Are these 2N3055s borderline spec?

Terry Pinnell · May 21, 2004

Stefan Heinzmann <stefan_heinzmann@yahoo.com> wrote:

Terry Pinnell wrote:

Stefan Heinzmann <stefan_heinzmann@yahoo.com> wrote:
[...]
I'm also still unsure about
your Vceo measurement. You keep talking about reverse breakdown, which
makes me suspect that you applied the test voltage the wrong way. For
Vceo on a NPN transistor you have to apply the test voltage with the
positive end on the collector. The base is left open. Again, it has
nothing to do with reverse breakdown.

That's down to my careless terminology. It's clear now that I did
measure Vceo, as I intended. (With correct polarity; that would have
been a reasonably easy error to spot <g>.) In fact I gave the unit I
built a decade or two ago the label 'Reverse Breakdown Tester', as its
anticipated primary purpose was to test zeners. It does, of course,
serve well as a 'Vceo Tester'.

Ok, that sorts this one. Thanks for the clarification.

If you did that with a 2N3055 and it shows a Vceo below 60V then the
device is damaged.

Specimens 1, 5 and 8 as you saw gave 33, 17 and 21, so they get
disqualified.

I realized in the meantime that your test current was probably too low
for this test. Somewhere you said that your tester applies 340V through
a 300k series resistance. That limits the current to something around
1mA. For a power transistor like the 3055 this is perilously close to
the leakage (or cut-off) current. In other words the values you measured
may not indicate the breakdown voltage, but be an indication of a high
leakage current. The leakage current tends to rise with temperature, so
if you heat up the transistor you may find the "apparent" breakdown
voltage falls markedly.

Some 2N3055 datasheets specify limits for the cut-off current. For
example, the Fairchild MJE3055T (same chip in different package)
specifies a maximum of 1mA at Vce=70V and the base voltage at 1.5V
/below/ the emitter. This rises to 5mA at 150°C.

Consequently, your measurement of Vceo needs to be done with a collector
current that is significantly above the leakage current. The said
datasheet specifies 200mA collector current as the mesurement condition
for Vceo. That leads to significant power dissipation in the transistor,
so you need to either ensure sufficient cooling or use pulsed
measurement techniques. The latter is probably beyond the means of a
hobbyist. So in your case I would probably try a current of about
10-20mA. The question is whether your breakdown tester can supply this
current level. If so, you may try replacing the series resistor of 300k
with a 15k resistor (or better yet, make it switchable). Watch the power
dissipation!

Before you throw away the suspect transistors, you may want to try the
test with a higher current just to make sure they're not just exemplars
with a higher cut-off current, and there's nothing wrong with the Vceo.

I found a bunch of MJE3055T in my drawer and took the opportunity to put
them into a curve tracer. They are from Wingshing, apparently made in
2000. My five samples showed a Vceo between 250V and 400V, despite their
specification of 60V minimum.

[...]
You can also short the base to the emitter, in which case you measure
Vces and not Vceo. Vces is usually higher than Vceo. You should get at
least 100V with a 2N3055.

I'll try that too.

Actually, i found some manufacturers specify only 70V minimum for Vces.
Whichever, it will be higher than Vceo.

The gain is only meaningful if you provide information about the
measurement conditions. At the very least, you should provide the
collector current and the collector-emitter voltage. HFe also depends on
the temperature, but that is harder to measure.

OK, but I still think a quick check of the sort I did can be useful.
It provides a helpful *comparative* measure of gain. Across my eight,
it ranged from 13 to 30. All things being equal, including passing the
Vceo>60V requirement, I'd choose specimens from the higher end.

That's a reasonable idea. The Fairchild datasheet contains an
interesting graph that shows the dependency between collector current
and gain at Vce=2V. At the left end of the graph the gain for Ic=10mA
shows as ~55. The maximum gain occurs at Ic=200mA, where it surpasses
100. Those are presumably typical values, not minimum ones.

This shows that the gain falls for lower currents. Your tools may well
use currents even below 10mA, as would be appropriate for small signal
transistors. I checked this with one of my MJE3055T devices, and it
shows a gain of about 30 at 150ľA collector current. The gain rises to
about 80 at 150mA collector current.

You see that the results of a measurement depend crucially on the
measurement conditions. If you don't know how your instruments measure a
certain value, you will have difficulties coming to a valid conclusion.

Many thanks, that's much appreciated. If I digress now, I'll never get
this Dog Alarm barking before our trip to Amsterdam and Germany in 8
days! But your suggestions, and a raft of other experiments, are now
on my fast-growing To Try list! My Vceo tester should manage a modest
current for a short period; I can always measure the output with my
'scope instead of a DMM, and that might tell me enough?

There's a saying in German that looses its rhyme when translating it to
English: "Wer mißt mißt Mist" (Who measures, measures rubbish).
Not a phrase to attempt after an evening in die Bierhalle <g>.

