OC45 transistors - UK

G

Gary Cavie

Guest
I am currently going 'back to the future' with my son, in that I'm
helping him build a radio using the Ladybird 'Making a Transistor Radio'
book. The transistors used in are OC45 and OC71s - I've got hold of the
'71s, but am having real trouble trying to find a source for the '45s.
Does anybody have any suggestions where I might get hold of some (2)?

Also in the search is the variable capacitor, which is 500pF, about 2.5
inches long, by about 1.25 inches high, and about 1/4 inch thick - if
you've ever seen the book, you'll know the one I mean! I could use a
modern one, and re-jog the coil to suit, but it would be nice to keep the
components the same if possible.

Many thanks

Gary
 
"Gary Cavie" <m0jjh@despammed.com> wrote in message
news:MPG.19af48015bba84d29896a7@news.freeserve.com...
I am currently going 'back to the future' with my son, in that I'm
helping him build a radio using the Ladybird 'Making a Transistor Radio'
book. The transistors used in are OC45 and OC71s - I've got hold of the
'71s, but am having real trouble trying to find a source for the '45s.
Does anybody have any suggestions where I might get hold of some (2)?

Also in the search is the variable capacitor, which is 500pF, about 2.5
inches long, by about 1.25 inches high, and about 1/4 inch thick - if
you've ever seen the book, you'll know the one I mean! I could use a
modern one, and re-jog the coil to suit, but it would be nice to keep the
components the same if possible.

Many thanks

Gary
Gary
Click to expand...
I remember that book, in fact I recently found my old copy at my parents'
place.
The OC45 is near impossible to source, I would guess that ebay might turn
something up with a LOT of luck; your best bet would probably be to locate
an old radio repair shop that's been in business since the '60s (precious
few of these left, sadly) and see if they've got any old stock; I bet 1000s
of these have been dumped in the last 10 -15 years. I think you'll have the
same problem with the tuner cap also.
I would guess that the only other way to get these parts now would be to
dismantle an old radio (from a car boot or jumble sale), but that would be
sacrilege!
Best of luck,
Martin.

--
martin<dot here>whybrow<at here>ntlworld<dot here>com
 
In article <U6e1b.1340$L15.745@newsfep4-winn.server.ntli.net>,
a_hole_in_the_ground@ntlworld.com mentioned...
"Gary Cavie" <m0jjh@despammed.com> wrote in message
news:MPG.19af48015bba84d29896a7@news.freeserve.com...
I am currently going 'back to the future' with my son, in that I'm
helping him build a radio using the Ladybird 'Making a Transistor Radio'
book. The transistors used in are OC45 and OC71s - I've got hold of the
'71s, but am having real trouble trying to find a source for the '45s.
Does anybody have any suggestions where I might get hold of some (2)?

Also in the search is the variable capacitor, which is 500pF, about 2.5
inches long, by about 1.25 inches high, and about 1/4 inch thick - if
you've ever seen the book, you'll know the one I mean! I could use a
modern one, and re-jog the coil to suit, but it would be nice to keep the
components the same if possible.

Many thanks

Gary
Gary
I remember that book, in fact I recently found my old copy at my parents'
place.
The OC45 is near impossible to source, I would guess that ebay might turn
something up with a LOT of luck; your best bet would probably be to locate
an old radio repair shop that's been in business since the '60s (precious
few of these left, sadly) and see if they've got any old stock; I bet 1000s
of these have been dumped in the last 10 -15 years. I think you'll have the
same problem with the tuner cap also.
I would guess that the only other way to get these parts now would be to
dismantle an old radio (from a car boot or jumble sale), but that would be
sacrilege!
Best of luck,
Martin.
Click to expand...
Yeah, shame. I don't know what the specs are for the OC-45, but
nowadays just about any silicon transistor would run rings around it.
So just use a PNP silicon, and if the bias resistors' ratio are set to
g ive .2V, change the ratio to give .6V. If it's a single bias
resistor, then you might not need to make any changes.

