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Interesting developments

T

Tim Williams

Jan 1, 1970
0
I decided to break out the breadboard and build a circuit reminiscient of
my Heathkit's deflection amp. This is, in order: a bipolar diff amp with
CCS tail and resistive collector load; a PNP gain stage (with emitter
degeneration), then the output, which in this case is cascode. To save
time and hassle, I built exactly one half, which means instead of a diff
pair, I grounded the input's emitter and biased its base with the function
generator and a resistor. Fair enough. I used 2N3904's for the NPNs and a
2N4403 for the PNP, being that I lack 3906's. Supply is +/- 9V, and bias
for the first stage around 5mA, second 15mA and cascode, 25mA or so.
Cascode is supplied from +150V through 2.6 kohms collector load.

So with this setup I went about testing some transistors in my parts box.
I know I have some of those chroma/video amplifier transistor guys in my
parts bin, several of them housemarked.

I found that the TO-202 things (Toshiba, pinout EBC, suprisingly) work
nicely, getting up to 2MHz or so off the bat (no emitter compensation
anywhere). That's about what the 2SC1569's do as well. I tried switching
transistors (like from switching supplies), which sucked (0.5-1MHz), I
tried other transistors, I even tried one that started oscillating at low
bias current. (In other words, high Vce --> avalanche. When biased "off",
touching the collector with a finger caused the amplitude to increase and
the falling edge to sharpen. I may have to see what fall time this
transistor produces, given a more substantial capacitance to work on. Heh,
and maybe see if the C-B junction snaps ala Larkin. ;-) )

I even tried a MOSFET, which was interesting: more voltage gain, somewhat
different bias voltage, but generally slower, probably in no small part
because I grabbed a 600V, 1 ohm device.

I tried a TO-126 transistor, 2SD986 I think it is. This was among the best
performers. I looked up the datasheet only to realize that it's a fucking
darlington! How can I get better performance from a darlington!? That ain
't right...

Finally, I explored my stash of faster transistors. I worked my way
through some TO-126 types, one rated as 400MHz fT. Pretty nice. Vcbo is
right on the bleeding edge though, like 180V. Still, I went for the last
stretch: BFQ225, a 1GHz, purportedly 100Vcbo unit! And, lo and behold,
there it worked! With emitter capacitors added (and various and sundry
ferrite beads and bypass caps to keep the breadboard from oscillating in
the hundreds of MHz..), I got out to about 20MHz -6dB.

This exploration smacks of Larkin... damn the ratings, just hook it up and
see if it burns!

I've got to wonder if there's possible damage from running over ratings
though. These aren't tubes...

On the theoretical side of things, I have a question: fT is defined for
current, correct? (h_fe = 1, an AC current parameter.) So, then the
maximum voltage gain (with respect to frequency) essentially depends on Ccb
and h_fe, right? And of course, you can get more if you restrain Vce
(cascode or emitter coupling), but that doesn't do any good when I want
absurdly high Vout here. So, how close to fT can you get while still
swinging a lot of collector voltage? What kind of voltage gain can be
generated?

How do they, like, Tek themselves for instance, do it in scopes? Well,
when they made good analog stuff anyway... The, what, 2465 is it, does 4
channels out to 500MHz or something like that, no sampling of any sort
needed. Now, I know part of that is tube design, but they still need to
make voltage. How much, how, and with what?

To get more than 20MHz at more than 20Vp-p I'm starting to have delusions
of vacuum tubes, but then, I keep trying to reassure myself that they have
the same problems (like Cgp), and that I already tried carefully to get the
best rise and fall times in that class D tube circuit...

Tim
 
J

John Devereux

Jan 1, 1970
0
Tim Williams said:
I decided to break out the breadboard and build a circuit reminiscient of
my Heathkit's deflection amp. This is, in order: a bipolar diff amp with
CCS tail and resistive collector load; a PNP gain stage (with emitter
degeneration), then the output, which in this case is cascode. To save
time and hassle, I built exactly one half, which means instead of a diff
pair, I grounded the input's emitter and biased its base with the function
generator and a resistor. Fair enough. I used 2N3904's for the NPNs and a
2N4403 for the PNP, being that I lack 3906's. Supply is +/- 9V, and bias
for the first stage around 5mA, second 15mA and cascode, 25mA or so.
Cascode is supplied from +150V through 2.6 kohms collector load.

