Date   

Re: 547 Recap

Dave Wise
 

Q1109 saturated is normal. It was added at S/N 2340 to protect Q1114 and Q1134 from excessive voltage when the amp is processing a common-mode transient from the plugin. It limits Vcc to 210V instead of 225V.

Dave Wise

From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of J via groups.io
Sent: Tuesday, May 11, 2021 10:33 PM
To: TekScopes@groups.io
Subject: Re: [TekScopes] 547 Recap

Harvey - I think you're onto something, but I'm not sure how to proceed. I did some more testing on the power supplies - loading the 100V as described in the TU-7 datasheet - I unfortunately don't have a load bank or power resistors that will work at the higher voltages. But all power supplies worked just fine with the 100V load. This gets me circling back to the potential of a bad part in the vertical amplifier - but I'm not quite sure how to test it to narrow it down. I've thought about shorting the collectors of the Q1114/Q1134 and Q1104/Q1124 pairs. I've done a DC voltage check and things looked okay. I was a little surprised to see Q1109 was in saturation and the base diodes were off - I'm not sure if that is the intended operation or not.


Re: WTB: Tek 576 and P6015A

Michael W. Lynch
 

On Wed, May 12, 2021 at 08:28 AM, Chris Wilkson wrote:


If those other things are fixable (some how) then I'm not too worried.
It's unobtainium things like transformers, custom ICs, and expecially CRTs
that I worry about.

If a 576 is working and calibratable....is there any shotgun preventative
maintenance that I should do?
Or just wait for a problem to develop and then attack it?
Chris,

Glad to be able to help. The only "unobtainium" IC's are those in the Display Unit. Those are almost impossible to find. I bought some of the very last ones that Q-Service had on hand. That brings to mind one issue that I failed to mention, regarding the display. When you are inspecting a used 576, it is important to carefully observe the display unit and check that all the lamps are functioning in all the various switch positions. In addition, your displayed value should always agree with the switch position on the panel.

There are three potential failure modes:

1. The display has "missing" dots, but the indicated value appears to agree with the switch position. Most likely burned out lamps in the display unit. A major PITA to replace these lamps, IMHO.

2. One of more of the displays does not agree with the corresponding switch position value. Could be a bad relay, contact or a bad IC.

3. The "beta" calculation does not "make sense" (either too high or too low) in relation to the switch settings. Usually a failed IC on the display board.

When using the 576, it helps to keep the Display illumination control set to less than max in order to save the lamps. No need to keep the display illumination control turned up if you are not using the display as a reference.

I also keep the CRT intensity down as low as possible whenever I can, to keep from burning the CRT.

One thing that you should always check on a new or unknown unit, are the various power supplies, their output and their ripple. The 5V supply is particularly prone to failure of the filter caps and this will either load the 5V supply down or throw it out of regulation to the point that the IC's fail to work.

There are also decoupling caps on the power rails on the various individual boards and these have occasionally caused issues.

There are some repairs shown for the 576 on TEKWiki. These may be helpful.

Use the later series Service manual. This is the one that the P/N ends in -01. The early manual is not as complete as the -01 version.

Good luck!

--
Michael Lynch
Dardanelle, AR


Re: Recapping Tektronix 2465

iv3ddm
 

Hi!
Not having received any recommendations for my last post, I had to fend for myself.
I finished replacing the components on A2, A3, A5, A9. Having no way to build the load for the power supply due to lack of suitable components, I just double-checked the job over and over again, then held my breath and pressed ON.
After a moment of suspense, the oscilloscope started up regularly and with satisfaction I saw that the screen and readout are much more defined and clear than before.

For information, here is a table with the ESR values ​​that I measured with an "AVR Component tester" of both the old and the new capacitors. Despite the possible limitations of the instrument used, I was surprised to find significantly higher ESR values ​​in the new 10uF 160v and 3.3uF 350v capacitors compared to the old ones removed from the instrument.

