Are these 2N3055s borderline spec?

[Spehro Pefhany]

On 24 May 2004 15:13:20 -0700, the renowned jeffm_@email.com (JeffM)
wrote:

Nooooo, NOT polyethelene. Something else.
"polyester materials based on tere- and iso- phthalates. The spectra
also suggested the possible presence of inorganic silicate
compounds."
Spehro Pefhany

Speff,
Were you a chemist in a previous life?
http://www.univarcanada.com/Personnel/Display?readform&group=Compounding&industry=Chemical+Compounding

Ah yes, my evil twin. Or something.

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

 

[Winfield Hill]

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.

And even before that in H C Lin's 1956 article and 1955 patent.
I'll send you a pdf file copy if you send me your email address.

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:

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

This schematic is missing a critical old ingredient, the bootstrap
capacitor to a split version of Rg, making it effectively a current
source. Greatly increasing the gain and reducing the distortion by
keeping the "CE preamp" collector current more nearly constant, hence
reducing the r_e swing - one of the big causes of distortion in this
type of old circuit.

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,
- Win

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

 

[Terry Pinnell]

John Popelish <jpopelish@rica.net> wrote:

Terry Pinnell wrote:
(snip)

I also thought I'd see what effect the D1/D2 type had, leaving aside
power diodes.
R7----------------
Type 47 120 150
------ ----- ----- ------
DEFAULT 5nA 36nA 850nA
1N4148 500nA 2.2mA 35mA
1N914 5nA 13nA 220nA
1N4001 5nA 7nA 54nA

I'm very surprised that what I'd always thought of as a 'typical'
small signal Si diode, the 1N914, gives virtually no quiescent current
at all, even at the 'high' values I selected.
(snip)

I suspect your model for the 1N914 is faulty.

That's bad news! When I do remember to specify anything other than
CM's DEFAULT diode, I tend to use either 1N4148 or 1N914.
Does anything jump out here please?
IN914 model
-----------
IS: Saturation current 7.075n
RS: Ohmic resistance 780.0m
N: Emission coefficient 1.950
TT: Transit-time 7.200n
CJO: Zero-bias junction capacitance 4.000p
VJ: Junction potential 657.0m
M: Grading coefficient 400.0m
EG: Activation energy 1.110
XTI: Saturation-current temperature exponent 3.000
KF: Flicker-noise coefficient 0.000
AF: Flicker-noise exponent 1.000
FC: Foward-bias depletion coefficient 500.0m
BV: Reverse breakdown voltage 100.0
IBV: Current at breakdown voltage 100.0u
TNOM: Parammeter measurement temperature 27.00

By the way, your bias adjust circuit has a suicide failure mode. If
the sliding contact becomes the least bit intermittent, the bias
current pops up destructively. The solution to this problem is to use
a transistor as a diode multiplier, with a fixed resistor collector to
base and an adjustable resistor base to emitter, so that the
adjustable element is what holds the bias voltage up. That way, if
the resistor opens, the bias voltage collapses to a 1 diode drop.

I have seen lots of Vbe multipliers with the sliding contact connected
to the base, and the ends connected to the collector and emitter (with
fixed resistors in series) but this configuration has the same fatal
failure mode as your diode resistor circuit does.

I'll have to be doubly alert to your BTWs, judging by that one! Thanks
for the warning.

--
Terry Pinnell
Hobbyist, West Sussex, UK

 

[Terry Pinnell]

"Tam/WB2TT" <t-tammaru@c0mca$t.net> wrote:

Terry, I think I solved your original question. Run SWCAD with the collector
of Q5 tied to the base, instead of to +24. Now put that back, but open up
the emitter of Q6, and tie that to the base. One will work, the other will
not. I bet the 2N2905 was running hot!

Not sure I follow you, Tam. Maybe I've missed a key point? I can't see
how tying base of Q5 to collector, or Q5 base to emitter can work.
Simulation in both SWCAD and CM confirms that.

--
Terry Pinnell
Hobbyist, West Sussex, UK

 

[Terry Pinnell]

Winfield Hill <Winfield_member@newsguy.com> 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.

And even before that in H C Lin's 1956 article and 1955 patent.
I'll send you a pdf file copy if you send me your email address.

