[King of the country of What.]

hi,

Looking at this schematic :

http://www.freewebs.com/willispage8/

What type of ohm reading should I expect across Q9 and Q11 ?

The C is equivalent to a plate on a tube ?

The Base ( center connection) is equivalent to the grid,

Emittor ( Cathode ) is the one with the arrow on it ? If I recall.

My SS skills are on slow recall ;-) .

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[John Popelish]

King of the country of What. wrote:
hi,

Looking at this schematic :

http://www.freewebs.com/willispage8/

What type of ohm reading should I expect across Q9 and Q11 ?

The way Q9 and Q11 are connected, there are 4 nodes between
them. If we call the common bases node 1, the common
collectors node 2 , Q9's emitter node 3 and Q11's emitter
node 4, that allows for resistance measurements between
nodes 1 and 2, 1 and 3 , 1 and 4, 2 and 3, 2 and 4, and 3
and 4. Do you want the whole list?

The C is equivalent to a plate on a tube ?

If by C, you mean the collector of a transistor, then yes,
it is similar to the plate on a triode. This is especially
true for NPN transistors, where the collector is usually the
most positive node. The polarity is reversed for PNP
transistors. So the collectors of PNP transistors would be
similar to the plates if the triode were made of anti mater.

The Base ( center connection) is equivalent to the grid,

Yes. Some big differences. The grid operates on voltage
with little bias current, while the base requires
considerable bias current to turn the collector current on.

Emittor ( Cathode ) is the one with the arrow on it ? If I recall.

Right. Arrows pointing out indicates NPN transistors.
Pointing in indicates PNP transistors.

[Peter Wieck]

On Mar 22, 11:03 pm, "King of the country of What."
wrote:
hi,

Looking at this schematic :

http://www.freewebs.com/willispage8/

What type of ohm reading should I expect across Q9 and Q11 ?

The C is equivalent to a plate on a tube ?

The Base ( center connection) is equivalent to the grid,

Emittor ( Cathode ) is the one with the arrow on it ? If I recall.

My SS skills are on slow recall ;-) .

----== Posted via Newsfeeds.Com - Unlimited-Unrestricted-Secure Usenet News==----http://www.newsfeeds.comThe #1 Newsgroup Service in the World! 120,000+ Newsgroups
----= East and West-Coast Server Farms - Total Privacy via Encryption =----

Imagine the transistor as a triggered diode and it will make your
diagnosis easier. You will need a VOM capable of forward-biasing that
particular transistor, most are, some are not. You will get near-
infinite resistance in one direction low resistance in another.

They are identical transistors, so the readings should be very close
to each other. Near-identical if they are even vaguely matched. I have
not looked up that particular transistor, but forward-bias resistance
could be anything from 30-or-so to 250 ohms or more.

You will have to measure them out-of-circuit unless you have a tester
capable of in-circuit use. Most VOMs will not do that. I keep a Heath
tester that does it well-enough in-circuit to determine if the
transistor is good or bad, and I can actually match them _OUT_ of
circuit.

Put another way, don't trust your VOM if you are testing them in-
circuit. You are including too many other parts of the circuit.

Are you trouble-shooting?

Peter Wieck
Wyncote, PA

[[email protected]]

On Mar 23, 8:04 am, "Peter Wieck" wrote:
(snip)
You will need a VOM capable of forward-biasing that
particular transistor, most are, some are not. You will get near-
infinite resistance in one direction low resistance in another.

They are identical transistors, so the readings should be very close
to each other. Near-identical if they are even vaguely matched. I have
not looked up that particular transistor, but forward-bias resistance
could be anything from 30-or-so to 250 ohms or more.

