Re: Reliability of electronics

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From	Trevor Wilson <trevor@rageaudio.com.au>
Newsgroups	aus.electronics
Subject	Re: Reliability of electronics
Date	Tue, 31 May 2022 14:05:36 +1000
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On 31/05/2022 2:02 pm, Phil Allison wrote:
> Trevor Wilson wrote:
> =================
>>>
>> **Good plan. FWIW: The Model 500 never overheated. Thermostat
>> controlled, two speed fan cooled. Output devices were all mica/thermal
>> paste mounted. Even after repair (using original output devices) the
>> amps failed. Only after the output devices were substituted with
>> Japanese types did reliability significantly improve.
>>
> 
> **   Were the SJs in steel or Aluminium paks?

**Like all Motorola TO3 devices of the early 1970s, they were in those 
horrible aluminium packs.

> 
> Early 70s Motorola TO3s had a big problem with thermal expansion of chip headers.
> The silicon and the header had differing tempcos of expansion.
> The end result was the chip developed micro cracks.

**Yep. I recall reading the RCA white paper on the issue.

> 
> Such devices were speced at a mere 5000 thermal cycles.
> OK for some apps but not class AB audio.
> Sudden, unaccountable failure was the norm.
> 
> Aluminium paks got dumped and were never seen again.

**Yep. Steel or copper is the way to go for TO3 devices. RCA won the 
argument.

Thread

Reliability of electronics Trevor Wilson <trevor@rageaudio.com.au> - 2022-05-30 17:24 +1000
  Re: Reliability of electronics Trevor Wilson <trevor@rageaudio.com.au> - 2022-05-30 19:33 +1000
  Re: Reliability of electronics Phil Allison <pallison49@gmail.com> - 2022-05-30 16:01 -0700
    Re: Reliability of electronics Trevor Wilson <trevor@rageaudio.com.au> - 2022-05-31 10:35 +1000
      Re: Reliability of electronics Phil Allison <pallison49@gmail.com> - 2022-05-30 17:59 -0700
        Re: Reliability of electronics Trevor Wilson <trevor@rageaudio.com.au> - 2022-05-31 11:31 +1000
          Re: Reliability of electronics Phil Allison <pallison49@gmail.com> - 2022-05-30 18:52 -0700
            Re: Reliability of electronics Trevor Wilson <trevor@rageaudio.com.au> - 2022-05-31 12:00 +1000
              Re: Reliability of electronics Phil Allison <pallison49@gmail.com> - 2022-05-30 20:03 -0700
                Re: Reliability of electronics Trevor Wilson <trevor@rageaudio.com.au> - 2022-05-31 13:45 +1000
                Re: Reliability of electronics Phil Allison <pallison49@gmail.com> - 2022-05-30 21:02 -0700
                Re: Reliability of electronics Trevor Wilson <trevor@rageaudio.com.au> - 2022-05-31 14:05 +1000
                Re: Reliability of electronics Trevor Wilson <trevor@rageaudio.com.au> - 2022-05-31 14:08 +1000
                Re: Reliability of electronics Trevor Wilson <trevor@rageaudio.com.au> - 2022-05-31 14:18 +1000
                Re: Reliability of electronics Phil Allison <pallison49@gmail.com> - 2022-05-30 21:32 -0700
                Re: Reliability of electronics Phil Allison <pallison49@gmail.com> - 2022-05-30 21:26 -0700

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