PSU Germanium transistor replacement? - Page 1
Forum section: electronics / projects

author: AmericanLocomotive
author_rank: Contributor
timestamp: January 19, 2014, 04:27:10 am
content: Hey guys,So I have this really ancient Lambda regulated linear power supply. It's pretty beefy at 5A 0-35v. It's got a pretty unique set up with 4 range switches and 16 possible voltage range combinations and a pot that can adjust a 5v range. They switches actually change out various secondary windings, so the passbank isn't rejecting a ton of heat at low voltage/high load situations.It's a real old beast; it weighs about 55 pounds and has an old U.S. Civil Defense sticker on it, so it's got some really cool history to it. Date codes on various parts inside seem to indicate around 1964-1965 build.Anyways, I got it broken, and it turned out just to be a shorted output transistor. Unfortunately they're very old germanium transistors, but I was able to find a replacement on e-bay. Well fast-forward a few months later, and another transistor kills itself. I'm wondering if there are any modern silicon transistors that would be a near drop-in replacement for these fragile germanium units? The regulation is also a bit dodgy, but I'll chalk that up to tired capacitors.Here's the schematic, provided to me by TDK-Lambda, and a few pictures. Thanks in advance.https://dl.dropboxusercontent.com/u/1667530/IMLA5003B.pdf

author: AmericanLocomotive
author_rank: Contributor
timestamp: January 19, 2014, 04:27:41 am
content: More pictures:

author: Rerouter
author_rank: Super Contributor
timestamp: January 19, 2014, 04:57:58 am
content: Please re-post the schematic outside of an archive, many people wont touch them

author: don.r
author_rank: Frequent Contributor
timestamp: January 19, 2014, 05:00:45 am
content: 1 left in stock!http://www.amazon.com/American-Microsemiconductor-2N1537/dp/B001IS6OGM

author: AmericanLocomotive
author_rank: Contributor
timestamp: January 19, 2014, 06:12:06 am
content: Quote from: Rerouter on January 19, 2014, 04:57:58 amFixed:https://dl.dropboxusercontent.com/u/1667530/IMLA5003B.pdfQuote from: don.r on January 19, 2014, 05:00:45 amThanks, but I'm trying to get away from the original germanium parts. They're proving not to be reliable.

author: calexanian
author_rank: Super Contributor
timestamp: January 19, 2014, 07:37:24 am
content: Oh man.... those 2N217's are gona be killers. NPN germaniums are a tricky business.... Honestly I would just use the chassis and transformer and build up a modern Silicon regulator circuit for it and just make it look vintagey.. For god sake there is even an old tantalum in there!

author: SeanB
author_rank: Super Contributor
timestamp: January 19, 2014, 09:39:54 am
content: This is an application where you replace all of those output transistors Q1 to Q6 with 2N2955 units. Those at least are going to fit, are available in TO3 and are likely to work with no problems. Some of those big capacitors are likely to be well past the use by date as well, and ideally you should replace all that have a rubber sealing bung. Glass seal no issue, but rubber must be replaced.

author: AmericanLocomotive
author_rank: Contributor
timestamp: January 19, 2014, 06:29:12 pm
content: Quote from: calexanian on January 19, 2014, 07:37:24 amCan you elaborate? The issue was with the output 2N1537's popping, not the regulation transistors.Quote from: SeanB on January 19, 2014, 09:39:54 amThanks a bunch. I planned on replacing most of the capacitors anyways. I just hope the main filter caps are alright though; those 10,000 mfd 55v caps are about $30/pc!Anyways, if the new transistors and caps don't get it stable, I probably will end up gutting it and rebuilding it with a modern circuit. Hopefully I'll be able to integrate the range switches in as well, to keep heat down.

author: calexanian
author_rank: Super Contributor
timestamp: January 19, 2014, 08:22:44 pm
content: You can get main filter caps from all electronics. They have reasonable prices for caps in those ranges.