You will have to measure them out-of-circuit unless you have a tester
capable of in-circuit use. Most VOMs will not do that. I keep a Heath
tester that does it well-enough in-circuit to determine if the
transistor is good or bad, and I can actually match them _OUT_ of
circuit.
(snip)

The concept of an in circuit tester is pretty simple. It is an ohm
meter that applies less voltage to make its measurement, than it takes
to forward bias a silicon diode (somewhere between .1 and .4 volts,
open circuit). This allows you to check if a silicon diode junction
is short circuited (no normal diode drop needed to produce a low
resistance value) or to measure the values of resistors connected to
transistors and diodes, while keeping all the junction voltages low
enough that nothing gets forward biased enough to conduct and distort
the ohm readings.

Diode check meters (usually show a diode symbol on the selector) apply
a limited current through the probes, while displaying the open
circuit voltage (often with an implied decimal point). So if you
connect the leads across a diode or base to collector junction, etc.
you may get a reading of 50 to 70 (or 500 to 700, depending on where
the implied decimal point is), indicating .5 to .7 volts forward bias
drop. A shorted junction will read very close to zero and an open
circuit usually blanks the display, instead of showing the open
circuit voltage. Testing diode junctions in circuit will include the
effect of any other current paths on the voltage drop across a
junction, so it is not generally an in circuit test.

[Peter Wieck]

On Mar 23, 10:52 am, wrote:
On Mar 23, 8:04 am, "Peter Wieck" wrote:
(snip) You will need a VOM capable of forward-biasing that
particular transistor, most are, some are not. You will get near-
infinite resistance in one direction low resistance in another.

They are identical transistors, so the readings should be very close
to each other. Near-identical if they are even vaguely matched. I have
not looked up that particular transistor, but forward-bias resistance
could be anything from 30-or-so to 250 ohms or more.

You will have to measure them out-of-circuit unless you have a tester
capable of in-circuit use. Most VOMs will not do that. I keep a Heath
tester that does it well-enough in-circuit to determine if the
transistor is good or bad, and I can actually match them _OUT_ of
circuit.

(snip)

The concept of an in circuit tester is pretty simple. It is an ohm
meter that applies less voltage to make its measurement, than it takes
to forward bias a silicon diode (somewhere between .1 and .4 volts,
open circuit). This allows you to check if a silicon diode junction
is short circuited (no normal diode drop needed to produce a low
resistance value) or to measure the values of resistors connected to
transistors and diodes, while keeping all the junction voltages low
enough that nothing gets forward biased enough to conduct and distort
the ohm readings.

Diode check meters (usually show a diode symbol on the selector) apply
a limited current through the probes, while displaying the open
circuit voltage (often with an implied decimal point). So if you
connect the leads across a diode or base to collector junction, etc.
you may get a reading of 50 to 70 (or 500 to 700, depending on where
the implied decimal point is), indicating .5 to .7 volts forward bias
drop. A shorted junction will read very close to zero and an open
circuit usually blanks the display, instead of showing the open
circuit voltage. Testing diode junctions in circuit will include the
effect of any other current paths on the voltage drop across a
junction, so it is not generally an in circuit test.

Yabbut...

Those two transistors (cited in the OP) are very nearly in parallel.
So any results are questionable if in-circuit. A simple diode tester
may not be enough to tell one from the other. Those resistors are only
5 ohms.

Peter Wieck
Wyncote, PA

[Rich Grise]

On Thu, 22 Mar 2007 23:37:21 -0400, John Popelish wrote:
King of the country of What. wrote:

Looking at this schematic :

http://www.freewebs.com/willispage8/

What type of ohm reading should I expect across Q9 and Q11 ?

The way Q9 and Q11 are connected, there are 4 nodes between
them. If we call the common bases node 1, the common
collectors node 2 , Q9's emitter node 3 and Q11's emitter
node 4, that allows for resistance measurements between
nodes 1 and 2, 1 and 3 , 1 and 4, 2 and 3, 2 and 4, and 3
and 4. Do you want the whole list?

The C is equivalent to a plate on a tube ?

If by C, you mean the collector of a transistor, then yes,
it is similar to the plate on a triode. This is especially
true for NPN transistors, where the collector is usually the
most positive node. The polarity is reversed for PNP
transistors. So the collectors of PNP transistors would be
similar to the plates if the triode were made of anti mater.