Furthermore, I found that the old capacitors removed have a capacity equal to or greater than the imprinted value, while the new ones on average almost always have a capacity lower than the rated value (data not shown in the table).
Orig.Value OLDValue ESRold ESRnew New Cap Mouser Part# Note
.056 uF 250v 58nF 12,00 12,23 594-2222-372-41563 Film capacitor .056uF 10% 250VDC Vishay sp10
.068 uF 250v broken broken 10,33 594-222233810683 Safety capacitors .068uF 20% 440VAC Vishay X1 17.5x8.5x15sp15
1 uF 50v 1uF 3,50 0,76 505-MKS2C041001FJC00 Film capacitors 63V 1uF 5% Wima 7x5x10sp5
10 uF 100v 15uF 0,60 3,50 647-ULD2C100MPD1TD Aluminum Electrolytic Capacitors - Radial 160V 10uF 20%
10 uF 160v 11uF 0,63 3,50 647-ULD2C100MPD1TD Aluminum Electrolytic Capacitors - Radial 160V 10uF 20%
10 uF 25v To do ---- 0,52 647-UPW1V100MDD Aluminum-radial electrolytic capacitor 35volt 10uF AEC-Q200
100 uF 25v 102uF 0,45 0,12 647-UHE1E101MED1TA Aluminum-radial electrolytic capacitor 25volt 100uF 6.3x11sp2.5 20%
180 uF 40v broken broken 0,07 647-UHE1H331MPD1TD Aluminum-radial electrolytic capacitor 330uF 50volts 10x25sp5
22 uF 10v To do ---- 0,28 647-UHE1H220MDD1TD Aluminum-radial electrolytic capacitor 50volts 22uF 5x11sp2 20%
220 uF 16v To do ---- 0,30 647-ULD1C221MPD1TD Aluminum Electrolytic Capacitors - Radial 16V 220UF 20%
250 uF 20v 300uF 0,15 0,07 647-UHE1H331MPD1TD Aluminum-radial electrolytic capacitor 330uF 50volts 10x25sp5
290 uF 200v 290uF 0,13 0,19 647-UPW2E331MRD Aluminum Electrolytic Capacitors - Radial 250volts 330uF AEC-Q200 22x50sp10
3.3 uF 350v 3,8uF 2,97 4,20 647-UPW2V3R3MPD Aluminum-radial electrolytic capacitor 350volt 3.3uF AEC-Q200
4.7 uF 10v 4,7uF 1,30 0,21 505-MKS2B044701KJC00 film capacitors - Wima 4.7uF 50 Volts 5%
4.7 uF 35v 4,7uF 2,00 0,72 647-UPW1H4R7MDD Aluminum Electrolytic Capacitors - Radial 50volts 4.7uF AEC-Q200 5x11sp2
47 uF 25v 45uF 0,45 0,36 647-UHE1E470MDD1TD Aluminum Electrolytic Capacitors - Radial 47uf 25V 105c 25V PET

Now I still have a bag of capacitors for the A1 board and am very undecided whether to replace them or leave the old ones that show no obvious signs of swelling or electrolyte leakage. In addition to the complexity of removing the A1 card, I am concerned about the possibility of static currents damaging it while I do the job. What precautions should I take to avoid the worst?

Gio


Re: WTB: Tek 576 and P6015A

Chris Wilkson
 

Thanks Michael!

I'm glad you chimed in. I followed your xfmr project and was quite impressed.
We need you over in the arcade hobby! (CRT flyback xfmrs and width coils)

I thought this 576 was ok, but I didn't know the exact serial # cut off.

If those other things are fixable (some how) then I'm not too worried.
It's unobtainium things like transformers, custom ICs, and expecially CRTs that I worry about.

If a 576 is working and calibratable....is there any shotgun preventative maintenance that I should do?
Or just wait for a problem to develop and then attack it?

Cheers,
Chris

On Tue, May 11, 2021 at 12:23 PM, Michael W. Lynch wrote:


On Tue, May 11, 2021 at 01:53 PM, Chris Wilkson wrote:


I have a line on a working 576...I'm going to look at it this Friday.