It would be nice to see a schematic. We could give you a bit of
advice to get it running with more modern parts.

BTW, NTE still sells germanium transistors, try www.nteinc.com.
Search for OC45 at
http://nte01.nteinc.com/nte/NTExRefSemiProd.nsf/$$Search?OpenForm


--
@@F@r@o@m@@O@r@a@n@g@e@@C@o@u@n@t@y@,@@C@a@l@,@@w@h@e@r@e@@
###Got a Question about ELECTRONICS? Check HERE First:###
http://users.pandora.be/educypedia/electronics/databank.htm
My email address is whitelisted. *All* email sent to it
goes directly to the trash unless you add NOSPAM in the
Subject: line with other stuff. alondra101 <at> hotmail.com
Don't be ripped off by the big book dealers. Go to the URL
that will give you a choice and save you money(up to half).
http://www.everybookstore.com You'll be glad you did!
Just when you thought you had all this figured out, the gov't
changed it: http://physics.nist.gov/cuu/Units/binary.html
@@t@h@e@@a@f@f@l@u@e@n@t@@m@e@e@t@@t@h@e@@E@f@f@l@u@e@n@t@@
 
In article <MPG.19b002f4e2136ecf989c20@news.inreach.net>,
alondra101@hotmail.com says...
In article <U6e1b.1340$L15.745@newsfep4-winn.server.ntli.net>,
a_hole_in_the_ground@ntlworld.com mentioned...

"Gary Cavie" <m0jjh@despammed.com> wrote in message
news:MPG.19af48015bba84d29896a7@news.freeserve.com...
I am currently going 'back to the future' with my son, in that I'm
helping him build a radio using the Ladybird 'Making a Transistor Radio'
book. The transistors used in are OC45 and OC71s - I've got hold of the
'71s, but am having real trouble trying to find a source for the '45s.
Does anybody have any suggestions where I might get hold of some (2)?

Also in the search is the variable capacitor, which is 500pF, about 2.5
inches long, by about 1.25 inches high, and about 1/4 inch thick - if
you've ever seen the book, you'll know the one I mean! I could use a
modern one, and re-jog the coil to suit, but it would be nice to keep the
components the same if possible.

Many thanks

Gary
Gary
I remember that book, in fact I recently found my old copy at my parents'
place.
The OC45 is near impossible to source, I would guess that ebay might turn
something up with a LOT of luck; your best bet would probably be to locate
an old radio repair shop that's been in business since the '60s (precious
few of these left, sadly) and see if they've got any old stock; I bet 1000s
of these have been dumped in the last 10 -15 years. I think you'll have the
same problem with the tuner cap also.
I would guess that the only other way to get these parts now would be to
dismantle an old radio (from a car boot or jumble sale), but that would be
sacrilege!
Best of luck,
Martin.

Yeah, shame. I don't know what the specs are for the OC-45, but
nowadays just about any silicon transistor would run rings around it.
So just use a PNP silicon, and if the bias resistors' ratio are set to
g ive .2V, change the ratio to give .6V. If it's a single bias
resistor, then you might not need to make any changes.

It would be nice to see a schematic. We could give you a bit of
advice to get it running with more modern parts.

BTW, NTE still sells germanium transistors, try www.nteinc.com.
Search for OC45 at
http://nte01.nteinc.com/nte/NTExRefSemiProd.nsf/$$Search?OpenForm
Click to expand...
Thanks for the link - browsing it at the moment. I've had a reply via
email from somebody who has a couple that they're prepared to send me -
all I need to do now is find the VC - which I feel slightly more
confident about, as Maplins IIRC were still selling them up to 3-4 years
ago
 
On Fri, 22 Aug 2003 02:12:22 +0100, Martin Whybrow wrote:

The OC45 is near impossible to source
Click to expand...
And if you find any, they'll leak like sieves. Most old germanium stock
is starting to show problems, now.

The OC45 is interesting in that it was one of the first transistors to
have a low enough feedback capacitance so as not to need neutralization.
Saved quite a lot of money on cheapo radio designs.

