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  #41   Report Post  
Paul Stamler
 
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"Arny Krueger" wrote in message
...

Slew rate and bandwidth. Those Philbrick and HP tube

op-amps
really did not have the bandwidth for anything

approaching
audio. --scott


When I was an undergraduate back in the 60s, I did some time
*programming* analog computers. My recollection is the
Philbrick parts posted at
http://www.national.com/rap/vacuumtubes.html were
bottom-of-the barrel parts.

The sort of vacuum tube op amps I'm thinking of were more on
the order of this one:

http://ed-thelen.org/dc_amp.gif

There's really no excuse for vacuum tube amplifiers to be
terribly slow, after all Tektronics made some pretty fast
'scopes out of bottles....


Right, but the Philbrock jobs were optimized for DC and low-frequency
operation, not audio. As you say, they were for analog computing, and that
usually didn't involve much in the way of high frequencies.

Peace,
Paul0


  #42   Report Post  
Adrian Tuddenham
 
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Pooh Bear wrote:


You should pop over to s.e.d and see what nonsence he's been posting there (
along with a couple of others ) about decibels.

See the thread - 'the truth about decibels'.


....and make up you own mind about who said what.

--
~ Adrian Tuddenham ~
(Remove the ".invalid"s and add ".co.uk" to reply)
www.poppyrecords.co.uk
  #43   Report Post  
Arny Krueger
 
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"Paul Stamler" wrote in message

"Arny Krueger" wrote in message
...

Slew rate and bandwidth. Those Philbrick and HP tube

op-amps
really did not have the bandwidth for anything

approaching
audio. --scott


When I was an undergraduate back in the 60s, I did some

time
*programming* analog computers. My recollection is the
Philbrick parts posted at
http://www.national.com/rap/vacuumtubes.html were
bottom-of-the barrel parts.


The sort of vacuum tube op amps I'm thinking of were more

on
the order of this one:


http://ed-thelen.org/dc_amp.gif


This op amp was part of the analog flight control computer
for a Nike system. This was one of those time-critical
applications. It looks more like what I was used to seeing
in higher-end analog computers (EIA, for example).

There's really no excuse for vacuum tube amplifiers to be
terribly slow, after all Tektronics made some pretty fast
'scopes out of bottles....


Right, but the Philbrick jobs were optimized for DC and
low-frequency operation, not audio. As you say, they were

for
analog computing, and that usually didn't involve much in

the
way of high frequencies.


The thing is, that speed was often of the essence in analog
computing. Many problems they were used for involve
optimization of parameters using large sets of
systematically-changed variables, intelligent searching
techniques, or Monte Carlo techniques.

I recall that the op amps in the EIA 680 that I worked with
later on, was speced to be something like 1% accurate while
reproducing a 10 KHz sine wave at 10 volt p-p. IOW, it was
0.1 dB down at 10 KHz while putting out maximum rated
output, so it had something like 50 KHz or better bandwidth.


  #46   Report Post  
Scott Dorsey
 
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Arny Krueger wrote:

The sort of vacuum tube op amps I'm thinking of were more on
the order of this one:

http://ed-thelen.org/dc_amp.gif


Man, that thing has a HUGE number of tubes in it!

There's really no excuse for vacuum tube amplifiers to be
terribly slow, after all Tektronics made some pretty fast
'scopes out of bottles....


There is indeed: remember that you can either have gain or you can
have bandwidth, and the whole point of the op-amp is that you can
trade one for the other. If you want wide bandwidth at high gains,
you need a whole lot of open loop gain inside the box, and that
means a big box with a lot of tubes in it. And it means some drift
issues.

For most of the things op-amps got used for back then, drift was
critical. If you didn't want response down to DC, there were plenty
of other solutions that were easier or cheaper (and often involved
transformers).

Look at those 1.8M plate resistors! Yow! Gain at all cost, indeed.
--scott

--
"C'est un Nagra. C'est suisse, et tres, tres precis."
  #47   Report Post  
Arny Krueger
 
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"Scott Dorsey" wrote in message

Arny Krueger wrote:

The sort of vacuum tube op amps I'm thinking of were more

on
the order of this one:

http://ed-thelen.org/dc_amp.gif


Man, that thing has a HUGE number of tubes in it!

There's really no excuse for vacuum tube amplifiers to be
terribly slow, after all Tektronics made some pretty fast
'scopes out of bottles....


There is indeed: remember that you can either have gain or

you
can have bandwidth, and the whole point of the op-amp is

that
you can trade one for the other. If you want wide

bandwidth
at high gains, you need a whole lot of open loop gain

inside
the box, and that means a big box with a lot of tubes in

it.
And it means some drift issues.

For most of the things op-amps got used for back then,

drift
was critical. If you didn't want response down to DC,

there
were plenty of other solutions that were easier or cheaper
(and often involved transformers).

