sad, sad

[David Lesher]

Guy Macon <http://www.guymacon.com> writes:

And leaving the rest of the circuit vacuum tubes?

Making new transistorized products that have the same basic circuit
topology (with sertain stanbdard changes) is something that any EE
used to be able to do. When they got to the classic HP Osc., they
found that getting rid of the monode (light bulb) was a *lot* harder
than getting rid of the other vacuum tubes.

Do note the 200CD has at least 2 generations. It started life
with octal tubes. After they vanished, it was redesigned with
miniature tubes.


--
A host is a host from coast to coast.................wb8foz@nrk.com
& no one will talk to a host that's close........[v].(301) 56-LINUX
Unless the host (that isn't close).........................pob 1433
is busy, hung or dead....................................20915-1433

 

[Phil Hobbs]

Joel Kolstad wrote:

I thought that (contemporary) Tektronix oscilloscopes also used a similar
CCD-type front end? (Very fast input, slow output.) My belief was that
whereas in the analog 'scope days the vertical amplifiers were considered
the most challenging part of the product, with today's digital scopes it's
the triggering because it's something that actually has to run at full
speed.

LeCroy's usual claim to fame seemed to be that they have (or used to have)
much deeper memories for the price than Tek or Agilent.

Analog scope vertical amplifiers are hard because they have to drive
deflection plates--high voltage, lots of capacitance, travelling-wave
excitation (because the electrons and the signal are both crossing the
plate). I hope the vertical amplifier and digitizer are going at full speed too.

Cheers,

Phil Hobbs

 

[Rich Grise]

On Monday 11 October 2004 09:56 am, Joel Kolstad did deign to grace us with
the following:

"Phil Hobbs" <pcdhSpamMeSenseless@us.ibm.com> wrote in message
news:4169F802.7040206@us.ibm.com...
Analog scope vertical amplifiers are hard because they have to drive
deflection plates--high voltage, lots of capacitance, travelling-wave
excitation (because the electrons and the signal are both crossing the
plate).

Ah, interesting.

I hope the vertical amplifier and digitizer are going at full speed too.

Well, I'm thinking the 'vertical amplifier' in a modern DSO is only
driving the load of the S/H of the digitizer -- a much easier design that
the
deflection plates, I would imagine. The digitizer goes full speed, yes,
but I believe it's relatively straightforward to use interleaved
converters so that you can readily sample at, say, 5GSsp while not needing
any invidiaul
converter to run at more than some hundreds of MHz. (On the other hand,
you do need full speed sample & holds... I suppose that's still
challenging...)

Just to poke my nose in, the actual deflection amps, that drive the plates

themselves, are really quite simple. I think you're exaggerating on the
capacitance - the plates are about a square cm. or 2, about a cm apart - and
it's less than hundred volts, if that. Well, < 100 differential - they'll
probably be biased up somewhere if the cathode (or control grid) is
grounded.

But then, I was raised on toobz, so to me 250V is "low." ;-) Just a couple
of volts on the grid can give you a hundred on the plate without even
thinking about it.

Cheers!
Rich

 

[John Larkin]

On Mon, 11 Oct 2004 20:21:11 GMT, Rich Grise <null@example.net> wrote:

On Monday 11 October 2004 09:56 am, Joel Kolstad did deign to grace us with
the following:

"Phil Hobbs" <pcdhSpamMeSenseless@us.ibm.com> wrote in message
news:4169F802.7040206@us.ibm.com...
Analog scope vertical amplifiers are hard because they have to drive
deflection plates--high voltage, lots of capacitance, travelling-wave
excitation (because the electrons and the signal are both crossing the
plate).

Ah, interesting.

I hope the vertical amplifier and digitizer are going at full speed too.

Well, I'm thinking the 'vertical amplifier' in a modern DSO is only
driving the load of the S/H of the digitizer -- a much easier design that
the
deflection plates, I would imagine. The digitizer goes full speed, yes,
but I believe it's relatively straightforward to use interleaved
converters so that you can readily sample at, say, 5GSsp while not needing
any invidiaul
converter to run at more than some hundreds of MHz. (On the other hand,
you do need full speed sample & holds... I suppose that's still
challenging...)

Just to poke my nose in, the actual deflection amps, that drive the plates
themselves, are really quite simple. I think you're exaggerating on the
capacitance - the plates are about a square cm. or 2, about a cm apart - and
it's less than hundred volts, if that. Well, < 100 differential - they'll
probably be biased up somewhere if the cathode (or control grid) is
grounded.

But then, I was raised on toobz, so to me 250V is "low." ;-) Just a couple
of volts on the grid can give you a hundred on the plate without even
thinking about it.

Cheers!
Rich

That's fine if you're happy with a few hundred KHz of bandwidth. My
Tek 545, 30 MHz, has 20 tubes in the vertical amp, with the final
stage being a dozen 6DK6's in a differential distributed amplifier
configuration, with roughly 80 passives. The vertical delay line has
an additional 180 passive parts, including 50 trimmer capacitors.

John