Simple audio amp design...

[Cursitor Doom]

Greetings, gentlemen,

I have a vintage MW/LW/SW 12V battery-powered radio I picked up recently
at a yard sale. Being 50 years old, however, it has a few faults and
needs realignment and whatnot. Before I can proceed with that, I\'ve
discovered that the transistors it uses (mostly obsolete germanium
devices) suffer from tin whiskers so I will need to re-jig the board so
they can be replaced with silicon ones instead. The design is very
simple so it *shouldn\'t* be a big deal. The bias requirements are of
course different between germaniums and silicons so perhaps it would be
better to start from scratch? I want to remain faithful to the original,
simple design ethos with its five discrete transistors whatever I do.
Any suggestions?

Here\'s the schematic:

https://disk.yandex.com/i/a2xX6_IadjbgIw

CD.

 

[Jan Panteltje]

On a sunny day (Sun, 19 Dec 2021 12:40:16 +0000) it happened Cursitor Doom
<cd@notformail.com> wrote in <spn97h$rou$1@dont-email.me>:

Greetings, gentlemen,

I have a vintage MW/LW/SW 12V battery-powered radio I picked up recently
at a yard sale. Being 50 years old, however, it has a few faults and
needs realignment and whatnot. Before I can proceed with that, I\'ve
discovered that the transistors it uses (mostly obsolete germanium
devices) suffer from tin whiskers so I will need to re-jig the board so
they can be replaced with silicon ones instead. The design is very
simple so it *shouldn\'t* be a big deal. The bias requirements are of
course different between germaniums and silicons so perhaps it would be
better to start from scratch? I want to remain faithful to the original,
simple design ethos with its five discrete transistors whatever I do.
Any suggestions?

Here\'s the schematic:

https://disk.yandex.com/i/a2xX6_IadjbgIw

That is a classical audio amp.
Apart from I have never had a transistor fail due to \'tin whiskers\',
if you replace ALL of those transistors with Si
then T2 R7/R8 will also change the bias to the output stage to 2 x Vbe, then 2 x .7V.
It should simply work.
But maybe you should increase R3 by 2 or more times or so to get enough bias for T3.

Or simply replace it with a LM380 or LM386!

Better even: Buy a nice Tecsun PL600 all band radio,
but... I bought one in 2014 for 60$, now I see them for 266$ on ebay!

Or the TECSUN PL660, perhaps, about 100$ on ebay.
Seems the PL600 is no longer made, and the 660 is the new model.

Do not hang on too much to old stuff.
(that said I hang on to my old analog scope).

 

[Cursitor Doom]

On Sun, 19 Dec 2021 13:05:36 GMT, Jan Panteltje
<pNaOnStPeAlMtje@yahoo.com> wrote:

On a sunny day (Sun, 19 Dec 2021 12:40:16 +0000) it happened Cursitor Doom
cd@notformail.com> wrote in <spn97h$rou$1@dont-email.me>:

Greetings, gentlemen,

I have a vintage MW/LW/SW 12V battery-powered radio I picked up recently
at a yard sale. Being 50 years old, however, it has a few faults and
needs realignment and whatnot. Before I can proceed with that, I\'ve
discovered that the transistors it uses (mostly obsolete germanium
devices) suffer from tin whiskers so I will need to re-jig the board so
they can be replaced with silicon ones instead. The design is very
simple so it *shouldn\'t* be a big deal. The bias requirements are of
course different between germaniums and silicons so perhaps it would be
better to start from scratch? I want to remain faithful to the original,
simple design ethos with its five discrete transistors whatever I do.
Any suggestions?

Here\'s the schematic:

https://disk.yandex.com/i/a2xX6_IadjbgIw

That is a classical audio amp.
Apart from I have never had a transistor fail due to \'tin whiskers\',

Really? The AF117 type in particular (ubiquitous in British broadcast
recievers of the late 1960s) was *notorious* for shorting internally
due to whiskers.

if you replace ALL of those transistors with Si
then T2 R7/R8 will also change the bias to the output stage to 2 x Vbe, then 2 x .7V.
It should simply work.
But maybe you should increase R3 by 2 or more times or so to get enough bias for T3.

