Date   

Re: 2440 and 2465B battery/ram replacement

n49ex
 

Not sure how many times I will need to post this on the forum, but here's Hugo Holden"s brilliant do-it-yourself battery/ram replacement with new technology:
http://worldphaco.com/uploads/TEKTRONIX_2465b_OSCILLOSCOPE_CALIBRATION___REPOWERING_THE_DS1225.pdf

And, yes, no matter how it's done, unless one has the means to read the old chip data and program it into the new, you will need to go through the full cal procedure. Probaly a good idea anyway given passage of time....

Reinhard


Re: Recapping Tektronix 2465

Chuck Harris <cfharris@...>
 

Not that I have ever seen. There are some versions of
the manual that have two capacitor numbers swapped on the
parts diagram... But, if you remove the old, and stuff
the new capacitors one at a time, that won't be a problem.

Where there is a problem is in replacing the SMD capacitors
on the late series 2465B's. The polarity of these electrolytics
is not marked in an obvious way in all cases. The capacitor
that is away on the corner of the board is not marked.

-Chuck Harris


On Fri, 26 Mar 2021 14:11:51 -0400 (EDT) "n4buq" <n4buq@knology.net>
wrote:
Thanks for clarifying that, Chuck.

Was there a different model where that was a problem? I seem to
recall the issue but don't recall which model(s) were affected.
Hopefully I'm not crossing up Tek and HP with this...

Barry - N4BUQ

----- Original Message -----
From: "Chuck Harris" <cfharris@erols.com>
To: TekScopes@groups.io
Sent: Friday, March 26, 2021 12:57:40 PM
Subject: Re: [TekScopes] Recapping Tektronix 2465

All of the capacitors on the 2465 supplies have their polarity
markers pointing in the same direction. A few are non-polar
electrolytics, which don't matter.

-Chuck Harris


On Fri, 26 Mar 2021 13:46:03 -0400 (EDT) "n4buq" <n4buq@knology.net>
wrote:
I don't recall exactly to which model(s) this may apply, but I
think one of the 24xx models have the polarity marked incorrectly
on the PC board for one of the filter capacitors. Apologies if I
have this confused with a completely different model/series but I
thought it worthy of mentioning here.

Thanks,
Barry - N4BUQ

----- Original Message -----
From: "Ozan" <ozan_g@erdogan.us>
To: TekScopes@groups.io
Sent: Friday, March 26, 2021 11:37:29 AM
Subject: Re: [TekScopes] Recapping Tektronix 2465

You may already know but at least in some service manuals
component placement diagram shows location of C1132 and C1115
swapped (wrong). This was the case for my 2467B, I assume it
also applies to 2465B. While desoldering take a note of the
original value to make sure. Ozan



iv3ddm

C1132 would be 160V. C1120 can be 100V. C1130 would be
160V. If you want
to use the original values of capacitance, fine. They can be
higher capacitance if you want. C1101 and C1102 would be 25V.
If I put 16V numbers there, it was my mistake. In mine, I
used 16V or 25V types (I do not have mine open at this time)
for the 5V supplies and 35V for the 15V supplies. These I had
in stock along with some other parts. I ordered what I
needed. The 330mfd Mr. Yachad says to use, I did. The kit he
sells is nice. He is exactly
right about the film caps! Replace those! The X1 and Y1 can be
used if you want even higher voltage capacity than the 2
types. In mine, the 1 types are
400-500VAC types. A 2 type can replace a 1 type. A 2 type is
not recommended
to replace a 1 type. The ones Mr. Yachad uses are also an
excellent/ideal choice. If you are on 230-240V mains, the
higher voltage caps are best. If you
have not already done so, go to Mr. Yachad's site about 2465B
recapping. I used that site as a reference do to mine. It
was my first time working on this
model. I did notice in mine the two 39meg resistors (R710 and
R910) on the bottom board were high, 45 and 50meg, and the
100meg on the high voltage board
was 170meg. They are now 40 and 100meg respectively. I could
not get 39meg without a long string of resistors. Mine also
did not have R1010 and R1019 across the NTCs. That was
factory done.

