2440 and 2465B battery/ram replacement
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
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Re: 485 super weak brightness control
On Fri, Mar 26, 2021 at 12:48 AM, Ozan wrote:
I agree sometimes stepping back and looking with fresh eyes helps. Let us know
when you want to bounce off ideas again.
Ozan
I fully concur, Ozan. Raymond
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Re: How to explain how negative feedback lowers noise?
I partially agree with Goran's statement, but only partially because, as written, it neglects an important subtlety.
It is certainly true that a large first-stage gain suppresses the noise contributions of subsequent stages, so that's all good and intuitively satisfying.
However, once you've succeeded at that endeavor, the first stage's noise figure dominates. Somewhat counterintuitively, matching impedance at the input to maximize gain does not necessarily minimize noise figure. So, it is possible (even probable) to degrade NF by focussing only on maximizing gain.
The reason, in a nutshell, is that the minimum noise figure for an amplifier occurs for a source impedance that is the ratio of the equivalent input noise voltage to the noise current (I'm neglecting possible correlations between the two to make the argument simple). There's no fundamental connection between that ratio and the actual input impedance. You match to the former for best NF, and to the latter for maximum gain. So maximizing the gain of the first stage is not guaranteed to lead to overall best NF.
--Tom
--
Prof. Thomas H. Lee
Allen Ctr., Rm. 205
350 Jane Stanford Way
Stanford University
Stanford, CA 94305-4070
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On 3/25/2021 16:27, Ed Breya via groups.io wrote: Goran wrote: "If you wish to design a multistage amplifier with low phase noise factor you should maximize the first amplifier gain and the noise factor contribution from the following stages will be small.
Does anyone want to comment on this?"
My comment is that I agree. The front-end of any system is the most critical, and especially when the nature of the signal needs to be changed into an electric circuit signal. This happens all the time, whether it's receiving radio waves, light, sound, physical quantities, and so on. Electric to electric is the most common and straightforward - it's what goes on inside circuits. Anything else to electric has more issues, due to needing a transducer of some sort.
Ed
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Re: 485 super weak brightness control
Just wanted to say thank you for continuous support. I haven't abandoned
the ship just yet but I realised I spent way too much time on a scope
project and haven't done enough paid repairs to bring the money back home
to the family. I need to put it aside for few days. Fresh start with bit of
a distance between the attempts won't hurt. I agree sometimes stepping back and looking with fresh eyes helps. Let us know when you want to bounce off ideas again. Ozan
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Re: How to explain how negative feedback lowers noise?
Goran wrote: "If you wish to design a multistage amplifier with low phase noise factor you should maximize the first amplifier gain and the noise factor contribution from the following stages will be small.
Does anyone want to comment on this?"
My comment is that I agree. The front-end of any system is the most critical, and especially when the nature of the signal needs to be changed into an electric circuit signal. This happens all the time, whether it's receiving radio waves, light, sound, physical quantities, and so on. Electric to electric is the most common and straightforward - it's what goes on inside circuits. Anything else to electric has more issues, due to needing a transducer of some sort.
Ed
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Re: More fun with avalanche pulsers
I bought ten BFR505 transistors which are supposed to be faster than 2N2369's. Unfortunately they come in SOT-23 packages (i.e. smaller than a mouse turd). I had a fun time installing one into my pulser. Dropped the first two (but found them later by lying on the floor for a really close look), the third sprang out of the forceps and I heard it "tick" somewhere across the room. Finally got the fourth mounted (emitter soldered directly to the SMA output connector).
I moved some components for the shortest possible lead lengths, but it still has a divot in the top of the pulse that I can't tune out. Could it be the open BNC hanging from the end of the charge line? Still likes 33 ohm better than 50 ohms of emitter load, too. Amplitude is decreased since the BFR505 avalanches at 30-32 volts instead of 50+ like the '2369.