I know there are problems with the HV transformers in the 576 but I think
later units corrected it with a redesign?.
Anyone know a safe cutoff for bad / good serial #'s? This one is SN B315461

Is there anything else I should be on the lookout for on a used 576 besides
the HV xfmr and the usual broken knobs/bent shafts?
Chris,

Your serial # is in the range that had the "Good" Black silicone potted HV
XFMR. The "BAD" ones are B024999 and below. Printact Relays are always a
problem with the 576. Dim or burned CRTs are another. There are a ton of
filter capacitors in these things, especially the power supply that can and do
go bad. Dirty and sticking switches are another huge issue. Most of this can
be fixed if necessary. Checking the calibration is also essential as there
are many adjustments that can drift over time.

--
Michael Lynch
Dardanelle, AR


Re: WTB: Tek 576 and P6015A

Chris Wilkson
 

Too bad.

I do have a 575 that I'm going to part with...maybe a partial trade? :)
(serious here!)

On another topic, I have a few 7704's which I think use the same readout card as the 7504.
At least one of my mainframes was crushed in shipping...if it's a 7704 I can rob it of the readout board for you.
Baseball is starting up now so free time is limited. I'll try to dig through this weekend.

Cheers,
Chris

On Tue, May 11, 2021 at 12:53 PM, ChuckA wrote:


Chris,

Sorry no, I am using both of them. One is dedicated as a tube CT, the
other for semiconductors.

Chuck


On 5/11/2021 2:48 PM, Chris Wilkson via groups.io wrote:
Chuck,

I just saw your post. Any chance you'd part with one of these? :)

On Tue, Mar 2, 2021 at 08:41 PM, ChuckA wrote:
I bought two 576's from ebay, paid $400 for one, excellent physical
condition, just needed new filters. The other was $350, again excellent
physical condition, just needed test fixture. Watched on-line for a week
and bought a couple for $50, no other work needed.





--
See Early TV at:

www.myvintagetv.com


Re: 2430A Repair - a first in many ways

Szabolcs Szigeti
 

Hi Jorg,

Just look at the specifications of most of the scopes. They are usually not
specified for anything better than a couple of percent and that may even
change with the input level or the amplitude of the signal. Also, there can
be much linearity error allowed. So in summary, I don't use any scope for
accurate voltage measurement. I just use it to get a general idea of what
is where or do comparison measurements with a known accurate value.
But, you can do tricks, like triggering your 8840A at the moment when you
want to measure and use the scope to time the trigger signal, etc. So in
combination with other instruments there is a place for the scope in
accurate voltage (or basically anything) measurement.

Szabolcs



Joerg <joerg.reichardt@gmail.com> ezt írta (időpont: 2021. máj. 11., K,
23:41):

So I finally got my old Hameg repaired - another capacitor short, this
time a ceramic, and could measure more on the 2430A.

I mainly checked the low DC voltages on the side board and they are all
spot on with about 5mV p-p ripple. The only one that that is not within a
view mV of specs is the 8V which measures as 7.85V, that that is still just
2% shy. So I'm very pleased. I also measured the 10MHz on the top board and
that also looks super clean and at the right frequency.

Next, I was looking for a good voltage reference and the only one I had
laying around was the bandgap in an LT1365 which is 200mV. On both
channels, limited to 20MHz, taking 128 averages and at 10mV / div and 10ms
/ div it measures 20.000mV with a 1:10 Probe (no readout pin, but a P6133).
That is pretty spectacular I thought, but it also worries me a bit, because
my Fluke 8840A tells me its somewhere near 202 mV although that meter has
not seen a calibration in a long, long time I think 1% of accuracy should
always be there (my Fluke also checks out against my other multimeter ...).
I measured on two specimen of the chip, same result. The initial accuracy
of the reference in the chip is 200mV typical with 190-210 min/max.

So, I'm a bit skeptical of this reading. It just seems too good. What
further makes me skeptical that the readings change with Volts/div in the
single percent range (I can kinda see that, you're getting toward the low /
high end of the range) and time / div (I can also see that - on shorter
time scales there is less averaging going on).

What are your experiences when abusing the scope as a multi meter
measuring DC voltages?






