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Old 25th Aug 2017, 9:41 am   #81
1100 man
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Default Re: Pilot PT650 "Spacemaker" Television

Quote:
I have to register an interest here as I restored a Murphy SAD94L which had been a home to mice for many years, and had a chassis which was half red-rusty and half intact. In fact it was scrap.
The rust removal and subsequent re-spray removed all the old ink stamps and all traces of Murphy workers' personal involvement but now the set still exists many years later.
Yes, I could have scrapped it or found another chassis but then even less of the original would exist, as I still sought to keep as much as I could of the actual original, despite it being easier not to do so.

Had I cleaned it up and "got it working" it would be impossible or even gone beyond hope by now.
We do what we do and what we think best to the best of our individual abilities, and if it gives personal satisfaction and pride while saving stuff from oblivion by putting it back whole, why not?

It's our hobby, after all.

So why did I spend so much time on a run of the mill set?... because I wanted to.

Pete
Good morning,
I think that describes my feelings about restoration pretty accurately. We all face the eternal restoration question 'how far do we go' whenever we do any work on an item whether it be a TV, radio, classic car, old building etc. The more work that is done, the more of the original that is lost.
If a chassis is fairly clean and tidy, I favour a minimal intervention policy- changing components to make the set perform as it did when it was new. Visually, the new components need to be at least similar in appearance to the originals.
Sometimes though, as was the case with the Pilot, everything is in such a bad state that the only course of action is a total strip down and rebuild. I have kept as much of the original as possible- its really only the resistors and capacitors that have been replaced.
Thank you for the praise, Hugo, but this is nowhere near the standard of your HMV904!! Your chassis really is beautiful- it's also very densely packed and I can well imagine the hours spent on it!!
However, I'm pleased with the result so far and have enjoyed the journey, but more importantly, I've reached the next stage- Pictures!!
All the best
Nick
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Old 25th Aug 2017, 9:59 am   #82
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Default Re: Pilot PT650 "Spacemaker" Television

I sorted out the HT rectifier tagstrip and wiring, connected up the makeshift mains dropper and switched on
I could hear the frame timebase purring away, but no line whistle. Measured the grid of the line output valve which was -35v so the line oscillator was working. Measured the boost volts- 500V so the output stage was at least doing something.
Rotated the line hold pot which brought the frequency within my hearing range, turned up the brightness and a raster appeared!!
That's all for now,
Cheers
Nick
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Old 25th Aug 2017, 5:59 pm   #83
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Default Re: Pilot PT650 "Spacemaker" Television

Just to continue the above, The guesstimate value for the HT mains dropper resulted in the HT being exact to the volt!! But that dropper sure does belch out some heat It dissipates 30 W for the heaters and another 15W for the HT. So 45W in total. Granted, some of that would have been shared with the metal rectifier originally, but even so that amount of heat in that part of the chassis, it's no wonder the components in the frame timebase cooked!! It wasn't long before the solder melted and the wire fell off (It is only for testing at the moment)
The main issue is that the EHT is very low so the picture balloons when the brightness is turned up. It measures 8KV but should be about 16KV. There is a very healthy arc from the overwind but no visible heater in the U26 rectifier. Does the U26 have an obviously glowing heater when it's running? I don't have a spare to hand so can't change it yet but I somehow suspect it's ok. The boost is also low at 400 odd volts so I have yet to investigate further.
I need to get some signals into it so I can do some more checks so that will be the next part of the plan.
All the best
Nick
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Old 26th Aug 2017, 12:26 am   #84
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Default Re: Pilot PT650 "Spacemaker" Television

[/QUOTE]

Thank you for the praise, Hugo

[/QUOTE]

Nick,

You are welcome and I would also like to say there is something else going on here that is equally praiseworthy. You have demonstrated that you have "vision" . In this context it means you were able to see past the rust and degradation of the set and imagine what it would be like restored. Pete also outlined this point.

When I acquired my KTE-5 it was just a grossly rusted chassis and a mangled mess underneath of years of modifications and decay. But I imagined what it might have once been like.

It is an interesting feature of human nature (and not ideal) that people treat beautiful looking things well and often abuse or don't care for what might look like rubbish.

One way as restorers that we can ensure the survival of vintage electronics into the future is to make it look beautiful again. It will be cared for and maintain financial value and less likely end up on a rubbish dump too.

