[MRCA] MRCA Digest, Vol 240, Issue 2

Tue Apr 2 14:48:26 EDT 2024

I recently purchased a RT-77/GRC-9  Receiver/Transmitter and am looking at getting all of the components for the set.  Looking for the following:   
   - Plug PL-294 and Cord CD-1056 (Power Cable)
   - Vibrator Power Unit PE-237
   - Dynamotor Power Supply DY-88
   - Generator GN-58 with Cranks GC-7
   - Leg LG-2A
   - Leg LG-3
   - Cord CD-1086 Power Cable 
Cord CD-1119 and Battery Plug for Battery BA-48

   - Loudspeaker LS-7
   - Key J-45
   - Counterpoise CP-12 & CP-13
   - Antenna AN-160
   - Halyards M-378 & M-379
   - Reels RL-29   

Dave
David Ostrander4205 25th Street NorthArlington, VA 22207
dave.ostrander at verizon.netMobile 703.798.4239

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Today's Topics:

  1. Parts Box Inverter (Ray Fantini)

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Message: 1
Date: Tue, 2 Apr 2024 15:11:50 +0000
From: Ray Fantini <RAFANTINI at salisbury.edu>
To: "milsurplus at mailman.qth.net" <milsurplus at mailman.qth.net>,
    "MMRCG at groups.io" <MMRCG at groups.io>, "mrca at mailman.qth.net"
    <MRCA at mailman.qth.net>
Subject: [MRCA] Parts Box Inverter
Message-ID:
    <DM8P220MB04724E14AD5D30399A310CF1B83E2 at DM8P220MB0472.NAMP220.PROD.OUTLOOK.COM>

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I wanted to throw together something that would provide between 90 to 135 volts for operating radios in the field along with using junk from around the shop and not buy anything.
Thought about doing a high frequency inverter but with all the issues with RFI and having to use high frequency transformers decided to go with low frequency. The power supply may be bigger and not suited for a small radio but with the WS, TBX or GRC stuff I am playing around with don't care about size and weight.
The inverter is built around a 555 developing a square wave output that is directly coupled to a Mosfet driving a power transformer in reverse. The 10 K pot allows you to adjust the pulse width of the oscillator and affects the output voltage. Combinations of the 0.33 and 12 K resistor set the frequency of the oscillator and figure its running around seventy or eighty Hz.
The RFP50N05 50V 50A 120A Pulsed N-Channel Power Mosfets is from an old UPS system and is magic, unlike a transistor they have almost no internal resistance when turned on and develop almost no heat.
The transformer is a 36 volt and although it is not happy about being driven by a square wave it works and provided a good range of output. Thru trial and error found this one to be best. Transformers work both ways so you can use the primary as the secondary and they don't know the difference. The trick is to not exceed the insulation value.  Cheap Radio Shack transformers tended to get hot or buzz.
The output side of the transformer, the old primary feeds a full wave bridge and conventional filter network.
Couple things that I would have liked to do different is maybe use a 400 cycle transformer because that way can use a smaller transformer and filters. The Mosfet I am using runs all day long under load and never gets warm so will keep it simple for now.

Ray F/KA3EKH
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