Dale, I've got a solid-state 4-band Sears AM/FM/SW1/SW2 portable (it has a handle on top and uses 4- D cells!) receiver I bought back in 1965 - I have only replaced the FM RF Amp transistor (back sometime in the late sixties - and this was after I probably fried it during a lightning storm when I had it connected to an external antenna) - - and the AC power supply in that radio uses a series regulator design and a push-pull audio stage that drives the built-in 5" x 7" speaker - nothing but that one RF transistor has failed in that portable in 37 years! I've also got a 1965 Motorola Motrac (commercial 2-way radio) that is all original as far as transistors - this includes some beefy TO-3 cased transistors that perform +12V conversion to +450 VDC for the 85% tubed transmitter ... I have had those beefy transistors blow on *other* Motrac radios (a 100W six meter 'trac conversion - it tripped the 40 Amp breaker in-line to the battery when it shorted). So, I guess I took the "20 years" too literally, but, as I point out that would only seeem to be part of the answer - it gets more complicated with time - and with "temperature cycling" as you also point out ... To that end - both I and a friend had the switching PSUs in our 83 channel (yes, 83 standard broadcast channels!) Emerson 20" colors TV die in the mid-late 80's (we had bought them about the same time mid 80's). After installing my replacement PSU I proceeded to do some temp tests - and discovered a 60 degree C rise above ambient on the heatsink! A fan installed inside the set pointed at that PSU (with attached stock heartsink) has apparently 'solved' the temperture induced failure mechanism and extended it's life greatly (now into late 2002). RF Jim ----- Original Message ----- From: "Dale Botkin" To: Sent: Tuesday, November 05, 2002 2:03 PM Subject: Re: [EE]: Power supply rework (again) > On Tue, 5 Nov 2002, Jim wrote: > > > "they're only 20 years old, what are they doing > > failing this soon?? " > > I was being facetious - I'm not surprsed when 20 year old power > transistors fail, especially considerign these had a thermostatic fan > control that probably allowed some pretty big thermal swings. A new pair > is on the way, that should fix it. > > Dale > > -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.