The Base ( center connection) is equivalent to the grid,

Yes. Some big differences. The grid operates on voltage
with little bias current, while the base requires
considerable bias current to turn the collector current on.

Emittor ( Cathode ) is the one with the arrow on it ? If I recall.

Right. Arrows pointing out indicates NPN transistors.
Pointing in indicates PNP transistors.

A mnemonic for absolute newbies is, NPN = Not Pointing iN, and
PNP = the other one. ;-)

Cheers!
Rich

[[email protected]]

On Mar 23, 3:11 pm, "Peter Wieck" wrote:
On Mar 23, 10:52 am, wrote:
The concept of an in circuit tester is pretty simple. It is an ohm
meter that applies less voltage to make its measurement, than it takes
to forward bias a silicon diode (somewhere between .1 and .4 volts,
open circuit). This allows you to check if a silicon diode junction
is short circuited (no normal diode drop needed to produce a low
resistance value) or to measure the values of resistors connected to
transistors and diodes, while keeping all the junction voltages low
enough that nothing gets forward biased enough to conduct and distort
the ohm readings.

Diode check meters (usually show a diode symbol on the selector) apply
a limited current through the probes, while displaying the open
circuit voltage (often with an implied decimal point). So if you
connect the leads across a diode or base to collector junction, etc.
you may get a reading of 50 to 70 (or 500 to 700, depending on where
the implied decimal point is), indicating .5 to .7 volts forward bias
drop. A shorted junction will read very close to zero and an open
circuit usually blanks the display, instead of showing the open
circuit voltage. Testing diode junctions in circuit will include the
effect of any other current paths on the voltage drop across a
junction, so it is not generally an in circuit test.

Yabbut...

Those two transistors (cited in the OP) are very nearly in parallel.
So any results are questionable if in-circuit. A simple diode tester
may not be enough to tell one from the other. Those resistors are only
5 ohms.

I'm agreeing with that. I was describing the limitations and
application of in circuit testing, andthe difference between in
circuit and diode junction tests. I recommend pulling the power
transistors and testing their junctions with a diode test function, to
discover any shorted junctions. While all 4 output transistors are
pulled, I think the rest of the amplifier can be tested for normal
bias operation with no load on the base driver section. The 4 output
transistors are essentially a high current voltage follower for the
base driver outputs.

[robert casey]

Those two transistors (cited in the OP) are very nearly in parallel.
So any results are questionable if in-circuit. A simple diode tester
may not be enough to tell one from the other. Those resistors are only
5 ohms.


Blown transistors usually go all open, or more often dead short. Dead
shorts are easy to spot with the meter, you see 0 ohms. An open here
with the parallel transistors is a little harder to identify. If the
circuit seems to operate, se if one transistor isn't getting warm. Or
see if there is any voltage drop across its emitter resistor. Exercise
care that you don't short something when fumbling with test leads, I
tend to blow stuff up worse with this mistake. Tube circuits are more
forgiving, and circuit nodes are further apart anyway. Another issue is
that some solid state stuff might degrade a little from abuse, and die
days later (when you think you had it fixed...).

Check both sides of a complementary pair (the NPNs and the PNPs here).
One might be shorted, and the other side blown open.

[Peter Wieck]

On Mar 23, 3:34 pm, wrote:
On Mar 23, 3:11 pm, "Peter Wieck" wrote:





On Mar 23, 10:52 am, wrote:
The concept of an in circuit tester is pretty simple. It is an ohm
meter that applies less voltage to make its measurement, than it takes
to forward bias a silicon diode (somewhere between .1 and .4 volts,
open circuit). This allows you to check if a silicon diode junction
is short circuited (no normal diode drop needed to produce a low
resistance value) or to measure the values of resistors connected to
transistors and diodes, while keeping all the junction voltages low
enough that nothing gets forward biased enough to conduct and distort
the ohm readings.

