[EADGBE]

I am a home hobbyist who enjoys restoring vintage stereo equipment. I
have a good working knowledge of electronic components and what they
do. I have decent test equipment and good soldering skills, and most
of the time I am able to track down and repair a particular problem.

However, I do feel that I need to know more about the theory behind
electronic circuits in order to improve my troubleshooting skills.

Sometimes I find myself looking at a schematic and thinking, "Boy, I
wish I knew more about what is supposed to be happening in this
circuit!"

Can anyone point to any good books or online sources where I can learn
more about how to analyze schematics and recognize what is supposed to
be happening?

CASE IN POINT: I am attempting to repair a tape deck. One channel
(the right channel) of the headphone amplifier doesn't work. The tape
deck has perfect output through the line out jacks.

Here is the schematic for one of the channels of the tape deck's
headphone amp:

http://i240.photobucket.com/albums/f.../amplifier.jpg

I have reproduced the schematic in my own handwriting because the
downloaded schematic was too fuzzy to scan. I *think* I have copied
everything correctly.

I cannot figure out why this particular circuit isn't working
correctly. I have checked each component--and even replaced a few
transistors even though all transistors tested fine--but nothing is
improving.

I have tested all of the electrolytics with my ESR meter and they all
check out OK.

I have checked all resistors and none of them have opened up or "gone
high".

Notice that there are some "typical" expected voltages indicated at
certain points. These "typical" voltages have come right out of the
service manual. All of the voltages marked "OK" are...well...OKAY.
But the three voltages marked with a star (*) are NOT okay...they are
all just a few millivolts each--around 20 to 30mV.

All capacitors are electrolytic with the exception of the 4.7pF
capacitor, which is ceramic.

All resistors are 1/4 watt. If there is no "K" after the number, then
that is the amount of actual ohms it has.

For the record, I replaced Q204, Q206, and Q208 but still got exactly
the same results.

What am I overlooking?

[Arny Krueger]

"EADGBE" wrote in message

I am a home hobbyist who enjoys restoring vintage stereo
equipment. I have a good working knowledge of electronic
components and what they do. I have decent test
equipment and good soldering skills, and most of the time
I am able to track down and repair a particular problem.

However, I do feel that I need to know more about the
theory behind electronic circuits in order to improve my
troubleshooting skills.

Sometimes I find myself looking at a schematic and
thinking, "Boy, I wish I knew more about what is supposed
to be happening in this circuit!"

Can anyone point to any good books or online sources
where I can learn more about how to analyze schematics
and recognize what is supposed to be happening?

http://jacquesricher.com/NEETS/

24 PDFs that make up a pretty fair basic electronics course, fairly current
as of 2003.

US Navy Electricity and Electronics Training Series

Module 1 - Introduction to Matter, Energy, and Direct Current
Module 2 - Introduction to Alternating Current and Transformers
Module 3 - Introduction to Circuit Protection, Control, and Measurement
Module 4 - Introduction to Electrical Conductors, Wiring Techniques, and
Schematic Reading
Module 5 - Introduction to Generators and Motors
Module 6 - Introduction to Electronic Emission, Tubes, and Power Supplies
Module 7 - Introduction to Solid-State Devices and Power Supplies
Module 8 - Introduction to Amplifiers
Module 9 - Introduction to Wave-Generation and Wave-Shaping Circuits
Module 10 - Introduction to Wave Propagation, Transmission Lines, and
Antennas
Module 11 - Microwave Principles
Module 12 - Modulation Principles
Module 13 - Introduction to Number Systems and Logic Circuits
Module 14 - Introduction to Microelectronics
Module 15 - Principles of Synchros, Servos, and Gyros
Module 16 - Introduction to Test Equipment
Module 17 - Radio-Frequency Communications Principles
Module 18 - Radar Principles
Module 19 - The Technician's Handbook
Module 20 - Master Glossary
Module 21 - Test Methods and Practices
Module 22 - Introduction to Digital Computers
Module 23 - Magnetic Recording
Module 24 - Introduction to Fiber Optics

[hr(bob) [email protected]]

On Apr 19, 2:40*pm, EADGBE wrote:
I am a home hobbyist who enjoys restoring vintage stereo equipment. *I
have a good working knowledge of electronic components and what they
do. *I have decent test equipment and good soldering skills, and most
of the time I am able to track down and repair a particular problem.

However, I do feel that I need to know more about the theory behind
electronic circuits in order to improve my troubleshooting skills.

