Vintage transistors and tin whiskers...

[Cursitor Doom]

Gentlemen,

I have some old OC171 transistors from an old Eddystone short wave radio
I\'m restoring. The problem is I suspect they\'ve developed whiskers, as
the resistance readings from e,c and b to the screen connection are all
far too low (sub 10 ohms). A colleague has suggested blasting the
whiskers by tying the ecb leads together and zapping them against the
screen with a 500nF cap charged to 500VDC. Now this seems a bit counter-
intuitive to me and I\'d have thought higher current lower voltage would
be safer for these delicate germanium devices, but WTF do I know?
Is it feasible to remove the whiskers by this sort of method or any other?

Thanks,

CD

 

[server]

Cursitor Doom <cd@not4mail.com> wrote in
news:r9rgu3$h74$1@dont-email.me:

Gentlemen,

I have some old OC171 transistors from an old Eddystone short wave
radio I\'m restoring. The problem is I suspect they\'ve developed
whiskers, as the resistance readings from e,c and b to the screen
connection are all far too low (sub 10 ohms). A colleague has
suggested blasting the whiskers by tying the ecb leads together
and zapping them against the screen with a 500nF cap charged to
500VDC. Now this seems a bit counter- intuitive to me and I\'d have
thought higher current lower voltage would be safer for these
delicate germanium devices, but WTF do I know? Is it feasible to
remove the whiskers by this sort of method or any other?

Thanks,

CD

Put it in your ten below freezer for an hour and let the cold
disintegrate the non alloyed tin.

Then give it a nice hard rap to break it all loosed like we used to
do to the old tube type TVs to get them going again.

Kidding of course... except for the TV thing. That worked. So
did taking the back off it and re-seating all the socketed tubes and
components. Worked every time. It is almost always a mechanical
connection.

 

[Pimpom]

On 5/17/2020 7:45 PM, Cursitor Doom wrote:

Gentlemen,

I have some old OC171 transistors from an old Eddystone short wave radio
I\'m restoring. The problem is I suspect they\'ve developed whiskers, as
the resistance readings from e,c and b to the screen connection are all
far too low (sub 10 ohms). A colleague has suggested blasting the
whiskers by tying the ecb leads together and zapping them against the
screen with a 500nF cap charged to 500VDC. Now this seems a bit counter-
intuitive to me and I\'d have thought higher current lower voltage would
be safer for these delicate germanium devices, but WTF do I know?
Is it feasible to remove the whiskers by this sort of method or any other?

Thanks,

CD

I don\'t know about the whiskers but Ge transistors have high
leakage and no sharp knee at low currents. I wonder if 10 ohms is
too low depending on the voltage applied by your meter. I have a
few of the later AC188 types. I\'ll dig them up tomorrow and
measure their resistances.

For quick go-no go checks of transistors, I prefer analog MMs.
The static forward resistance depends highly on the current
applied through the probes.

I used to have some OC71s and OC72s a long time ago. They made
neat phototransistors with the paint scraped off from their glass
enclosures.

 

[Pimpom]

On 5/17/2020 8:26 PM, Pimpom wrote:

On 5/17/2020 7:45 PM, Cursitor Doom wrote:
Gentlemen,

I have some old OC171 transistors from an old Eddystone short wave radio
I\'m restoring. The problem is I suspect they\'ve developed whiskers, as
the resistance readings from e,c and b to the screen connection are all
far too low (sub 10 ohms). A colleague has suggested blasting the
whiskers by tying the ecb leads together and zapping them against the
screen with a 500nF cap charged to 500VDC. Now this seems a bit counter-
intuitive to me and I\'d have thought higher current lower voltage would
be safer for these delicate germanium devices, but WTF do I know?
Is it feasible to remove the whiskers by this sort of method or any other?

Thanks,

CD

I don\'t know about the whiskers but Ge transistors have high
leakage and no sharp knee at low currents. I wonder if 10 ohms is
too low depending on the voltage applied by your meter. I have a
few of the later AC188 types. I\'ll dig them up tomorrow and
measure their resistances.