Or simply replace it with a LM380 or LM386!

No! No! NO!! No ICs thanks very much! I may even try potting the new
silicon replacements into hollowed- out casings of the Ge devices to
keep it original looking.

Better even: Buy a nice Tecsun PL600 all band radio,
but... I bought one in 2014 for 60$, now I see them for 266$ on ebay!

Or the TECSUN PL660, perhaps, about 100$ on ebay.
Seems the PL600 is no longer made, and the 660 is the new model.

Do not hang on too much to old stuff.

I specialise in old obsolete stuff. I prefer it!

>(that said I hang on to my old analog scope).

I have about 13 of \'em.

 

[Jan Panteltje]

On a sunny day (Sun, 19 Dec 2021 13:21:46 +0000) it happened Cursitor Doom
<cd@notformail.com> wrote in <63curgddjaitboe4872itb788d5i9n1fdg@4ax.com>:

On Sun, 19 Dec 2021 13:05:36 GMT, Jan Panteltje
pNaOnStPeAlMtje@yahoo.com> wrote:

On a sunny day (Sun, 19 Dec 2021 12:40:16 +0000) it happened Cursitor Doom
cd@notformail.com> wrote in <spn97h$rou$1@dont-email.me>:

Greetings, gentlemen,

I have a vintage MW/LW/SW 12V battery-powered radio I picked up recently
at a yard sale. Being 50 years old, however, it has a few faults and
needs realignment and whatnot. Before I can proceed with that, I\'ve
discovered that the transistors it uses (mostly obsolete germanium
devices) suffer from tin whiskers so I will need to re-jig the board so
they can be replaced with silicon ones instead. The design is very
simple so it *shouldn\'t* be a big deal. The bias requirements are of
course different between germaniums and silicons so perhaps it would be
better to start from scratch? I want to remain faithful to the original,
simple design ethos with its five discrete transistors whatever I do.
Any suggestions?

Here\'s the schematic:

https://disk.yandex.com/i/a2xX6_IadjbgIw

That is a classical audio amp.
Apart from I have never had a transistor fail due to \'tin whiskers\',

Really? The AF117 type in particular (ubiquitous in British broadcast
recievers of the late 1960s) was *notorious* for shorting internally
due to whiskers.

if you replace ALL of those transistors with Si
then T2 R7/R8 will also change the bias to the output stage to 2 x Vbe, then 2 x .7V.
It should simply work.
But maybe you should increase R3 by 2 or more times or so to get enough bias for T3.

Or simply replace it with a LM380 or LM386!

No! No! NO!! No ICs thanks very much! I may even try potting the new
silicon replacements into hollowed- out casings of the Ge devices to
keep it original looking.


Better even: Buy a nice Tecsun PL600 all band radio,
but... I bought one in 2014 for 60$, now I see them for 266$ on ebay!

Or the TECSUN PL660, perhaps, about 100$ on ebay.
Seems the PL600 is no longer made, and the 660 is the new model.

Do not hang on too much to old stuff.

I specialise in old obsolete stuff. I prefer it!

(that said I hang on to my old analog scope).

I have about 13 of \'em.

I was so happy when I bought my first PLL radio,
just type in the frequency!

I have always used scopes for fault finding, even worked at Tek.
build my own ones at home.
But as collectors item? No way!
Things are moving so fast, a good Rigol will get you value for money.
And I do not have space for all those boat anchors anyways,

 

[server]

On Sun, 19 Dec 2021 12:40:16 +0000, Cursitor Doom <cd@notformail.com>
wrote:

Greetings, gentlemen,

I have a vintage MW/LW/SW 12V battery-powered radio I picked up recently
at a yard sale. Being 50 years old, however, it has a few faults and
needs realignment and whatnot. Before I can proceed with that, I\'ve
discovered that the transistors it uses (mostly obsolete germanium
devices) suffer from tin whiskers so I will need to re-jig the board so
they can be replaced with silicon ones instead. The design is very
simple so it *shouldn\'t* be a big deal. The bias requirements are of
course different between germaniums and silicons so perhaps it would be
better to start from scratch? I want to remain faithful to the original,
simple design ethos with its five discrete transistors whatever I do.
Any suggestions?

