[ARC5] DM-32/ 12 and 28 volt dynamotors

[Brian Clarke]

Command receivers are now about 80 years old; they were probably only
designed for the average life of an airman - about 6 weeks. Dave Stinson and
others have been achieving good results with reduced HT on Command
receivers. The advantage of this is that those potted capacitors don't eject
their innards, or dry out and fail OC. 
But there are two negative effects of lower HT:
* The screen Voltages on the RF stages are rather too low for good
performance - lower sensitivity and worse S/N
* The audio output is rather lower.
Possible fixes:
* Feed the screens from the top of the screen Voltage divider; maybe even
disconnect the screen Voltage divider and reduce the under-chassis heating
to get better drift performance
* Run the audio output into a dummy load and feed the audio to an ordinary
amplifier.

You can get more HT out of a DM-32 run on 12 Vdc; connect the field windings
in parallel.

To answer Dennis' query: you can swap the DM-32 body for the DM-53Z; they
are the same size and use the same fastenings. However, then you run the
risk of damaging the potted bypass capacitors. I have cut open the potted
capacitors and replaced the contents with capacitors rated at 400 V and 630
V, depending on their position in the circuit. Shortly after WWII, the later
Series 12 receivers used potted capacitors rated at 400 V - if you can find
these, they can be a straight drop in.

73 de Brian, VK2GCE

On Sunday, 9 June 2019 4:45 PM, Bill Pileggi said:

You can use a 28 volt dynamotor even though the filaments are wired for 12
volts. The dynamotor will simply turn a little slower and put out approx.
100-110 volts.  The receiver will still be very happy. (You did replace all
the bypass capacitors in the receiver, didn't you? Otherwise, you might have
a problem or 2 with high voltage in the receiver...)

I've run the 28 volt dynamotors from as little as 8 volts reliably...Bill
KA3AIS

i have a bc-455 Rx that has been converted to 12vdc i know that the
dynamotor should 
be the dm-32 for 28vdc can i use a dm-53(az) dyno 12v/220vdc are they the
same size 
thanks for any help ka9dzr dennis