Re: 547 Recap

stevenhorii
 

I saw a set of Tek timing caps on the Sphere Research (Walter Shawlee’s)
site. You likely have some messages in your in-box about their “Stuff Day”
sale. If you open the link and scroll down through the items, I think you
will find them.

Steve H.

On Tue, May 11, 2021 at 08:52 Jim Adney <jadney@vwtype3.org> wrote:

On Sun, May 9, 2021 at 06:42 PM, J wrote:

* If I recap the timing caps while I'm doing this - what voltage rating
should I use? It's not specified in the parts list.

I'll second the recommendation to NOT replace any of the timing
capacitors. In the first place, I doubt if any of those are electrolytics,
so they don't have that tendency to dry out and fail over time. Secondly, I
believe Tek generally supplied these in matched sets, to assure the correct
1-2-5 ratio steps.

I have a couple such Tek sets of matched timing caps, bought decades ago
via ebay. I bought them because they were cheap, they were Tek, and they
were local (no shipping.) I've never needed them and I probably never will.
If anyone needs a set, the part number I have is 295-0134-00, dated Dec 7,
1984. There's a Tek note attached to the bag that says, "DO NOT MIX
SUBPARTS BETWEEN SETS." Each set contains 4 of the special silver metal
cased Tek caps plus one brown silver mica. I'd be willing to sell them if
anyone needs a set.

Anyone know what scope these were used on?

I also discovered that I have a LARGE random bag of those very nice Tek
silver metal caps. I don't remember where these came from, but each appears
to be marked with a Tek part number. So if anyone needs some such thing,
please send me the approx length and diameter, to help pick it out of the
haystack, and the part number, and I'll see if I have one.






Re: Looking for sensitive audio RMS meter

 

I can verify that I don't care whether Liam sticks the tubes in LN2,
up his nose, or elsewhere, as long as it works. I've seen enough weird
stuff inexplicably work in audio engineering that I'm not going to
assume anything. But I can easily imagine some ways in which this
could work. Personally I use cryogenically annealed knives. They work
well. Until I heard of it I had no idea this was a thing. It smacks of
snake oil. But as it turns out it's the process recommended by the
steel manufacturer, and performed by NASA for some of their parts.
It's easy to look at things you aren't familiar with and immediately
assume FUD. But the polite thing especially towards someone like Liam
who obviously contributes some quality knowledge to the list would be
to ask nicely so you can learn, not to deride.

On Wed, May 12, 2021 at 3:32 AM Bob Albert via groups.io
<bob91343=yahoo.com@groups.io> wrote:

I can neither verify nor dispute this stuff but it certainly smacks of snake oil.
On Tuesday, May 11, 2021, 06:26:21 PM PDT, Roy Thistle <roy.thistle@mail.utoronto.ca> wrote:

On Tue, May 11, 2021 at 11:32 AM, Liam Perkins wrote:


https://www.pearl-hifi.com/03_Prod_Serv/Cryo/Cryo_Intro.html
I've a broken wrist... so typing hurts... but what hurts worse if the above link.
I like to think TekScopes is about the art, science, and technology of Tektronix.
The above link, IMHO... and it is my opinion!... has nothing to do with this.
I'll call what the link purports non-sense. Again, my opinion.
The link has appeared on TekScopes before.
--
Roy Thistle










Re: 547 Recap

J
 

Harvey - I think you're onto something, but I'm not sure how to proceed. I did some more testing on the power supplies - loading the 100V as described in the TU-7 datasheet - I unfortunately don't have a load bank or power resistors that will work at the higher voltages. But all power supplies worked just fine with the 100V load. This gets me circling back to the potential of a bad part in the vertical amplifier - but I'm not quite sure how to test it to narrow it down. I've thought about shorting the collectors of the Q1114/Q1134 and Q1104/Q1124 pairs. I've done a DC voltage check and things looked okay. I was a little surprised to see Q1109 was in saturation and the base diodes were off - I'm not sure if that is the intended operation or not.