So congratulations to you for having this vision. It sets a wonderful benchmark for your peers.
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Old 26th Aug 2017, 2:50 pm   #85
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Default Re: Pilot PT650 "Spacemaker" Television

Hi Nick,
Yes the U26 should just about glow in order to be able to provide enough current for stable EHT. The low boost voltage is surely connected to the low EHT problem, so if you solve that the EHT may well come back up to the right voltage. Lets hope the LOPT is ok.

Anyway, great work so far. I always love to see basket cases brought back from the brink. There are many ways to go about a restoration, but I feel it is with the real basket cases that we have the most options. You know that preserving originality is impossible anyway, so in a sense you have a blank canvas to restore it in which ever way you like.

Cheers
Andy
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Old 26th Aug 2017, 7:09 pm   #86
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Default Re: Pilot PT650 "Spacemaker" Television

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Originally Posted by 1100 man View Post
that dropper sure does belch out some heat It dissipates 30 W for the heaters and another 15W for the HT. So 45W in total.
I once had a similar problem with an AC/DC set and the heat dissipation from the heater dropper resistor was extreme. I took the bold step of modifying it by adding a series silicon power rectifier to run the heaters off half wave (which has an rms voltage of about 170V for a 240V supply). It was critically important that with the now lower value of dropper resistor that it had a good Brimistor (large NTC resistor) to limit the inrush current with cold heaters because the overall series resistance was now lower. I think I had to change it to another type.

The mains supply has a very low internal resistance and the heaters when cold have a very low resistance, the small sized ones heat up very fast and explode in a flash of light with high inrush current without the Brimistor.

There was no evidence of added hum in any of the circuits half waving the heaters and while its not ideal to draw current off half the mains waveform, I think I had it so the HT was supplied by the + half cycles and the heater by the - which balanced it up better than it was before. Obviously if a set was modified like this, one wouldn't want the added rectifiers failing, probably best to use two 1000V 5A or 6A rated silicon rectifiers in series as extra protection in case one failed.

It is interesting when a transformer runs the heaters in sets with parallel heaters. When the transformer has about the right power ratings to run them, when they are hot, at turn on the low resistance load causes the transformer output to collapse so the heaters get a nice soft start. So in this sense the larger tubes protect the smaller ones, unlike in a series chain. One trap to fall into is, with a large multi-valve set, is to plug in a single cold small signal valve after all the other heaters are up and running, this causes a large peak current, that the transformer can support for a single cold tube and the heater in the small tube can fail just like in a series heater set.

One other method to eliminate some heat could be to add a small autotransformer to the heater supply and drop some voltage there rather than in the dropper resistor.

I guess though the manufacturers made it to handle the heat, but it does sound like a toaster oven in there.
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Old 27th Aug 2017, 11:00 am   #87
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Default Re: Pilot PT650 "Spacemaker" Television

Hi Hugo,
It doesn't help that this set has such a low valve count. There is only 11 including the CRT. Had there been more valves, especially an HT rectifier, the total heater plus dropper dissipation would have been the same, but the heat would have been spread out round the chassis rather than concentrated in the dropper.
We also have high mains voltage in the UK, typically 245 but sometimes even 250V!!
When the chassis is in the cabinet, there is only about 1/2 inch between the top of the chassis and the woodwork. The heat at the top would be intense especially with the back on I imagine the back would have ended up a big charred mess!!
Still, one of the interesting things with restoring a TV, is seeing what it's shortcomings were and how it would have performed at the time. I'm not sure yet what my ultimate solution will be, but I might investigate the series diode idea- thanks for the suggestion.

Andy, I wasn't sure how much glow you got from a U26- I'm much more familiar with DY87's and the like which glow like a normal valve.
I'd already tried a NOS U191 but that made no difference, so I dug out the only spare 30P4 I could find- a really dreadful looking thing!! That made quite a bit of difference and brought the EHT up to 12KV and a tiny glow from the U26.
Suspecting that this 30P4 might also not be 'top notch', I hooked up a brand new PL504 using terminal block to connect to the pins!! That worked fine but no better than the 30P4- still 12KV eht.
Obviously I would like to try another U26 but the only spare I have seems to be full of air!! I must order some next week.
The boost voltage is now about right at 525V so things are getting better!
Many thanks for your input,
All the best
Nick
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Old 27th Aug 2017, 3:07 pm   #88
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Default Re: Pilot PT650 "Spacemaker" Television