--
Terry Pinnell
Hobbyist, West Sussex, UK

Fred Bloggs · May 21, 2004

Terry Pinnell wrote:

Here are the respective waveforms:

http://www.terrypin.dial.pipex.com/Images/PushPullBreadboardPuzzle.gif

The power section of the circuit looks pretty symmetrical to me. So
why should this non-symmetrical behaviour occur please?

Well- "pretty symmetrical" is not nearly as good as "ugly symmetrical"
on many occasions. It is clear from the rightmost graph that the output
is outright flat-lining at something like -1V with absolutely no hint of
the buffer following the input excursion beyond that point negative (
deviation below a desired DC level of 12V which actually should be more
like 15V because of the sloppy 2xVbe multiplier Q1-Q2). Also- it is
pointless for you to record the unattenuated input since the gain is of
most interest in distortion investigations and you have no measurement
data whatsoever for that. Getting back to the flat-lining, it is clear
that the composite emitter follower Q4-Q6 cannot overcome the current
delivered by Darlington Q3-Q5 in addition to the load, so that the Q4
loading on CE Q2 goes STRAIGHT-TO-HELL and kills your main gain element-
which is already very weak to begin with- something like 46dB and not
really a number associated with high linearity and low distortion. The
D2-D1-R7 voltage drop is partitioned between the Vbe's of Q3-Q5-Q4 and
it will not take much drop across Vbe Q5 to swamp Q4 with excessive
current because Q6 is not providing enough of an assist to load Q5 with
its much weaker hfe-lowering Q4 base input impedance, diverting Q2
collector current and thus reducing voltage gain. This condition
therefore prevents Q2 from pulling Q5 into cut-off, and the output hangs
for negative excursions. If you split R8 into R8A and R8B (47 ohms each)
in series with Q3 and Q4 emitters resp with junction at output node-
then this effect will be eliminated.

More important, are my old 2N3055s still OK for this application? Or
showing signs of their age and their likely origin in a 'surplus'
bulk buy?

[Also posted with attachments in alt.binaries.schematics.electronic.]

Terry Pinnell · May 21, 2004

Fred Bloggs <nospam@nospam.com> wrote:

Terry Pinnell wrote:
Here are the respective waveforms:

http://www.terrypin.dial.pipex.com/Images/PushPullBreadboardPuzzle.gif

The power section of the circuit looks pretty symmetrical to me. So
why should this non-symmetrical behaviour occur please?

Well- "pretty symmetrical" is not nearly as good as "ugly symmetrical"
on many occasions. It is clear from the rightmost graph that the output
is outright flat-lining at something like -1V with absolutely no hint of
the buffer following the input excursion beyond that point negative (
deviation below a desired DC level of 12V which actually should be more
like 15V because of the sloppy 2xVbe multiplier Q1-Q2).

Can't pretend I understand that. First time anyone's ventured to
suggest DC output level should be anything but 12V...

Also- it is
pointless for you to record the unattenuated input since the gain is of
most interest in distortion investigations and you have no measurement
data whatsoever for that.

Not entirely pointless. I was simply demonstrating that the *input*
was a clean sine.

Getting back to the flat-lining, it is clear
that the composite emitter follower Q4-Q6 cannot overcome the current
delivered by Darlington Q3-Q5 in addition to the load, so that the Q4
loading on CE Q2 goes STRAIGHT-TO-HELL and kills your main gain element-
which is already very weak to begin with- something like 46dB and not
really a number associated with high linearity and low distortion. The
D2-D1-R7 voltage drop is partitioned between the Vbe's of Q3-Q5-Q4 and
it will not take much drop across Vbe Q5 to swamp Q4 with excessive
current because Q6 is not providing enough of an assist to load Q5 with
its much weaker hfe-lowering Q4 base input impedance, diverting Q2
collector current and thus reducing voltage gain. This condition
therefore prevents Q2 from pulling Q5 into cut-off, and the output hangs
for negative excursions. If you split R8 into R8A and R8B (47 ohms each)
in series with Q3 and Q4 emitters resp with junction at output node-
then this effect will be eliminated.

As I expect you've seen from my post in the main thread

Newsgroups: sci.electronics.design
Subject: Re: Distortion from audio power amp
Date: Fri, 21 May 2004 12:35:02 +0100
Message-ID: <rfora0h95ts066ii4i72qe8jgnstesuvjt@4ax.com>

I now have the circuit working to spec, essentially in its original
form. Seems hard to square that with what seems your castigation
above.

I simulated your 'split' suggestion (prior to possibly trying it on
breadboard), but if anything it makes cross-over distortion marginally
worse, as you see here:
http://www.terrypin.dial.pipex.com/Images/PushPull-SplitR8.gif

--
Terry Pinnell
Hobbyist, West Sussex, UK

Jim Thompson · May 21, 2004

On Fri, 21 May 2004 23:10:40 +0100, Terry Pinnell
<terrypinDELETE@THESEdial.pipex.com> wrote:

Fred Bloggs <nospam@nospam.com> wrote:

Terry Pinnell wrote:
Here are the respective waveforms:

http://www.terrypin.dial.pipex.com/Images/PushPullBreadboardPuzzle.gif

The power section of the circuit looks pretty symmetrical to me. So
why should this non-symmetrical behaviour occur please?

