In article ,
rowdy yates beanboy wrote:
TO-92 case, NPN, M logo, (Motorola?). From a Tanberg 3008-A preamp.
Any suggestions for an easy sub or a spec sheet would be appreciated.
Thank you.

Motorola does make some parts with Pro-Electron numbers, but I don't
see a BC651. I do see an MPS651 NPN, 60V, 75 MHz Ft, 2000 mA max,
min hFE of 75 with no max. The lack of a maximum Hfe spec and the
high current makes me think that's a switching transistor.

With discrete transistors, you can generally substitute with impunity
on audio circuits as long as you are replacing with a part that has
the same hFE and the same or higher maximum voltage and current ranges.

If this a stereo preamp, you are in luck because you can find the
identical transistor in the good channel, measure the voltage across
collector and emitter, and then take it out and measure the hFE with
the transistor tester function on a multimeter. This gives you enough
information to get a good match, though you will want to replace both
channels to make sure they are exactly the same.
--scott

10 to 500 which makes it look more like a switching transistor to me.


--
"C'est un Nagra. C'est suisse, et tres, tres precis."

TO-92 case, NPN, M logo, (Motorola?). From a Tanberg 3008-A preamp.
Any suggestions for an easy sub or a spec sheet would be appreciated.
Thank you.

Hmmm. A quick look an in "Ye Olde Towers Selector" lists no equivs for the
BC651, BC651D or BC651E :-(

I can give you the basic spec if you want to try and find a match by
scouring the data sheets though.

Al.

TO-92 case, NPN, M logo, (Motorola?). From a Tanberg 3008-A preamp.
Any suggestions for an easy sub or a spec sheet would be appreciated.
Thank you.

Oh, forgot to say in my earlier post that BC651's are still available, but
not DS spec.

Al.

rowdy yates wrote:

TO-92 case, NPN, M logo, (Motorola?). From a Tanberg 3008-A preamp.
Any suggestions for an easy sub or a spec sheet would be appreciated.
Thank you.

No sign of a spec sheet anywhere including the usual archives.

As Scott notes, just about any decent modern general purpose device will
likely do the job. You need to be aware of the lead pinout though. Do you
know how to check this ?

It would help if you could advise where the part is used in the circuit.
Supply voltage etc... A low noise part may or may not be required.

BC549 comes to mind as a widely available possible substitute ( centre
base connection btw ). C suffix gives the highest current gain for this
part.


Graham

Scott Dorsey wrote:

In article ,
rowdy yates beanboy wrote:
TO-92 case, NPN, M logo, (Motorola?). From a Tanberg 3008-A preamp.
Any suggestions for an easy sub or a spec sheet would be appreciated.
Thank you.

Motorola does make some parts with Pro-Electron numbers, but I don't
see a BC651. I do see an MPS651 NPN, 60V, 75 MHz Ft, 2000 mA max,
min hFE of 75 with no max. The lack of a maximum Hfe spec and the
high current makes me think that's a switching transistor.

With discrete transistors, you can generally substitute with impunity
on audio circuits as long as you are replacing with a part that has
the same hFE and the same or higher maximum voltage and current ranges.

Since most hfe bands ( for selected evices ) usually cover a 2:1 range or
thereabouts and unselected devices are often specced around 8:1, I don't
agree with your concern about accurate hfe matching. I would select a
device with high hfe in any replacement application like this..


If this a stereo preamp, you are in luck because you can find the
identical transistor in the good channel, measure the voltage across
collector and emitter, and then take it out and measure the hFE with
the transistor tester function on a multimeter. This gives you enough
information to get a good match, though you will want to replace both
channels to make sure they are exactly the same.
--scott

10 to 500 which makes it look more like a switching transistor to me.

hfe is a critical parameter only in poorly designed low-level ( i.e using
TO-92 parts ) circuits ! It's rather more important in power amp output
stages.

Graham

On Sat, 01 Jan 2005 01:47:24 +0000, Pooh Bear
wrote:

It would help if you could advise where the part is used in the circuit.
Supply voltage etc... A low noise part may or may not be required.

Looking over the schematic, the only obvious ones are Q201 and Q202,
in the MM phono input stage. It's a fabulously strange circuit with
a non-differential first stage fed by an active constant current
source; two gain steps with loop feedback, complementary followers,
the whole schebang, each; the first flat and the second RIAA.