It probably won't help you, but my father ran the 17" 'portable' version of this set (Ultra VP17-72) for many years with a PL36 line output valve and a KY80 EHT rectifier. Not exact equivalents if you look at the data, but it's what the chap in the local shop sold him as replacements for the 30P4 and U26, and it worked, as I said, for years.
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Old 27th Aug 2017, 3:23 pm   #89
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Default Re: Pilot PT650 "Spacemaker" Television

Thanks Tony. I've never come across a KY80 before- I'll have to look it up! I don't have many spare valves with me on the Island, so a PL504 was all I could find which has a similar heater voltage and current. It seemed to work fine lashed in with terminal block . It was only to prove a point, which it did. I couldn't find anything to replace the U26- only a DY86 and an EY87 which have different heater requirements.
I imagine the portable also acted as a very efficient room heater!!
Cheers
Nick
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Old 27th Aug 2017, 4:07 pm   #90
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Default Re: Pilot PT650 "Spacemaker" Television

Actually, according to the 'valve museum' page, the U26 and the KY80 are equivalents. An article linked from one of those pages suggests a DY86 or DY87 can be used in place of them 'with a shortened life' (the filament of the U26 and KY80 is 2V, that of the DY86/7 is 1.4V). I've not tried it (not being a vintage TV person), but you might give it a go if you don't care if the DY86 burns out...

The 'portable' was the same chassis in a grey rexine-covered cabinet with a CME1703 CRT. There may have been other component changes, but it was the same layout, with the big dropper resistor mounted horizontally at the back and a big metal rectifier under the bottom chassis member. I don't remember it getting that hot, but I was quite young at the time and possibly though the heat was normal for a TV.
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Old 27th Aug 2017, 7:54 pm   #91
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Default Re: Pilot PT650 "Spacemaker" Television

A number of Mazda valves were marketed by Mullard Ltd and were given pro-electron type numbers. Examples: KY80 = U26, PL302 = 30P19, PY301 = U191. All these valves were made by Mazda and have a unique symbol on the bulb to indicate the valves were sourced from third parties.

DFWB.
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Old 27th Aug 2017, 9:49 pm   #92
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Default Re: Pilot PT650 "Spacemaker" Television

Of course, it makes a lot more sense if you know that 'K' is a Mullard code for a 2V heater- I never knew that
I had always thought that Mullard and Mazda were in competition with each other. I never dreamed that Mullard would re-brand Mazda valves! How much connection did these two companies have?
Cheers
Nick
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Old 28th Aug 2017, 12:16 am   #93
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Default Re: Pilot PT650 "Spacemaker" Television

Good evening,
As you can see from the attached pictures, the Pilot is once again, for the first time in probably 40 years, displaying testcard 'c'
The EHT is still too low at 11KV although the picture is not bad. So far, the most I can get is 12KV and that's using the PL504 output valve. I tried Tony's suggestion of using the DY87 which did work but didn't increase the EHT. I will obtain a new 30P4 and new U26 and then investigate further.

I need to modify the temporary HT part of the mains dropper. At the moment, it's using one 100 ohm section which is only 1/2 inch long. This runs so hot that after a while the solder melts and the stench is unbearable According to my infra red thermometer, it runs at 250 degrees!! 100 ohms gives the correct HT though.

The IF alignment is way off- unsurprisingly given the conditions the board has been exposed to over the years. The definition is dreadful- only the lowest frequency grating is resolved! I don't know about the sound yet as there is no speaker connected. I will need to do a full alignment which will be an interesting learning curve as I have never needed to do that to a set before.
The linearity on both line and frame is pretty good. I suffered from enormous height initially as I had forgotten that I had used a 500K height pot rather than a 1meg.!! A 470K series resistor soon put that right. I need to repair the line linearity sleeve- it's only poked in temporarily but even so, line lin is pretty good.
Both timebases lock solidly so the sync side of things seems to be working well.
I love the big 21" screen- I think once all the deficiencies have been sorted, this will be a great set to watch. That's certainly what I plan to do with it anyway!
So pretty good so far, but still a long way to go before all the issues are ironed out.
All the best
Nick
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Old 28th Aug 2017, 12:52 am   #94
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Default Re: Pilot PT650 "Spacemaker" Television

Amazing acheivment considering what you started with !
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Old 28th Aug 2017, 7:06 am   #95
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Default Re: Pilot PT650 "Spacemaker" Television

The KY80 is the only 2V Mullard valve that I have seen 'in the flesh', but there was a whole range of octal-based 2V valves used in old portable radios with a single lead-acid cell for LT.