Well- "pretty symmetrical" is not nearly as good as "ugly symmetrical"
on many occasions. It is clear from the rightmost graph that the output
is outright flat-lining at something like -1V with absolutely no hint of
the buffer following the input excursion beyond that point negative (
deviation below a desired DC level of 12V which actually should be more
like 15V because of the sloppy 2xVbe multiplier Q1-Q2).

Can't pretend I understand that. First time anyone's ventured to
suggest DC output level should be anything but 12V...

480)460-2350 | |
| E-mail Address at Website Fax

Fred Bloggs · May 22, 2004

Terry Pinnell wrote:

Fred Bloggs <nospam@nospam.com> wrote:

Terry Pinnell wrote:

Here are the respective waveforms:

http://www.terrypin.dial.pipex.com/Images/PushPullBreadboardPuzzle.gif

The power section of the circuit looks pretty symmetrical to me. So
why should this non-symmetrical behaviour occur please?

Well- "pretty symmetrical" is not nearly as good as "ugly symmetrical"
on many occasions. It is clear from the rightmost graph that the output
is outright flat-lining at something like -1V with absolutely no hint of
the buffer following the input excursion beyond that point negative (
deviation below a desired DC level of 12V which actually should be more
like 15V because of the sloppy 2xVbe multiplier Q1-Q2).

Can't pretend I understand that. First time anyone's ventured to
suggest DC output level should be anything but 12V...

Also- it is
pointless for you to record the unattenuated input since the gain is of
most interest in distortion investigations and you have no measurement
data whatsoever for that.

Not entirely pointless. I was simply demonstrating that the *input*
was a clean sine.

Getting back to the flat-lining, it is clear
that the composite emitter follower Q4-Q6 cannot overcome the current
delivered by Darlington Q3-Q5 in addition to the load, so that the Q4
loading on CE Q2 goes STRAIGHT-TO-HELL and kills your main gain element-
which is already very weak to begin with- something like 46dB and not
really a number associated with high linearity and low distortion. The
D2-D1-R7 voltage drop is partitioned between the Vbe's of Q3-Q5-Q4 and
it will not take much drop across Vbe Q5 to swamp Q4 with excessive
current because Q6 is not providing enough of an assist to load Q5 with
its much weaker hfe-lowering Q4 base input impedance, diverting Q2
collector current and thus reducing voltage gain. This condition
therefore prevents Q2 from pulling Q5 into cut-off, and the output hangs
for negative excursions. If you split R8 into R8A and R8B (47 ohms each)
in series with Q3 and Q4 emitters resp with junction at output node-
then this effect will be eliminated.

As I expect you've seen from my post in the main thread

Newsgroups: sci.electronics.design
Subject: Re: Distortion from audio power amp
Date: Fri, 21 May 2004 12:35:02 +0100
Message-ID: <rfora0h95ts066ii4i72qe8jgnstesuvjt@4ax.com

I now have the circuit working to spec, essentially in its original
form. Seems hard to square that with what seems your castigation
above.

I simulated your 'split' suggestion (prior to possibly trying it on
breadboard), but if anything it makes cross-over distortion marginally
worse, as you see here:
http://www.terrypin.dial.pipex.com/Images/PushPull-SplitR8.gif

Okay- I have located this amplifier in the OLD-OLD-OLD literature- we
are talking state of the art developmental work presented to the Audio
Engineering Society circa 1957!-LOL. This particular topology is termed
"quasicomplementary symmetry" because of the predriver phase splitter
driving the the two NPNs in push pull. The NPN-PNP driver should be
changed like so:

View in a fixed-width font such as Courier.

B+ =24-36V
----+-------------------------+---------+------
| | |
| | |
| c |
| Rg |/ Q2 |
+--/\/\---------+-------| 2N2222 |
2X | |\ |
TEMP --- e c
COMP \ / | |/ Q4
DIODES --- +-------| 2N3055
| | |\
/ / e HFE>25 @ Imax
Rb 100 |
/ / |
\ \ |
| | | + 1000U
DC&AC FDBK <--------------------+---------+-----||----+------+
| | | C | |
| e | c | |
| |/ Q3 | | | /|
TO CE <----------+-------| 2N2907 | | | / |
PRE-AMP |\ | | +- |
c c Q5 | | |
| |/ | ---\ |
+-------| 2N3055 | | \|
| |\ | |
Rb ADJUSTED FOR / e HFE>25 | |
VBE,Q5=VBE,Q4=0.5V 100 | @ Imax | |
AT Q-POINT / | | |
\ | | |
| | | |
--------------------+---------+------------------+
GND |
TO PRE-AMP |
AC FDBK <----/\/\------||---------------------------+
INPUT SHUNT
ADJ FOR 600 OHM INPUT
& BROADBAND SPEC GAIN

