# #15 Directronic Rectifier voltage loss



## cramden (Oct 13, 2015)

Thought I would ask if any one has any experience with this model from 1948. Having not used it in about 5 years I hooked it up to the transformer and couldn't get any response at the track. I checked input voltage to the rectifier and got a 16 volt reading at max. throttle but only 6.25 volts on the output side. I could be wrong but I believe it's a Selenium rectifier. In looking for info. on the internet I learned that usually this type of rectifier fails catastrophically, but sometimes it can slowly degrade over time, especially if it has sat for long periods of non-use. Is this correct? If not, can someone school me in old electrical devices. Thanks.


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## flyernut (Oct 31, 2010)

Out of my field of experience buddy; I can only re-face armatures,lol..I have 0 DC engines, so I'm no good to you.


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## Mikeh49 (Sep 20, 2015)

Your internet info is consistent with mine. I replaced the selenium rectifier in a tube audio amplifier with a diode as a preventive measure. I'm sure someone has done a diode replacement for the AF #15. Gunrunner John will probably be along to provide the definitive answer. A replacement diode will have to have a current rating of several amps, like 6 or more; I'd be comfortable with 10. Looking at the wiring of the #15, it might be a full wave (2 diodes) or bridge (4 diodes) arrangement. The heat sink indicates its current capacity.


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## cramden (Oct 13, 2015)

Thanks for the responses guys. Flyernut, you do a lot more than re-face armatures, and I wouldn't hesitate to send you anything for repair. We should call you the " Wizard of Williamson." Thanks Mikeh49... I was hoping I might get a different answer but maybe it's time to retire the #15 and get something modern. The #15 is rated 4 amps so 6 to 10 would work. Maybe I'll post this question in the technical forum and someone could give me an idea what would be a good alternative. Thanks again.


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## Mikeh49 (Sep 20, 2015)

Or, post in the electronics section, or even S scale section of the OGR forum. I'm surprised that gunrunner has not replied here. He's the go-to guy for electronics.


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## T-Man (May 16, 2008)

Could you use a DC transformer?

I have upgraded selenium discs in a ZW with a 40 amp diode in a special case. This diode fits right in the space for the disc. I am no sure what the AF version looks like.


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## mopac (Feb 24, 2011)

Cramden I guess you could get another rectifier. I would suggest getting a decent
MRC DC transformer. Probably in the 20 to 30 dollar range for a good used one. You
probably have more than one loop on your layout. Dedicate one loop to DC and you
will be able to run any flyer you have. Your 334DC will run on it and any AC/DC loco
you have will run on it. That would eliminate changing transformers for different locos.
Like I said, I have run my 282 and a few different 302s on DC and did not notice any difference in performance. I have 3 or 4 MRC transformers from my HO days. They have
AC terminals for accessories. I don't remember what amp they are rated at but they
handled my flyers just fine. I don't know what their start voltage is but I am sure below
the 7 volt start of an AF transformer, so slower running if desired.


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## cramden (Oct 13, 2015)

All valid points guys. I don't belong to OGR but I read it at times. This is a pic of it T-man.














I'd like to keep it vintage if possible but might end up with the same problem buying another one. A DC transformer is an option and yes, I was going to use it on just one loop but I only have the one DC engine so it's not critical at the moment. I could hook up the #15 in a moment and run it without getting crazy with all of the track trips and accessories getting affected.The wiring to accessories is different for AC vs. DC so if I can find something like T-man suggested that might be the best way to go. Thanks again for all of your input.


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## BrokeCurmudgeon (Feb 8, 2016)

Cramden, I use a 4 way bridge (solid state) on the output of the AF 15B transformer that I switch between AC and DC to the track. For some reason I cannot find a part number this morning. (tough getting old!:laugh::laugh::laugh One transformer and two outputs with just a little of inconvenience.


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## AmFlyer (Mar 16, 2012)

In the past I used a cheap 5A bridge rectifier from Radio Shack plus a DPDT switch. The 15B only outputs 6A so a 5A rated bridge is ok for one engine plus illuminated cars.


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## cramden (Oct 13, 2015)

That's most likely the way I''ll go Fred and Tom. Just want something that can be hooked up easily with another transformer and just run the DC loco when the mood strikes.


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## Mikeh49 (Sep 20, 2015)

You could probably fit the bridge rectifier inside the base of the #15, and connect the 4 wires that go to the selenium disk stack to the bridge (appropriately, of course) and keep the original transformer and track connections, direction switch and appearance. It looks like the yellow wires are the AC and the red are the DC based on this photo:


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## cramden (Oct 13, 2015)

That's a good idea as long as I don't screw up the connections.:laugh:


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## Mikeh49 (Sep 20, 2015)

Check twice or three times before you turn it on. + and - are the DC, the other two are the AC, doesn't matter which yellow goes to the AC or which red goes to + or -. The switch takes care of the direction. 

Or, buy two rectifiers in case the smoke leaks out of the first.


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## cramden (Oct 13, 2015)

Maybe I should get a dozen.


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## AmFlyer (Mar 16, 2012)

The yellow wires come from the 7-15V input from transformer connections. The Black wires go to the DC Connect to Tracks terminals. The Red are the internal + and - DC rectifier output to the DPDT Reversing Switch. You can see the two short Black wires connected in an "X" between the two pairs of terminals at the ends of the DPDT switch. This is how the + and - outputs to the rails are reversed so the DC engine can run in either direction. 
Beware of reverse loops on DC layouts. They are more complex than AC because polarity must be maintained when the reverse loop is used.


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## cramden (Oct 13, 2015)

So am I correct in thinking only two posts on the new rectifier would be marked plus and minus? The other two are for the AC inputs from the trans.


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## AmFlyer (Mar 16, 2012)

Correct.


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## Mikeh49 (Sep 20, 2015)

The AC posts may be marked with a sine wave-like shape or just marked AC.


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## cramden (Oct 13, 2015)

Thanks AmFlyer and Mikeh49. I'll get around to it at some point.


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