[Collins] 516E-1 DC power supply

[Gerald]

On Sun, 2005-04-10 at 13:35 -0500, Jim Isbell, W5JAI wrote:
> I am restoring a 516E-1 power supply.  This is the 12 volt input
> mobile supply for use with KWM-1, KWM-2 and S Line.  The transistors
> are 727-1742 Delco. 
727-1742 is sure to be the Collins part number.

>  and somewhere else I picked up the following two
> numbers, 2N278 and 2N442. 

The schematic in my 1959 yellow book shows 2N278 and 2N442 in TO-36
cases. PNP Germanium.

>  I dont know if either of those last two
> numbers are correct for substitution but would like to know what
> transistors CAN be used.
> 
> I am considering taking the 6 TO-5 transistors out and replacing them
> with more modern tab mount transistors and then I could add a heat
> sink along the back that they could be bolted to.

Its unlikely you will find any tab mounted Germanium transistors.
> 
> But for now its working so I am just looking to the future for
> replacement possibilities

The 2N442 is the smaller of the two transistors rated at 15 amps while
the 2N278 (at least the ECG replacement) is rated for 25 amps. There is
a note on the schematic shorting out a pair of drive resistors on the
low voltage converter when using the 2N278.

Silicon transistors will NOT work in place of germanium in these
circuits. These converter circuits drive the transistor bases with
VOLTAGE and the 0.2 volt junction drop of the germanium transistor is
critical to their functioning. Silicon transistors need 0.6 volt
junction drop. They simply won't oscillate. Takes at least three time
the turns on the base windings to make silicon work.

-- 
73, Jerry, K0CQ, Technical Advisor to the CRA
All content copyright Dr. Gerald N. Johnson, electrical engineer