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Electronics Repair (sci.electronics.repair) Discussion of repairing electronic equipment. Topics include requests for assistance, where to obtain servicing information and parts, techniques for diagnosis and repair, and annecdotes about success, failures and problems. |
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#42
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On 2021/04/22 2:04 a.m., piglet wrote:
On 22/04/2021 5:00 am, bitrex wrote: There's this patent from '66 that describes a solid-state thyratron replacement: https://patentimages.storage.googleapis.com/42/6a/0d/6e35c415a3f0e0/US3293449.pdf It uses a couple of SCRs. It's to replace high-power thyratrons but I don't see why it couldn't be scaled-down. Thanks Bitrex, that patent even mentions a tunnel diode and UJT which are now very exotic devices. The struggle was to emulate the high impedance thyratron grid. It seems to me (I have never seen a thyratron) that a modern depletion mode mosfet would make a good front-end to a SCR in that a negative grid bias is required to keep the device non-conducting (if I understand thyratrons correctly). Here is a conceptual sketch: https://www.dropbox.com/s/al1b8hj07i7jfpq/SED_Thyratron_Idea.pdf?dl=0 Possible fets could be BSS126 or LND150 and SCR with sensitive gates X0402NF or BT149G. piglet Yes, that might work - at least as a starting point. Need to poke at the values a bit and keep the patent design in mind too - I suspect the sensitive gate SCR didn't exist then. Thanks! John :-#)# -- (Please post followups or tech inquiries to the USENET newsgroup) John's Jukes Ltd. MOVED to #7 - 3979 Marine Way, Burnaby, BC, Canada V5J 5E3 (604)872-5757 (Pinballs, Jukes, Video Games) www.flippers.com "Old pinballers never die, they just flip out." |
#43
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Posted to sci.electronics.design,sci.electronics.repair
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On 4/22/2021 1:53 PM, John Robertson wrote:
On 2021/04/22 2:04 a.m., piglet wrote: On 22/04/2021 5:00 am, bitrex wrote: There's this patent from '66 that describes a solid-state thyratron replacement: https://patentimages.storage.googleapis.com/42/6a/0d/6e35c415a3f0e0/US3293449.pdf It uses a couple of SCRs. It's to replace high-power thyratrons but I don't see why it couldn't be scaled-down. Thanks Bitrex, that patent even mentions a tunnel diode and UJT which are now very exotic devices. The struggle was to emulate the high impedance thyratron grid. It seems to me (I have never seen a thyratron) that a modern depletion mode mosfet would make a good front-end to a SCR in that a negative grid bias is required to keep the device non-conducting (if I understand thyratrons correctly). Here is a conceptual sketch: https://www.dropbox.com/s/al1b8hj07i7jfpq/SED_Thyratron_Idea.pdf?dl=0 Possible fets could be BSS126 or LND150 and SCR with sensitive gates X0402NF or BT149G. piglet Yes, that might work - at least as a starting point. Need to poke at the values a bit and keep the patent design in mind too - I suspect the sensitive gate SCR didn't exist then. Thanks! John :-#)# Could use an optocoupler to level-shift the trigger pulse and a PIC...that's not much fun either, though... |
#44
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On 4/21/21 11:43 PM, bitrex wrote:
On 4/22/2021 1:07 AM, bitrex wrote: On 4/21/2021 3:47 PM, John Robertson wrote: On 2021/04/21 11:19 a.m., bitrex wrote: On 4/21/2021 2:14 PM, John Larkin wrote: On Wed, 21 Apr 2021 10:28:02 -0700, John Robertson wrote: In my field of arcade repairs we run into older jukeboxes - one particular model which uses the 2D21 tube and was from about 1954. I have the spec sheet he https://www.flippers.com/pdfs/2D21_Thyratron_tube.pdf It would be fun to make a solid state replacement for it as nothing seems to exist. These tubes are still available from several sources, but they get wonky with age. Being able to simply wire in a TRIAC or SCR (with appropriate bits of electronic glue) to remove this tube from the suspect list when servicing this classic Seeburg V200 jukebox would simplify future servicing. I always like to make things easier for the next tech to work on machines that passed through my shop... I should point out that Seeburg only used these 2D21s (three 2D21s used) on their very first control center for their Tormat (200 x magnetic cores) memory and dropped it like a hot potato. There were numerous service bulletins culminating in the factory providing a low cost replacement for the control centers that used 2D21s (three of these) and the replacement used a single 2050 tube and was a very reliable design. Not everyone took advantage of the program and all these replacement were used up long, long ago. John :-#)# Got a schematic? It might be easy. The 1954 gear was probably designed to run on old-timey line voltage of ~110 AC. Dialing back the heater voltage on the thyratrons to compensate for higher modern AC supply voltage might extend their life. This controlled a solenoid at around 24VAC or regulated (0A2 = -150VDC) power supply for the tormat write-in and readout circuits. John :-#)# I can't find a solid reference on what the gas in the 2D21 is, anyway. Only few references from the time period I can find don't agree, one paper says it's hydrogen: https://books.google.com/books?id=IdB5E4STz5kC&lpg=RA5-PA37&ots=T6ZN06aJWy&dq=hydrogen%20in%202d21&pg=RA5-PA37#v=onepage&q=hydrogen%20in%202d21&f=false Another says it's xenon: http://phylab.fudan.edu.cn/lib/exe/fetch.php?media=exp:ajp000701.pdf I think it must be xenon, the first one is just wrong Nah, they are just xenon-phobic :-) |
#45
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Posted to sci.electronics.design,sci.electronics.repair
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bitrex wrote in :
Sounds like you have something to prove. Your pschologist attitude is not matched by your education. Stay out of the personal assessment opinion crap. |
#46
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