Mark
















Re: Recapping Tektronix 2465

n4buq
 

Thanks for clarifying that, Chuck.

Was there a different model where that was a problem? I seem to recall the issue but don't recall which model(s) were affected. Hopefully I'm not crossing up Tek and HP with this...

Barry - N4BUQ

----- Original Message -----
From: "Chuck Harris" <cfharris@erols.com>
To: TekScopes@groups.io
Sent: Friday, March 26, 2021 12:57:40 PM
Subject: Re: [TekScopes] Recapping Tektronix 2465

All of the capacitors on the 2465 supplies have their polarity
markers pointing in the same direction. A few are non-polar
electrolytics, which don't matter.

-Chuck Harris


On Fri, 26 Mar 2021 13:46:03 -0400 (EDT) "n4buq" <n4buq@knology.net>
wrote:
I don't recall exactly to which model(s) this may apply, but I think
one of the 24xx models have the polarity marked incorrectly on the PC
board for one of the filter capacitors. Apologies if I have this
confused with a completely different model/series but I thought it
worthy of mentioning here.

Thanks,
Barry - N4BUQ

----- Original Message -----
From: "Ozan" <ozan_g@erdogan.us>
To: TekScopes@groups.io
Sent: Friday, March 26, 2021 11:37:29 AM
Subject: Re: [TekScopes] Recapping Tektronix 2465

You may already know but at least in some service manuals component
placement diagram shows location of C1132 and C1115 swapped
(wrong). This was the case for my 2467B, I assume it also applies
to 2465B. While desoldering take a note of the original value to
make sure. Ozan



iv3ddm

C1132 would be 160V. C1120 can be 100V. C1130 would be 160V.
If you want
to use the original values of capacitance, fine. They can be
higher capacitance if you want. C1101 and C1102 would be 25V. If
I put 16V numbers there, it was my mistake. In mine, I used 16V
or 25V types (I do not have mine open at this time) for the 5V
supplies and 35V for the 15V supplies. These I had in stock along
with some other parts. I ordered what I needed. The
330mfd Mr. Yachad says to use, I did. The kit he sells is nice.
He is exactly
right about the film caps! Replace those! The X1 and Y1 can be
used if you want even higher voltage capacity than the 2 types.
In mine, the 1 types are
400-500VAC types. A 2 type can replace a 1 type. A 2 type is not
recommended
to replace a 1 type. The ones Mr. Yachad uses are also an
excellent/ideal choice. If you are on 230-240V mains, the higher
voltage caps are best. If you
have not already done so, go to Mr. Yachad's site about 2465B
recapping. I used that site as a reference do to mine. It was my
first time working on this
model. I did notice in mine the two 39meg resistors (R710 and
R910) on the bottom board were high, 45 and 50meg, and the 100meg
on the high voltage board
was 170meg. They are now 40 and 100meg respectively. I could not
get 39meg without a long string of resistors. Mine also did not
have R1010 and R1019 across the NTCs. That was factory done.

Mark













Re: Recapping Tektronix 2465

Chuck Harris <cfharris@...>
 

All of the capacitors on the 2465 supplies have their polarity
markers pointing in the same direction. A few are non-polar
electrolytics, which don't matter.

-Chuck Harris


On Fri, 26 Mar 2021 13:46:03 -0400 (EDT) "n4buq" <n4buq@knology.net>
wrote:
I don't recall exactly to which model(s) this may apply, but I think
one of the 24xx models have the polarity marked incorrectly on the PC
board for one of the filter capacitors. Apologies if I have this
confused with a completely different model/series but I thought it
worthy of mentioning here.