R Legg posted the web link to that article in the main thread some
while ago:
From: legg <legg@nospam.magma.ca>
Date: Sat, 15 May 2004 06:36:22 GMT
Newsgroups: sci.electronics.design
Subject: Re: Distortion from audio power amp
Message-ID: <ko6aa0dei6ut83b9jc2ku0r3aflqgf25pu@4ax.com>

--
Terry Pinnell
Hobbyist, West Sussex, UK

 

[Tam/WB2TT]

"Terry Pinnell" <terrypinDELETE@THESEdial.pipex.com> wrote in message
news:sps5b0ttce67pm56dumj18uev1v0h7ivkr@4ax.com...

"Tam/WB2TT" <t-tammaru@c0mca$t.net> wrote:

Terry, I think I solved your original question. Run SWCAD with the
collector
of Q5 tied to the base, instead of to +24. Now put that back, but open up
the emitter of Q6, and tie that to the base. One will work, the other
will
not. I bet the 2N2905 was running hot!

Not sure I follow you, Tam. Maybe I've missed a key point? I can't see
how tying base of Q5 to collector, or Q5 base to emitter can work.
Simulation in both SWCAD and CM confirms that.

--
Terry Pinnell
Hobbyist, West Sussex, UK

Maybe I should have mentioned what the intent was, not how I did it. SWCAD

shows that by removing Q6, the amp will not work, because Q3 can not drive
the load. If you remove Q6 instead, there is still a 0 impedance path from
the emitter of Q4 to the load, and the amp will work until Q4 possibly melts
down. Note that the base current of Q3 is limited by resistors R5 and R6.
The base current of Q4 is limited only by the drive capability of Q2. I did
this for a closed loop gain of 10; R3=47K, R2=5.3K.

To get back to your previous question, my original model did not have
crossover distortion. When I replaced generic diodes D1 and D2 with 1N4148
types, I did get crossover distortion until I made R7=120 Ohms. This biased
Q6 at something less than 1 ma. Q5 will always have some quiescent current
because it has to drive current into Q1 and R3. I don't know what convention
says about quiescent current, but you really want to reduce voltage dead
time between the Q5 and Q6 conduction times. Looked at an old RCA schematic.
They did not say what current they biased the output at, but by deduction, I
can say it was less than 10 ma. The more the current, the more important it
is to get thermal tracking of the diodes with the output transistors.

To measure quiescent current, you might want to temporarily increase the
value of R11, or remove it, and put a ma meter in its place.

Tam

 

[Tam/WB2TT]

Should have mentioned, my Q4 is a 2N2905A.

Tam

 

[John Popelish]

Terry Pinnell wrote:

John Popelish <jpopelish@rica.net> wrote:

Terry Pinnell wrote:
(snip)

I also thought I'd see what effect the D1/D2 type had, leaving aside
power diodes.
R7----------------
Type 47 120 150
------ ----- ----- ------
DEFAULT 5nA 36nA 850nA
1N4148 500nA 2.2mA 35mA
1N914 5nA 13nA 220nA
1N4001 5nA 7nA 54nA

I'm very surprised that what I'd always thought of as a 'typical'
small signal Si diode, the 1N914, gives virtually no quiescent current
at all, even at the 'high' values I selected.
(snip)

I suspect your model for the 1N914 is faulty.

That's bad news! When I do remember to specify anything other than
CM's DEFAULT diode, I tend to use either 1N4148 or 1N914.
Does anything jump out here please?
IN914 model
-----------
IS: Saturation current 7.075n
RS: Ohmic resistance 780.0m
N: Emission coefficient 1.950
TT: Transit-time 7.200n
CJO: Zero-bias junction capacitance 4.000p
VJ: Junction potential 657.0m
M: Grading coefficient 400.0m
EG: Activation energy 1.110
XTI: Saturation-current temperature exponent 3.000
KF: Flicker-noise coefficient 0.000
AF: Flicker-noise exponent 1.000
FC: Foward-bias depletion coefficient 500.0m
BV: Reverse breakdown voltage 100.0
IBV: Current at breakdown voltage 100.0u
TNOM: Parammeter measurement temperature 27.00
(snip)

I am not familiar with spice models to glance at this list and surmise
what isn't right. You might compare these numbers to your models of
the 1N4148 and 1N4001 and see how they differ and how they are
similar.