Sometimes I find myself looking at a schematic and thinking, "Boy, I
wish I knew more about what is supposed to be happening in this
circuit!"

Can anyone point to any good books or online sources where I can learn
more about how to analyze schematics and recognize what is supposed to
be happening?

CASE IN POINT: I am attempting to repair a tape deck. *One channel
(the right channel) of the headphone amplifier doesn't work. *The tape
deck has perfect output through the line out jacks.

Here is the schematic for one of the channels of the tape deck's
headphone amp:

http://i240.photobucket.com/albums/f.../amplifier.jpg

I have reproduced the schematic in my own handwriting because the
downloaded schematic was too fuzzy to scan. *I *think* I have copied
everything correctly.

I cannot figure out why this particular circuit isn't working
correctly. *I have checked each component--and even replaced a few
transistors even though all transistors tested fine--but nothing is
improving.

I have tested all of the electrolytics with my ESR meter and they all
check out OK.

I have checked all resistors and none of them have opened up or "gone
high".

Notice that there are some "typical" expected voltages indicated at
certain points. *These "typical" voltages have come right out of the
service manual. *All of the voltages marked "OK" are...well...OKAY.
But the three voltages marked with a star (*) are NOT okay...they are
all just a few millivolts each--around 20 to 30mV.

All capacitors are electrolytic with the exception of the 4.7pF
capacitor, which is ceramic.

All resistors are 1/4 watt. *If there is no "K" after the number, then
that is the amount of actual ohms it has.

For the record, I replaced Q204, Q206, and Q208 but still got exactly
the same results.

What am I overlooking?

Do you have an oscilloscope?? If you do, it is a simple matter of
tracking the signal on the good side and comparing it to the "lack of
signal" in the bad side, stage by stage.

The training source given by the 2nd poster looks to be great!!!.

Bob Hofmann

[DaveM]

Arny gave you a list of some teaching materials for electronics theory, however,
most of them seem to focus on more advanced systems theory. I don't know to
what level these texts assume the reader has progressed. It's been so long
since I looked at a basic theory text that I can't recommend any without a bit
of searching. Perhaps another reader can be of more assistance.

If your focus is on solid state equipment, then you'll need to focus your
studies on theories of transistor circuits. The most basic component that
you'll need to study hard and really understand is, of course, the transistor.

In reference to your tape deck problem, If you could think about how the various
voltages in the circuit are derived, then it might be a little clearer.
Remember that transistors are current operated devices, that is, a small current
through the base-emitter of the transistor modifies the current between the
collector and emitter. In normal linear circuits, a transistor's B-E junction
is forward biased, while the B-C junction is reverse biased.
Forward-biased: current flows; reverse-biased: no current flows.

Assuming silicon transistors, the B-E junction is forward-biased with a voltage
of approximately 0.5 to 0.7 volts between the base and emitter. Always use the
emitter as a reference point for voltage measurements around a transistor. For
an NPN device, the base is positive with reference to the emitter. For a PNP,
the base is negative to the emitter.

In your tape circuit, the big clue to the problem is lack of any voltage at the
collector of Q205. Q205 must be turned on, at least partially, in order for any
voltage to appear at its collector (which is showing no voltage). It is the
only path that can supply the current to Q203 is through the E-C circuit of
Q205. If Q205's B-E is properly forward biased, current should flow through the
C-E circuit.
Measure the B-E voltage of Q205. If it's in the vicinity of 0.5 - 0.7 volts,
then the transistor should be conducting current from its emitter to its
collector. If the voltage there is less than that, then the transistor can't
conduct, thereby shutting off the C-E circuit.

If the transistor's B-E junction is properly forward biased, then it should be
conducting. If it isn't conducting, then the transistor is either open or there
is another fault, and further troubleshooting is needed. My bet on your tape
deck's fault is on Q205. Let me know if that fixes it.

Hope this helps you get started,
--
Dave M
MasonDG44 at comcast dot net (Just substitute the appropriate characters in the
address)

Some people are like Slinkies. Not really good for anything, but they bring a
smile to your face when pushed down the stairs.
"EADGBE" wrote in message
...
I am a home hobbyist who enjoys restoring vintage stereo equipment. I
have a good working knowledge of electronic components and what they
do. I have decent test equipment and good soldering skills, and most
of the time I am able to track down and repair a particular problem.

However, I do feel that I need to know more about the theory behind
electronic circuits in order to improve my troubleshooting skills.