Here\'s the schematic:

https://disk.yandex.com/i/a2xX6_IadjbgIw

CD.

Why are some people so adverse to drawing a simple straight 4-wire
connection? It\'s not as if dots slide off the page or anything.





--

I yam what I yam - Popeye

 

[Cursitor Doom]

On Sun, 19 Dec 2021 15:07:33 GMT, Jan Panteltje
<pNaOnStPeAlMtje@yahoo.com> wrote:

On a sunny day (Sun, 19 Dec 2021 13:21:46 +0000) it happened Cursitor Doom
cd@notformail.com> wrote in <63curgddjaitboe4872itb788d5i9n1fdg@4ax.com>:

On Sun, 19 Dec 2021 13:05:36 GMT, Jan Panteltje
pNaOnStPeAlMtje@yahoo.com> wrote:

On a sunny day (Sun, 19 Dec 2021 12:40:16 +0000) it happened Cursitor Doom
cd@notformail.com> wrote in <spn97h$rou$1@dont-email.me>:

Greetings, gentlemen,

I have a vintage MW/LW/SW 12V battery-powered radio I picked up recently
at a yard sale. Being 50 years old, however, it has a few faults and
needs realignment and whatnot. Before I can proceed with that, I\'ve
discovered that the transistors it uses (mostly obsolete germanium
devices) suffer from tin whiskers so I will need to re-jig the board so
they can be replaced with silicon ones instead. The design is very
simple so it *shouldn\'t* be a big deal. The bias requirements are of
course different between germaniums and silicons so perhaps it would be
better to start from scratch? I want to remain faithful to the original,
simple design ethos with its five discrete transistors whatever I do.
Any suggestions?

Here\'s the schematic:

https://disk.yandex.com/i/a2xX6_IadjbgIw

That is a classical audio amp.
Apart from I have never had a transistor fail due to \'tin whiskers\',

Really? The AF117 type in particular (ubiquitous in British broadcast
recievers of the late 1960s) was *notorious* for shorting internally
due to whiskers.

if you replace ALL of those transistors with Si
then T2 R7/R8 will also change the bias to the output stage to 2 x Vbe, then 2 x .7V.
It should simply work.
But maybe you should increase R3 by 2 or more times or so to get enough bias for T3.

Or simply replace it with a LM380 or LM386!

No! No! NO!! No ICs thanks very much! I may even try potting the new
silicon replacements into hollowed- out casings of the Ge devices to
keep it original looking.


Better even: Buy a nice Tecsun PL600 all band radio,
but... I bought one in 2014 for 60$, now I see them for 266$ on ebay!

Or the TECSUN PL660, perhaps, about 100$ on ebay.
Seems the PL600 is no longer made, and the 660 is the new model.

Do not hang on too much to old stuff.

I specialise in old obsolete stuff. I prefer it!

(that said I hang on to my old analog scope).

I have about 13 of \'em.

I was so happy when I bought my first PLL radio,
just type in the frequency!

Stability-wise they are of course far superior. However, if you want
to have a good, thorough snoop around the bands for what\'s on, then
analogue tuning still rules IMO. No serious SWL should be without a
tuning knob!

I have always used scopes for fault finding, even worked at Tek.
build my own ones at home.
But as collectors item? No way!
Things are moving so fast, a good Rigol will get you value for money.
And I do not have space for all those boat anchors anyways,

Then make it!

