fewer through-hole transistors available

"Jon Elson" <jmelson@wustl.edu> wrote in message
news:B46dnd2UOdMJpjvFnZ2dnUU7-cXNnZ2d@giganews.com...
dansabrservices@yahoo.com wrote:

Jon,

You have spoken of generic issues and some specs for a replacement. What
was the original part number? Perhaps there are existing substitutions
available.

Dan
The part on the board was a Fairchild FMT1190. The part on the schematic
was an A430, which I can't even find a datasheet for.
Click to expand...

Was it PNP - could start with 2SA....
 
"Phil Hobbs" <pcdhSpamMeSenseless@electrooptical.net> wrote in message
news:0OadnXHO3KuahDrFnZ2dnUU7-T2dnZ2d@supernews.com...
On 02/16/2017 12:46 PM, Clifford Heath wrote:
On 17/02/17 09:03, Dave Platt wrote:
I was repairing a piece of old equipment, and needed a replacement RF
transistor. Checking at Digi-Key, I found very thin pickings, so i
checked
a few other distributors, and found the same situation. They seemed
to have
a modest choice of SMT transistors, but REALLY thin variety in T0-92
and
similar plastic packages. Not a good sign, as we have a lot of 30 -
40 year
old nuclear instrumentation here.

Yup. The last five years or so have been dire times for through-hole
semiconductors. A lot of the popular parts are now gone, past the
end of the "lifetime buy" cycle from their original manufacturers.

I've been trying to stock up my own (hobbyist-level) supplies of
useful TO-92 transistors...

Why? You're not doing production if 100 is lifetime. If it's for
prototyping, why not just learn to prototype in SMT? It's not that
hard. A lot of RF things are easier because stuff is physically
smaller.

SMT prototyping is about a factor of 10 slower than dead bug using
through-hole parts. Every DIP package gets you a bunch of nice strong
standoffs.
Click to expand...

I regularly include SMD parts in dead-bug prototypes. With a bit of thought
and planning they can reduce wire links instead of increasing them, they
also tend toward adding rigidity to the assembly.
 
"Michael Black" <et472@ncf.ca> wrote in message
news:alpine.LNX.2.02.1702171429360.15904@darkstar.example.org...
On Fri, 17 Feb 2017, Jon Elson wrote:

Dave Platt wrote:


Thinking about it... I wonder whether those poor old transistors might
not just have been Plumb Tuckered Out?
Yes, that is another possibility I considered. If the module had been in
use for a long time, with no cooling, these are the highest power
dissipation of all the signal transistors in the unit. Always on at 23
mA.

I repaired an HP synthesizer that had about 400 Germanium transistors in
it,
and about a dozen had failed. I replaced them with Silicon transistors
and
then sold it on eBay before any more units went out.

I thought germanium transistors in general had a tendency to go bad over
time. They'd start leaking. Maybe manufacturing improved over time, but
then at some point, silicon took over completely, except for a handful of
uses. So you can't easily get replacements, because few germanium devices
are made now.
Click to expand...

In the very early days, germanium transistors were epoxy potted - it wasn't
very moisture proof.

They've been much better since hermetically sealed metal cans.

If you're used to silicon, the leakage on germanium devices is going to seem
pretty dire anyway.
 
"Phil Hobbs" <pcdhSpamMeSenseless@electrooptical.net> wrote in message
news:kPmdnSfq3aVxizrFnZ2dnUU7-cGdnZ2d@supernews.com...
On 02/16/2017 02:57 PM, Jon Elson wrote:
I was repairing a piece of old equipment, and needed a replacement RF
transistor. Checking at Digi-Key, I found very thin pickings, so i
checked
a few other distributors, and found the same situation. They seemed to
have
a modest choice of SMT transistors, but REALLY thin variety in T0-92 and
similar plastic packages. Not a good sign, as we have a lot of 30 - 40
year
old nuclear instrumentation here.

Another issue is the circuit is a differential NPN pair set up as a one-
shot. So, it was running about 23 mA through one transistor at idle, and
all of these on-at-idle transistors have failed. (The other transistors
in
the pairs seem fine.) The part actually in the unit is an FMT1190, which
certainly seems like it should have been able to handle that current
long-
term. After replacing it with the best thing I could find, the
transistor
only has about 2V C-E, so the power dissipation is less than 50 mW,
shouldn't have burned them out. I'm wondering if somehow the startup
condition exceeded the base ratings.

Anyway, I'll replace the transistors and burn it in for a while and see
if
it gives any more trouble.

Jon


A whole lot of TO92s went away in the last couple of years. I bought
several thousand as a lifetime prototyping supply.
Click to expand...

What I've harvested from scrap gear should last some time yet.
 
On 02/17/2017 03:55 PM, Benderthe.evilrobot wrote:
"Phil Hobbs" <pcdhSpamMeSenseless@electrooptical.net> wrote in message
news:0OadnXHO3KuahDrFnZ2dnUU7-T2dnZ2d@supernews.com...
On 02/16/2017 12:46 PM, Clifford Heath wrote:
On 17/02/17 09:03, Dave Platt wrote:
I was repairing a piece of old equipment, and needed a replacement RF
transistor. Checking at Digi-Key, I found very thin pickings, so i
checked
a few other distributors, and found the same situation. They seemed
to have
a modest choice of SMT transistors, but REALLY thin variety in
T0-92 and
similar plastic packages. Not a good sign, as we have a lot of 30 -
40 year
old nuclear instrumentation here.

Yup. The last five years or so have been dire times for through-hole
semiconductors. A lot of the popular parts are now gone, past the
end of the "lifetime buy" cycle from their original manufacturers.

I've been trying to stock up my own (hobbyist-level) supplies of
useful TO-92 transistors...

Why? You're not doing production if 100 is lifetime. If it's for
prototyping, why not just learn to prototype in SMT? It's not that
hard. A lot of RF things are easier because stuff is physically
smaller.

SMT prototyping is about a factor of 10 slower than dead bug using
through-hole parts. Every DIP package gets you a bunch of nice strong
standoffs.

I regularly include SMD parts in dead-bug prototypes. With a bit of
thought and planning they can reduce wire links instead of increasing
them, they also tend toward adding rigidity to the assembly.
Click to expand...

Sure, me too. I disagree about rigidity though. RN60C resistors are
pretty rigid. ;)

I've recently done a mid-air proto using 0402s--like five in a row in
mid air--but that was a 100-ps sampler, so it was worth the trouble.
Ordinary dead bug is good to 1 GHz or so, and it's a lot easier.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics

160 North State Road #203
Briarcliff Manor NY 10510

hobbs at electrooptical dot net
http://electrooptical.neth
 
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