Thanks,
Barry - N4BUQ

----- Original Message -----
From: "Ozan" <ozan_g@erdogan.us>
To: TekScopes@groups.io
Sent: Friday, March 26, 2021 11:37:29 AM
Subject: Re: [TekScopes] Recapping Tektronix 2465

You may already know but at least in some service manuals component
placement diagram shows location of C1132 and C1115 swapped
(wrong). This was the case for my 2467B, I assume it also applies
to 2465B. While desoldering take a note of the original value to
make sure. Ozan



iv3ddm

C1132 would be 160V. C1120 can be 100V. C1130 would be 160V.
If you want
to use the original values of capacitance, fine. They can be
higher capacitance if you want. C1101 and C1102 would be 25V. If
I put 16V numbers there, it was my mistake. In mine, I used 16V
or 25V types (I do not have mine open at this time) for the 5V
supplies and 35V for the 15V supplies. These I had in stock along
with some other parts. I ordered what I needed. The
330mfd Mr. Yachad says to use, I did. The kit he sells is nice.
He is exactly
right about the film caps! Replace those! The X1 and Y1 can be
used if you want even higher voltage capacity than the 2 types.
In mine, the 1 types are
400-500VAC types. A 2 type can replace a 1 type. A 2 type is not
recommended
to replace a 1 type. The ones Mr. Yachad uses are also an
excellent/ideal choice. If you are on 230-240V mains, the higher
voltage caps are best. If you
have not already done so, go to Mr. Yachad's site about 2465B
recapping. I used that site as a reference do to mine. It was my
first time working on this
model. I did notice in mine the two 39meg resistors (R710 and
R910) on the bottom board were high, 45 and 50meg, and the 100meg
on the high voltage board
was 170meg. They are now 40 and 100meg respectively. I could not
get 39meg without a long string of resistors. Mine also did not
have R1010 and R1019 across the NTCs. That was factory done.

Mark








Re: Recapping Tektronix 2465

Chuck Harris <cfharris@...>
 

Shielded mains cords just move the noise to the
next open spot, which is the unshielded plastic
boxes, and unshielded ROMEX wiring used in most
USA houses.

Better would be to put one of the snap-on ferrite
suppressors on the cord close to the scope.

I have done this on most of my electrically noisy
equipment, and it has done a super job of knocking
down the noise.

-Chuck Harris


On Fri, 26 Mar 2021 10:37:57 -0700 "Mark Vincent"
<orangeglowaudio@gmail.com> wrote:
Ozan,
...
One thing that I have not seen mentioned, although it may have
in the past, is using shielded mains cords to reduce noise. I have
these on things that use IEC cords.
...

Mark


Re: Recapping Tektronix 2465

n4buq
 

I don't recall exactly to which model(s) this may apply, but I think one of the 24xx models have the polarity marked incorrectly on the PC board for one of the filter capacitors. Apologies if I have this confused with a completely different model/series but I thought it worthy of mentioning here.

Thanks,
Barry - N4BUQ

----- Original Message -----
From: "Ozan" <ozan_g@erdogan.us>
To: TekScopes@groups.io
Sent: Friday, March 26, 2021 11:37:29 AM
Subject: Re: [TekScopes] Recapping Tektronix 2465

You may already know but at least in some service manuals component placement
diagram shows location of C1132 and C1115 swapped (wrong). This was the case
for my 2467B, I assume it also applies to 2465B. While desoldering take a
note of the original value to make sure.
Ozan