 

[Cursitor Doom]

On Sun, 19 Dec 2021 08:17:12 -0800, jlarkin@highlandsniptechnology.com
wrote:

On Sun, 19 Dec 2021 12:40:16 +0000, Cursitor Doom <cd@notformail.com
wrote:

Greetings, gentlemen,

I have a vintage MW/LW/SW 12V battery-powered radio I picked up recently
at a yard sale. Being 50 years old, however, it has a few faults and
needs realignment and whatnot. Before I can proceed with that, I\'ve
discovered that the transistors it uses (mostly obsolete germanium
devices) suffer from tin whiskers so I will need to re-jig the board so
they can be replaced with silicon ones instead. The design is very
simple so it *shouldn\'t* be a big deal. The bias requirements are of
course different between germaniums and silicons so perhaps it would be
better to start from scratch? I want to remain faithful to the original,
simple design ethos with its five discrete transistors whatever I do.
Any suggestions?

Here\'s the schematic:

https://disk.yandex.com/i/a2xX6_IadjbgIw

CD.

Why are some people so adverse to drawing a simple straight 4-wire
connection? It\'s not as if dots slide off the page or anything.

I know! Stupid things like that really hinder my understanding of a
circuit\'s function as I\'m focusing on that rather than anything else.

So anyways. Are you going to redesign this damn thing for me or what?
;-)

 

[server]

On Sun, 19 Dec 2021 17:32:52 +0000, Cursitor Doom <cd@notformail.com>
wrote:

On Sun, 19 Dec 2021 08:17:12 -0800, jlarkin@highlandsniptechnology.com
wrote:

On Sun, 19 Dec 2021 12:40:16 +0000, Cursitor Doom <cd@notformail.com
wrote:

Greetings, gentlemen,

I have a vintage MW/LW/SW 12V battery-powered radio I picked up recently
at a yard sale. Being 50 years old, however, it has a few faults and
needs realignment and whatnot. Before I can proceed with that, I\'ve
discovered that the transistors it uses (mostly obsolete germanium
devices) suffer from tin whiskers so I will need to re-jig the board so
they can be replaced with silicon ones instead. The design is very
simple so it *shouldn\'t* be a big deal. The bias requirements are of
course different between germaniums and silicons so perhaps it would be
better to start from scratch? I want to remain faithful to the original,
simple design ethos with its five discrete transistors whatever I do.
Any suggestions?

Here\'s the schematic:

https://disk.yandex.com/i/a2xX6_IadjbgIw

CD.

Why are some people so adverse to drawing a simple straight 4-wire
connection? It\'s not as if dots slide off the page or anything.

I know! Stupid things like that really hinder my understanding of a
circuit\'s function as I\'m focusing on that rather than anything else.

So anyways. Are you going to redesign this damn thing for me or what?
;-)

I dislike audio. Why not buy some germanium transistors from Ebay?

Or a decent modern amp?



--

I yam what I yam - Popeye

 

[Cursitor Doom]

On Sun, 19 Dec 2021 09:44:17 -0800, jlarkin@highlandsniptechnology.com
wrote:

>I dislike audio. Why not buy some germanium transistors from Ebay?

No point. The only parts available are NOS which will have whiskers
growing in them anyway, so they\'ll fail eventually guaranteed.

>Or a decent modern amp?

Naw. Gotta be discretes to keep it original. Fortunately, this is a
hybrid radio which uses both Si and Ge trannies, so I can get away
with replacing the Ge with Si devices whilst remainiing faithful to
the original concept. Of course I could stick an audio IC in there,
but it would be a cop-out and the kind of solution only a cad, a
bounder or possibly even a blackguard would consider.
So get your slide rule out.

 

[Ralph Mowery]

In article <hisurgda6flk6vrr51fiehes54s0cpe6g8@4ax.com>,
cd@notformail.com says...

Naw. Gotta be discretes to keep it original. Fortunately, this is a
hybrid radio which uses both Si and Ge trannies, so I can get away
with replacing the Ge with Si devices whilst remainiing faithful to
the original concept. Of course I could stick an audio IC in there,
but it would be a cop-out and the kind of solution only a cad, a
bounder or possibly even a blackguard would consider.
So get your slide rule out.