For quick go-no go checks of transistors, I prefer analog MMs.
The static forward resistance depends highly on the current
applied through the probes.

I used to have some OC71s and OC72s a long time ago. They made
neat phototransistors with the paint scraped off from their glass
enclosures.

OK, I got the AC188s. With a DMM they measure 25-50 ohms forward
and a few Ks in the reverse direction.

 

[Cursitor Doom]

On Sun, 17 May 2020 21:06:23 +0530, Pimpom wrote:

I used to have some OC71s and OC72s a long time ago. They made neat
phototransistors with the paint scraped off from their glass
enclosures.

OK, I got the AC188s. With a DMM they measure 25-50 ohms forward and a
few Ks in the reverse direction.

I think you\'ve misunderstood the problem here, Pimpom. The leakage in
question is between the case (\"screen\") and the die and significantly pre-
date the black-painted phototransistors we all fondly recall from 50
years ago.

 

[Pimpom]

On 5/17/2020 10:04 PM, Cursitor Doom wrote:

On Sun, 17 May 2020 21:06:23 +0530, Pimpom wrote:

I used to have some OC71s and OC72s a long time ago. They made neat
phototransistors with the paint scraped off from their glass
enclosures.

OK, I got the AC188s. With a DMM they measure 25-50 ohms forward and a
few Ks in the reverse direction.

I think you\'ve misunderstood the problem here, Pimpom. The leakage in
question is between the case (\"screen\") and the die and significantly pre-
date the black-painted phototransistors we all fondly recall from 50
years ago.

Ah, sorry. Then those low-ohm figures can\'t be normal.

My dad bought a Sony transistor radio in the early 60s. I
remember that it used Japanese Ge transistors like 2SA12, 2SA15
for RF and 2SB75 and 2SB77 for audio. One of my regrets in life
is that I never got around to restoring it when he was still
alive. This is the model -
https://priceguide.thecollector.com.au/wp-content/gallery/auction-928/1960s-Sony-TR-812-allwave-transistor-radio-Sold-for-56-2019.jpg

 

[Adrian Tuddenham]

Cursitor Doom <cd@not4mail.com> wrote:

Gentlemen,

I have some old OC171 transistors from an old Eddystone short wave radio
I\'m restoring. The problem is I suspect they\'ve developed whiskers, as
the resistance readings from e,c and b to the screen connection are all
far too low (sub 10 ohms). A colleague has suggested blasting the
whiskers by tying the ecb leads together and zapping them against the
screen with a 500nF cap charged to 500VDC. Now this seems a bit counter-
intuitive to me and I\'d have thought higher current lower voltage would
be safer for these delicate germanium devices, but WTF do I know?
Is it feasible to remove the whiskers by this sort of method or any other?

I have had some success with an Eddystone EB35 by replacing them with
silicon transistors and adjusting the base bias to get approximately the
same collector current.

(I was a tester on the production line at Eddystones when EB35s were
going through, so I am the one to blame if they don\'t meet spec.)


--
~ Adrian Tuddenham ~
(Remove the \".invalid\"s and add \".co.uk\" to reply)
www.poppyrecords.co.uk

 

[Michael Terrell]

On Sunday, May 17, 2020 at 10:15:34 AM UTC-4, Cursitor Doom wrote:

Gentlemen,

I have some old OC171 transistors from an old Eddystone short wave radio
I\'m restoring. The problem is I suspect they\'ve developed whiskers, as
the resistance readings from e,c and b to the screen connection are all
far too low (sub 10 ohms). A colleague has suggested blasting the
whiskers by tying the ecb leads together and zapping them against the
screen with a 500nF cap charged to 500VDC. Now this seems a bit counter-
intuitive to me and I\'d have thought higher current lower voltage would
be safer for these delicate germanium devices, but WTF do I know?
Is it feasible to remove the whiskers by this sort of method or any other?

