Advice with germanium transistors

[Stephen C. Finch]

Doug,

 

As I am sure you have found, the 2N2553/R265A is an NTE121.  The Mouser cost
is $16 which is about right for almost any pass transistor at its rating.

 

The 2N2869/2N301 is an NTE179,.  Mouser has this one at about $21.  However,
if either of these transistors are the bad ones, they need to be replaced by
a matched pair (NTE179MP - $50 – whew!!).

 

I had to replace the pass transistors in a Kenwood power supply and the
matched pair cost $35.  However, the PS was useless without them.  I had to
“bite the bullet.”  I never thought about trying a silicon replacement that
may have been less expensive.  

 

I have an IP-27, and looking at the circuit, I suspect that any PNP power
pass transistor that has the proper voltage and current ranges should work.
The base to emitter voltage drop difference between germanium and silicon
should not make a difference in this application.  You may have to adjust
R23 to get the proper biasing.  I’m not sure how much base current
differences there may be between the germanium and a similar silicon given
the difference in junction drop.

 

If you make it work, and I suspect you will, please post your findings as
I’m sure others will have the same problem.

 

Steve

AIØW

 

 

 

 

-----Original Message-----
From: Heathkit Owners and Collectors List [mailto:HEATH at LISTSERV.TEMPE.GOV]
On Behalf Of Doug Shields
Sent: Tuesday, May 18, 2004 7:29 PM
To: HEATH at LISTSERV.TEMPE.GOV
Subject: Advice with germanium transistors

 

Hello all,

      I have done a lot of design with transistors and integrated circuits

but not with germanium parts.  I just got a "working" Heathkit IP-27 power

supply and found two of the three germanium power transistors are shorted

(collector to emitter.)    Replacement germanium parts are available but

VERY expensive.  I have thought about replacing them with modern silicon

power transistors.  What should I watch for in the conversion?  Any help

from the real semiconductor gurus out there?  Thanks very much.

 

Doug  W4DAS

 

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