Have you tried this place, they list germanium transistors but at a
steep for some of them.

https://ntepartsdirect.com/

 

[server]

On Sun, 19 Dec 2021 18:03:13 +0000, Cursitor Doom <cd@notformail.com>
wrote:

On Sun, 19 Dec 2021 09:44:17 -0800, jlarkin@highlandsniptechnology.com
wrote:

I dislike audio. Why not buy some germanium transistors from Ebay?

No point. The only parts available are NOS which will have whiskers
growing in them anyway, so they\'ll fail eventually guaranteed.

Or a decent modern amp?

Naw. Gotta be discretes to keep it original. Fortunately, this is a
hybrid radio which uses both Si and Ge trannies, so I can get away
with replacing the Ge with Si devices whilst remainiing faithful to
the original concept. Of course I could stick an audio IC in there,
but it would be a cop-out and the kind of solution only a cad, a
bounder or possibly even a blackguard would consider.
So get your slide rule out.

You\'ll need to replace the horrible germanium biasing with horrible
silicon biasing.

20% distortion? 20% ain\'t bad.



--

I yam what I yam - Popeye

 

[Jan Panteltje]

On a sunny day (Sun, 19 Dec 2021 17:30:55 +0000) it happened Cursitor Doom
<cd@notformail.com> wrote in <lsqurghujn6etdecbprdvvrq5j0gi356df@4ax.com>:

On Sun, 19 Dec 2021 15:07:33 GMT, Jan Panteltje
pNaOnStPeAlMtje@yahoo.com> wrote:

On a sunny day (Sun, 19 Dec 2021 13:21:46 +0000) it happened Cursitor Doom
cd@notformail.com> wrote in <63curgddjaitboe4872itb788d5i9n1fdg@4ax.com>:

On Sun, 19 Dec 2021 13:05:36 GMT, Jan Panteltje
pNaOnStPeAlMtje@yahoo.com> wrote:

On a sunny day (Sun, 19 Dec 2021 12:40:16 +0000) it happened Cursitor Doom
cd@notformail.com> wrote in <spn97h$rou$1@dont-email.me>:

Greetings, gentlemen,

I have a vintage MW/LW/SW 12V battery-powered radio I picked up recently
at a yard sale. Being 50 years old, however, it has a few faults and
needs realignment and whatnot. Before I can proceed with that, I\'ve
discovered that the transistors it uses (mostly obsolete germanium
devices) suffer from tin whiskers so I will need to re-jig the board so
they can be replaced with silicon ones instead. The design is very
simple so it *shouldn\'t* be a big deal. The bias requirements are of
course different between germaniums and silicons so perhaps it would be
better to start from scratch? I want to remain faithful to the original,
simple design ethos with its five discrete transistors whatever I do.
Any suggestions?

Here\'s the schematic:

https://disk.yandex.com/i/a2xX6_IadjbgIw

That is a classical audio amp.
Apart from I have never had a transistor fail due to \'tin whiskers\',

Really? The AF117 type in particular (ubiquitous in British broadcast
recievers of the late 1960s) was *notorious* for shorting internally
due to whiskers.

if you replace ALL of those transistors with Si
then T2 R7/R8 will also change the bias to the output stage to 2 x Vbe, then 2 x .7V.
It should simply work.
But maybe you should increase R3 by 2 or more times or so to get enough bias for T3.

Or simply replace it with a LM380 or LM386!

No! No! NO!! No ICs thanks very much! I may even try potting the new
silicon replacements into hollowed- out casings of the Ge devices to
keep it original looking.


Better even: Buy a nice Tecsun PL600 all band radio,
but... I bought one in 2014 for 60$, now I see them for 266$ on ebay!

Or the TECSUN PL660, perhaps, about 100$ on ebay.
Seems the PL600 is no longer made, and the 660 is the new model.