If the Tin Man in the Wizzard of Oz tried to grow a beard, they would be really big tin whiskers. ;-)

 

[abrsvc]

On Sunday, May 17, 2020 at 10:15:34 AM UTC-4, Cursitor Doom wrote:

Gentlemen,

I have some old OC171 transistors from an old Eddystone short wave radio
I\'m restoring. The problem is I suspect they\'ve developed whiskers, as
the resistance readings from e,c and b to the screen connection are all
far too low (sub 10 ohms). A colleague has suggested blasting the
whiskers by tying the ecb leads together and zapping them against the
screen with a 500nF cap charged to 500VDC. Now this seems a bit counter-
intuitive to me and I\'d have thought higher current lower voltage would
be safer for these delicate germanium devices, but WTF do I know?
Is it feasible to remove the whiskers by this sort of method or any other?

Thanks,

CD

I have 4 ECG160 transistors (2 that are unused and 2 that look like they may have been used to test something). Send me your address and I\'ll send them along if you think that these will resolve your problem. I doubt that I will ever use these.

Dan

 

[Cursitor Doom]

On Mon, 18 May 2020 05:43:18 -0700, abrsvc wrote:

I have 4 ECG160 transistors (2 that are unused and 2 that look like they
may have been used to test something). Send me your address and I\'ll
send them along if you think that these will resolve your problem. I
doubt that I will ever use these.

Thanks for the advice and offers of parts, guys; much appreciated. On
reflection I decided to replace with silicon. The purists would go to the
trouble of hollowing out the old transitors and fitting the silicons
inside them. Fortunately, I\'m no purist. :-D

 

[Cursitor Doom]

On Mon, 18 May 2020 05:43:18 -0700, abrsvc wrote:

I have 4 ECG160 transistors (2 that are unused and 2 that look like they
may have been used to test something). Send me your address and I\'ll
send them along if you think that these will resolve your problem. I
doubt that I will ever use these.

Thanks for the advice and offers of parts, guys; much appreciated. On
reflection I decided to replace with silicon. The purists would go to the
trouble of hollowing out the old transitors and fitting the silicons
inside them. Fortunately, I\'m no purist. :-D

 

[Brian Gregory]

On 18/05/2020 12:59, Adrian Tuddenham wrote:

I have had some success with an Eddystone EB35 by replacing them with
silicon transistors and adjusting the base bias to get approximately the
same collector current.

And if something starts oscillating because you have too much gain with
the silicon replacements then adding a low value R in series with their
emitters will usually fix.

--
Brian Gregory (in England).

 

[Brian Gregory]

On 18/05/2020 12:59, Adrian Tuddenham wrote:

I have had some success with an Eddystone EB35 by replacing them with
silicon transistors and adjusting the base bias to get approximately the
same collector current.

And if something starts oscillating because you have too much gain with
the silicon replacements then adding a low value R in series with their
emitters will usually fix.

--
Brian Gregory (in England).

 

[abrsvc]

On Tuesday, May 19, 2020 at 1:43:26 PM UTC-4, Cursitor Doom wrote:

On Mon, 18 May 2020 05:43:18 -0700, abrsvc wrote:

I have 4 ECG160 transistors (2 that are unused and 2 that look like they
may have been used to test something). Send me your address and I\'ll
send them along if you think that these will resolve your problem. I
doubt that I will ever use these.

Thanks for the advice and offers of parts, guys; much appreciated. On
reflection I decided to replace with silicon. The purists would go to the
trouble of hollowing out the old transitors and fitting the silicons
inside them. Fortunately, I\'m no purist. :-D

No problems here. If you want to use the ECGs to verify that everything works prior to \"upgrading\" to Si, the parts are available. These are small enough that they will fit into a small padded envelope, so shipping will be next to nothing.

Let me know if you want them (no charge).
Dan

 

[abrsvc]

On Tuesday, May 19, 2020 at 1:43:26 PM UTC-4, Cursitor Doom wrote:

On Mon, 18 May 2020 05:43:18 -0700, abrsvc wrote:

I have 4 ECG160 transistors (2 that are unused and 2 that look like they
may have been used to test something). Send me your address and I\'ll
send them along if you think that these will resolve your problem. I
doubt that I will ever use these.