--
Then there's duct tape ...
(Garrison Keillor)
nofr@sbhevre.pbzchyvax.pb.hx
 
On Sun, 24 Aug 2003 04:37:20 +0100, Watson A.Name - 'Watt Sun' wrote:


I'm wondering if, when you say "Most old germanium stock", you mean most
old stock of OC45s, or most old stock of any germanium transistors. I'm
thinking that the euro makers used the glass cases on germanium
transistors, and they weren't hermetically sealed. The standard TO-5
metal case used on most JEDEC germanium transistors is hermetically
sealed, so there should be no contamination after several decades. Same
with most other metal cased germaniums.
Click to expand...
Just that, most old germanium stock. It isn't atmospheric contamination,
it's doping migrating in the slice. Remember that germanium transistors
used fairly primitive alloying techniques.


So what's an equivalent replacement in silicon?
Click to expand...
Good question, OC45 was 15V, 12mA with an ft of 4MHz (wow!) and Hfe 50.
Cob was 12pF.

You'll need to play with biasing arrangements. you can't usually just
drop a silicon replacement in. PNP silicon with suitable characteristics
will need a bit of research.

Try a 2N3906, and push the value of the emitter resistor up if it
oscillates. If that doesn't work, you're on your own :)

Hell, it's only a crummy 455KHz IF, isn't it?

--
Then there's duct tape ...
(Garrison Keillor)
nofr@sbhevre.pbzchyvax.pb.hx
 
In article <pan.2003.08.24.15.41.12.386027.4925@cerebrumconfus.it>,
excretatauris@cerebrumconfus.it mentioned...
On Sun, 24 Aug 2003 04:37:20 +0100, Watson A.Name - 'Watt Sun' wrote:


I'm wondering if, when you say "Most old germanium stock", you mean most
old stock of OC45s, or most old stock of any germanium transistors. I'm
thinking that the euro makers used the glass cases on germanium
transistors, and they weren't hermetically sealed. The standard TO-5
metal case used on most JEDEC germanium transistors is hermetically
sealed, so there should be no contamination after several decades. Same
with most other metal cased germaniums.


Just that, most old germanium stock. It isn't atmospheric contamination,
it's doping migrating in the slice. Remember that germanium transistors
used fairly primitive alloying techniques.


So what's an equivalent replacement in silicon?

Good question, OC45 was 15V, 12mA with an ft of 4MHz (wow!) and Hfe 50.
Cob was 12pF.

You'll need to play with biasing arrangements. you can't usually just
drop a silicon replacement in. PNP silicon with suitable characteristics
will need a bit of research.

Try a 2N3906, and push the value of the emitter resistor up if it
oscillates. If that doesn't work, you're on your own :)

Hell, it's only a crummy 455KHz IF, isn't it?
Click to expand...
Yeah, I think the problem will be getting the AGC to work right.
That's what the germaniums had to do.

I had an old Heathkit handheld CB walkie-talkie, and I played around
with the transistors in it. It didn't work out very well. The
'improvements' I made didn't improve things.

--
@@F@r@o@m@@O@r@a@n@g@e@@C@o@u@n@t@y@,@@C@a@l@,@@w@h@e@r@e@@
###Got a Question about ELECTRONICS? Check HERE First:###
http://users.pandora.be/educypedia/electronics/databank.htm
My email address is whitelisted. *All* email sent to it
goes directly to the trash unless you add NOSPAM in the
Subject: line with other stuff. alondra101 <at> hotmail.com
Don't be ripped off by the big book dealers. Go to the URL
that will give you a choice and save you money(up to half).
http://www.everybookstore.com You'll be glad you did!
Just when you thought you had all this figured out, the gov't
changed it: http://physics.nist.gov/cuu/Units/binary.html
@@t@h@e@@a@f@f@l@u@e@n@t@@m@e@e@t@@t@h@e@@E@f@f@l@u@e@n@t@@
 
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