iv3ddm

C1132 would be 160V. C1120 can be 100V. C1130 would be 160V. If you
want
to use the original values of capacitance, fine. They can be higher
capacitance if you want. C1101 and C1102 would be 25V. If I put 16V numbers
there, it was my mistake. In mine, I used 16V or 25V types (I do not have
mine open at this time) for the 5V supplies and 35V for the 15V supplies.
These I had in stock along with some other parts. I ordered what I needed.
The
330mfd Mr. Yachad says to use, I did. The kit he sells is nice. He is
exactly
right about the film caps! Replace those! The X1 and Y1 can be used if you
want even higher voltage capacity than the 2 types. In mine, the 1 types
are
400-500VAC types. A 2 type can replace a 1 type. A 2 type is not
recommended
to replace a 1 type. The ones Mr. Yachad uses are also an excellent/ideal
choice. If you are on 230-240V mains, the higher voltage caps are best. If
you
have not already done so, go to Mr. Yachad's site about 2465B recapping. I
used that site as a reference do to mine. It was my first time working on
this
model. I did notice in mine the two 39meg resistors (R710 and R910) on the
bottom board were high, 45 and 50meg, and the 100meg on the high voltage
board
was 170meg. They are now 40 and 100meg respectively. I could not get 39meg
without a long string of resistors. Mine also did not have R1010 and R1019
across the NTCs. That was factory done.

Mark





Tektronix 2205 value as donor?

 

Hi all, what is an OK functioning Tek 2205 worth in terms of
replacement parts? Does it have anything that's worth in order to
repair other scopes? I have someone who might give me one of those for
free but I'm not sure it's worth the shipping, to be honest. I already
have a bunch of good functioning Tek scopes, none from the 2k series,
mostly just 7k.

Thanks


Re: Recapping Tektronix 2465

Mark Vincent
 

Ozan,

I do know these can be swapped in some manuals. I made sure to change the parts one at a time to make sure. It is good to remind us to keep from blowing parts. Anyone of us can make a mistake somewhere.

One thing that I have not seen mentioned, although it may have in the past, is using shielded mains cords to reduce noise. I have these on things that use IEC cords. Computers, monitors, SMPS, being near enough to a-m/s-w/ssb transmitter, etc. generate noise that can interfere with other things. The shielding does help with the noise. I will use shielded cords on things as a replacement on other things that are or should be grounded.

Mark


Re: Recapping Tektronix 2465

Ozan
 

You may already know but at least in some service manuals component placement diagram shows location of C1132 and C1115 swapped (wrong). This was the case for my 2467B, I assume it also applies to 2465B. While desoldering take a note of the original value to make sure.
Ozan


iv3ddm

C1132 would be 160V. C1120 can be 100V. C1130 would be 160V. If you want
to use the original values of capacitance, fine. They can be higher
capacitance if you want. C1101 and C1102 would be 25V. If I put 16V numbers
there, it was my mistake. In mine, I used 16V or 25V types (I do not have
mine open at this time) for the 5V supplies and 35V for the 15V supplies.
These I had in stock along with some other parts. I ordered what I needed. The
330mfd Mr. Yachad says to use, I did. The kit he sells is nice. He is exactly
right about the film caps! Replace those! The X1 and Y1 can be used if you
want even higher voltage capacity than the 2 types. In mine, the 1 types are
400-500VAC types. A 2 type can replace a 1 type. A 2 type is not recommended
to replace a 1 type. The ones Mr. Yachad uses are also an excellent/ideal
choice. If you are on 230-240V mains, the higher voltage caps are best. If you
have not already done so, go to Mr. Yachad's site about 2465B recapping. I
used that site as a reference do to mine. It was my first time working on this
model. I did notice in mine the two 39meg resistors (R710 and R910) on the
bottom board were high, 45 and 50meg, and the 100meg on the high voltage board
was 170meg. They are now 40 and 100meg respectively. I could not get 39meg
without a long string of resistors. Mine also did not have R1010 and R1019
across the NTCs. That was factory done.

