[Heathkit] IP-27 transistor replacement info

[Ken Kaplan]

I have a couple of IP-27 power supplies in my shop. One works great and 
the other only sorta worked. It wouldn't hold a voltage with a light 
load. I finally got round-to-it. All of the transistors were fine. Long 
story short, capacitors C4, C6 and C8 were no longer electrolytic 
capacitors. I'm not sure what they are now. Perhaps incapacitors. They 
measure about 12pf and have a very high ESR. On a positive note, they 
have practically zero leakage. Guess I'll sell'em on ebay <g>.

As for the transistors, I recall someone asked about an 
affordable/findable replacement for the DTG-600 germanium power 
transistor used as the current limiter. I have been using a 2N3791 with 
much success. Mouser sells them for $2.28. That's a lot better than 
$39.66 for the NTE179 replacement for the DTG-600! I'm also using 
2N3791s for Q4 & Q5. The supply calibrates OK up to 50v and it current 
limits right at 1.5 amps (I put 12.3 volts into 8.2 ohms before the 
relay tripped).

I'm very happy with my units. They perform well. If you have an ailing 
IP-27, perhaps this info can help you get it working. I also have the 
Sherwin-Williams paint codes to make one of the several shades of brown 
cabinet paint. Holler if you want.

Note that there is a service bulletin for the IP-27.

73 Ken kb7rgg