The Rb is selected to put the output NPNs on the verge of conduction at
the Q-point of (B+)/2- and the pre-amp usually included an emitter
degeneration resistor to stabilize its operating point against
temperature- so that the series bias diodes compensate for Vbe's of
Q2/Q3 and their emitter current remains constant. The ultimate amplifier
distortion is a function of the matching of the Q4/Q5 HFE and the
instantaneous variation of those HFEs at maximum output signal levels-
because the minimal discrete component circuit does not provide much
feedback desensitization loop transmission- it also necessary to drive
this output pair with a close approximation to a split-phase voltage
source Q2/Q3 pair- hence the 100 ohm resistor at *each* base. The output
drive transistor emitter resistors are not necessary for this direct
coupled drive circuit at moderate power output- their main purpose was
DC-stabilization against Icbo at elevated temperatures and to linearize
the transconductance against excessive variation for very large signal
excursions. This type of amplifier is capable of 70% efficiency and
distortion levels less than 3% at maximum output power. All
semiconductors thermally coupled on heatsink-obviously.

Fred Bloggs · May 22, 2004

Terry Pinnell wrote:

Can't pretend I understand that. First time anyone's ventured to
suggest DC output level should be anything but 12V...

Hey- why'd you up R2 from 47K->72.5K? A nicer color scheme? :_)

Stefan Heinzmann · May 22, 2004

Fred Bloggs wrote:

Okay- I have located this amplifier in the OLD-OLD-OLD literature- we
are talking state of the art developmental work presented to the Audio
Engineering Society circa 1957!-LOL.

Good forensic work!

Have you got the AES preprint number?

Could be Preprint 6 or 11 maybe...

--
Cheers
Stefan

Fred Bloggs · May 22, 2004

Stefan Heinzmann wrote:

Fred Bloggs wrote:

Okay- I have located this amplifier in the OLD-OLD-OLD literature- we
are talking state of the art developmental work presented to the Audio
Engineering Society circa 1957!-LOL.

Good forensic work!

Have you got the AES preprint number?

Could be Preprint 6 or 11 maybe...

Author is Marvin B. Herscher, Radio Corporation of America, Camden, NJ

Presented to Audio Engineering Society Convention, New York, October 1957

My source is a collection of Electronics magazine articles from the era.

Fred Bloggs · May 22, 2004

Stefan Heinzmann wrote:

Fred Bloggs wrote:

Okay- I have located this amplifier in the OLD-OLD-OLD literature- we
are talking state of the art developmental work presented to the Audio
Engineering Society circa 1957!-LOL.

Good forensic work!

Have you got the AES preprint number?

Could be Preprint 6 or 11 maybe...

Speaking of forensic work, there was CNN article yesterday about the US
NTSB re-opening the investigation into a Cessna Caravan cargo airplane
crash on the night of Oct 23, 2002 near Mobile, Alabama. To date the
exact cause is unknown and the wreckage was characterized as a mid-air
impact that sliced the engine in half, splattered elements of the
fuselage with a polyethylene based red colored material, and left an
embedded piece of mystery anodized aluminum. The only other aircraft in
the vicinity was a FedEx DC-10 traveling on a perpendicular trajectory
1000 feet above the victim aircraft at 4000 feet. It is obvious to me
that the ONLY credible explanation is a midair collision with an
"unscheduled" delivery being made by that damned FedEx DC 10- a small
RCS tightly bound volumetrically dense bundle that hit that Cessna like
a cannon ball- dropped approximately 10 seconds prior to impact so that
it retained a substantial amount of initial horizontal velocity. The
anodized aluminum is most likely the remnants of an RF package most
likely for GPS location of the delivery by the ground recovery
recipients- what little drug residue that did attach to the victim
aircraft was dissolved or washed away by the watery crash site. It is
also an incredible coincidence that this is a high activity drug
smuggling area- and the FAA allowed their ATC data recording capability
to be out of service for months. This scenario is too perfect- low
altitude drop requiring no suspicious flight path deviation- small RCS
delivery designed to free fall off the radar screen in minimum time-
altitude activated parachute at safe unobservable height- GPS location
of drop in remote inaccessible area. Who the hell do these people think
they are fooling?

Terry Pinnell · May 22, 2004

Fred Bloggs <nospam@nospam.com> wrote:

Okay- I have located this amplifier in the OLD-OLD-OLD literature- we
are talking state of the art developmental work presented to the Audio
Engineering Society circa 1957!-LOL. This particular topology is termed
"quasicomplementary symmetry" because of the predriver phase splitter
driving the the two NPNs in push pull. The NPN-PNP driver should be
changed like so:

View in a fixed-width font such as Courier.