But based on the similar size package, current rating and technology
of the 1N914 and 1N4148, I would have expected them to be much more
similar than either was to a 1N4001. In fact, I seem to remember
seeing (just in the last weekend) a graph of forward voltage versus
current that showed the 1N914 has higher drop above a milliamp or so
than the 1N4148, but I can't relocate it at the moment.

Fairchild uses the same data sheet for both the 1N914 and 1N4148.
This doesn't guarantee that early versions of these diodes were not
more different.


--
John Popelish

 

[Terry Pinnell]

"Tam/WB2TT" <t-tammaru@c0mca$t.net> wrote:

"Terry Pinnell" <terrypinDELETE@THESEdial.pipex.com> wrote in message
news:sps5b0ttce67pm56dumj18uev1v0h7ivkr@4ax.com...
"Tam/WB2TT" <t-tammaru@c0mca$t.net> wrote:

Terry, I think I solved your original question. Run SWCAD with the
collector
of Q5 tied to the base, instead of to +24. Now put that back, but open up
the emitter of Q6, and tie that to the base. One will work, the other
will
not. I bet the 2N2905 was running hot!

Not sure I follow you, Tam. Maybe I've missed a key point? I can't see
how tying base of Q5 to collector, or Q5 base to emitter can work.
Simulation in both SWCAD and CM confirms that.

--
Terry Pinnell
Hobbyist, West Sussex, UK

Maybe I should have mentioned what the intent was, not how I did it. SWCAD
shows that by removing Q6, the amp will not work, because Q3 can not drive
the load. If you remove Q6 instead, there is still a 0 impedance path from
the emitter of Q4 to the load, and the amp will work until Q4 possibly melts
down. Note that the base current of Q3 is limited by resistors R5 and R6.
The base current of Q4 is limited only by the drive capability of Q2. I did
this for a closed loop gain of 10; R3=47K, R2=5.3K.

To get back to your previous question, my original model did not have
crossover distortion. When I replaced generic diodes D1 and D2 with 1N4148
types, I did get crossover distortion until I made R7=120 Ohms. This biased
Q6 at something less than 1 ma. Q5 will always have some quiescent current
because it has to drive current into Q1 and R3. I don't know what convention
says about quiescent current, but you really want to reduce voltage dead
time between the Q5 and Q6 conduction times. Looked at an old RCA schematic.
They did not say what current they biased the output at, but by deduction, I
can say it was less than 10 ma. The more the current, the more important it
is to get thermal tracking of the diodes with the output transistors.

To measure quiescent current, you might want to temporarily increase the
value of R11, or remove it, and put a ma meter in its place.

Tam

Thanks for the clarification, Tam. I'll study that and experiment

along those lines as soon as I can.

Meanwhile, quiescent voltage across R11 is about 3mV. It starts out
from cold at around 1mV and rises to that level in about 5 mins.


--
Terry Pinnell
Hobbyist, West Sussex, UK



--
Terry Pinnell
Hobbyist, West Sussex, UK

 

[Tam/WB2TT]

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

Meanwhile, quiescent voltage across R11 is about 3mV. It starts out
from cold at around 1mV and rises to that level in about 5 mins.


--
Terry Pinnell
Hobbyist, West Sussex, UK



--
Terry Pinnell
Hobbyist, West Sussex, UK




I think that is good.

BTW, I think I figured out how to measure open loop response without messing
up the bias. Make R3 into two resistors, and bypass the center with a
capacitor to ground.

Tam

 

[Terry Pinnell]

Stefan Heinzmann <stefan_heinzmann@yahoo.com> wrote:

Talking about thermal stability: Has anyone mentioned that it would be a
good idea to thermally couple D1 and D2 to the output transistors to
reduce bias voltage at higher temperatures?

I built them in between Q5 and Q6 on the case, as mentioned here:
Newsgroups: alt.binaries.schematics.electronic
Subject: Re: Hobbyists old amplifier
Date: Sun, 16 May 2004 19:16:52 +0100
Message-ID: <usbfa0lfjl0vmi74rn6752dt60srbo9hj0@4ax.com>

--
Terry Pinnell
Hobbyist, West Sussex, UK