So with this setup I went about testing some transistors in my parts box.
I know I have some of those chroma/video amplifier transistor guys in my
parts bin, several of them housemarked.

I found that the TO-202 things (Toshiba, pinout EBC, suprisingly) work
nicely, getting up to 2MHz or so off the bat (no emitter compensation
anywhere). That's about what the 2SC1569's do as well. I tried switching
transistors (like from switching supplies), which sucked (0.5-1MHz), I
tried other transistors, I even tried one that started oscillating at low
bias current. (In other words, high Vce --> avalanche. When biased "off",
touching the collector with a finger caused the amplitude to increase and
the falling edge to sharpen. I may have to see what fall time this
transistor produces, given a more substantial capacitance to work on. Heh,
and maybe see if the C-B junction snaps ala Larkin. ;-) )

I even tried a MOSFET, which was interesting: more voltage gain, somewhat
different bias voltage, but generally slower, probably in no small part
because I grabbed a 600V, 1 ohm device.

I tried a TO-126 transistor, 2SD986 I think it is. This was among the best
performers. I looked up the datasheet only to realize that it's a fucking
darlington! How can I get better performance from a darlington!? That ain
't right...

Finally, I explored my stash of faster transistors. I worked my way
through some TO-126 types, one rated as 400MHz fT. Pretty nice. Vcbo is
right on the bleeding edge though, like 180V. Still, I went for the last
stretch: BFQ225, a 1GHz, purportedly 100Vcbo unit! And, lo and behold,
there it worked! With emitter capacitors added (and various and sundry
ferrite beads and bypass caps to keep the breadboard from oscillating in
the hundreds of MHz..), I got out to about 20MHz -6dB.

This exploration smacks of Larkin... damn the ratings, just hook it up and
see if it burns!

I've got to wonder if there's possible damage from running over ratings
though. These aren't tubes...

On the theoretical side of things, I have a question: fT is defined for
current, correct? (h_fe = 1, an AC current parameter.) So, then the
maximum voltage gain (with respect to frequency) essentially depends on Ccb
and h_fe, right? And of course, you can get more if you restrain Vce
(cascode or emitter coupling), but that doesn't do any good when I want
absurdly high Vout here. So, how close to fT can you get while still
swinging a lot of collector voltage? What kind of voltage gain can be
generated?

How do they, like, Tek themselves for instance, do it in scopes? Well,
when they made good analog stuff anyway... The, what, 2465 is it, does 4
channels out to 500MHz or something like that, no sampling of any sort
needed. Now, I know part of that is tube design, but they still need to
make voltage. How much, how, and with what?

There is an chapter on the development history of Tektronix vertical
amplifiers in the book "Analog Circuit Design: Art, Science and
Personalities" edited by Jim Williams.

<http://www.amazon.com/Analog-Circuit-Design-Personalities-Engineers/dp/0750696400>

You might find it interesting - the 7104 went up to 1GHz, still the
fastest analog scope made AFIAK. It uses a circuit configuration they
invented called an "Ft doubler" :)
To get more than 20MHz at more than 20Vp-p I'm starting to have delusions
of vacuum tubes, but then, I keep trying to reassure myself that they have
the same problems (like Cgp), and that I already tried carefully to get the
best rise and fall times in that class D tube circuit...

It *is* interesting. I was thinking of making a higher voltage, higher
current buffer for my arb signal generator. I could use it to test
things like surge protection and PSRR on power supply regulators,
e.g. automotive load dump simulation.
 
J

Jan Panteltje

Jan 1, 1970
0
There is an chapter on the development history of Tektronix vertical
amplifiers in the book "Analog Circuit Design: Art, Science and
Personalities" edited by Jim Williams.