Mark


Re: Recapping Tektronix 2465

Mark Vincent
 

iv3ddm

C1132 would be 160V. C1120 can be 100V. C1130 would be 160V. If you want to use the original values of capacitance, fine. They can be higher capacitance if you want. C1101 and C1102 would be 25V. If I put 16V numbers there, it was my mistake. In mine, I used 16V or 25V types (I do not have mine open at this time) for the 5V supplies and 35V for the 15V supplies. These I had in stock along with some other parts. I ordered what I needed. The 330mfd Mr. Yachad says to use, I did. The kit he sells is nice. He is exactly right about the film caps! Replace those! The X1 and Y1 can be used if you want even higher voltage capacity than the 2 types. In mine, the 1 types are 400-500VAC types. A 2 type can replace a 1 type. A 2 type is not recommended to replace a 1 type. The ones Mr. Yachad uses are also an excellent/ideal choice. If you are on 230-240V mains, the higher voltage caps are best. If you have not already done so, go to Mr. Yachad's site about 2465B recapping. I used that site as a reference do to mine. It was my first time working on this model. I did notice in mine the two 39meg resistors (R710 and R910) on the bottom board were high, 45 and 50meg, and the 100meg on the high voltage board was 170meg. They are now 40 and 100meg respectively. I could not get 39meg without a long string of resistors. Mine also did not have R1010 and R1019 across the NTCs. That was factory done.

Mark


Re: FTAGH: Ciebo DS-750

Stephen
 

On Fri, Mar 26, 2021 at 04:30 AM, Oz-in-DFW wrote:


Free to a good home: Ciebo DS-750 development tools kit for Philips 87C750

I expect this is largely limited to historical interest, but I hate sending
this to the landfill if there is the remotest chance someone can use it.

Pick up in DFW area, or you cover shipping - it will fit in a medium flat rate
box ($15.50 in the US)

Pics are here:

https://www.richosman.com/Ciebo/

--
Oz (in DFW) N1OZ
I’ll be more than happy to take it.

Cheers


FTAGH: Ciebo DS-750

Oz-in-DFW
 

Free to a good home: Ciebo DS-750 development tools kit for Philips 87C750

I expect this is largely limited to historical interest, but I hate sending this to the landfill if there is the remotest chance someone can use it.

Pick up in DFW area, or you cover shipping - it will fit in a medium flat rate box ($15.50 in the US)

Pics are here:

https://www.richosman.com/Ciebo/

--
Oz (in DFW) N1OZ


Re: 2440 and 2465B battery/ram replacement

Mark Hatch
 

Mark,

Reach out to Chuck Harris on this list. He replaced my NVRAM. Not sure if he would do just a board or well he needs the whole scope, but you can ask him.

Mark


Re: Recapping Tektronix 2465

iv3ddm
 

647-ULD2C100MPD1TD for 10mfd. These are 160V.
647-UHE1C121MED for replacing the two 100mfd to the TO-220 rectifier. The additional capacitance of 20mfd will not hurt.
Sorry Mark, I ask for 2 clarifications:
I should use 647-ULD2C100MPD1TD (10uF, 160v.) Also instead of 10uF, 100v. (C1120 etc.) or only for C1132?

Which are the capacitors where to use of the 647-UHE1C121MED (120uF, 16v.) For the replacement of the two 100mfd to the TO-220 rectifier?
I only find 100uF, 25v capacitors.

Thanks a lot


Re: Persuading a 7S12 to play nice with a 7934.

Albert Otten
 

The connection of the base to R593 is deleted.
It's strange. With a DMM I could not find a connection of 2N2907A-base to any other component in the neighborhood or a A/B contact. But then the pair of NPN transistors with their bases to the B7 and A16 inputs would be useless. Do I overlook something?
Albert


On Thu, Mar 25, 2021 at 09:00 PM, Albert Otten wrote:


The solution with reduced value of R693 seems to have disadvantages also,
otherwise Tek would have done so I think.
That might be the reason that P600 has been introduced to enable/disable
interdot blanking. In the open position the PNP 2N2907A is shut off
completely. In the closed position the situation is as before. (I avoid
Q690/Q694 numbering.)
The next version of P600 is wired differently. When closed it it ties the
base of the 2N2907A to GND. The connection of the base to R593 is deleted. In
the closed position interdot blanking works, and works always, i.e.
independent of what happens at A16 and B7. When P600 is open the situation is
the same as with the previous P600 version. This version explains why I see
the dot blanking in other traces so clearly. About 50% blank of between
samples period is completely blanked.