Do not hang on too much to old stuff.

I specialise in old obsolete stuff. I prefer it!

(that said I hang on to my old analog scope).

I have about 13 of \'em.

I was so happy when I bought my first PLL radio,
just type in the frequency!

Stability-wise they are of course far superior. However, if you want
to have a good, thorough snoop around the bands for what\'s on, then
analogue tuning still rules IMO. No serious SWL should be without a
tuning knob!

Of course, my Tecsun radio has SSB, PLL, a BFO knob and a tuning knob.
Very good allband radio.
But my rtl-sdr stick with the xpsa spectrum analyzer software I wrote can use the mouse wheel for tuning to 1 Hz accuracy.
Just specify jump size 1:
http://panteltje.com/pub/xpsa-0.7.gif

I have always used scopes for fault finding, even worked at Tek.
build my own ones at home.
But as collectors item? No way!
Things are moving so fast, a good Rigol will get you value for money.
And I do not have space for all those boat anchors anyways,

Then make it!

 

[Phil Allison]

On Monday, December 20, 2021 at 3:17:22 AM UTC+11, jla...@highlandsniptechnology.com wrote:

On Sun, 19 Dec 2021 12:40:16 +0000, Cursitor Doom <c...@notformail.com
wrote:
Greetings, gentlemen,

I have a vintage MW/LW/SW 12V battery-powered radio I picked up recently
at a yard sale. Being 50 years old, however, it has a few faults and
needs realignment and whatnot. Before I can proceed with that, I\'ve
discovered that the transistors it uses (mostly obsolete germanium
devices) suffer from tin whiskers so I will need to re-jig the board so
they can be replaced with silicon ones instead. The design is very
simple so it *shouldn\'t* be a big deal. The bias requirements are of
course different between germaniums and silicons so perhaps it would be
better to start from scratch? I want to remain faithful to the original,
simple design ethos with its five discrete transistors whatever I do.
Any suggestions?

Here\'s the schematic:

https://disk.yandex.com/i/a2xX6_IadjbgIw

CD.
Why are some people so adverse to drawing a simple straight 4-wire
connection? It\'s not as if dots slide off the page or anything.

** The schem looks like it is from the UK.
Think the 45 degree angle convention is exactly because dots can disappear when making copies.

Amusing what autistics like JL find annoying......


....... Phil

 

[Phil Allison]

jla...@highlandsniptechnology.com wrote:
====================================

You\'ll need to replace the horrible germanium biasing with horrible
silicon biasing.

20% distortion? 20% ain\'t bad.
--

** Audiophobic JL just loves to piss on anything that does not help bloat his pathological ego.

The THD of that tiny amp is 1% at most, ffs it\'s in a portable radio.


...... Phil

 

[LM]

First transistor BC108, it is a silicon one.
On Sun, 19 Dec 2021 12:40:16 +0000, Cursitor Doom <cd@notformail.com>
wrote:

Greetings, gentlemen,

I have a vintage MW/LW/SW 12V battery-powered radio I picked up recently
at a yard sale. Being 50 years old, however, it has a few faults and
needs realignment and whatnot. Before I can proceed with that, I\'ve
discovered that the transistors it uses (mostly obsolete germanium
devices) suffer from tin whiskers so I will need to re-jig the board so
they can be replaced with silicon ones instead. The design is very
simple so it *shouldn\'t* be a big deal. The bias requirements are of
course different between germaniums and silicons so perhaps it would be
better to start from scratch? I want to remain faithful to the original,
simple design ethos with its five discrete transistors whatever I do.
Any suggestions?

Here\'s the schematic:

https://disk.yandex.com/i/a2xX6_IadjbgIw

CD.