<http://www.amazon.com/Analog-Circuit-Design-Personalities-Engineers/dp/0750696400>

You might find it interesting - the 7104 went up to 1GHz, still the
fastest analog scope made AFIAK. It uses a circuit configuration they
invented called an "Ft doubler" :)


It *is* interesting. I was thinking of making a higher voltage, higher
current buffer for my arb signal generator. I could use it to test
things like surge protection and PSRR on power supply regulators,
e.g. automotive load dump simulation.

I just managed to download the whole Tek465 (100MHz analog) service,
calibration, and diagrams, partlist, and manual, from here:
http://www.eserviceinfo.com/download.php?fileid=23085
Just looking at the vertical amp.
Now there is some fun.

I downloaded all 15 sections one by one, and then did in Linux:
unrar e Tek465_Service_Manual.part01.rar
This generated one big 291 page 465.pdf, with everything in it.

Maybe some here have a 465, well here is the docs :)
 
N

Nico Coesel

Jan 1, 1970
0
John Devereux said:
There is an chapter on the development history of Tektronix vertical
amplifiers in the book "Analog Circuit Design: Art, Science and
Personalities" edited by Jim Williams.

<http://www.amazon.com/Analog-Circuit-Design-Personalities-Engineers/dp/0750696400>

You might find it interesting - the 7104 went up to 1GHz, still the
fastest analog scope made AFIAK. It uses a circuit configuration they
invented called an "Ft doubler" :)

IIRC Iwatsu has analog scopes that go beyond 1GHz.
 
T

Tim Williams

Jan 1, 1970
0
Jan Panteltje said:
I just managed to download the whole Tek465 (100MHz analog) service,
calibration, and diagrams, partlist, and manual, from here:
http://www.eserviceinfo.com/download.php?fileid=23085
Just looking at the vertical amp.
Now there is some fun.

I downloaded all 15 sections one by one, and then did in Linux:
unrar e Tek465_Service_Manual.part01.rar
This generated one big 291 page 465.pdf, with everything in it.

Maybe some here have a 465, well here is the docs :)

I have a 475 and the docs, but I don't recall seeing a schematic inside.
Probably just as well, all the junk is integrated (thick film IIRC?).

Down in the schematics, it appears to be some sort of cross-coupled
differential cascode?

Hmm...

Tim
 
J

Jan Panteltje

Jan 1, 1970
0
I have a 475 and the docs, but I don't recall seeing a schematic inside.
Probably just as well, all the junk is integrated (thick film IIRC?).

I have worked for Tek, last scope I remember was 100MHz analog + 1Gsamples.
They used thick film restors in the vertical output stages (quite a bit
of power there).
The digital part was just a x86 board (286??), but of course with fast
ADC and RAM to grab stuff.
Cannot remember the model number, but for the rest I think there were no
thick film, but only normal transistors, in the design.
Too long ago, sorry.

Down in the schematics, it appears to be some sort of cross-coupled
differential cascode?

Yep.

Somebody will perhaps make a scope on a chip one day,
with build in driver for touchscreen.
Like an Iphone, networked of course.

Those touch screens seem way cool, no more buttons needed.
 
T

Tim Williams

Jan 1, 1970
0
Nico Coesel said:
IIRC Iwatsu has analog scopes that go beyond 1GHz.

Ya know, that's an absurdly fast slew rate...

I've gotta wonder, do you get into troubles when swinging the electron beam
that fast? Does it just spray out wherever you point it, regardless of the
rate? The bend in the beam isn't exactly negligible, especially as the
beam isn't going nearly the speed of light, and it has some mass.

I wonder if you can hook up the CRT to a waveguide and get interesting TWT
style responses from it. Not at much power of course.

Tim
 
A

Arie de Muynck

Jan 1, 1970
0
"Tim Williams" ...
Ya know, that's an absurdly fast slew rate...

I've gotta wonder, do you get into troubles when swinging the electron
beam
that fast? Does it just spray out wherever you point it, regardless of
the
rate? The bend in the beam isn't exactly negligible, especially as the
beam isn't going nearly the speed of light, and it has some mass.

I wonder if you can hook up the CRT to a waveguide and get interesting TWT
style responses from it. Not at much power of course.