B+ =24-36V
----+-------------------------+---------+------
| | |
| | |
| c |
| Rg |/ Q2 |
+--/\/\---------+-------| 2N2222 |
2X | |\ |
TEMP --- e c
COMP \ / | |/ Q4
DIODES --- +-------| 2N3055
| | |\
/ / e HFE>25 @ Imax
Rb 100 |
/ / |
\ \ |
| | | + 1000U
DC&AC FDBK <--------------------+---------+-----||----+------+
| | | C | |
| e | c | |
| |/ Q3 | | | /|
TO CE <----------+-------| 2N2907 | | | / |
PRE-AMP |\ | | +- |
c c Q5 | | |
| |/ | ---\ |
+-------| 2N3055 | | \|
| |\ | |
Rb ADJUSTED FOR / e HFE>25 | |
VBE,Q5=VBE,Q4=0.5V 100 | @ Imax | |
AT Q-POINT / | | |
\ | | |
| | | |
--------------------+---------+------------------+
GND |
TO PRE-AMP |
AC FDBK <----/\/\------||---------------------------+
INPUT SHUNT
ADJ FOR 600 OHM INPUT
& BROADBAND SPEC GAIN

The Rb is selected to put the output NPNs on the verge of conduction at
the Q-point of (B+)/2- and the pre-amp usually included an emitter
degeneration resistor to stabilize its operating point against
temperature- so that the series bias diodes compensate for Vbe's of
Q2/Q3 and their emitter current remains constant. The ultimate amplifier
distortion is a function of the matching of the Q4/Q5 HFE and the
instantaneous variation of those HFEs at maximum output signal levels-
because the minimal discrete component circuit does not provide much
feedback desensitization loop transmission- it also necessary to drive
this output pair with a close approximation to a split-phase voltage
source Q2/Q3 pair- hence the 100 ohm resistor at *each* base. The output
drive transistor emitter resistors are not necessary for this direct
coupled drive circuit at moderate power output- their main purpose was
DC-stabilization against Icbo at elevated temperatures and to linearize
the transconductance against excessive variation for very large signal
excursions. This type of amplifier is capable of 70% efficiency and
distortion levels less than 3% at maximum output power. All
semiconductors thermally coupled on heatsink-obviously.

Thanks. Much to study there.

Did you also see the Torrens original that I posted, FWIW? It was a
rather poor scan, and scarred with my notes, but just about readable.
http://www.terrypin.dial.pipex.com/Images/AudioPowerAmpOriginal1.jpg
http://www.terrypin.dial.pipex.com/Images/AudioPowerAmpOriginalText.gif

--
Terry Pinnell
Hobbyist, West Sussex, UK

Stefan Heinzmann · May 22, 2004

Fred Bloggs schrieb:

Stefan Heinzmann wrote:

Fred Bloggs wrote:

Okay- I have located this amplifier in the OLD-OLD-OLD literature- we
are talking state of the art developmental work presented to the
Audio Engineering Society circa 1957!-LOL.

Good forensic work!

Have you got the AES preprint number?

Could be Preprint 6 or 11 maybe...

Author is Marvin B. Herscher, Radio Corporation of America, Camden, NJ

Presented to Audio Engineering Society Convention, New York, October 1957

My source is a collection of Electronics magazine articles from the era.

Ok, it is Preprint 6 then. Downloadable from the AES website
(www.aes.org) for $4.00 if you're a member ;-)

Thanks Fred!

--
Cheers
Stefan

Terry Pinnell · May 22, 2004

Fred Bloggs <nospam@nospam.com> wrote:

Hey- why'd you up R2 from 47K->72.5K? A nicer color scheme? :_)

That was explained in my summary earlier.
Newsgroups: sci.electronics.design
Subject: Re: Distortion from audio power amp
Date: Fri, 21 May 2004 12:35:02 +0100
Message-ID: <rfora0h95ts066ii4i72qe8jgnstesuvjt@4ax.com>

In short, I arrived at that by trial and error, to give a simulated
output waveform that looked like my *actual* one, and a DC output
level identical to mine. Real circuit had R2 = '47k', measured
subsequently at 53k. Still some way off 72k, which puzzled me.

One of CircuitMaker's many shortcomings is that it unfortunately
doesn't dynamically illustrate resistor colour codes <g>.

--
Terry Pinnell
Hobbyist, West Sussex, UK

Winfield Hill · May 22, 2004

Fred Bloggs wrote...

Stefan Heinzmann wrote:
Fred Bloggs wrote:

Okay- I have located this amplifier in the OLD-OLD-OLD literature- we
are talking state of the art developmental work presented to the Audio
Engineering Society circa 1957!-LOL.

Good forensic work!

Have you got the AES preprint number?
Could be Preprint 6 or 11 maybe...

Author is Marvin B. Herscher, Radio Corporation of America, Camden, NJ
Presented to Audio Engineering Society Convention, New York, October 1957
My source is a collection of Electronics magazine articles from the era.

It'd be great if you could scan and post that presentation / article.
I'd like to compare it to H.C. Lin's similar design, c. 1956 - 1957.

Thanks,
- Win

(email: use hill_at_rowland-dot-org for now)

Fred Bloggs · May 22, 2004

Terry Pinnell wrote:

Fred Bloggs <nospam@nospam.com> wrote:

Okay- I have located this amplifier in the OLD-OLD-OLD literature- we
are talking state of the art developmental work presented to the Audio
Engineering Society circa 1957!-LOL. This particular topology is termed
"quasicomplementary symmetry" because of the predriver phase splitter
driving the the two NPNs in push pull. The NPN-PNP driver should be
changed like so:

View in a fixed-width font such as Courier.