 

[Phil Hobbs]

Cursitor Doom wrote:

On Sun, 19 Dec 2021 13:05:36 GMT, Jan Panteltje
pNaOnStPeAlMtje@yahoo.com> wrote:

On a sunny day (Sun, 19 Dec 2021 12:40:16 +0000) it happened Cursitor Doom
cd@notformail.com> wrote in <spn97h$rou$1@dont-email.me>:

Greetings, gentlemen,

I have a vintage MW/LW/SW 12V battery-powered radio I picked up recently
at a yard sale. Being 50 years old, however, it has a few faults and
needs realignment and whatnot. Before I can proceed with that, I\'ve
discovered that the transistors it uses (mostly obsolete germanium
devices) suffer from tin whiskers so I will need to re-jig the board so
they can be replaced with silicon ones instead. The design is very
simple so it *shouldn\'t* be a big deal. The bias requirements are of
course different between germaniums and silicons so perhaps it would be
better to start from scratch? I want to remain faithful to the original,
simple design ethos with its five discrete transistors whatever I do.
Any suggestions?

Here\'s the schematic:

https://disk.yandex.com/i/a2xX6_IadjbgIw

That is a classical audio amp.
Apart from I have never had a transistor fail due to \'tin whiskers\',

Really? The AF117 type in particular (ubiquitous in British broadcast
recievers of the late 1960s) was *notorious* for shorting internally
due to whiskers.

if you replace ALL of those transistors with Si
then T2 R7/R8 will also change the bias to the output stage to 2 x Vbe, then 2 x .7V.
It should simply work.
But maybe you should increase R3 by 2 or more times or so to get enough bias for T3.

Or simply replace it with a LM380 or LM386!

No! No! NO!! No ICs thanks very much! I may even try potting the new
silicon replacements into hollowed- out casings of the Ge devices to
keep it original looking.


Better even: Buy a nice Tecsun PL600 all band radio,
but... I bought one in 2014 for 60$, now I see them for 266$ on ebay!

Or the TECSUN PL660, perhaps, about 100$ on ebay.
Seems the PL600 is no longer made, and the 660 is the new model.

Do not hang on too much to old stuff.

I specialise in old obsolete stuff. I prefer it!

(that said I hang on to my old analog scope).

I have about 13 of \'em.

If it\'s really 1971 vintage, that should work fine, with perhaps a bit
of attention to the biasing.

Back in the really old days, germaniums were sometimes leaky enough that
their apparent DC betas _changed sign_.

When I interviewed at Tektronix Beaverton back in 1987, one of their
crusty old vertical amp wizards (might have been Thor Hallen) gave me a
circuit to analyze that made no sense to me whatever--not at DC, not at
AC--its biasing was impossible, and I said so.

Turned out to have been an astable that only worked when the DC beta was
negative, but didn\'t much care how negative--it was guaranteed to start
up regardless.

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

 

[whit3rd]

On Sunday, December 19, 2021 at 10:03:19 AM UTC-8, Cursitor Doom wrote:

On Sun, 19 Dec 2021 09:44:17 -0800, jla...@highlandsniptechnology.com
wrote:
I dislike audio. Why not buy some germanium transistors from Ebay?
No point. The only parts available are NOS which will have whiskers
growing in them anyway, so they\'ll fail eventually guaranteed.

Germanium doesn\'t generally have tin-whisker problems (those are particular to
a case design, not the transistor inside); it has additional failure modes and
aging issues, but so does any technology.

Be aware, though, that Si replacements for Ge transistors does change all the bias
currents, I\'ve seen items burned up because of a naiive replace-with-modern-Si strategy.