I remember CRT's with multiple section deflection plates connected by an
internal delay line so the "wave" over the deflection plates matched the
electron beam speed.


Y+ ----UUUUUUUUUUUUUUUUUUUUU
_|_ _|_ _|_ _|_ _|_ _|_
] | ........................................ > to screen
] | - - - - - - - - - - - -
| | | | | |
Y- ----UUUUUUUUUUUUUUUUUUUUU


Arie de Muynck
 
I decided to break out the breadboard and build a circuit reminiscient of
my Heathkit's deflection amp. This is, in order: a bipolar diff amp with
CCS tail and resistive collector load; a PNP gain stage (with emitter
degeneration), then the output, which in this case is cascode. To save
time and hassle, I built exactly one half, which means instead of a diff
pair, I grounded the input's emitter and biased its base with the function
generator and a resistor. Fair enough. I used 2N3904's for the NPNs and a
2N4403 for the PNP, being that I lack 3906's. Supply is +/- 9V, and bias
for the first stage around 5mA, second 15mA and cascode, 25mA or so.
Cascode is supplied from +150V through 2.6 kohms collector load.

So with this setup I went about testing some transistors in my parts box.
I know I have some of those chroma/video amplifier transistor guys in my
parts bin, several of them housemarked.

I found that the TO-202 things (Toshiba, pinout EBC, suprisingly) work
nicely, getting up to 2MHz or so off the bat (no emitter compensation
anywhere). That's about what the 2SC1569's do as well. I tried switching
transistors (like from switching supplies), which sucked (0.5-1MHz), I
tried other transistors, I even tried one that started oscillating at low
bias current. (In other words, high Vce --> avalanche. When biased "off",
touching the collector with a finger caused the amplitude to increase and
the falling edge to sharpen. I may have to see what fall time this
transistor produces, given a more substantial capacitance to work on. Heh,
and maybe see if the C-B junction snaps ala Larkin. ;-) )

I even tried a MOSFET, which was interesting: more voltage gain, somewhat
different bias voltage, but generally slower, probably in no small part
because I grabbed a 600V, 1 ohm device.

I tried a TO-126 transistor, 2SD986 I think it is. This was among the best
performers. I looked up the datasheet only to realize that it's a fucking
darlington! How can I get better performance from a darlington!? That ain
't right...

Finally, I explored my stash of faster transistors. I worked my way
through some TO-126 types, one rated as 400MHz fT. Pretty nice. Vcbo is
right on the bleeding edge though, like 180V. Still, I went for the last
stretch: BFQ225, a 1GHz, purportedly 100Vcbo unit! And, lo and behold,
there it worked! With emitter capacitors added (and various and sundry
ferrite beads and bypass caps to keep the breadboard from oscillating in
the hundreds of MHz..), I got out to about 20MHz -6dB.

This exploration smacks of Larkin... damn the ratings, just hook it up and
see if it burns!

I've got to wonder if there's possible damage from running over ratings
though. These aren't tubes...

On the theoretical side of things, I have a question: fT is defined for
current, correct? (h_fe = 1, an AC current parameter.) So, then the
maximum voltage gain (with respect to frequency) essentially depends on Ccb
and h_fe, right? And of course, you can get more if you restrain Vce
(cascode or emitter coupling), but that doesn't do any good when I want
absurdly high Vout here. So, how close to fT can you get while still
swinging a lot of collector voltage? What kind of voltage gain can be
generated?

How do they, like, Tek themselves for instance, do it in scopes? Well,
when they made good analog stuff anyway... The, what, 2465 is it, does 4
channels out to 500MHz or something like that, no sampling of any sort
needed. Now, I know part of that is tube design, but they still need to
make voltage. How much, how, and with what?

To get more than 20MHz at more than 20Vp-p I'm starting to have delusions
of vacuum tubes, but then, I keep trying to reassure myself that they have
the same problems (like Cgp), and that I already tried carefully to get the
best rise and fall times in that class D tube circuit...

