video amp valve using a 0.1uF capacitor. The cut-off was approx 200Hz and reducing the level of the frame sync pulses. I increased the coupling to 3uF and all is in lock now.
So, I'm slowly getting there.

regards
Craig

Re: Help with a HMV TV
 

Hi Craig, Thanks again for your help with the tv. Ive looked long & hard at your problem with this set ; check the line lin coil & c90 / c91 failing that the only thing is as we said it could be a scan coil fault if the insulation is breaking down (disintegrating ) as you said i would try a replacement first ..Chris