20 Sep
2010
20 Sep
'10
6:07 p.m.
On 2010 Sep 20, at 3:15 PM, Dave McGuire wrote:
On 9/20/10 2:49 PM, Brent Hilpert wrote:
TO-99 709s are difficult to find, but not impossible. For most
applications I believe a 741 can be used as a drop-in replacement for
a 709; this being a voltage regulator I'd guess it probably isn't all
that demanding on the 709's particular specifications.
It wouldn't be 100% historically correct, but if you think about it,
that would likely have been a reasonable repair method during this
machine's service lifetime.
I'd say do it.
The 741 was well available by the time of the Altos introduction, and
simpler to use than the 709. Mildly surprising to hear the Altos used
the 709, perhaps the 741 was still a fair bit more expensive.
Pins 1 & 5 (TO-99) connect to external compensation components on the
709, they are for offset null on the 741. One should probably snip off
or leave open those pins if replacing a 709 with a 741.
I think I have one 709 in TO-99 from my first op-amp project (a
square-wave generator) ca 1972.
Was a
great time and really a blast to dig into the Alto. We
definitely
improvised, not having a stock of uA709 opamp on hand... we just
bypassed
that regulator circuit and stuck a 7805 there instead, which was
pilfered
from Vince Briel's spare parts stock for his Altair8800micro kits.
Too much fun.
If the 709 was a TO-99 (can) package and you need to replace it, I
have
lots of 741's in TO-99.
Just mentioning it in case it is difficult to find a 709 in TO-99.
(DIP
should be easy to find something to substitute.)