B+ =24-36V
----+-------------------------+---------+------
| | |
| | |
| c |
| Rg |/ Q2 |
+--/\/\---------+-------| 2N2222 |
2X | |\ |
TEMP --- e c
COMP \ / | |/ Q4
DIODES --- +-------| 2N3055
| | |\
/ / e HFE>25 @ Imax
Rb 100 |
/ / |
\ \ |
| | | + 1000U
DC&AC FDBK <--------------------+---------+-----||----+------+
| | | C | |
| e | c | |
| |/ Q3 | | | /|
TO CE <----------+-------| 2N2907 | | | / |
PRE-AMP |\ | | +- |
c c Q5 | | |
| |/ | ---\ |
+-------| 2N3055 | | \|
| |\ | |
Rb ADJUSTED FOR / e HFE>25 | |
VBE,Q5=VBE,Q4=0.5V 100 | @ Imax | |
AT Q-POINT / | | |
\ | | |
| | | |
--------------------+---------+------------------+
GND |
TO PRE-AMP |
AC FDBK <----/\/\------||---------------------------+
INPUT SHUNT
ADJ FOR 600 OHM INPUT
& BROADBAND SPEC GAIN

The Rb is selected to put the output NPNs on the verge of conduction at
the Q-point of (B+)/2- and the pre-amp usually included an emitter
degeneration resistor to stabilize its operating point against
temperature- so that the series bias diodes compensate for Vbe's of
Q2/Q3 and their emitter current remains constant. The ultimate amplifier
distortion is a function of the matching of the Q4/Q5 HFE and the
instantaneous variation of those HFEs at maximum output signal levels-
because the minimal discrete component circuit does not provide much
feedback desensitization loop transmission- it also necessary to drive
this output pair with a close approximation to a split-phase voltage
source Q2/Q3 pair- hence the 100 ohm resistor at *each* base. The output
drive transistor emitter resistors are not necessary for this direct
coupled drive circuit at moderate power output- their main purpose was
DC-stabilization against Icbo at elevated temperatures and to linearize
the transconductance against excessive variation for very large signal
excursions. This type of amplifier is capable of 70% efficiency and
distortion levels less than 3% at maximum output power. All
semiconductors thermally coupled on heatsink-obviously.

Thanks. Much to study there.

Did you also see the Torrens original that I posted, FWIW? It was a
rather poor scan, and scarred with my notes, but just about readable.
http://www.terrypin.dial.pipex.com/Images/AudioPowerAmpOriginal1.jpg
http://www.terrypin.dial.pipex.com/Images/AudioPowerAmpOriginalText.gif

Oaky-thnx- Torrens work is usually good.

Fred Bloggs · May 22, 2004

Stefan Heinzmann wrote:

Fred Bloggs schrieb:

Stefan Heinzmann wrote:

Fred Bloggs wrote:

Okay- I have located this amplifier in the OLD-OLD-OLD literature-
we are talking state of the art developmental work presented to the
Audio Engineering Society circa 1957!-LOL.

Good forensic work!

Have you got the AES preprint number?

Could be Preprint 6 or 11 maybe...

Author is Marvin B. Herscher, Radio Corporation of America, Camden, NJ

Presented to Audio Engineering Society Convention, New York, October 1957

My source is a collection of Electronics magazine articles from the era.

Ok, it is Preprint 6 then. Downloadable from the AES website
(www.aes.org) for $4.00 if you're a member ;-)

Thanks Fred!

I don't know- the article I have is by Herscher in Design Manual for
Transistor Circuits, Carrol, John M., McGraw-Hill, 1961, page 56,
"Designing Audio Power Amplifiers".

Stefan Heinzmann · May 22, 2004

Fred Bloggs wrote:

Stefan Heinzmann wrote:

Ok, it is Preprint 6 then. Downloadable from the AES website
(www.aes.org) for $4.00 if you're a member ;-)

Thanks Fred!

I don't know- the article I have is by Herscher in Design Manual for
Transistor Circuits, Carrol, John M., McGraw-Hill, 1961, page 56,
"Designing Audio Power Amplifiers".

Preprint 6, 9th AES convention 1957: Marvin B. Herscher "High Power
Audio Amplifiers".

Abstract:
"Several models of high power audio amplifiers have been developed and
constructed, capable of 45 watts output. These amplifiers utilize a
ribbed chassis for cooling and are stable up to an ambient temperature
of 50 degrees C. One amplifier uses a series type circuit, and the other
a quasi-complementary type circuit. Amplifier size and weight are
reduced since neither circuit employs driver or output transformers
These circuits will be described and performance data for amplifiers
will be presented."

I hesitate to pay $4.00 for the document. It's not worth that much for
me. Maybe someone here has got it...

