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Old 15th November 2007, 02:28 AM   #11
7N7 is offline 7N7  United Kingdom
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I remember my transformer for the train set; somehow the wires "got together" and a lot of waxy stuff ran out... Still worked though - for years.

As for the valve CCS Ray suggests, I suppose you could float the whole thing at say 150V and sit it up on top of a nice pentode. That would discourage those busy tongues...

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Old 15th November 2007, 02:41 AM   #12
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Hmm...

I once laid out a strip of track, put an engine on one end and somehow managed to connect one of those coffee pot cords to the track and plugged her in... Smoke.. lots of sparks and the engine screaming across the room... Mother had a very perplexed look when she came into the room I was eight at the time...

ck
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Old 15th November 2007, 02:47 AM   #13
7N7 is offline 7N7  United Kingdom
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Quote:
Originally posted by Ciscokid
Hmm...

I once laid out a strip of track, put an engine on one end and somehow managed to connect one of those coffee pot cords to the track and plugged her in... Smoke.. lots of sparks and the engine screaming across the room... Mother had a very perplexed look when she came into the room I was eight at the time...

ck
Superb!

I wasn't quite as ingenious; at around six I wired up a plug to a piece of cable, and proceeded to plug in to a wall socket (240v).

All well and good, except that I hadn't had a good look at the other end of the cable, where the wires were nicely "entwined".

The results were really very dramatic and the fuse-box didn't like it all, something it shared with my parents...

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Old 15th November 2007, 03:07 AM   #14
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Quote:
Originally posted by ray_moth
The tracks and wheels make intermittent, generally not very good contact, so I would think that voltage regulation is not very much use.
Well, yes and no. There are simple throttles that do not do any regulation, and in fact some are intentionally half wave rectifiers so that the voltage peaks make the motor overcome friction better for slow speed running. However, all the DIY analog throttles I have seen use an LM317 or LM338 as a voltage regulator.
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Old 15th November 2007, 04:06 AM   #15
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Well, how about a hybrid? A BIG tube rectifier followed by a ubiquitous LM317. Is there a damper diode with a higher rating than the 250 mA of 6AX4 and similar?
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Old 15th November 2007, 05:29 AM   #16
Colt45 is offline Colt45  Serbia
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6CL3 and the like are beefier, but they still drop a good 10-15v at load. when all you have is 15v, that becomes an issue...
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Old 15th November 2007, 06:41 AM   #17
bob_v5 is offline bob_v5  England
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ha ha, with me it was my sisters tounge and a scalextric. And the best part was I was young and managed to convince my mum i didnt know about electricity, I was only trying to run it over, honest!
Anyway, is there any reason you want to use valves for the controller, or just for the fun of it?
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Old 15th November 2007, 02:50 PM   #18
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Quote:
Originally posted by Colt45
6CL3 and the like are beefier, but they still drop a good 10-15v at load. when all you have is 15v, that becomes an issue...
Well, no, since this will be scratchbuilt, I can make the input transformer whatever I like. Using an LM317HV should accomodate a reasonably large variance in voltage drop with current draw. However, even 6CL3 isn't really beefy enough, a decent home throttle should be able to put out one amp of juice.
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Old 15th November 2007, 05:07 PM   #19
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Found one, the 6CE3 & 6CG3 look like they do the job, but the compactron socket is a pain.
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Old 15th November 2007, 09:11 PM   #20
EC8010 is offline EC8010  United Kingdom
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Quote:
Originally posted by leadbelly
Yes; nice tease. And?
I wasn't intending to tease. As has been pointed out, there are two main problems with model cars and trains. Intermittent high resistance contacts and stiction. The solution in both cases is the same; short high voltage pulses. Of course, it's not going to be EMC compliant (not with those pulses connected to an aerial), but it will give good control. What you would need would be a line scan valve as your series pass element, driven by variable width pulses from a 555 or similar. A simple triode amplifier between the 555 and the PL519 would suffice. Poor smoothing before the controller would be useful.

The 317 approach is the exact opposite of what is needed.
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