[MRCA] AN/PRC-70 continued

[jkarlow at comcast.net]

Ray -

 

There were actually 2 versions of the PRC-70 radio from Cincinnati
Electronics that have been on the surplus market. The earlier one (a design
prove-out unit) was made between about 1970 and 1976. It included components
like the "Flyback/Trigger." There were probably 15 to 20 of these units
produced. Once the design was approved, Cincinnati Electronics in 1977 went
into production with a design with many improvements over the original. They
made about 2500 of these for the US Army Special Forces. The newer design
units look very close in external appearance but they are quite different in
internal content from the original. These are the more common units on the
surplus market. Make sure that you check the unit you have to see which
version it is. Many of the parts are not interchangeable between the two
versions. 

 

The later PRC-70 is an outstanding performer when properly used and
maintained. Years ago I put together a series of modifications to improve
the radio for Ham Radio use. These include one to add the LSB mode, one to
allow FM transmit below 30 MHz and one to provide internal switching power
supply shutdown when the battery voltage drops below 19.5 volts, to keep the
switching power supply in the A4 module from overheating and burning out
under low voltage conditions. The low voltage shutdown also allowed me to
throw away the "frezzolini board" on the top of the BB-542/U battery and to
be able to mount 10AH NIMH D - Cell batteries in the battery case to extend
battery life with Hi Power transmitting.

 

Good luck with your project and let me know if you have any questions about
this radio!

 

73's

 

Jim

 

Jim Karlow

KA8TUR

                           

4907 Oakwood Court

Commerce Township,  Mi 48382

E-Mail:  <mailto:jkarlow at comcast.net> jkarlow at comcast.net

Tel/Cell: 248-961-2034

 

 

 

 

From: mrca-bounces at mailman.qth.net <mrca-bounces at mailman.qth.net> On Behalf
Of Ray Fantini
Sent: Monday, November 21, 2022 11:16 AM
To: MMRCG at groups.io; MRCA <mrca at mailman.qth.net>; milsurplus at mailman
<milsurplus at mailman.qth.net>
Subject: [MRCA] AN/PRC-70 continued

 

Wow, just downloaded the TM 11-5820-553-23 and its way more useful then the
TM 11-5820-553-34

With that at least have an idea of the DC distribution in the radio, also
starting to think maybe the two shelled cans that the book says are the
Flyback/Trigger may indeed be that and I just that was not seeing any
voltages on them. It appears that the radio never receives any DC from the
battery unless the "X-Mode" connector is in place, wonder if that's the
problem? Will look and see if it's in place.

 

 

Ray F/KA3EKH

 

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