Re: Wanted - Tektronix 305 Oscilloscope Knobs and Caps

Sampler_one
 

On Tue, May 11, 2021 at 05:22 PM, Jeff Dutky wrote:


7A18A
Ill measure it out tomorrow and get back.
Thanks


Re: Tektronix Plug-ins And Other Equipment For Sale

Dave Peterson
 

Now that things are live I can see a couple of things I should have done with the Google Drive folder:

I'll post the text list files to the folder.

I'll change the picture names to the modules.

Pardon the disruption if it's changing while you're looking at it.

Dave


Re: Looking for sensitive audio RMS meter

Liam Perkins
 

And no, the thread is not exactly about Tek, by whom my just mentioned
friend was educated in her youth, it's about T & M issues. I intended to
mention that I lately got some LSK389 dual, low-noise JFET samples from
Linear as they designed that part at Tek's behest when the 2N5565 used in
the Q133A & B positions in the 5- & 7A22 diff plug-in became unavailable. I
had great hopes as it's a great part but alas the 2N5565 was alsoa great
part so the swap didn't produce noticeable improvement.

On Tue, May 11, 2021 at 8:47 PM Bill Perkins <hifi@telus.net> wrote:

I linked to my page in respect of -noise measurement-, vacuum tube
equivalent input noise measurement to be specific.
Your snake oil -opinions- you are free to take up with my 100s of
satisfied end users over a 15 year period.
And at 71 years of age, that is my final word on the matter, I am not here
to argue the physics/field theories/metallurgy/dielectric issues/.etc, etc.
of high-end audio; a field admittedly rife with BS and snake oil and which
incurs the disdain of not only myself but every other designer who actually
knows what he/she is doing; and there are several women in this business
who -do- know what they are doing; my best fiend in life amoung them.
I hope you noticed that 'cheater' wants to build a recording studio and
that Matt has been building microphone preamps and developed a nV capable
measuring instrument and -that- is what the thread is about so kindly
desist from your high-handed, wholly uniformed derision.

On Tue, May 11, 2021 at 7:32 PM Bob Albert via groups.io <bob91343=
yahoo.com@groups.io> wrote:

I can neither verify nor dispute this stuff but it certainly smacks of
snake oil.
On Tuesday, May 11, 2021, 06:26:21 PM PDT, Roy Thistle <
roy.thistle@mail.utoronto.ca> wrote:

On Tue, May 11, 2021 at 11:32 AM, Liam Perkins wrote:


https://www.pearl-hifi.com/03_Prod_Serv/Cryo/Cryo_Intro.html
I've a broken wrist... so typing hurts... but what hurts worse if the
above link.
I like to think TekScopes is about the art, science, and technology of
Tektronix.
The above link, IMHO... and it is my opinion!... has nothing to do with
this.
I'll call what the link purports non-sense. Again, my opinion.
The link has appeared on TekScopes before.
--
Roy Thistle











Re: Looking for sensitive audio RMS meter

Liam Perkins
 

I linked to my page in respect of -noise measurement-, vacuum tube
equivalent input noise measurement to be specific.
Your snake oil -opinions- you are free to take up with my 100s of satisfied
end users over a 15 year period.
And at 71 years of age, that is my final word on the matter, I am not here
to argue the physics/field theories/metallurgy/dielectric issues/.etc, etc.
of high-end audio; a field admittedly rife with BS and snake oil and which
incurs the disdain of not only myself but every other designer who actually
knows what he/she is doing; and there are several women in this business
who -do- know what they are doing; my best fiend in life amoung them.
I hope you noticed that 'cheater' wants to build a recording studio and
that Matt has been building microphone preamps and developed a nV capable
measuring instrument and -that- is what the thread is about so kindly
desist from your high-handed, wholly uniformed derision.