If you have a bench supply, you could compare the KY80 filament glow when powered from that, set to 2V, (obviously with the valve out of the set, no EHT around) as against the glow when the valve is in the line output stage. It would give you an idea of whether the KY80 was getting anything like the right filament voltage.
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Old 28th Aug 2017, 10:12 am   #96
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Default Re: Pilot PT650 "Spacemaker" Television

Two examples of valves that were made by Mazda and marketed by Mullard. A 30PL1 and a 6F23. These have been given pro-electron codes and are designated PCL801 and EF812. Note the "U" symbol to the right of the type numbers, this indicates that the valves were sourced from a third party rather than from Mazda.

DFWB.
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Old 29th Aug 2017, 10:15 am   #97
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Default Re: Pilot PT650 "Spacemaker" Television

1100 man wrote: "I need to modify the temporary HT part of the mains dropper. At the moment, it's using one 100 ohm section which is only 1/2 inch long. This runs so hot that after a while the solder melts and the stench is unbearable According to my infra red thermometer, it runs at 250 degrees!! 100 ohms gives the correct HT though."

The total value of the tapped HT section of the mains resistor is 93 ohms. The reason why the resistor has a much lower value per section compared with the heater part of the dropper is because the ripple current of the reservoir capacitor has to be taken into consideration. The HT current demand of the receiver might only be in the region of 220mA but we have to bear in mind that the reservoir capacitor has to accept it's charge during the positive half cycles of the mains supply, hence the reason why the HT section dissipates so much heat. To sum up: receiver HT current + reservoir capacitor current.
I'll look through my stock to see if there is a suitable mains dropper available for the PT650.

DFWB.
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Old 29th Aug 2017, 10:58 am   #98
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Default Re: Pilot PT650 "Spacemaker" Television

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Originally Posted by FERNSEH View Post
The total value of the tapped HT section of the mains resistor is 93 ohms. The reason why the resistor has a much lower value per section compared with the heater part of the dropper is because the ripple current of the reservoir capacitor has to be taken into consideration. The HT current demand of the receiver might only be in the region of 220mA but we have to bear in mind that the reservoir capacitor has to accept it's charge during the positive half cycles of the mains supply, hence the reason why the HT section dissipates so much heat.
To sum up: receiver HT current + reservoir capacitor current.

DFWB.
Hi David,
During the positive half cycle's, the current through the dropper will be the HT current plus the charging current of the capacitors, so the dissipation will be higher than expected. Conversely though, during the negative half cycle's, there will be no current at all and hence no heat generated. So the dissipation will average out, or am I missing something?
I had added on a bit to the value to account for the silicon rectifier and there just happened to be a 100 Ohm section on the dropper I was using for the heaters. I was also careful to select a reservoir capacitor with a decent ripple current when I rebuilt the main smoothing can!
The 30P19 would seem to be a better valve to use than the 30P4 as it is specified for 110 degree tubes. I guess it was not yet available when the set was designed.
Thanks for your input
All the best
Nick
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Old 29th Aug 2017, 11:43 am   #99
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Default Re: Pilot PT650 "Spacemaker" Television

Power is dissipated during the positive half cycle, the negative half cycle is a different time, you can't undo what's already gone.

Lawrence.

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Old 29th Aug 2017, 9:23 pm   #100
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Default Re: Pilot PT650 "Spacemaker" Television

Hi Lawrence,
I presume the current needed to recharge the capacitors during the positive half cycle will be at least as much as the HT current. This will effectively double the current through the dropper and the heat generated will increase by a factor of four (I squared * R). So in the case of this set, without considering the ripple current, dissipation =5Watt. Factor in the ripple and the dissipation goes up to 20W!! Well, I'd never thought about that before- that might explain why in old TV's it seems to be the HT section of the dropper that has failed rather than the heater section.
Theoretically then, if we were to use a bridge to full wave rectify the HT supply, the ripple current would be greatly reduced. That would imply that the series dropper would need to dissipate less power. Is that true?
Many thanks for your help.
Cheers
Nick
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