Thanks for the advice and offers of parts, guys; much appreciated. On
reflection I decided to replace with silicon. The purists would go to the
trouble of hollowing out the old transitors and fitting the silicons
inside them. Fortunately, I\'m no purist. :-D

No problems here. If you want to use the ECGs to verify that everything works prior to \"upgrading\" to Si, the parts are available. These are small enough that they will fit into a small padded envelope, so shipping will be next to nothing.

Let me know if you want them (no charge).
Dan

 

[Cursitor Doom]

On Tue, 19 May 2020 17:23:37 -0700, abrsvc wrote:

No problems here. If you want to use the ECGs to verify that everything
works prior to \"upgrading\" to Si, the parts are available. These are
small enough that they will fit into a small padded envelope, so
shipping will be next to nothing.

Let me know if you want them (no charge).
Dan

Thanks Dan, much appreciated.

 

[Cursitor Doom]

On Tue, 19 May 2020 17:23:37 -0700, abrsvc wrote:

No problems here. If you want to use the ECGs to verify that everything
works prior to \"upgrading\" to Si, the parts are available. These are
small enough that they will fit into a small padded envelope, so
shipping will be next to nothing.

Let me know if you want them (no charge).
Dan

Thanks Dan, much appreciated.

 

[Adrian Tuddenham]

Brian Gregory <void-invalid-dead-dontuse@gmail.com> wrote:

On 18/05/2020 12:59, Adrian Tuddenham wrote:
I have had some success with an Eddystone EB35 by replacing them with
silicon transistors and adjusting the base bias to get approximately the
same collector current.

And if something starts oscillating because you have too much gain with
the silicon replacements then adding a low value R in series with their
emitters will usually fix.

There are already emitter resistors, but they are bypassed, so adding
resistance in series with the bypass capacitors (or removing them
altogether) would be the way to go.

I used fairly mundane silicon transistors with a lowish cutoff frequency
and didn\'t have any trouble.


--
~ Adrian Tuddenham ~
(Remove the \".invalid\"s and add \".co.uk\" to reply)
www.poppyrecords.co.uk

 

[Phil Hobbs]

On 2020-05-20 10:40, Adrian Tuddenham wrote:

Brian Gregory <void-invalid-dead-dontuse@gmail.com> wrote:

On 18/05/2020 12:59, Adrian Tuddenham wrote:
I have had some success with an Eddystone EB35 by replacing them with
silicon transistors and adjusting the base bias to get approximately the
same collector current.

And if something starts oscillating because you have too much gain with
the silicon replacements then adding a low value R in series with their
emitters will usually fix.

There are already emitter resistors, but they are bypassed, so adding
resistance in series with the bypass capacitors (or removing them
altogether) would be the way to go.

I used fairly mundane silicon transistors with a lowish cutoff frequency
and didn\'t have any trouble.

Retrofitting germanium transistor circuits can be tricky, especially the
ones where they rely on the apparent beta being negative, i.e. the CB
leakage being larger than I_C/(true beta).

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com

 

[Adrian Tuddenham]

Brian Gregory <void-invalid-dead-dontuse@gmail.com> wrote:

On 18/05/2020 12:59, Adrian Tuddenham wrote:
I have had some success with an Eddystone EB35 by replacing them with
silicon transistors and adjusting the base bias to get approximately the
same collector current.

And if something starts oscillating because you have too much gain with
the silicon replacements then adding a low value R in series with their
emitters will usually fix.

There are already emitter resistors, but they are bypassed, so adding
resistance in series with the bypass capacitors (or removing them
altogether) would be the way to go.

I used fairly mundane silicon transistors with a lowish cutoff frequency
and didn\'t have any trouble.


--
~ Adrian Tuddenham ~
(Remove the \".invalid\"s and add \".co.uk\" to reply)
www.poppyrecords.co.uk