On Tue, May 11, 2021 at 7:32 PM Bob Albert via groups.io <bob91343=
yahoo.com@groups.io> wrote:

I can neither verify nor dispute this stuff but it certainly smacks of
snake oil.
On Tuesday, May 11, 2021, 06:26:21 PM PDT, Roy Thistle <
roy.thistle@mail.utoronto.ca> wrote:

On Tue, May 11, 2021 at 11:32 AM, Liam Perkins wrote:


https://www.pearl-hifi.com/03_Prod_Serv/Cryo/Cryo_Intro.html
I've a broken wrist... so typing hurts... but what hurts worse if the
above link.
I like to think TekScopes is about the art, science, and technology of
Tektronix.
The above link, IMHO... and it is my opinion!... has nothing to do with
this.
I'll call what the link purports non-sense. Again, my opinion.
The link has appeared on TekScopes before.
--
Roy Thistle











Re: Tek TLA700 software images. Suitable place to submit them to?

vhdlman
 

I have created a new subdirectory tree "TLA700/Software disks" under the "Tektronix" directory in the groups.io Logic Analyzers group Files area. Your software disks would be a welcome addtion to the repository.


Re: Looking for sensitive audio RMS meter

Bob Albert
 

I can neither verify nor dispute this stuff but it certainly smacks of snake oil.

On Tuesday, May 11, 2021, 06:26:21 PM PDT, Roy Thistle <roy.thistle@mail.utoronto.ca> wrote:

On Tue, May 11, 2021 at 11:32 AM, Liam Perkins wrote:


https://www.pearl-hifi.com/03_Prod_Serv/Cryo/Cryo_Intro.html
I've a broken wrist... so typing hurts... but what hurts worse if the above link.
I like to think TekScopes is about the art, science, and technology of Tektronix.
The above link, IMHO... and it is my opinion!... has nothing to do with this.
I'll call what the link purports  non-sense. Again, my opinion.
The link has appeared on TekScopes before.
--
Roy Thistle


Re: Looking for sensitive audio RMS meter

Roy Thistle
 

On Tue, May 11, 2021 at 11:32 AM, Liam Perkins wrote:


https://www.pearl-hifi.com/03_Prod_Serv/Cryo/Cryo_Intro.html
I've a broken wrist... so typing hurts... but what hurts worse if the above link.
I like to think TekScopes is about the art, science, and technology of Tektronix.
The above link, IMHO... and it is my opinion!... has nothing to do with this.
I'll call what the link purports non-sense. Again, my opinion.
The link has appeared on TekScopes before.
--
Roy Thistle


Re: Tek TLA700 software images. Suitable place to submit them to?

Bruce Lane
 

Please submit them to the KO4BB web archive. I would also like copies
(you can attach them to Emails or put them in a file-sharing spot where
I can vacuum them up).

Thanks much!

On 11-May-21 15:09, Martin Whybrow wrote:
I've just repaired a TLA704 and I'm upgrading the HDD and putting Win98 and 3.2 on it, so these images would be massively helpful.

Martin




--
---
Bruce Lane, ARS KC7GR
http://www.bluefeathertech.com
kyrrin (at) bluefeathertech dot com
"Quando Omni Flunkus Moritati" (Red Green)


Re: Looking for sensitive audio RMS meter

 

Hi Liam,
thanks, I appreciate your extensive experience in this. I'm sure I'll
have a lot of questions that you'll be able to also answer along the
way. I'm setting up a mastering studio (as a hobby) and one of the
things I'd like to do is to be able to measure the noise floor of my
monitoring chain. Some elements claim to be -100 dBV noise, but I
don't necessarily trust that, so I'd like to measure that. Some other
circuits are claiming to be -120 dBV to -110 dBV self-noise. But also
for the future, I'd like to be able to measure other circuits. I'll be
replacing parts of my monitoring chain in the near future as well and
that'll require some noise measurement as well (among other things,
but low noise measurement is one of the hardest things). For the
future I'd like to be able to use the set up I learn about in this
process in designing analog audio circuits. I don't think I'll be
creating ultra low noise mic amplifiers, but I'll be creating analog
audio electronics none the less.

Thanks

On Tue, May 11, 2021 at 8:32 PM Liam Perkins <hifi@telus.net> wrote:

OK, look: what you want to do is not. easy. and short of something
modern like a Keithley nanovoltmeter there's essentially nothing off the
shelf that will get you there, ballpark but not there.