For an input device I like the Toshiba 2SC2240, but they're
hardly exotic. There's got to be a nice European device that's
burning up the charts.

Thanks, and Happy Gregorian New Year,

Chris Hornbeck
"They'd meet at the Tout Va Bien."
-JLG, _Bande a part_, 1964

In article ,
Al wrote:
TO-92 case, NPN, M logo, (Motorola?). From a Tanberg 3008-A preamp.
Any suggestions for an easy sub or a spec sheet would be appreciated.
Thank you.

Oh, forgot to say in my earlier post that BC651's are still available, but
not DS spec.

What IS the DS spec? Is that just a package design, or is it specified for
low noise or specific hFE?
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

In article beanboy writes:

History: The unit has lived with it's cover off for the past 10 years
so I can jiggle the interconnect board (J801 - J804) and revive the
left channel when it goes out once every 3 months or so or when there
is an unbalanced load in the washing machine.

You have this receiver on top of the washing machine?


--
I'm really Mike Rivers )
However, until the spam goes away or Hell freezes over,
lots of IP addresses are blocked from this system. If
you e-mail me and it bounces, use your secret decoder ring
and reach me he double-m-eleven-double-zero at yahoo

On Sun, 02 Jan 2005 08:40:52 GMT, rowdy yates
wrote:

My latest fumbling guess is Q415, Selector Board 4A, Page 5, coming
out of the Bass/Treble pots for those of you following your text at
home. With a square wave to the tuner input of 140mv I have a square I
can change with the vol pot all the way to the base of Q415 with
nothing on the collector or downstream. The rail end of it's collector
resistor, R469 is 21.5vdc, the collector end is 20v. The spec test
voltage is .6v at the base of Q415 but I measure 20mv vdc. 122mv vac.
Test voltage at the base of the working channel, Q416 is .6vdc like
it's supposed to be.

The base DC voltage certainly seem damning. Swapping xstr's
between channels is bulletproof confimation that/if one is
bad.

The test voltages at the Tone Defeat are correct
for both channels at 1vdc, 15 and 16 e,h.

By "test voltages", do you actually mean 1.0 v AC? There should be
no DC present. Also, it might be useful to remove C417 and C427 to
see what the DC voltages look like. Electrolytic cap's old enough
to vote cause all kinds of grief.

Action Update: Whoops, now I have no signal past the Bass/Treble pots.

This is a Baxandall tone control, so you won't see signal at
the inputs (summing junction).

I'm sorry I missed those device locations. Now I also see a pair
at Q405 and Q406, and at Q501 and Q502. If you do decide that one is
bad, replace them all. Parts are cheap.

Good fortune, and let us know your progress,

Chris Hornbeck
"They'd meet at the Tout Va Bien."
-JLG, _Bande a part_, 1964

What IS the DS spec? Is that just a package design, or is it
specified for low noise or specific hFE?

BC651 hFE = 400
BC651D hFE = 640
BC651E hFE = 900

Everything else seems to be the same.

Not sure about the 'S' part - Maybe a 'select' device?

Al.

Al wrote:
What IS the DS spec? Is that just a package design, or is it
specified for low noise or specific hFE?

BC651 hFE = 400
BC651D hFE = 640
BC651E hFE = 900

Everything else seems to be the same.

Not sure about the 'S' part - Maybe a 'select' device?

Maybe, but it sounds like time to get a box of BC651s and a multimeter and
do some selection yourself.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

On Tue, 04 Jan 2005 16:50:20 GMT, roudy yates
wrote:

Now I have another problem it seems. The MM phono circuit has a
channel out but the MC input works fine. I'm using a MM cartridge into
it and it sounds ok to me. The two inputs have minor differences in
what would be grid leak resistors in a tube circuit and one transistor
has different characteristics. Otherwise they are the same layout
exactly. This is to accommodate a different input impedance? Would
they sound different if they were both working? It would only sound
different if you plugged a MC cartridge into the MM input, right?
Thanks again.

The MC input loads the phono cartridge with 150 ohms, quite a bit
lower than the usual 47 K ohms, and so will sound dull. You're on a
roll now, so repairing the MM input will be a piece of cake.

Good fortune,

Chris Hornbeck
"They'd meet at the Tout Va Bien, a cafe just off the highway."
-JLG, _Bande a part_, 1964