Albert


Re: How to explain how negative feedback lowers noise?

Tom Lee
 

Your comment about cathode resistors for bias stability will force me to do a little more background checking, but I don't think indirectly-heated cathodes were in production before 1929, so there could not have been cathode resistors for at least two years after Black. I did a quick perusal through a few schematics from that era, and I don't see cathode resistors of any kind showing up until around 1930 or 1931, and unbypassed ones don't show up for a couple of years after that. Blumlein doesn't invent the cathode follower until he starts working on radar on the eve of WWII. So my initial quick pass suggests that Black's invention does precede other forms of electronic negative feedback constructions. If you have earlier examples, I would be grateful to know about them. I'll look through other references in the meantime.

Tom

Sent from an iThing; please excuse the terseness and typos

On Mar 25, 2021, at 23:14, "Ed Breya via groups.io" <edbreya=yahoo.com@groups.io> wrote:

I don't know about this history, but am surprised that this didn't happen until 1929, well into the electronics era. Surely the concept of negative feedback in control systems has existed in nature, throughout human history, and in industry - at least since the steam era - look at the fly-ball governor, for example. Maybe in electronics, it wasn't so obvious, although it already existed in some forms, say for instance, with degenerative feedback in a vacuum tube, stabilizing the bias with the cathode resistor. People were driving horses, trains, planes, and automobiles successfully before 1929, using that PID controller in the skull.

Ed





Re: How to explain how negative feedback lowers noise?

Tom Lee
 

The reason it didn't happen for electronics until 1927 is that the preoccupation until that point was getting more gain per tube. Positive feedback (Armstrong's regenerative amplifier) was the magic elixir that had enabled the age of electronics to begin, around WWI. Early tubes struggled to achieve voltage gains of five. The first generation of EEs was thus trained to think of getting enough gain as the main problem.

It wasn't until AT&T ran into troubles with transcontinental telephony that someone had to invent a fix for a different problem: distortion. A cascade of hundreds of repeaters demanded individual amplifiers of unprecedented linearity. This necessity was the mother of negative feedback.

Black's invention required quite a change in thinking. Now he was recommending "throwing away" precious gain in exchange for reduced distortion. This went against the training of a generation of EEs. Given that, I'm not surprised negative feedback took that long to get formalized.

Although you are absolutely right that a basic intuitive notion of negative feedback was appreciated long before electronics came along, Black was the first in history to understand explicitly that excess gain could be used as currency to pay for reductions in distortion. It is as subtle a notion as it is powerful.

The very first mathematical treatment of negative feedback was by Maxwell himself, but his analysis was limited to understanding why speed governors for steam engines could go unstable. Until technology ran into the need for exquisite precision in control, there was no need for Black to come along.

Cheers
Tom

Sent from an iThing; please excuse the terseness and typos

On Mar 25, 2021, at 23:14, "Ed Breya via groups.io" <edbreya=yahoo.com@groups.io> wrote

I don't know about this history, but am surprised that this didn't happen until 1929, well into the electronics era. Surely the concept of negative feedback in control systems has existed in nature, throughout human history, and in industry - at least since the steam era - look at the fly-ball governor, for example. Maybe in electronics, it wasn't so obvious, although it already existed in some forms, say for instance, with degenerative feedback in a vacuum tube, stabilizing the bias with the cathode resistor. People were driving horses, trains, planes, and automobiles successfully before 1929, using that PID controller in the skull.