The good news is that the risetime is indeed quite a bit faster. As best as I could measure, 10-90% is 400 ps with a 6.5 volt top :) This quite noticeable when using the 350 ps S-1 head, so I went back to the 75 ps S-2. Pics added to "Sampling with 3S2" album. (If I could figure out how to link individual pics in a post, I would!)
But the bad news (which others have noted) is that the jitter and noise is also increased. It's not really bad especially while smoothing, but I guess that's a consequence of a small, very fast (Ft=9 GHz) transistor?
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Re: How to explain how negative feedback lowers noise?
Gentlemen,
I have been following this splendid discussion with great interest. There are so many ways you can discuss amplification and noise, negative feedback or no feedback, hopefully not positive feedback. However, in all statements and comments made so far one important term is never mentioned and that is Transfer Function, the relationship between input and output.
When you have an input signal plus noise you wish to predict what you would have at the amplifier output. And the answer should be to use the amplifier transfer function. I believe most amplifiers would have a transfer function describing a low-pass filter.
If you have an amplifier using negative feedback and the gain of is set to +1, then the input signal will appear at the output unaffected. Thus no noise attenuation. There is no cancellation but instead a continuous balance occurs keeping the output the same as the input. Low frequency components track better than high frequency components do because the open loop gain drops at higher frequencies.
If you wish to design a multistage amplifier with low phase noise factor you should maximize the first amplifier gain and the noise factor contribution from the following stages will be small.
Does anyone want to comment on this?
G?ran
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Re: How to explain how negative feedback lowers noise?
Barry,
Yes! In fact AGC is negative feedback.
GOD Bless and Thanks,
rich!
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On 3/25/2021 4:16 PM, n4buq wrote: So is negative feedback more analogous to AGC?
Thanks,
Barry - N4BUQ
----- Original Message -----
From: "Jeff Dutky" <jeff.dutky@...>
To: [email protected]
Sent: Thursday, March 25, 2021 4:04:37 PM
Subject: Re: [TekScopes] How to explain how negative feedback lowers noise?
Barry,
The sighs were because the idea that negative feedback in an amplifier
reduces noise in the output signal, whether that noise is present in the
input, or is introduced elsewhere in the amplifier, is erroneous. In the
example of noise cancelling headphones the noise is a separate source from
the main signal being amplified. In that case converting the noise signal to
an inverted signal and adding it to the signal of interest does, indeed,
reduce the noise in the summed output, but that bears little relation to the
erroneous idea that negative feedback just reduces noise.
The sighs were specifically because there had been several posts debunking
and bemoaning the error, followed by a post, presumably from someone who had
not read the rest of the thread, modeling exactly the erroneous belief that
had just been debunked and providing a purported explanation that only
served to promote the error.
-- Jeff Dutky
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Re: How to explain how negative feedback lowers noise?
So is negative feedback more analogous to AGC?
Thanks,
Barry - N4BUQ
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Show quoted text
----- Original Message ----- From: "Jeff Dutky" <jeff.dutky@...>
To: [email protected]
Sent: Thursday, March 25, 2021 4:04:37 PM
Subject: Re: [TekScopes] How to explain how negative feedback lowers noise?
Barry,
The sighs were because the idea that negative feedback in an amplifier
reduces noise in the output signal, whether that noise is present in the
input, or is introduced elsewhere in the amplifier, is erroneous. In the
example of noise cancelling headphones the noise is a separate source from
the main signal being amplified. In that case converting the noise signal to
an inverted signal and adding it to the signal of interest does, indeed,
reduce the noise in the summed output, but that bears little relation to the
erroneous idea that negative feedback just reduces noise.
The sighs were specifically because there had been several posts debunking
and bemoaning the error, followed by a post, presumably from someone who had
not read the rest of the thread, modeling exactly the erroneous belief that
had just been debunked and providing a purported explanation that only
served to promote the error.
-- Jeff Dutky
|
Re: How to explain how negative feedback lowers noise?