Sometimes I find myself looking at a schematic and thinking, "Boy, I
wish I knew more about what is supposed to be happening in this
circuit!"

Can anyone point to any good books or online sources where I can learn
more about how to analyze schematics and recognize what is supposed to
be happening?

CASE IN POINT: I am attempting to repair a tape deck. One channel
(the right channel) of the headphone amplifier doesn't work. The tape
deck has perfect output through the line out jacks.

Here is the schematic for one of the channels of the tape deck's
headphone amp:

http://i240.photobucket.com/albums/f.../amplifier.jpg

I have reproduced the schematic in my own handwriting because the
downloaded schematic was too fuzzy to scan. I *think* I have copied
everything correctly.

I cannot figure out why this particular circuit isn't working
correctly. I have checked each component--and even replaced a few
transistors even though all transistors tested fine--but nothing is
improving.

I have tested all of the electrolytics with my ESR meter and they all
check out OK.

I have checked all resistors and none of them have opened up or "gone
high".

Notice that there are some "typical" expected voltages indicated at
certain points. These "typical" voltages have come right out of the
service manual. All of the voltages marked "OK" are...well...OKAY.
But the three voltages marked with a star (*) are NOT okay...they are
all just a few millivolts each--around 20 to 30mV.

All capacitors are electrolytic with the exception of the 4.7pF
capacitor, which is ceramic.

All resistors are 1/4 watt. If there is no "K" after the number, then
that is the amount of actual ohms it has.

For the record, I replaced Q204, Q206, and Q208 but still got exactly
the same results.

What am I overlooking?

[Eeyore]

EADGBE wrote:

Notice that there are some "typical" expected voltages indicated at
certain points. These "typical" voltages have come right out of the
service manual. All of the voltages marked "OK" are...well...OKAY.
But the three voltages marked with a star (*) are NOT okay...they are
all just a few millivolts each--around 20 to 30mV.

There's something amiss with the biasing of the output emitter-follower
stage. The voltage on the base of Q208 should be about 1.2V less (not 0.2V
less I think that 6.8V should be 5.8V) than the voltage on the base of
Q207. That suggests possibly zero or very low current in Q205's collector
circuit. Suggest you measure the voltage across the 12k connected to
Q205's base-emitter.

Graham

[EADGBE]

On Apr 19, 5:04 pm, "DaveM" wrote:

In your tape circuit, the big clue to the problem is lack of any voltage at the
collector of Q205. Q205 must be turned on, at least partially, in order for any
voltage to appear at its collector (which is showing no voltage). It is the
only path that can supply the current to Q203 is through the E-C circuit of
Q205. If Q205's B-E is properly forward biased, current should flow through the
C-E circuit.

Could you repeat this part, please?

There is no Q203 in this circuit.

Thanks for your help!

[EADGBE]

On Apr 19, 5:17 pm, Eeyore
wrote:

There's something amiss with the biasing of the output emitter-follower
stage. The voltage on the base of Q208 should be about 1.2V less (not 0.2V
less I think that 6.8V should be 5.8V) than the voltage on the base of
Q207. That suggests possibly zero or very low current in Q205's collector
circuit. Suggest you measure the voltage across the 12k connected to
Q205's base-emitter.

You are ABSOLUTELY CORRECT. I took another good, hard look at the
service manual schematic (very fuzzy), and the base voltage of Q208 is
indeed +5.8V.

How did you deduce this?

I'm not sure about the 12K resistor across Q205's base-emitter. I
will take a voltage measurement across that resistor and post it here.

[Charles[_7_]]

http://www.amazon.com/Electronics-Pr...8642336&sr=1-2

[Chris Hornbeck]

On Sat, 19 Apr 2008 12:40:50 -0700 (PDT), EADGBE
wrote:

http://i240.photobucket.com/albums/f.../amplifier.jpg

As others have said, replace Q205. Or, first lift one
end of the 15K feedback resistor for a surprise about
the output DC voltage. Then replace Q205.

All good fortune,

Chris Hornbeck

[DaveM]

"EADGBE" wrote in message
...
On Apr 19, 5:04 pm, "DaveM" wrote:

In your tape circuit, the big clue to the problem is lack of any voltage at
the
collector of Q205. Q205 must be turned on, at least partially, in order for
any
voltage to appear at its collector (which is showing no voltage). It is the
only path that can supply the current to Q203 is through the E-C circuit of
Q205. If Q205's B-E is properly forward biased, current should flow through
the
C-E circuit.