 

[server]

On Sun, 19 Dec 2021 15:55:57 -0500, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:

Cursitor Doom wrote:
On Sun, 19 Dec 2021 13:05:36 GMT, Jan Panteltje
pNaOnStPeAlMtje@yahoo.com> wrote:

On a sunny day (Sun, 19 Dec 2021 12:40:16 +0000) it happened Cursitor Doom
cd@notformail.com> wrote in <spn97h$rou$1@dont-email.me>:

Greetings, gentlemen,

I have a vintage MW/LW/SW 12V battery-powered radio I picked up recently
at a yard sale. Being 50 years old, however, it has a few faults and
needs realignment and whatnot. Before I can proceed with that, I\'ve
discovered that the transistors it uses (mostly obsolete germanium
devices) suffer from tin whiskers so I will need to re-jig the board so
they can be replaced with silicon ones instead. The design is very
simple so it *shouldn\'t* be a big deal. The bias requirements are of
course different between germaniums and silicons so perhaps it would be
better to start from scratch? I want to remain faithful to the original,
simple design ethos with its five discrete transistors whatever I do.
Any suggestions?

Here\'s the schematic:

https://disk.yandex.com/i/a2xX6_IadjbgIw

That is a classical audio amp.
Apart from I have never had a transistor fail due to \'tin whiskers\',

Really? The AF117 type in particular (ubiquitous in British broadcast
recievers of the late 1960s) was *notorious* for shorting internally
due to whiskers.

if you replace ALL of those transistors with Si
then T2 R7/R8 will also change the bias to the output stage to 2 x Vbe, then 2 x .7V.
It should simply work.
But maybe you should increase R3 by 2 or more times or so to get enough bias for T3.

Or simply replace it with a LM380 or LM386!

No! No! NO!! No ICs thanks very much! I may even try potting the new
silicon replacements into hollowed- out casings of the Ge devices to
keep it original looking.


Better even: Buy a nice Tecsun PL600 all band radio,
but... I bought one in 2014 for 60$, now I see them for 266$ on ebay!

Or the TECSUN PL660, perhaps, about 100$ on ebay.
Seems the PL600 is no longer made, and the 660 is the new model.

Do not hang on too much to old stuff.

I specialise in old obsolete stuff. I prefer it!

(that said I hang on to my old analog scope).

I have about 13 of \'em.


If it\'s really 1971 vintage, that should work fine, with perhaps a bit
of attention to the biasing.

Back in the really old days, germaniums were sometimes leaky enough that
their apparent DC betas _changed sign_.

Just cap couple into the base, no bias needed.

(Electret mikes did that with jfets. I did that in my alligator
detector.)



--

I yam what I yam - Popeye

 

[server]

On Sun, 19 Dec 2021 12:44:35 -0800 (PST), Phil Allison
<pallison49@gmail.com> wrote:

On Monday, December 20, 2021 at 3:17:22 AM UTC+11, jla...@highlandsniptechnology.com wrote:
On Sun, 19 Dec 2021 12:40:16 +0000, Cursitor Doom <c...@notformail.com
wrote:
Greetings, gentlemen,

I have a vintage MW/LW/SW 12V battery-powered radio I picked up recently
at a yard sale. Being 50 years old, however, it has a few faults and
needs realignment and whatnot. Before I can proceed with that, I\'ve
discovered that the transistors it uses (mostly obsolete germanium
devices) suffer from tin whiskers so I will need to re-jig the board so
they can be replaced with silicon ones instead. The design is very
simple so it *shouldn\'t* be a big deal. The bias requirements are of
course different between germaniums and silicons so perhaps it would be
better to start from scratch? I want to remain faithful to the original,
simple design ethos with its five discrete transistors whatever I do.
Any suggestions?

Here\'s the schematic:

https://disk.yandex.com/i/a2xX6_IadjbgIw

CD.
Why are some people so adverse to drawing a simple straight 4-wire
connection? It\'s not as if dots slide off the page or anything.


** The schem looks like it is from the UK.
Think the 45 degree angle convention is exactly because dots can disappear when making copies.

Amusing what autistics like JL find annoying......


...... Phil

Cheap British dots do fall off the paper. We use macho USA dots.



--

I yam what I yam - Popeye

 

[Phil Allison]

LM wrote:
========

First transistor BC108, it is a silicon one.

** Dates the radio to the mid/late 60s.

Next step up was to use AD161/162 output devices.
Germanium compliments in TO37 paks.


...... Phil