Barry,
The sighs were because the idea that negative feedback in an amplifier reduces noise in the output signal, whether that noise is present in the input, or is introduced elsewhere in the amplifier, is erroneous. In the example of noise cancelling headphones the noise is a separate source from the main signal being amplified. In that case converting the noise signal to an inverted signal and adding it to the signal of interest does, indeed, reduce the noise in the summed output, but that bears little relation to the erroneous idea that negative feedback just reduces noise.
The sighs were specifically because there had been several posts debunking and bemoaning the error, followed by a post, presumably from someone who had not read the rest of the thread, modeling exactly the erroneous belief that had just been debunked and providing a purported explanation that only served to promote the error.
-- Jeff Dutky
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Re: 485 super weak brightness control
Just wanted to say thank you for continuous support. I haven't abandoned
the ship just yet but I realised I spent way too much time on a scope
project and haven't done enough paid repairs to bring the money back home
to the family. I need to put it aside for few days. Fresh start with bit of
a distance between the attempts won't hurt.
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Show quoted text
On Thu, 25 Mar 2021, 13:00 Raymond Domp Frank, <hewpatek@...> wrote: On Thu, Mar 25, 2021 at 06:50 AM, Ozan wrote:
In this video I think I know what is happening. You have variable
horizontal
knob out (time 0:13 in the video). Your 5ns B gate is 300ns wide instead of ~
130ns Raymond measured so this is supporting the theory of variable time
scale. When you switch to 10ns it is the same RC time constant as 5ns (2x is
in horizontal amp) but because variable time is disabled for B other than
1/2/5n, B-gate suddenly looks like it became shorter. If you push in the
variable time scale knob my guess is you will see 5ns width same as 10ns
width, not jumping to a smaller time. I tried it and can replicate what you
are seeing with variable time scale set.
I noticed this a few days ago, when I observed the unlocked variable
timebase knob and had to fine-tune my settings in order to get exactly the
screens that Ondrej showed in his video, so I wrote and suggested:
*** QUOTE ***
Gentlemen,
First of all, in order to make life as easy as possible, it would help
me/us if we would "standardise" our settings:
- A-ramp at top
- A-gate below that
- B-gate below that again
- Variable timebase knob in the "calibrated" position (pushed in)
- Delay Time Position to minimum (0)
- Observation 'scope (2465B?) in non-delayed mode
- Trigger on A- gate trace
My observations match Ozan's latest ones.
** UNQUOTE **
I thought that things were made unnecessarily complex by using the delayed
display on the observation 'scope and variable time base in the video.
Raymond
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Re: How to explain how negative feedback lowers noise?
Yes, I understand how these work. My question was more about why the explanation where noise from the first stage of an amplifier is fed back (negated, inverted, or, ?) to the input which seems much like a noise-canceling headset to me. I inferred from the sighs that the previous explanation was incorrect and (sorry) but I don't understand why that's the case.
Were the "sighs" meant to indicate that the example given was incorrect or, perhaps, just more of the same already-covered explanations? Sorry - sighs can a bit more meaningful when combined with an eyeroll.
Thanks,
Barry - N4BUQ
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----- Original Message ----- From: "G?ran Krusell" <mc1648pp@...>
To: [email protected]
Sent: Thursday, March 25, 2021 3:18:58 PM
Subject: Re: [TekScopes] How to explain how negative feedback lowers noise?
Hi Barry,
No sighs from my desk, your question is a good one. I think these modern
headphones work in the following manner, a small amount of noise comes
through the leather in your headphones. At the same time the external noise
is picked up by a small microphone in the headset, amplified by an inverting
amplifier and added to the direct noise to you ear in equal amounts. The
noise is thus attenuated. And it does work, I have one such headphone from a
well-known company.
G?ran
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Re: How to explain how negative feedback lowers noise?
Hi Barry,
No sighs from my desk, your question is a good one. I think these modern headphones work in the following manner, a small amount of noise comes through the leather in your headphones. At the same time the external noise is picked up by a small microphone in the headset, amplified by an inverting amplifier and added to the direct noise to you ear in equal amounts. The noise is thus attenuated. And it does work, I have one such headphone from a well-known company.