I spent 15 years measuring vacuum tube equivalent input noise and know
exactly what I'm on about. See this:

https://www.pearl-hifi.com/03_Prod_Serv/Cryo/Cryo_Intro.html

I measured 1,000s upon 1,000s of the very best of the legendary NOS
parts for people who then went on to sell them for 100s of dollars. I
provided a 13 month sliding scale warranty and during that time never
needed to replace more than a mere handful of parts because anything that
made it thru what I put parts thru was a good part.

I recommended Jim Williams work and that of Geller labs.
The Williams LT app notes you want are nos. 124 and 159 and Geller Labs you
can find on the WayBack about 2013 and the J-can article is here:

http://physicsopenlab.org/wp-content/uploads/2016/10/JCan-NV-article.pdf

Further, at the bottom of this page on my site, here:


https://www.pearl-hifi.com/06_Lit_Archive/07_Misc_Downloads/Misc_Downloads.html

see nos. 100, 103 and 105 as goldmine info on electrolytic caps and a
little known NIST paper from the days when it was NBS on a clever way to
use two-channel FFT to correlate the noise floor of the lowest noise amps
you can build down about 20dB; takes all day to run 10K averages but it
gets you there.

I spent hours on the restoration of that doc and the included refs.
That same method is well known in low noise metrology and Google on that
topic will keep you out the bar for at least the next month wading thru it
all.

Ralph Morrison is someone whose many, many works you need to know
backwards. I have about 6 of his titles in hardcopy, one of which I I
photocopied 30 years ago and had hardbound into a proper book. I also have
about 6 more in indexed PDF I'll provide free for the asking.

Although I pulled them down here:

https://b-ok.cc/

it ain't exactly legal to be puttin' them up on my site for all and sundry,
nor the highly useful works of Burkhard Vogel nor Horowitz & Hill whose
"Art of Electronics" which has been a standard for decades. The 3rd edn is
also found at Z-Lib.

Now, -what- are you trying to do, exactly; because until we know we're
all just throwing sh*t at one wall or another.

Do you need HF and if so how high, are you looking at 1/f and if so how
low, do you -really- need true rms and if so, why, because HP's earlier
400-series rms-reading, average-responding AC voltmeters will get you
within about a dB if you're measuring noise.

The 400GL and the 400F provide FSDs of -80dB, I have two of each and
plans to swap out the input JFETS in the 'Fs for modern much quieter parts
from Linear Integrated Systems.

Put Matt's +60db LN gain block in front of one of those and you are
home and dry.

Liam

On Tue, May 11, 2021 at 9:44 AM cheater cheater <cheater00social@gmail.com>
wrote:

On Tue, May 11, 2021 at 3:07 PM Matt <mhofmann@sbcglobal.net> wrote:

I have used an HP 3400A to measure the noise in circuits for several
applications since the 1970s, both for business and pleasure. I found it
useful for determining the equivalent input noise for various microphone
preamps that I had built. Typically I used a low noise solid-state preamp
on the front end of the HP 3400 with a low-pass filter on the input of the
3400A to reduce the bandwidth to the audible range. With this arrangement
I could get 60 dB of gain on the preamp, and I could measure the equivalent
input noise of the microphone preamp I was testing. I could get quite a
bit of sensitivity with this arrangement. I would set the HP 3400A to 1
mVrms and add another 60 dB of gain with the low noise preamp, resulting in
1 uVrms full-scale sensitivity on the meter.

It seems like this is the kind of scenario I should be looking at.
What LNA were you using?

Liam mentioned the J-Can and he had parts for it available. I think
this should be the way to go.

Is it possible to modify the HP 3400A to have a dBV scale?

Thanks.

I used this arrangement for solid-state microphone preamps that I was
designing and building as well as a tube based microphone preamp that later
on I built for my boss.
I have also used an FFT based spectrum analyzer program on an old laptop
PC that was useful in identifying the noise floor of these preamps.
I bought the HP 3400A on eBay a number of years ago for about $50 (I
could have been a bit more).