--
Cheers
Stefan

Spehro Pefhany · May 22, 2004

On Sat, 22 May 2004 16:55:28 GMT, the renowned Fred Bloggs
<nospam@nospam.com> wrote:

Speaking of forensic work, there was CNN article yesterday about the US
NTSB re-opening the investigation into a Cessna Caravan cargo airplane
crash on the night of Oct 23, 2002 near Mobile, Alabama. To date the
exact cause is unknown and the wreckage was characterized as a mid-air
impact that sliced the engine in half, splattered elements of the
fuselage with a polyethylene based red colored material,

Nooooo, NOT polyethelene. Something else.

http://www.ntsb.gov/ntsb/brief2.asp?ev_id=20021029X05400&ntsbno=ATL03FA008&akey=1

"polyester materials based on tere- and iso- phthalates. The spectra
also suggested the possible presence of inorganic silicate compounds."

Maybe something like this boating type fiberglass fuel tank

http://continuouswave.com/whaler/reference/images/redPate531x340.jpeg

made by:

Pate Plastics Inc
(305) 754-0896 360 NW 71st St
Miami, FL

The sort of thing that would be familar to the kind of people you are
talking about.

and left an
embedded piece of mystery anodized aluminum. The only other aircraft in
the vicinity was a FedEx DC-10 traveling on a perpendicular trajectory
1000 feet above the victim aircraft at 4000 feet. It is obvious to me
that the ONLY credible explanation is a midair collision with an
"unscheduled" delivery being made by that damned FedEx DC 10- a small
RCS tightly bound volumetrically dense bundle that hit that Cessna like
a cannon ball- dropped approximately 10 seconds prior to impact so that
it retained a substantial amount of initial horizontal velocity. The
anodized aluminum is most likely the remnants of an RF package most
likely for GPS location of the delivery by the ground recovery
recipients- what little drug residue that did attach to the victim
aircraft was dissolved or washed away by the watery crash site. It is
also an incredible coincidence that this is a high activity drug
smuggling area- and the FAA allowed their ATC data recording capability
to be out of service for months. This scenario is too perfect- low
altitude drop requiring no suspicious flight path deviation- small RCS
delivery designed to free fall off the radar screen in minimum time-
altitude activated parachute at safe unobservable height- GPS location
of drop in remote inaccessible area. Who the hell do these people think
they are fooling?

But how do you get stuff to drop out of a DC-10? Why the
cloak-and-dagger stuff if the DC-10 was already customs-cleared, a
white van would suffice, no? But I don't see what the origin of the
FedEx flight was....

Best regards,
Spehro Pefhany
--
"it's the network..." "The Journey is the reward"
speff@interlog.com Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog Info for designers: http://www.speff.com

Fred Bloggs · May 22, 2004

Stefan Heinzmann wrote:

Fred Bloggs wrote:

Stefan Heinzmann wrote:

Ok, it is Preprint 6 then. Downloadable from the AES website
(www.aes.org) for $4.00 if you're a member ;-)

Thanks Fred!

I don't know- the article I have is by Herscher in Design Manual for
Transistor Circuits, Carrol, John M., McGraw-Hill, 1961, page 56,
"Designing Audio Power Amplifiers".

Preprint 6, 9th AES convention 1957: Marvin B. Herscher "High Power
Audio Amplifiers".

Abstract:
"Several models of high power audio amplifiers have been developed and
constructed, capable of 45 watts output. These amplifiers utilize a
ribbed chassis for cooling and are stable up to an ambient temperature
of 50 degrees C. One amplifier uses a series type circuit, and the other
a quasi-complementary type circuit. Amplifier size and weight are
reduced since neither circuit employs driver or output transformers
These circuits will be described and performance data for amplifiers
will be presented."

I hesitate to pay $4.00 for the document. It's not worth that much for
me. Maybe someone here has got it...

That's exactly the article I have- the series circuit refers to a single
transistor phase splitter preamp that is ac-coupled into two stacked
darlington drivers- he calls this a DC- series and AC-parallel circuit-
plus three thermistors for temperature compensation- all very leaky
germanium 2N301A's for driver- diagrams all screwed up PNP symbols with
emitters at GND and collectors at "B+"- maybe he means a negative B+

Frank Bemelman · May 22, 2004

"Spehro Pefhany" <speffSNIP@interlogDOTyou.knowwhat> schreef in bericht
news:06bva0dg6010dbd75f3uohfqptqqahfe7u@4ax.com...

[snip]

But how do you get stuff to drop out of a DC-10? Why the

Flush it down the toilet?

--
Thanks, Frank.
(remove 'x' and 'invalid' when replying by email)

Tam/WB2TT · May 22, 2004

Terry,

I ran SWCAD on your amp, and got the following results:

1. Maximum output before clipping 10V peak, or 7 VRMS.
2. To get symmetrical clipping I had to change R2 to 51K. Since the bias
point depends on the VBE of Q1 and Q2, a little trimming makes sense.
3. Input signal for 10V peak output was around 0.1V peak. Since R3 and R1
set the closed loop voltage gain at 100, this makes sense.
4. I haven't looked at this yet, but I suspect you have very little negative
feedback. I will take a look at what your open loop gain is.
5. Your problem might have to do with leakage currents of Q5 and Q6 having
nowhere to go which might explain why it worked when you switched the
transistors.

6. With no signal, the DC voltage at the collector of Q6 should be about 12
V. If not, you got problems - see 5).

Tam

Tam
"Terry Pinnell" <terrypinDELETE@THESEdial.pipex.com> wrote in message
news

u0sa0t6dnujqcjac3l7veaqfqbrqs2r1j@4ax.com...