G?ran
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Re: How to explain how negative feedback lowers noise?
On Thu, Mar 25, 2021 at 08:29 PM, n4buq wrote:
Is there an analogy between this subject and the way noise-canceling
headphones work? I'm sorry if that's a silly thing to introduce into this
conversation but it might help me understand this a bit better (or not).
There certainly is, in a way, between the title of this thread and noise-canceling headphones: In noise-canceling headphones, a fraction of the outside environmental noise is in anti-phase added to (effectively subtracted from) the intentional sound (music, speech) and the result is produced by the speakers in the headphone; a nice example of negative feedback. The system works within a limited frequency-dependent amplitude band. The electronics' automatic adjustment usually is audible for a short period after putting on the headphones and when changing its position on the head, causing some sort of audible "sinking in" impression. The noise-canceling headphones' circuits can not remove oreven reduce noise present in the signal as fed from the source. OTOH, many noise-canceling headphones have a limited frequency response, effectively forming a low-pass filter for all audio, giving a noise-suppressing effect but that's got nothing to do with the noise-canceling "mechanism" itself. Raymond
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Re: Persuading a 7S12 to play nice with a 7934.
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
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Re: How to explain how negative feedback lowers noise?
Is there an analogy between this subject and the way noise-canceling headphones work? I'm sorry if that's a silly thing to introduce into this conversation but it might help me understand this a bit better (or not).
(I think I hear the sighs already but I'm still going to send this...)
Thanks,
Barry - N4BUQ
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----- Original Message ----- From: "Raymond Domp Frank" <hewpatek@...>
To: [email protected]
Sent: Thursday, March 25, 2021 2:12:48 PM
Subject: Re: [TekScopes] How to explain how negative feedback lowers noise?
On Thu, Mar 25, 2021 at 07:14 PM, Tom Lee wrote:
Sigh.
I never knew sighing in chorus existed, defies relativity's simultaneity
concept.
Raymond
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Re: How to explain how negative feedback lowers noise?
On Thu, Mar 25, 2021 at 07:14 PM, Tom Lee wrote:
Sigh.
I never knew sighing in chorus existed, defies relativity's simultaneity concept. Raymond
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Re: TEK465 Horizontal trace
On Thu, Mar 25, 2021 at 06:45 PM, Dave Peterson wrote:
If it's just the "A-fire" diode dead, then I have 7 to pick 4 from. I'm hoping
I can use our hacked curve tracer to match two pairs. It certainly allowed me
to see the variation in the 151-0212-00 vert amp xtors.
Those TD's should work. Just go through the applicable adjustment procedure in the SM, no special equipment needed. Results will be better than by matching. Raymond
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Re: TEK465 Horizontal trace
On Thu, Mar 25, 2021 at 05:25 PM, Dave Peterson wrote:
I found it likely _not_ merely coincidence that this transistor has failed
_and_ has some form of manufacturing defect. An engineering axiom brought to
my attention some time ago is that engineers/designers/manufacturers rarely do
or add anything without good reason. I doubt the "goo" is there only to secure
the leads. Mind too that these particular components were manufactured by
Tektronix in the late 60's or early 70's. I don't think the industry had quite
settled down at that time. Wink. My use of passivation seemed an apt term.
Perhaps I should have stuck with goo. Wink.
I really don't see a manufacturing defect. Your image shows the underside (base) of the package, with its glass(-like) lead feed-throughs. Packages are purchased by the transistor manufacturer complete with leads and feed-throughs. There is a plateau on top, where the semiconductor chip (die) is affixed by the transistor manufacturer. The chip itself is passivated/glassivated during chip production. A cap is placed on top of the base during manufacturing, completely enclosing the die hermetically. TO-5 cases' bottoms often look similar. With TO-39's, the glass is usually just visible as a thin "ring" around each lead (usually base and emitter), flush with the package bottom. Raymond
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Raymond Domp Frank
G?ran Krusell