Double current interface card

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M1ECY
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Double current interface card

#1

Beitrag von M1ECY » So 24. Nov 2019, 10:31

Probably a topic best covered by Fred or Henning.

One of the biggest problems with getting I-Telex to take off in the UK is the lack of an interface that works with British machines.

I know there was some development work carried out for a double current interface - I have seen the schematics on Sourceforge.

I see some problems with the concept - I-Telex should be a "one box" solution, at present there is no dual rail power supply for the machine interface.

I think it would be possible to modify the existing power supply board to give two voltage multiplier chains - this should then allow for maybe 60-0-60 for the signalling supply (the people I have spoken to so far regarding possible new subscribers always come back to "British Teleprinters use 80-0-80v" - I think that this is not really needed, we are not running long distance lines for our purposes, but I do appreciate that the higher voltage is needed to allow for a quick and positive operation of the receive magnets.

So, some questions from me

1, Was the existing schematic tested in any way?

2, Are there any modified boards available?

3, Any reason why the double current interface went to transistors rather than power fets?

4, Looking at the datasheet for the transistors I see a maximum VCEO of 100v - surely this means we can use 60v as the signalling level?

5, What about Back EMF - at present I can see no "snubber" across the lines

My final question - seeing as I am one of the few existing subscribers that could really use a double current interface, can I help in any way?
459724 SEAN G - Te Ka De FS200 - Working 24/7
666507 JONAB G - BT Cheetah 85 - Working sometimes
350470 Ersatz G - J-Term - Working 24/7
BT Cheetah 87 "Kranken" a spares donor now :(
Siemens T68d - A work in progress
BT Super Cheetah - Functional, but awaiting SVCF I-Telex Card

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Re: Double current interface card

#2

Beitrag von DF3OE » So 24. Nov 2019, 11:02

The basic schematic is from Richard in Australia who uses it with his machines.
I have two modified boards and also used them successfully with my Creed 444 and Sagem TX21.
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M1ECY
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Re: Double current interface card

#3

Beitrag von M1ECY » So 24. Nov 2019, 11:18

Interesting Henning, so the modification works, even at low voltage?

If this is the best solution, then production line required :)

So, I will try to build one, perhaps as an interim measure make an external interface module with DC power supply on the same board.

I could use standard TW39 board with all output components removed.
459724 SEAN G - Te Ka De FS200 - Working 24/7
666507 JONAB G - BT Cheetah 85 - Working sometimes
350470 Ersatz G - J-Term - Working 24/7
BT Cheetah 87 "Kranken" a spares donor now :(
Siemens T68d - A work in progress
BT Super Cheetah - Functional, but awaiting SVCF I-Telex Card

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