Diode check meters (usually show a diode symbol on the selector) apply
a limited current through the probes, while displaying the open
circuit voltage (often with an implied decimal point). So if you
connect the leads across a diode or base to collector junction, etc.
you may get a reading of 50 to 70 (or 500 to 700, depending on where
the implied decimal point is), indicating .5 to .7 volts forward bias
drop. A shorted junction will read very close to zero and an open
circuit usually blanks the display, instead of showing the open
circuit voltage. Testing diode junctions in circuit will include the
effect of any other current paths on the voltage drop across a
junction, so it is not generally an in circuit test.

Yabbut...

Those two transistors (cited in the OP) are very nearly in parallel.
So any results are questionable if in-circuit. A simple diode tester
may not be enough to tell one from the other. Those resistors are only
5 ohms.

I'm agreeing with that. I was describing the limitations and
application of in circuit testing, andthe difference between in
circuit and diode junction tests. I recommend pulling the power
transistors and testing their junctions with a diode test function, to
discover any shorted junctions. While all 4 output transistors are
pulled, I think the rest of the amplifier can be tested for normal
bias operation with no load on the base driver section. The 4 output
transistors are essentially a high current voltage follower for the
base driver outputs.- Hide quoted text -

- Show quoted text -

Thanks for the clarification. I do understand where you were going,
and it is a useful technique. But in this specific case, additional
caveats apply. As Robert does state if not in so many words. Take
care.

Peter Wieck
Wyncote, PA

[jasen]

On 2007-03-23, Rich Grise wrote:

A mnemonic for absolute newbies is, NPN = Not Pointing iN, and
PNP = the other one. ;-)

I say "PNP = Pointing inwards pointer"

have you got one for FETs

Bye.
Jasen

[Tom Del Rosso]

"jasen" wrote in message

On 2007-03-23, Rich Grise wrote:

A mnemonic for absolute newbies is, NPN = Not Pointing iN, and
PNP = the other one. ;-)

I say "PNP = Pointing inwards pointer"

have you got one for FETs

Bye.
Jasen

FETs are easier. When I was a kid I started remembering it simply as N
channel points iN, and P channel looks like it's taking a Pee. I still like
to look at them that way.


--

Reply in group, but if emailing add another
zero, and remove the last word.

[Fred Bartoli]

jasen a écrit :
On 2007-03-23, Rich Grise wrote:

A mnemonic for absolute newbies is, NPN = Not Pointing iN, and
PNP = the other one. ;-)

I say "PNP = Pointing inwards pointer"

have you got one for FETs


The N channel (drain source channel) JFET can more or less be seen as a
diode with source and drain taken each side of the cathode. Which it
almost is physically.


--
Thanks,
Fred.

[Jim Thompson]

On Sat, 31 Mar 2007 07:26:06 GMT, "Tom Del Rosso"
wrote:

"jasen" wrote in message

On 2007-03-23, Rich Grise wrote:

A mnemonic for absolute newbies is, NPN = Not Pointing iN, and
PNP = the other one. ;-)

I say "PNP = Pointing inwards pointer"

have you got one for FETs

Bye.
Jasen

FETs are easier. When I was a kid I started remembering it simply as N
channel points iN, and P channel looks like it's taking a Pee. I still like
to look at them that way.

The pointy end of the arrow is always "N"

Non-pointy = "P"

...Jim Thompson
--
| James E.Thompson, P.E. | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona Voice480)460-2350 | |
| E-mail Address at Website Fax480)460-2142 | Brass Rat |
| http://www.analog-innovations.com | 1962 |

America: Land of the Free, Because of the Brave

[Tom Del Rosso]

"Jim Thompson" wrote
in message
On Sat, 31 Mar 2007 07:26:06 GMT, "Tom Del Rosso"
wrote:

FETs are easier. When I was a kid I started remembering it simply
as N channel points iN, and P channel looks like it's taking a Pee.
I still like to look at them that way.

The pointy end of the arrow is always "N"

Non-pointy = "P"

Yeah, but that's for bipolar.


--

Reply in group, but if emailing add another
zero, and remove the last word.