Tim

I interviewed with the Tek chip/hybrid group in the darks ages, then
ran into a few of them again after Maxim bought the business. They had
an in-house design manual full of tricks. I don't know if it ever made
it outside the company. Anyway, I recall one of the designers
mentioning that they did some design where they took a low voltage
buffer and turned it into a high voltage buffer by floating the power
supply rails with the input signal, i.e. create a power supply window
suitable for tracking the input.

Interestingly enough, flipping through that manual during the
interview, it was the first place I ever heard of thermal distortion.
However, if you think about the low amount of feedback in analog scope
circuits, I could see why they ran into such problems.
 
F

Frank Miles

Jan 1, 1970
0
"Tim Williams" ...
Ya know, that's an absurdly fast slew rate...

I've gotta wonder, do you get into troubles when swinging the electron
beam
that fast? Does it just spray out wherever you point it, regardless of
the
rate? The bend in the beam isn't exactly negligible, especially as the
beam isn't going nearly the speed of light, and it has some mass.

I wonder if you can hook up the CRT to a waveguide and get interesting TWT
style responses from it. Not at much power of course.

I remember CRT's with multiple section deflection plates connected by an
internal delay line so the "wave" over the deflection plates matched the
electron beam speed.


Y+ ----UUUUUUUUUUUUUUUUUUUUU
_|_ _|_ _|_ _|_ _|_ _|_
] | ........................................ > to screen
] | - - - - - - - - - - - -
| | | | | |
Y- ----UUUUUUUUUUUUUUUUUUUUU


Arie de Muynck

This was called "distributed deflection". It was used, IIRC, as far back as some
5xx series 'scopes. And in any 'scope Tek made that worked over 100MHz, including
the portable 454. If you looked at the schematic for the vertical deflection
system, it had a wizard on a skateboard (or some such thing).

I don't know if I ever saw a "manual" of high-speed design such as what someone
else described. Perhaps that was assembled after I left Tek. It would have been
based on the "AFTR" (Amplifier Frequency and Transient Response) course, which
was really a wonderful class. I took it when Carl Battjes taught it, and again
with Bruce Hofer. They were excellent and inspiring teachers, though they had
somewhat different styles. I've found only some of the concepts taught in the
course in "outside" references since that time.

------------------------------

Ft doublers and such were really the province of the integrated circuit. Of course,
Tek had serious difficulties in the early days of their IC manufacturing. For
example, when the 465 was originally designed, it had an IC-based vertical deflection
amplifier (which, IIRC, had an Ft doubler). As shipping date approached, they found
they couldn't produce enough for it and the 7000 series, which needed the same IC.
Jim Woo - another great Tek engineer - took just one weekend to design a discrete
version which was used through the entire life of the original 465 (including B,
but not the M version). Some years after he had designed this amplifier, I asked
him a question about the particular coupling method he had used in connecting the
amplifier to the deflection plates. This is a critical area, one of the fundamental
limits to the bandwidth of a 'scope - due to the resonant combination of the lead
inductance with the capacitance between the plates. It turns out that it hadn't
been done by him, but someone in production engineering! He'd never noticed it.
Of course, distributed deflection overcomes this limitation, becoming a transmission
line (complete with termination resistors, which aren't shown in the drawing above).

Fun times.

-f
 
J

JosephKK

Jan 1, 1970
0
Arie de Muynck [email protected] posted to sci.electronics.design:
"Tim Williams" ...
Ya know, that's an absurdly fast slew rate...

I've gotta wonder, do you get into troubles when swinging the
electron beam
that fast? Does it just spray out wherever you point it,
regardless of the
rate? The bend in the beam isn't exactly negligible, especially as
the beam isn't going nearly the speed of light, and it has some
mass.

I wonder if you can hook up the CRT to a waveguide and get
interesting TWT
style responses from it. Not at much power of course.

I remember CRT's with multiple section deflection plates connected
by an internal delay line so the "wave" over the deflection plates
matched the electron beam speed.


Y+ ----UUUUUUUUUUUUUUUUUUUUU
_|_ _|_ _|_ _|_ _|_ _|_
] | ........................................ > to screen
] | - - - - - - - - - - - -
| | | | | |
Y- ----UUUUUUUUUUUUUUUUUUUUU


Arie de Muynck

Yep, Tektronix strikes again. It really improved the deflection
sensitivity, to on the order if 1 v/cm as well.
 
