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Tractor Talk Discussion Forum

CUB points

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Wess C

02-04-2007 11:10:42




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On a 1948 CUB with original 6 volt positive ground I cleaned and set the point to .20 and disconnected the condenser , separated the wire from the points to the coil and installed a TIP3055 npn transistor (276-2020) and one diode and guess what....instead of 4.6 amps at the points now its only 70 ma (.07)amps the points go to the base , emitter to the coil , and the collector to the positive ground ,diode is 6 amp 50 volt (276-1661) between the collector and the emitter band towards the collector . The fire is a lot hotter ,so I Doubled the spark gap from .23 to .45 and the points are still at .07 amps .There is no spark or arc visible at the points , the only wear would be at the wiper or spring in about 15 years . I just have it hanging there on a pease of aluminum now but it will bolt down with a small heat sink(276-1368)in place of the condenser under the cap. not bad for under $6.00 A LED could be added between the emitter and collector with a 100 ohm resister that would light to indicate the open points which is when the spark occurs . This may be handy for adjusting timing however it is not needed and if you don't move the distributor the timing shouldn't change if the point gap is correct. This is not true breakerless electronic ignition , more like a electronic switch that takes the high current off the points contacts , if a good lube is used un the wiper, and just a touch where the spring attaches who knows how long they would last. Numbers in parenthesis are Radio Shack catalog numbers.

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dan hill

02-05-2007 05:43:53




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 Re: CUB points in reply to Wess C, 02-04-2007 11:10:42  
Tried this on a 38 dodge 50 years ago.I wondered about the increased voltage on the coil ,dist cap and ignition wires.Didnt use it long so didnt have any problems.You may need to use a higher voltage rating on the diode because of the high inductive voltage being switched.



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Wess C

02-05-2007 14:07:20




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 Re: CUB points in reply to dan hill, 02-05-2007 05:43:53  
50 years ago...are you sure it wasn't a tube lol..the test circiut used a big old 2N3055 in a TO3 can with the shacks 50 volt diode , the old girl hasn't ran much above 45 deg.outside but I did check the roter and cap after both idle and wide open , there was no heat on the electrodes. I have a heat lamp and temp. probe , I will simulate a 95 or 100 deg.day and check that out. The wires are new copper , no resistance or arcing and no heat . back to the diode your correct , 50 volts is at the upper limit and on a older coils core that has gotten weak the voltages could get higher . Radio shack cant help help here ,ocean state electronics has 100 volt for .80 and 200 volt for .85 wich is cheaper than the shack anyway . The diode needs to be at least 5 amp....but 6amp at 100 or 200 volt being the better choice . Thanks for the correction . Wess

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RAB

02-04-2007 12:51:52




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 Re: CUB points in reply to Wess C, 02-04-2007 11:10:42  
The main trouble you may encounter could be dirty points. With only 70mA going through the points any oil mist or dirt may interrupt the base feed.
Probably need smaller surface area contact than standard CB points to keep pressure between point contact a bit higher than with the large contacts. If points are a sliding contact, could be OK for years.
How is spark duration with this set up?
One last thing. Never get the polarity wrong or it will be a new transistor.
Regards, RAB

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Wess C

02-04-2007 13:07:47




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 Re: CUB points in reply to RAB, 02-04-2007 12:51:52  
good point , may try a 200 ohm resister to load the points and add just a little heat to them.The spark duration im not sure..as the points start to lift the resistance encreases witch allows the primary to discharge some before it collaps , the transister switches off quicker so a larger current is induced onto the secondary (I think) And your right about the polarity which is also the case for the diode...Wess

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Wess C

02-04-2007 12:12:26




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 Re: CUB points in reply to Wess C, 02-04-2007 11:10:42  
its not about changing the condensor or the points its about tuneups not needed . the contacts don't have any current so they don't need replaced,cleaned,or adjusted as much, the spark is hotter the plugs stay cleaner and it starts better .no need for a condensor or drop resistors and it works with 6 or 12 volt coils positive ground .I still enjoy breaking out the old feeler gauges but after holding the end of the coil wire close to the block and seeing a spark that was gone at 3/8 in. to a real bright 3/4 in. spark that you can hear...wow..I just had to share it with everyone...Wess

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John M

02-04-2007 14:44:03




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 Re: CUB points in reply to Wess C, 02-04-2007 12:12:26  
Why would this not work Negative ground? Several of my tractors have alternators.



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Wess C

02-04-2007 15:26:19




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 Re: CUB points in reply to John M, 02-04-2007 14:44:03  
Electronic ignition module kit K2543 is a great kit that has been out for a long time works great with negative ground for like 16 bucks...same set up but a lot more parts...you could do the same thing by changing from a npn to a pnp transister like say a MJE2955 but the hook up is different,look up the SIM2 transister ignition on the internet ,The Velman kit is adaptable for 6 or 12 volts and is known world wide..Wess

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John M

02-04-2007 11:42:54




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 Re: CUB points in reply to Wess C, 02-04-2007 11:10:42  
So why would you do this?Sounds like alot of work for a two minute job of changing a condensor.



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