[Boatanchors] DM-28 Dynamotor Restoration Questions

[Mark K3MSB]

Same with my BC-348Q.

Mark K3MSB


On Wed, Apr 8, 2020, 12:38 PM Mike Bracey <mikebracey at att.net> wrote:

>  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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