"Trevor Wilson"

**Back in the 1970s, I worked on a lot of Marantz products (as the
Australian service manager). Back then, there were a couple of Japanese
suppliers and one US supplier of output devices for Marantz products. The
US supplier was Motorola and their devices were in the, now infamous,
aluminium TO3 cases.

** Infamous ??

That IS putting it a bit strongly !!

FYI:

1. Motorola chips were never bonded direct to Aluminium ( or steel) - but
instead to a small copper alloy slug that sat in a depression in the base of
the Al pack. Solder like material held the chip to the slug and the slug to
the base metal.

( Steel devices have a rather large copper slug that sits on top of the
thin base. )

2. I must have cut a hundred or more TO3 devices open ( mostly Motorola ) to
see the internal construction and identify fakes.


The Japs were supplied in (usually) copper cases, though some may have
been steel. The Motorola devices were far less reliable than the Japanese
ones.

** For some reason other than the one you are crapping on about.


About that time, I read a white paper published by RCA where it was
claimed that their steel TO3 cases could provide more than 1 million
hot/cold cycles without failure, whereas the aluminium cases used by
Motorola could only sustain 100,000 hot/cold cycles.

** I think you have moved the decimal point one place to the right.

HOWEVER a "hot / cold cycle " is one where the chip goes from room temp to
rated max - so would be a rare event in a domestic hi-fi amp.

( Different story for a linear regulated PSU or pro audio amplifiers )

Early plastic packs could only manage around 10,000 cycles. Anecdotal
evidence and chatting to a couple of people in the industry seemed to bear
this out.

** Gossip is very cheap.

And every plastic power device I have ever seen uses a copper heatsinking
base.


..... Phil