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Old 13th Mar 2019, 9:31 pm   #1
greg_simons
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Default Thorn rectifier sticks

Hi folks
At some point I'm going to have to rebuild the multiplier tray for my thorn 2000 ctv, does anyone know to a source of the selenium sticks?, possibly the ones for the 3500 chassis will fit, also a cheap source of the aircraft grade sealant used to pot them.
Greg.
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Old 15th Mar 2019, 12:19 pm   #2
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Default Re: Thorn rectifier sticks

Bump....
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Old 15th Mar 2019, 2:16 pm   #3
dazzlevision
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Default Re: Thorn rectifier sticks

I think you are unlikely to find any of the original ITT/STC Selenium stick rectifiers and even if you did, they would be very old stock and possibly u/s or unreliable. Better, I would think, to use high voltage Silicon rectifiers. The 2000 tripler incorporates a high value resistor, which feeds the focus control (and possibly the EHT generator board), if it weren’t for that, you might be able to use a “universal” type tripler.
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Old 15th Mar 2019, 4:27 pm   #4
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Default Re: Thorn rectifier sticks

Hi dazzle,
Yes indeed, my preferred method would be new silicon hv diodes, there seems to be some problem with them being too efficient, might have to leave out one leg, the original diodes were quite hight resistance with a sizable voltage drop across each one, I'll ponder the situation for a while.
Greg.
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Old 15th Mar 2019, 7:08 pm   #5
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Default Re: Thorn rectifier sticks

Hi Greg
If you go over to " radios-tv vrat forum " and click colour television and then select page 17 , you will see a thread by crusty tv called brc 2000 tripler trouble .
Chris attempted to repair an open type tripler but as far as I can see he never finished it but it makes interesting reading.
Well done on getting one of these sets and I hope you get it going.

Robin
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Old 15th Mar 2019, 7:43 pm   #6
G6Tanuki
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Default Re: Thorn rectifier sticks

Sourcing ancient NOS selenium-sticks is a fool's errand - they'll either be just as bad as the ones you are replacing, or will become so after a few hundred hours of use, meaning you get to do the replacement again.

And again. And again.

Go for a modern Silicon-rectifier replacement - and if the resultant voltage is too-high stick a bleeder-network on the output. That will pull the EHT down, and also - by providing a consistent load - reduce any issues of random program-content-brightness/contrast-created fluctuations [which were in the early days of flyback-EHT a real issue].
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Old 15th Mar 2019, 8:03 pm   #7
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Default Re: Thorn rectifier sticks

The EHT generator schematic can be seen in the 2nd link in post 6 here:

https://www.vintage-radio.net/forum/...d.php?t=135994

Lawrence.
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Old 17th Mar 2019, 12:58 pm   #8
greg_simons
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Default Re: Thorn rectifier sticks

Doesn't look any original sticks are available so a more modern fix is going to be required, probably some 20kv piv diodes, mods, this thread can be closed.
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