Matt












Re: 2430A Repair - a first in many ways

-
 

In my experience, a scope isn't a good instrument to use for measuring
voltages with a high degree of accuarcy. it's too easy to have parallax
errors on a scope and the lines themselves are too large for high
resolution readings. Scopes, IMO, are more for looking at wave FORMS
instead of voltages.

YMMV.

On Tue, May 11, 2021 at 5:41 PM Joerg <joerg.reichardt@gmail.com> wrote:

So I finally got my old Hameg repaired - another capacitor short, this
time a ceramic, and could measure more on the 2430A.

I mainly checked the low DC voltages on the side board and they are all
spot on with about 5mV p-p ripple. The only one that that is not within a
view mV of specs is the 8V which measures as 7.85V, that that is still just
2% shy. So I'm very pleased. I also measured the 10MHz on the top board and
that also looks super clean and at the right frequency.

Next, I was looking for a good voltage reference and the only one I had
laying around was the bandgap in an LT1365 which is 200mV. On both
channels, limited to 20MHz, taking 128 averages and at 10mV / div and 10ms
/ div it measures 20.000mV with a 1:10 Probe (no readout pin, but a P6133).
That is pretty spectacular I thought, but it also worries me a bit, because
my Fluke 8840A tells me its somewhere near 202 mV although that meter has
not seen a calibration in a long, long time I think 1% of accuracy should
always be there (my Fluke also checks out against my other multimeter ...).
I measured on two specimen of the chip, same result. The initial accuracy
of the reference in the chip is 200mV typical with 190-210 min/max.

So, I'm a bit skeptical of this reading. It just seems too good. What
further makes me skeptical that the readings change with Volts/div in the
single percent range (I can kinda see that, you're getting toward the low /
high end of the range) and time / div (I can also see that - on shorter
time scales there is less averaging going on).

What are your experiences when abusing the scope as a multi meter
measuring DC voltages?






7934 free for the taking, Two of them.

Karin Johnson
 

THIS IS GOING TO BE LONG SO GRAB A CUP OF COFFEE.
Well it finally happened. My beloved 7934 just stopped working today. Actually I've got two of them, and the other one is flaky too.
SOOOOOOOO... The symptom has nothing to do with the dreaded "tick". The inverter will not start at all. Checked fuses, all OK.
The line voltage feeding the diode bridge which feeds the two "line capacitors" producing the inverter input DC all OK. But the inverter
will just not start. I wanted to swap the power supply module with the other 7934, because that one worked. I say "worked" because I will explain
later. Swapping power supply modules is not easy, as the input line AC is hardwired into the chassis. So here is where is gets really insane.
I completely tore apart the first 7934. It is pieces all of the boards are out, the chassis is in several parts. I did take some pictures with the intent
of putting it back together. But after fiddling with it all afternoon, I am totally disgusted. I don't think the 7934 I tore apart will ever go back together again.
The other 7934 that sort of works, is a unit that had a failed HV transformer. This unit has a rewound HV transformer in it that I did several years ago.
I just put this unit in the closet, as sort of a spare. But today when I powered it up the focus would not clear up the read out numbers the trace focused OK
but the read out was wonky. Also with my 7L12 plugin selected the trace had a lot of distortion on it. Don't know what else to call it. After being powered
on for a few minutes I detected a burning smell. Initially I thought it was from my rewound transformer, but after taking the power supply out of this unit
actually just sliding it out the back I could smell the same burning odor from the power supply unit.
So now I've got two wonky 7934.
I really don't have the energy and patience at this point to continue the troubleshooting effort. I consider these two 7934 parts unit at this point.
One of them definitely a parts unit. The other may be able to be resurrected, I honestly don't know.

So here's the offer.
First come first served, Two FREE 7934 one in pieces the other in one piece sort of functional.
I really would like local pickup if at all possible, but if need be I can ship, but would like some sort of sharing of cost on shipping.
I actually have also a real Tektronix HV transformer that I purchase some years ago. It appears to be NOS. I'll even throw in couple of plug
ins if you desire.

Karin Anne Johnson
Palm Harbor, FL

5821 - 5840 of 188158