Could you repeat this part, please?

There is no Q203 in this circuit.

Thanks for your help!

Yes, you're right... I should have said
The only path that can supply the current to Q206 is through the E-C circuit of
Q205.
The voltages around Q205 are the clues to your problem. Find out why Q205 isn't
conducting and you'll find the problem.
--
Dave M
MasonDG44 at comcast dot net (Just substitute the appropriate characters in the
address)

Some people are like Slinkies. Not really good for anything, but they bring a
smile to your face when pushed down the stairs.

[EADGBE]

FWIW, the base voltage of Q205 is +11.09V. This was measured at the
junction of the base terminal and the 12K resistor.

[Don Pearce]

On Sat, 19 Apr 2008 14:36:36 -0700 (PDT), EADGBE
wrote:

On Apr 19, 5:04 pm, "DaveM" wrote:

In your tape circuit, the big clue to the problem is lack of any voltage at the
collector of Q205. Q205 must be turned on, at least partially, in order for any
voltage to appear at its collector (which is showing no voltage). It is the
only path that can supply the current to Q203 is through the E-C circuit of
Q205. If Q205's B-E is properly forward biased, current should flow through the
C-E circuit.

Could you repeat this part, please?

There is no Q203 in this circuit.

Thanks for your help!

Q205 is biased just fine. It has nearly 5V emitter to collector, There
is a problem around Q206, though. This transistor provides thermal
regulation for the quiescent current in the output stage. If you look
at the base and emitter voltages, you will see that it has become
reverse biased by 0.4V and there is possibly no voltage difference
between collector and emitter. It is not easy to see why this might
be. What is the voltage on the collector of Q208? It is misbiased
right now, possible by a bad Q206.

Just looking at the basic bias conditions, I would say

Q204 ok
Q205 ok
Q206 problem - maybe C-E short
Q207 ok
Q208 reverse biased B/E

So whatever is wrong, I think it is happening down around that bottom
right hand corner.

Perhaps more to the point, how do all these points measure on the good
channel?

--
Pearce Consulting
http://www.pearce.uk.com

[EADGBE]

Don:

I'm not sure, but you might be reading my schematic incorrectly.

There SHOULD be +7V at Q205's collector...but right now, there is only
20 - 30mV.

The +7V figure is what the service manual indicates is the "proper"
voltage for Q205's collector.

Regarding Q206, the actual voltages for the base and emitter are both
currently reading just a few millivolts, just like the collector of
Q205.

The indicated voltages for Q206 are, once again, merely from the
service manual, and the figure for the emitter was written
incorrectly. The proper voltage for the emitter of Q206 is +5.8V.

[[email protected]]

alt.binaries.e-book.technical

[Eeyore]

EADGBE wrote:

Eeyore wrote:

There's something amiss with the biasing of the output emitter-follower
stage. The voltage on the base of Q208 should be about 1.2V less (not 0.2V
less I think that 6.8V should be 5.8V) than the voltage on the base of
Q207. That suggests possibly zero or very low current in Q205's collector
circuit. Suggest you measure the voltage across the 12k connected to
Q205's base-emitter.

You are ABSOLUTELY CORRECT. I took another good, hard look at the
service manual schematic (very fuzzy), and the base voltage of Q208 is
indeed +5.8V.

How did you deduce this?

Because there should be 2 Vbe's difference betwen those 2 points (to turn on the
complementary emitter follower stage).


I'm not sure about the 12K resistor across Q205's base-emitter. I
will take a voltage measurement across that resistor and post it here.

That will be helpful.

Graham

[Eeyore]

EADGBE wrote:

FWIW, the base voltage of Q205 is +11.09V. This was measured at the
junction of the base terminal and the 12K resistor.

That suggests a Vbe of 0.81V in which case Q205 *ought* to be well
turned on and conducting strongly but it isn't.

Replace Q205.

Graham

[Eeyore]

Don Pearce wrote:

On Sat, 19 Apr 2008 14:36:36 -0700 (PDT), EADGBE
wrote:

On Apr 19, 5:04 pm, "DaveM" wrote:

In your tape circuit, the big clue to the problem is lack of any voltage at the
collector of Q205. Q205 must be turned on, at least partially, in order for any
voltage to appear at its collector (which is showing no voltage). It is the
only path that can supply the current to Q203 is through the E-C circuit of
Q205. If Q205's B-E is properly forward biased, current should flow through the
C-E circuit.

Could you repeat this part, please?