T

Tim Williams

Jan 1, 1970
0
Ordered some 2SC3502's earlier this week (heyyy, Mouser upgraded my
shipping for free!), among other items I needed. I set up approximately
the same circuit described below. With some puttering, I've got a pretty
nice 10MHz bandwidth out of the thing, including peaking coil, emitter
compensation cap (on only the output stage: the MPS3653 and 2N3906 "half
diff" and volt amp stages are amply fast on their own, giving <=10ns
rise/fall time), and lots of PS caps on the breadboard.

I wonder how these 2SC3502's handle capacitance. It can't be pretty. I've
only got 30mA to play around with here. Maybe I can use that
peaking-series-coil trick to patch it over.

Which, incidentially, provides a good segue into something else that
crossed my mind: would it be useful to build a relatively slow amp to
supply the low frequency range (perhaps 500kHz to DC), then using a series
pulse transformer, couple in the 500kHz-20MHz+ from a good amp? The
advantage being, you can pump a whole lot more current into the transformer
using fast 40Vcbo transistors, while the turns ratio gets you the same
voltage swing needed. The rub is you need to balance the crossover region
and gain and phase.

I also found a chunk of twin lead laying around. Oooh, twin lead... Think
I'll desolder the wires on the Heathkit's vert amp board and run pair out
to the breadboard so I can putter around with my amp.. see what kind of
practical voltage swing I need, etc.

Tim
 
K

Ken S. Tucker

Jan 1, 1970
0
Ordered some 2SC3502's earlier this week (heyyy, Mouser upgraded my
shipping for free!), among other items I needed. I set up approximately
the same circuit described below. With some puttering, I've got a pretty
nice 10MHz bandwidth out of the thing, including peaking coil, emitter
compensation cap (on only the output stage: the MPS3653 and 2N3906 "half
diff" and volt amp stages are amply fast on their own, giving <=10ns
rise/fall time), and lots of PS caps on the breadboard.

I wonder how these 2SC3502's handle capacitance. It can't be pretty. I've
only got 30mA to play around with here. Maybe I can use that
peaking-series-coil trick to patch it over.

Which, incidentially, provides a good segue into something else that
crossed my mind: would it be useful to build a relatively slow amp to
supply the low frequency range (perhaps 500kHz to DC), then using a series
pulse transformer, couple in the 500kHz-20MHz+ from a good amp? The
advantage being, you can pump a whole lot more current into the transformer
using fast 40Vcbo transistors, while the turns ratio gets you the same
voltage swing needed. The rub is you need to balance the crossover region
and gain and phase.

I also found a chunk of twin lead laying around. Oooh, twin lead... Think
I'll desolder the wires on the Heathkit's vert amp board and run pair out
to the breadboard so I can putter around with my amp.. see what kind of
practical voltage swing I need, etc.

Tim

--
Deep Fryer: A very philosophical monk.
Website @http://webpages.charter.net/dawill/tmoranwms


news:[email protected]...

Here's something close,
http://www.ortodoxism.ro/datasheets/nationalsemiconductor/DS005507.PDF
but it may not give the voltage swing you want.

Do you guys remember when tuner's used tubes to
tune UHF. Tim hasn't been forthcoming with entire
spec, frequency range, distortion, power output, and
voltage Vp-Vp/current output, have you Tim?
Ken
 
T

Tim Williams

Jan 1, 1970
0
Ken S. Tucker said:
Here's something close,
http://www.ortodoxism.ro/datasheets/nationalsemiconductor/DS005507.PDF
but it may not give the voltage swing you want.

Yeah, I want it in the 200V supply range.
Do you guys remember when tuner's used tubes to
tune UHF.

I do, if not personally. I have some 6HA5, 6AK5, et al., even a pair of
Nuvistors laying around.
Tim hasn't been forthcoming with entire
spec, frequency range, distortion, power output, and
voltage Vp-Vp/current output, have you Tim?

No, I haven't. Funny how that is. ;-)

Tim
 
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