[Boatanchors] DM-28 Dynamotor Restoration Questions

[Mike Bracey]

 Mike,
I totally agree with you. When my 348 is buttoned up the dynamotor is just a pleasant hum. 

73, Mike, KE5YTV

    On Wednesday, April 8, 2020, 11:11:14 AM CDT, Michael Hanz <aaf-radio-1 at aafradio.org> wrote:  
 
 Thanks for the update, Scott.

Good work on the brush repair!

On the dyno noise, is this with the dyno inside the receiver and 
buttoned up in the rear cabinet?  I've never been bothered by mine - the 
command sets are noisier because the dynos are out in the open, but the 
224/348, not so much because of the sealed case.  Did you replace the 
bearings?  Just curious.

If it is the normal dynamotor noise that bothers, I have modified a 
couple of the command set solid state DY-10 andPP-5792/ARN-30 inverters 
to fit on an adapter plate for the BC-348.  One of the guys that worked 
on the WWII radio sets in the B-29 Fifi was blowing out DM-28s like they 
were popcorn - something about the flaky primary power system on the 
aircraft, not the receiver load.  I sent him one of the inverters and a 
mounting plate (you need to put a 1N5363 30v 5W zenerin series to get 
the voltage down) and last I heard, it solved the problem.

- Mike  KC4TOS

On 4/8/2020 10:06 AM, whitebear1122 at comcast.net wrote:
> I put the dynamotor back together, loaded the brushes, and fired it up with
> a switching power supply.  The dynamotor actually worked.  That was a
> surprise also.  My expectations are so darn low that anything good is a
> surprise :)  I was measuring around 217 volts DC.
>
> Now that the dynamotor is running, I didn't realize just how noisy they are.
> While it might have been fine for the B17 Radioman since he couldn't hear
> the dynamotor whine over the noise of the engines, it would drive me nutso I
> think in the shack :)  I think I'll make an external supply for it.
>
> I found the replacement film capacitors and plan to start recapping today.
> 73, Scott WA9WFA

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