There is no Q203 in this circuit.

Thanks for your help!

Q205 is biased just fine. It has nearly 5V emitter to collector,

NO. Those are the service manual values. Q205's collector is actually almost at ground
potential, i.e. not conducting.

Graham

[Eeyore]

EADGBE wrote:

I am a home hobbyist who enjoys restoring vintage stereo equipment. I
have a good working knowledge of electronic components and what they
do. I have decent test equipment and good soldering skills, and most
of the time I am able to track down and repair a particular problem.

However, I do feel that I need to know more about the theory behind
electronic circuits in order to improve my troubleshooting skills.

Sometimes I find myself looking at a schematic and thinking, "Boy, I
wish I knew more about what is supposed to be happening in this
circuit!"

Can anyone point to any good books or online sources where I can learn
more about how to analyze schematics and recognize what is supposed to
be happening?

In order to troubleshoot *discrete* transistor circuits that may be a tall
order. They don't even teach this stuff much at college or Uni any more !

Graham

[Dave Plowman (News)]

In article
,
hr(bob) wrote:
Do you have an oscilloscope?? If you do, it is a simple matter of
tracking the signal on the good side and comparing it to the "lack of
signal" in the bad side, stage by stage.

That's an expensive way - although of course a good one. For many years I
managed with a small battery amp and speaker.

--
*White with a hint of M42*

Dave Plowman London SW
To e-mail, change noise into sound.

[e-micro]

On 19 Apr, 22:40, EADGBE wrote:
I am a home hobbyist who enjoys restoring vintage stereo equipment. I
have a good working knowledge of electronic components and what they
do. I have decent test equipment and good soldering skills, and most
of the time I am able to track down and repair a particular problem.

However, I do feel that I need to know more about the theory behind
electronic circuits in order to improve my troubleshooting skills.

Sometimes I find myself looking at a schematic and thinking, "Boy, I
wish I knew more about what is supposed to be happening in this
circuit!"

Can anyone point to any good books or online sources where I can learn
more about how to analyze schematics and recognize what is supposed to
be happening?
Visit http://www.e-micro.ro/index.php?topic=57.0

[Randy Yates]

EADGBE writes:
[...]
Can anyone point to any good books or online sources where I can learn
more about how to analyze schematics and recognize what is supposed to
be happening?

I had this text in one of my engineering courses at the University of
South Florida (Tampa) and in my opinion it would be an excellent book
for the purpose you have in mind:

@BOOK{sedra,
title = "{Microelectronic Circuits}",
author = "Adel~S.~Sedra and Kenneth~C.~Smith",
publisher = "Saunders College Publishing",
edition = "third",
year = "1991"}

--
% Randy Yates % "My Shangri-la has gone away, fading like
%% Fuquay-Varina, NC % the Beatles on 'Hey Jude'"
%%% 919-577-9882 %
%%%% % 'Shangri-La', *A New World Record*, ELO
http://www.digitalsignallabs.com

[EADGBE]

OK, the plot thickens somewhat...

Some of you have told me that, in my non-functioning amplifier
circuit, the most likely culprit was Q205.

I have replaced Q205 and the circuit STILL doesn't work. It is
exactly the same as before.

There is only 131.1mV on the collector of Q205, despite +11.09V on its
base and +11.59V on its emitter.

Aaargh!

[Eeyore]

EADGBE wrote:

OK, the plot thickens somewhat...

Some of you have told me that, in my non-functioning amplifier
circuit, the most likely culprit was Q205.

I have replaced Q205 and the circuit STILL doesn't work. It is
exactly the same as before.

There is only 131.1mV on the collector of Q205, despite +11.09V on its
base and +11.59V on its emitter.

And yet you continue to refuse to *directly* measure it's Vbe which is
what's important.

One other thing. Do you know how to test a transistor ?

Graham

[EADGBE]

On Apr 21, 6:41 pm, Eeyore
wrote:

And yet you continue to refuse to *directly* measure it's Vbe which is
what's important.

According to the datasheet for Q205, the Vbe is:

MINIMUM: -0.58
TYPICAL: -0.62
MAXIMUM: -0.68

These figures were arrived at using the following test conditions:

Vce = -6.0V
Ic = -1.0mA

As I have said, I am a hobbyist. Not sure how to do "real world"
testing for Vbe or why it's important. I do know how to test NPN and
PNP transistors using the diode function of a multimeter, that's it.