Look at those 1.8M plate resistors! Yow! Gain at all

cost,
indeed. --scott


Look again - they 1.8 meggers are in series with the grids
and are bypassed. The plate resistors are 620K, 180K, and
240K. The 620K plate resistors for the input stage are a bit
misleading because there's 24K worth of local feedback.


  #48   Report Post  
Scott Dorsey
 
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In article ,
Pooh Bear wrote:

Scott Dorsey wrote:

Pooh Bear wrote:
Ohhh - talking of which you'll easily get an open loop gain of around
4000 with a transistor operating off 250V. It's kinda necessary to use
feedback to tame the gain.


This is a major irritation to my mind, and you can hardly even _get_
small signal semis at that voltage.


MPSA 42 and 92 ( 43 / 93 ) to name a couple ( of complementary pairs ) !
Cheap and wickedly good. Low Cob etc etc .... etc ! Blah blah blah. And
they're 'mercun and yet you don't know them !!!!

I've used them *everywhere* ! You find a gem - you use it !


This is the kind of thing I was talking about... how much does the hFE
vary? There is a minimum rating of 40 on the data sheet, but no maximum
rating at all.

But the series I was specifically talking about as being designed for
CRT stuff was the MPSW42, which is actually a great device if you can live
with the wide hFE range. I think it's pretty much the same as the MPSA42,
just with higher dissipation. For all I know, it could be the same die in
a bigger package.

I think the Motorola guys turned me onto these things when I asked them
for a higher voltage MPS L01.

I saw some folks who made a preamp for moving coil phono cartridges,
who used the 2N3055 as a front end, because the large area allowed them
to better match the very low output impedance of the cartridge.


Noooooo ! Not 'match' ! They were purely looking for low Rbb and Ree. Another
story entirely and one that a 2N3055 might do ok at, but that line of
approach has been *very* discredited ! There are far better devices that fill
that bill without being power semis ! The 'nice devices' even have an hfe
worth talking about !


The THAT large area array seems like a good idea. (And I confess, I think
of the low base resistance as being an impedance matching sort of thing,
which is probably not so good.)

Well..... I'd actually be quite interested in pursuing the discussion about
thermionics but I reckon only a few ppl frankly care ! More are simply into
the 'toobs are best' ****wit mentality and I'd hate to be associated with
them !


I think that's kind of depressing. Because I like tubes, and I like
designing with tubes and listening to tubes. And it's a shame that
crowd has given tubes something of a bad name.

What is worse is that some of the finest tubes made are TV and military
designs that you can't give away today. Those Raytheon subminis have
some of the best high-gain low-microphonic performance of anything around,
and people are using them as jewelry because there's no demand for them
for anything else. Don't even get me going on compactrons, which are
the height of unfashionability.
--scott

--
"C'est un Nagra. C'est suisse, et tres, tres precis."
  #49   Report Post  
Arny Krueger
 
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"Scott Dorsey" wrote in message


What is worse is that some of the finest tubes made are TV

and
military designs that you can't give away today. Those
Raytheon subminis have some of the best high-gain
low-microphonic performance of anything around, and people

are
using them as jewelry because there's no demand for them

for
anything else.


My radars had literally 100's of 'em, all neatly wired to
carefully swaged silver-plated posts on FRP circuit boards,
clipped to heat sinks that were mounted on the back of the
cakepan-like chassis. I believe they were rated for 10,000
hour MTBF. My largest radar had over 400 of them, and it
dutifully went down about once every 24 hours. Do the math!

They subminis pretty well duplicated the common
signal-handling tubes of the day. There was one that was
12AX7-like, another that was 12AU7-like, others that were
like 6AU6s, and even a 6AL5 work-alike. The biggest
concentration of them in one chassis was a triple IF strip
with about 10 transformer IF stages per channel.

Perhaps the most impressive item in teh system was the
spectrum analyzer. Balanced mixers converted three adjoining
frequency ranges of the inbound signal to the same range of
intermediate frequencies which passed through three
identical sets of additional tuned circuits and rectifiers
to provide a fast-response spectrum analysis of the inbound
signal as the antenna rotated.


  #50   Report Post  
Scott Dorsey
 
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Arny Krueger wrote:

Perhaps the most impressive item in teh system was the
spectrum analyzer. Balanced mixers converted three adjoining
frequency ranges of the inbound signal to the same range of
intermediate frequencies which passed through three
identical sets of additional tuned circuits and rectifiers
to provide a fast-response spectrum analysis of the inbound
signal as the antenna rotated.


AN/APR-6?
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."


  #51   Report Post  
Arny Krueger
 
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"Scott Dorsey" wrote in message

Arny Krueger wrote:

Perhaps the most impressive item in teh system was the
spectrum analyzer. Balanced mixers converted three

adjoining
frequency ranges of the inbound signal to the same range

of
intermediate frequencies which passed through three
identical sets of additional tuned circuits and

rectifiers
to provide a fast-response spectrum analysis of the

inbound
signal as the antenna rotated.


AN/APR-6?


The AN/MPQ-34 had the spectrum analyzer, the AN/MPQ-39 had
over 400 subminiature tubes.


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