Ed





Re: 2440 and 2465B battery/ram replacement

Szabolcs Szigeti
 

Hi Mark,

I can't help in replacing the RAMs, but I have some experience with the
2440/2432 etc DSOs. Don't be afraid to replace the RAM without saving it's
content, it is much easier to get calibrated than the 2465.
The first time I calibrated a 2440 I used a DC supply, and an old, low end
function generator's square wave output. Since then I have much improved
instruments, but it was possible to get it calibrated with minimum
equipment.
Especially, that if it is has not been calibrated for long you will
probably need to do an internal adjustment and readjust the screen geometry
and the CCD timing anyway (for that you'll need some kind of a signal
generator) which requires clearing the nvram as a first step, so there is
absolutely no need to save the ram or worry about losing its content. There
is absolutely no point in saving and reloading the old data.

Szabolcs


Mark Vincent <orangeglowaudio@gmail.com> ezt írta (időpont: 2021. márc.
26., P, 2:45):

I have both of these and would like to get these replaced with the new
style of chip that does not need the back-up battery. The (real) 2465B is
still good. I do not know how long it will keep the data before becoming
dead. The 2440 needs replacing. I know these original devices will go bad
soon. I do not have or access to a programmer. I know I have the newer A5
board in the B with S/N 063838 (1994). I am in the mid-Atlantic area of the
US. The caps and resistors in both have already been done. Mr. Yachad's
2465B site was used. Thank you Mr Yachad. I do not know what I would send.
The whole piece, board, what. Is there anyone willing to do this and give
me a price on these? I do not know if calibration is needed after the chip
replacement. I know enough people in this group are good to expert at using
and knowing the 2465B features. I got this one because of the praise it
gets.

The 2440 I have used some. The B is recent and I need to learn the
features. This is new to me. I am used to the 7000 series and older. The
2440 has some FAIL modes. I think the CCDs are good. It likely needs
calibration to clear the fail. This one still shows signals like should. I
know I need to learn what all this one can do when it is working right.

I have adjusted the power supplies to within a couple of mV to exact
of the adjustments on each scope. I do this on other models as well.

If anyone wants to contact in private, you can use the email. I will
give my telephone number in a private email if any want it. That is a much
faster way to get me and discuss anything necessary.

Mark






Re: How to explain how negative feedback lowers noise?

Ed Breya
 

I don't know about this history, but am surprised that this didn't happen until 1929, well into the electronics era. Surely the concept of negative feedback in control systems has existed in nature, throughout human history, and in industry - at least since the steam era - look at the fly-ball governor, for example. Maybe in electronics, it wasn't so obvious, although it already existed in some forms, say for instance, with degenerative feedback in a vacuum tube, stabilizing the bias with the cathode resistor. People were driving horses, trains, planes, and automobiles successfully before 1929, using that PID controller in the skull.

Ed


Re: How to explain how negative feedback lowers noise?

J Hunt
 

**********
Tom Lee wrote ...

Yes, Black invented both feedforward and negative feedback amplifiers, the latter indeed on the Lackawanna ferry in that year.

**********

Tom is right, our hero Harold Black came up with the amazing idea of applying negative feedback to an amplifier in 1929 during his commute to work on the Lackawanna Ferry. His objective was to reduce distortion in repeater amplifiers for long distance telephone service. He said that the idea came to him "in a flash" (though he had been working on the problem for four years).

If you are an IEEE member you can download the fascinating paper Black wrote in IEEE Spectrum (pp. 55 - 60, Dec. 1977) "Inventing the negative feedback amplifier". I would post it for our group but the download has restricted use.

In the article Black says that experts at the time were not persuaded. "... the director of research at Bell Labs objected. He insisted that a negative feedback amplifier would never work." Once it was proved to be practical they filed patents and ... " the concept was so contrary to established beliefs that the Patent Office initially did not believe it would work. ... In England, our patent application was treated in the same manner as one for a perpetual-motion machine."

It is reasonable that even today the concept can be challenging. But Black's objective to reduce distortion caused by the amplifier still is the main advantage.

John Hunt
Portland, OR

5661 - 5680 of 186336