[Geoff]

EADGBE wrote:
On Apr 21, 6:41 pm, Eeyore
wrote:

And yet you continue to refuse to *directly* measure it's Vbe which
is what's important.

According to the datasheet for Q205, the Vbe is:

MINIMUM: -0.58
TYPICAL: -0.62
MAXIMUM: -0.68

These figures were arrived at using the following test conditions:

Vce = -6.0V
Ic = -1.0mA

As I have said, I am a hobbyist. Not sure how to do "real world"
testing for Vbe or why it's important. I do know how to test NPN and
PNP transistors using the diode function of a multimeter, that's it.

That's a good starting point, and will likely identify 95% of any problems
in an amp. Transistors and diodes, that is.

Other things to look for are blown emitter resistors, other burned
resistors, and bulging capacitors. Problms relalting to drifting component
values are pretty rare.

geoff

[Mr.T]

"EADGBE" wrote in message
...
On Apr 21, 6:41 pm, Eeyore
wrote:
There is only 131.1mV on the collector of Q205, despite +11.09V on its
base and +11.59V on its emitter.

And yet you continue to refuse to *directly* measure it's Vbe which is
what's important.

According to the datasheet for Q205, the Vbe is:

MINIMUM: -0.58
TYPICAL: -0.62
MAXIMUM: -0.68

These figures were arrived at using the following test conditions:

Vce = -6.0V
Ic = -1.0mA


And from your own measurements there is only 0.50V Base-emitter, so the
transistor is not correctly biased.
Possibly a fault in a preceding stage, or even an O/C resistor or possibly a
dry joint.
Keep looking and measuring other voltages.

MrT.

[Serge Auckland[_2_]]

"Mr.T" MrT@home wrote in message
u...

"EADGBE" wrote in message
...
On Apr 21, 6:41 pm, Eeyore
wrote:
There is only 131.1mV on the collector of Q205, despite +11.09V on its
base and +11.59V on its emitter.

And yet you continue to refuse to *directly* measure it's Vbe which is
what's important.

According to the datasheet for Q205, the Vbe is:

MINIMUM: -0.58
TYPICAL: -0.62
MAXIMUM: -0.68

These figures were arrived at using the following test conditions:

Vce = -6.0V
Ic = -1.0mA


And from your own measurements there is only 0.50V Base-emitter, so the
transistor is not correctly biased.
Possibly a fault in a preceding stage, or even an O/C resistor or possibly
a
dry joint.
Keep looking and measuring other voltages.

MrT.



Silly thought, but you *have* connected 205 the right way round when you
replaced it.........

S.


--
http://audiopages.googlepages.com

[William Sommerwerck]

One of the basic principles of troubleshooting -- which I think other
posters have been trying to get across -- is to look at the DC voltages on a
device to see what they tell you about the device's operation.

For example, in "normal" operation, a tube's plate voltage should be at
least 100V higher than the cathode *, while the grid should be several volts
lower. If this isn't so, something is wrong and you need to find out why.

I was recently troubleshooting an electronic crossover with about 10 volts
DC output. The output stage used an op amp driving a current-boost device. I
had no schematic. The parts were difficult to remove, as there was no easy
way to remove and flip over the PC board. I didn't want to go through the
hassle of removed a 14-pin op amp from the top of the board, if it wasn't
defective.

A friend (a well-known audio designer -- yes, I'm name dropping) said "Look,
the current-boost thingy has a gain of 1 for both AC and DC. The input and
output should be the same, regardless of circuit design. What are you
getting?"

"There's 1V on the input, -3V on the output."

"Then it _must_ be defective. Right?"

Right. I clipped the leads and sucked out the stubs. Then I shoved in the
replacement and carefully applied solder.

It worked.

Voltage checks provide really good troubleshooting clues -- if you know how
to interpret them.


* Obviously, the exact nominal voltages vary with the tube, the circuit,
etc.

[EADGBE]

William:

That was very good advice. In a way, I'm trying to do the same thing,
but from a "functional" standpoint as well.

In other words, I know what the expected voltages should be, but I
can't help thinking that if I knew how this circuit actually amplified
the signal, I would be in a better position to troubleshoot it, hence
my original request for good sources for learning electronic theory.
(Some of the sources that have been recommended so far seem to be
excellent, by the way.) Where exactly does the signal go?, what
should happen when it gets there?, etc. I believe that these are
questions that I should be able to answer.

So far, what I have is a collection of components that all seem to
test perfectly OK, but don't work, for some as-yet unknown reason.