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Tech Chat Hypothetical proposition; Modifying a PYE 697 to fully solid state

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slidertogrid
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Towards the 691 life in the early 80s when the solid state CDA panel was available there was talk from one of the reps (I don't know if it was LEDCO or DR developments as both did SS CDA boards) about making a solid state replacement Timebase board to make the set fully transistorised! It never went into production or even got to prototype as far as I know. It may even have just been 'Rep tales'.

 
Posted : 31/07/2023 9:59 pm
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crustytv
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Posted by: @slidertogrid

Towards the end of the set's life in the early 80s when the solid state CDA panel was available there was talk from one of the reps (I don't know if it was LEDCO or DR developments as both did SS CDA boards) about making a solid state replacement Timebase board to make the set fully transistorised! It never went into production or even got to prototype as far as I know.

Hmmmm, now there's a challenge, a possible winter project to ignite the grey-cells of Mr @jayceebee

I wonder, can you model thermionic circuits as well as solid state in the LTspice simulation software?

If so, perhaps the existing valved circuit could be recreated and then maybe modified to accommodate the conversion to solid state? LTspice can produce netlists, which can then be exported to Kicads PCB layout software.

John has already produced a new, direct replacement CDA although not solid state. For giggles, you could use PL802/T which, as I'm sure you're all aware, are solid state replacements. With the above modified timebase, that would make it all solid state.

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Posted : 01/08/2023 6:59 am
slidertogrid
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What about the PCL84s?  The only thing with the solid state CDA boards was the necessity to keep the heater chain intact so this nice cool running well designed board had a bloomin' great wire wound heater dropper mounted over the top of it which tended to fry it after a few years. It didn't really matter much back then as the sets had served their purpose and were end of useful life.

If the time base was made to be solid state and a solid state CDA board found the heater dropper could be dispensed with. The base part of the time base unit would have to be retained as in has the LT supply circuit built on it, only the PCB ( he says 'only'! ) would need to be redesigned, maybe a base circuit could be taken from the 725 that used the same tube, so might do. A lot of work though! 

I think the BEAB requirements were what caused the CT205 vent slots in the back to be smaller than the previous model which caused the 22" sets to run so hot which caused a lot of problems with the CDA and time base. Add to that the scorchio summer of '76 and the fact that a lot of renters had the set on 'all day' and it was a recipe for disaster....

 
Posted : 01/08/2023 8:54 am
crustytv
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Posted by: @slidertogrid

What about the PCL84s?

Ah yes, total brain fart there 🙃 

However, Chris F has one of those solid state CDA (new unused) boards, John could copy and replicate that.

It would be just a fun exercise to see how it performed, compared to the original, not a planned long-term mod.

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Posted : 01/08/2023 9:02 am
Jayceebee
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I must admit when I read Rich’s comment about fully a solid state conversion late last night the cogs immediately started grind and inevitably when I went to bed it took me a while to get to sleep. A stabilised 200v or so power supply would be needed and what LOPT to use? As Rich suggested I also thought stick with PYE and adapt the 725 might be best, I don’t have a circuit to hand but I think it should be feasible. @Crustytv Do you a 725 LOPT in stock? 

John.

 
Posted : 01/08/2023 9:50 am
slidertogrid
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@crustytv From what I can remember there wasn't anything to choose between the Ledco and the DR developments panels they both worked well. I bonus was if the tube was a little past it's best a SS CDA would improve things. Some sets suffered from shading and 'Green banding' when the tube was worn, possibly slightly "gassy"? a SS CDA cured that problem.

We fitted a lot in I think 1980 but by '83 the rules had changed and the sets were disposed of. I had left at that point and had gone self-employed. My Uncle had a large factory unit so we went halves and bought up a large quantity of ex- rental sets from local dealers and I ended up with a couple of Luton van loads from my ex employer so I got to do up sets that I had probably worked on previously!  We had a few one day sales on Saturdays and did very well out of it, It paid towards my first new van a 1984 Astra, it seemed a hell of an upgrade from a 1977 Escort! 

 
Posted : 01/08/2023 10:22 am
crustytv
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Posted by: @jayceebee

Do you a 725 LOPT in stock? 

Afraid not, here's the 725 LTB extract, full manual in the usual area.

