[ARC5] [Milsurplus] Dear Vibrating Smart People....

[Paul Kraemer]

David
Since you indicated you were not interested in any solid state improvents 
I'll mention one anyway. Just because.
I breadboarded a couple designs to replace vibrators using small power 
mosfets that would make you put that vibrator on the relic shelf.
Also made a way cool 12v to 24v dc dc converer circuit from my experimenting
If anyone is interested I can scan my notes and email or figure how someone 
can post them
Paul K0UYA
----- Original Message ----- 
From: "David Stinson" <arc5 at ix.netcom.com>
To: <milsurplus at mailman.qth.net>; <arc5 at mailman.qth.net>
Sent: Wednesday, December 05, 2012 10:34 AM
Subject: [Milsurplus] Dear Vibrating Smart People....


> I'm working on an RCA Light Aircraft set using the AVA-126A
> Vibrator Pack power supply.  Here's a drawing of the input
> of that supply, wired for 12 volt operation per the design:
>
> http://home.netcom.com/~arc5/AVRAVT/AVA126Vib.JPG
>
> All the old caps have been subbed.
> The OZ4 rectifier tests good.
> The 10K resistor in the "snubber" is rated at 1/2 watt.
> With or without load, it is drastically overheating.
> I'm having this problem with two of these supplies.
> A .02 temporarily touched across the resistor shows
> sparks, so it's "snubbing" some hefty spikes.
>
> My current theory:  The vibrator is very old and the
> pressed-in, oxidized contacts are creating more "noisy,"
> higher-voltage spikes than those for which the set
> was designed.  These are causing higher spikes
> in the secondary than the snubber can handle.
> I got one of these vibrators working by soldering the
> contact bases to the contact springs, but the top layer
> of the bi-metal contacts themselves will not take solder.
> The other worked without opening it.
>
> I assume the RCA engineers knew what they were doing,
> so I don't want to "(dis)improve" their design.  But they
> could walk to the Supply Sargent and get a new vibrator.
> I can't.  I don't want to fry them out with 115 VAC
> as I've often heard mentioned, and I'd rather not replace them
> with solid-state parts if I can avoid it.
>
> Possible solution:  Modern MOVs (spike killers) are available
> cheap for voltages from 2 to 500 volts that will handle amps.
> Either low-voltage MOVs tacked-across the primary windings
> or a high-voltage MOV on the secondary, or both to eat the spikes.
> That's what A.R.C. did on the MD-7 modulation transformer
> secondary; that large, conical-ended doodad under the chassis
> is a big "varistor" (caveman MOV) that eats audio spikes
> to save the transformer.
>
> Take a look at the diagram.
> Do you think MOVs might solve the problem?
> If so, what values would you recommend?
>
> TNX OM ES 73 DE Dave AB5S
>
>
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