Stefan Heinzmann <stefan_heinzmann@yahoo.com> wrote:

Terry Pinnell wrote:

Stefan Heinzmann <stefan_heinzmann@yahoo.com> wrote:
[...]
I'm also still unsure about
your Vceo measurement. You keep talking about reverse breakdown, which
makes me suspect that you applied the test voltage the wrong way. For
Vceo on a NPN transistor you have to apply the test voltage with the
positive end on the collector. The base is left open. Again, it has
nothing to do with reverse breakdown.

That's down to my careless terminology. It's clear now that I did
measure Vceo, as I intended. (With correct polarity; that would have
been a reasonably easy error to spot <g>.) In fact I gave the unit I
built a decade or two ago the label 'Reverse Breakdown Tester', as its
anticipated primary purpose was to test zeners. It does, of course,
serve well as a 'Vceo Tester'.

Ok, that sorts this one. Thanks for the clarification.

If you did that with a 2N3055 and it shows a Vceo below 60V then the
device is damaged.

Specimens 1, 5 and 8 as you saw gave 33, 17 and 21, so they get
disqualified.

I realized in the meantime that your test current was probably too low
for this test. Somewhere you said that your tester applies 340V through
a 300k series resistance. That limits the current to something around
1mA. For a power transistor like the 3055 this is perilously close to
the leakage (or cut-off) current. In other words the values you measured
may not indicate the breakdown voltage, but be an indication of a high
leakage current. The leakage current tends to rise with temperature, so
if you heat up the transistor you may find the "apparent" breakdown
voltage falls markedly.

Some 2N3055 datasheets specify limits for the cut-off current. For
example, the Fairchild MJE3055T (same chip in different package)
specifies a maximum of 1mA at Vce=70V and the base voltage at 1.5V
/below/ the emitter. This rises to 5mA at 150°C.

Consequently, your measurement of Vceo needs to be done with a collector
current that is significantly above the leakage current. The said
datasheet specifies 200mA collector current as the mesurement condition
for Vceo. That leads to significant power dissipation in the transistor,
so you need to either ensure sufficient cooling or use pulsed
measurement techniques. The latter is probably beyond the means of a
hobbyist. So in your case I would probably try a current of about
10-20mA. The question is whether your breakdown tester can supply this
current level. If so, you may try replacing the series resistor of 300k
with a 15k resistor (or better yet, make it switchable). Watch the power
dissipation!

Before you throw away the suspect transistors, you may want to try the
test with a higher current just to make sure they're not just exemplars
with a higher cut-off current, and there's nothing wrong with the Vceo.

I found a bunch of MJE3055T in my drawer and took the opportunity to put
them into a curve tracer. They are from Wingshing, apparently made in
2000. My five samples showed a Vceo between 250V and 400V, despite their
specification of 60V minimum.

[...]
You can also short the base to the emitter, in which case you measure
Vces and not Vceo. Vces is usually higher than Vceo. You should get at
least 100V with a 2N3055.

I'll try that too.

Actually, i found some manufacturers specify only 70V minimum for Vces.
Whichever, it will be higher than Vceo.

The gain is only meaningful if you provide information about the
measurement conditions. At the very least, you should provide the
collector current and the collector-emitter voltage. HFe also depends
on
the temperature, but that is harder to measure.

OK, but I still think a quick check of the sort I did can be useful.
It provides a helpful *comparative* measure of gain. Across my eight,
it ranged from 13 to 30. All things being equal, including passing the
Vceo>60V requirement, I'd choose specimens from the higher end.

That's a reasonable idea. The Fairchild datasheet contains an
interesting graph that shows the dependency between collector current
and gain at Vce=2V. At the left end of the graph the gain for Ic=10mA
shows as ~55. The maximum gain occurs at Ic=200mA, where it surpasses
100. Those are presumably typical values, not minimum ones.

This shows that the gain falls for lower currents. Your tools may well
use currents even below 10mA, as would be appropriate for small signal
transistors. I checked this with one of my MJE3055T devices, and it
shows a gain of about 30 at 150ľA collector current. The gain rises to
about 80 at 150mA collector current.

You see that the results of a measurement depend crucially on the
measurement conditions. If you don't know how your instruments measure a
certain value, you will have difficulties coming to a valid conclusion.

Many thanks, that's much appreciated. If I digress now, I'll never get
this Dog Alarm barking before our trip to Amsterdam and Germany in 8
days! But your suggestions, and a raft of other experiments, are now
on my fast-growing To Try list! My Vceo tester should manage a modest
current for a short period; I can always measure the output with my
'scope instead of a DMM, and that might tell me enough?

There's a saying in German that looses its rhyme when translating it to
English: "Wer mißt mißt Mist" (Who measures, measures rubbish).
Not a phrase to attempt after an evening in die Bierhalle <g>.

--
Terry Pinnell
Hobbyist, West Sussex, UK

Are these 2N3055s borderline spec?

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