725ltb2
725pn1
725ltbcct

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Posted : 01/08/2023 11:00 am
Till Eulenspiegel
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In about I980 I fitted the all-transistor CDA board into a small number of Pye 693 series CTVs.  The new unit worked well enough but the advantages of employing transistors to replace the PL802 and three PCL84s was negated by the large heater ballast resistor mounted on the board.                 Considering frame timebase circuits are transistorised there was only the line timebase which employed valves. The sound amplifier was solid state right from the start, Mullard LP1162 module or the Texas SN76013 IC.

So we are left with three valves. Remember GEC employed in some early single standard sets a special silicon diode type BY147P to replace the PY500A boost diode. Unlikely such a device is still available but there will an alternative silicon diode to perform the boost diode function.

Till Eulenspiegel.

 
Posted : 01/08/2023 9:10 pm
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slidertogrid
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If a solid- state PCF802 and PL509 could be made the set could be solid state retaining the original PCB!  I guess not... I'll get my coat....! 😀 

 
Posted : 02/08/2023 12:38 pm
malcscott
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I was told that LEDCO did produce a solid state line output pcb for the 697. It never made mass production due to the high cost to produce it. I have a nos solid state cda board, Malc.

 
Posted : 02/08/2023 9:06 pm
Jayceebee
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@malcscott Any chance of some pics of the LEDCO CDA Malc? I've not seen one before, does a circuit diagram of it exist?

John.

 
Posted : 02/08/2023 9:21 pm
Jayceebee
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Looking at the manual a PYE 725 would be the simplest way to go solid state but after talking to fellow member @The_Teleman he says that LOPTs for these are very scarce. Another potential one would be the GEC 2110 but apparently these are also quite rare in the wild, that leaves the G8, Rank A823 and Thorn 9800 which the latter is a diode split type but of Philips manufacture. I don't think I would like to go with the G8 or the 9800 due to Philips reputation for dreadful LOPT reliability and as the A823 was pretty bomb proof it would be another which is again probably pretty scarce. 

John.

 
Posted : 02/08/2023 9:49 pm
malcscott
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@jayceebee Call in and take it for a good look.

 
Posted : 02/08/2023 9:50 pm
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The_Teleman
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@jayceebee 

hi John I too have a solid state cda panel it looks very cheaply made I think it has the circuit diagram with it I’ll check tomorrow and let you know 

if I recall these never had the tint control socket for the Dynatron sets 

 
Posted : 02/08/2023 10:38 pm
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Marconi_MPT4
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Posted by: @jayceebee

@malcscott Any chance of some pics of the LEDCO CDA Malc? I've not seen one before, does a circuit diagram of it exist?

Hi, A while back I did did supply a copy of the schematic and set-up instructions for the LEDCO solid state board. If not available in the library, PM me and will e-mail it to you.

Rich

 

 
Posted : 03/08/2023 12:47 pm
slidertogrid
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Posted by: @jayceebee

Looking at the manual a PYE 725 would be the simplest way to go solid state the A823 was pretty bomb proof it would be another which is again probably pretty scarce. 

I have an A823 LOPT which is labelled OK, happy to donate that if required. Just a thought, I know the G11 was 110 degree but would a G11 LOPT be any where near useable? I have a NOS G11 line panel somewhere... It sounds like a massive task though!

What is really needed is a basket case 725 of course and you never know... There was an incomplete one on ebay a few years ago, they are out there... 

 

 
Posted : 03/08/2023 1:04 pm
crustytv
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Posted by: @marconi_mpt4

Hi, A while back I did did supply a copy of the schematic and set-up instructions for the LEDCO solid state board.

You did indeed, I've just put it into the temporary library for those interested to download.

LEDCO MODEL No. 705 CDA PANEL FOR PYE 691 693 697

I wish I had enough server space left to locate the library back, I have a devil of a job remembering what I do and don't have.

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Posted : 03/08/2023 1:05 pm
Marconi_MPT4
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Posted by: @crustytv
I wonder, can you model thermionic circuits as well as solid state in the LTspice simulation software?

If so, perhaps the existing valved circuit could be recreated and then maybe modified to accommodate the conversion to solid state?

Modelling thermionic line deflection stages can be done in LTSpice. During the first lock down in 2020 I spent a while modelling one of the STC/Brimar application note designs based around 6CD6G.

Valve models were not available from the usual places so had to set about creating my own with a bit of trial and error. Diode models were based on using Child-Langmuir law with a perveance value to calculate the Ia/Va curve. The simulation worked after a fashion but there were many gotchas! Managed to obtain EHT and a decent undistorted scan current albeit with a high current consumption!

Rich

 

 

 
Posted : 03/08/2023 3:00 pm
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