[Milsurplus] Bendix High Voltage Supply - Switcheroo

[Jim Whartenby]

DaveYou seem to be having too much fun with power supplies!  Please share whatever fixes you come up to replace leaky  Germanium power transistors.  Perhaps this problem will only get worse with the passage of time?  I have had similar issues with small signal PNP Germaniums.  Seems that hfe has fallen to the point that nothing is behaving as expected.  
Silicon may have similar problems due to high E/B reverse bias.  This is exactly what happens when using a simple transformer coupled multivibrator power supply with nothing done to limit reverse bias voltage.See:   https://downloads.hindawi.com/journals/apec/2001/053209.pdf

Whatever happened with the Magic 5Y3 thread?  Did you ever solve that mystery?Jim

Too much agreement kills a chat.  E. Cleaver

-----Original Message-----
From: David Stinson <arc5 at ix.netcom.com>
To: boatanchors at mailman <boatanchors at mailman.qth.net>; milsurplus at mailman <milsurplus at mailman.qth.net>
Sent: Sat, Oct 9, 2021 4:16 pm
Subject: [Milsurplus] Bendix High Voltage Supply - Switcheroo

  I'm (very) slowly working on a Bendix Skipper 135 marine
 AM transceiver, circa 1960s.  Primary power is 12 VDC, 
 It has a receiver full of PNP germanium transistors, of which
 I had spares.  A few caps and some replaced transistors
 and it's working fine on Rcv.
 
 The transmitter uses tube crystal oscillator / PA, powered
 by a simple transistorized multivibrator/transformer/
 voltage doubler.  The power transistors are PNP germaniums 
 and, like many power germaniums at this late date, they
 are leaky.  Power supply will only do about half the required
 B+ voltages (caps and diodes replaced, no unusual load on
 the B+ busses).  
 
 Here's the deal- Power PNP germaniums which aren't leaky 
 are getting hard to find, but NPN Silicon are common as sand
 (see what I did there? :-D )  Maybe 2N3055?
 I'm thinking I can swap the Collectors and Emitters, move 
 R34, the Base bias resistor from the Negative buss to the 
 Positive buss, then play with R34's value until I get reliable 
 start and minimal dissipation.  Diagram attached.
 Comments?  Ideas?
 TNX OM ES 73 DE Dave AB5S
 
  


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