Date   

Re: Looking for sensitive audio RMS meter

cmjones01
 

My Datron 1061A has the "high performance true RMS ACV" option fitted,
which has 100nV resolution, 6.5 digits, up to 100kHz. I'm not
intending to sell it, especially as it's nowhere near me at the
moment, but it might not be too hard to find another one.

Chris

On Mon, May 10, 2021 at 11:18 PM cheater cheater
<cheater00social@gmail.com> wrote:

Hi all, looking for a true RMS meter that can do roughly ~DC to ~100
kHz measurement down to 1 uV and up to say tens of volts. Hoping to
find something inexpensive and can be calibrated. Can someone suggest
anything? Either Tek or HP/A/K or something else. Bench or portable is
fine. Battery operation a big plus either way. I'd like 5 digits or
more, but fewer is fine around 1 uV. My budget is a few hundred $.

Thanks





TEK 7504

ChuckA
 

Does anyone have a readout board (670-0635-01) for a 7504 scope they would be interested in
selling or ?

Contact me off list.

Chuck


--

See Early TV at:

www.myvintagetv.com


Re: 465 Capacitor Refit Adapters

Bill
 

All was well. Helped to have a window behind the PCB with bright sun coming in.
Bill


Re: WTB: Tek 576 and P6015A

ChuckA
 

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: WTB: Tek 576 and P6015A

Michael W. Lynch
 

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
 

Hi All,

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?

Thanks,
-Chris


Re: WTB: Tek 576 and P6015A

Chris Wilkson
 

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.


Re: Looking for sensitive audio RMS meter

Liam Perkins
 

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: 465 Capacitor Refit Adapters

Dave Peterson
 

Once all is cleaned up well, test continuity between the front and back of the board to verify the integrity of the vias. See the picture in the album I pointed to earlier with the red circle around the C1512 (I think) + terminal. This via became stripped in the removal process creating an open to only a portion of the +55v unregulated node.

Was _very_ confusing to debug as it was only part of the node that was unconnected.

Much easier to fix before soldering in the new caps.

Dave

On Tuesday, May 11, 2021, 11:18:01 AM PDT, Bill via groups.io <ko4nrbs=yahoo.com@groups.io> wrote:

I got all the old capacitors out.  Took a while but I didn't damage the PCB or the traces.

I found, as someone else had found, that using solder wick with solder rosin flux smeared on it did a good job of removing the solder.  In fact it worked so well I was able to use a 30 watt Velleman soldering iron to do it.  After removing as much solder as I could I used an old Weller 100/140 watt solder gun to heat the capacitors connections as I wiggled them out very carefully.  This worked very well.  Just go slow and don't get carried away when wiggling them.

Many thanks to all for current and past recommendations here on how to do it!!

Bill


Re: 465 Capacitor Refit Adapters

Bill
 

I got all the old capacitors out. Took a while but I didn't damage the PCB or the traces.

I found, as someone else had found, that using solder wick with solder rosin flux smeared on it did a good job of removing the solder. In fact it worked so well I was able to use a 30 watt Velleman soldering iron to do it. After removing as much solder as I could I used an old Weller 100/140 watt solder gun to heat the capacitors connections as I wiggled them out very carefully. This worked very well. Just go slow and don't get carried away when wiggling them.

Many thanks to all for current and past recommendations here on how to do it!!

Bill


Re: front cover for 2445B

Paul Amaranth
 

Hi John

I have a cover on my 2465b. If you need any pictures or dimensions, drop
me a note

Paul

On Tue, May 11, 2021 at 01:53:03PM -0400, John Ferguson via groups.io wrote:
I've only seen one of these things and all too briefly.  It was on a 2465B
in a stack and not easily removed for inspection.

I want to 3D Print a couple of them. I can do it in two parts glued
together.  Not having seen one in detail means I get to design it myself. 
It looks like it ought to press-fit/latch over the flange which runs around
the plastic front plate on the scope.

It then needs to be deep enough to clear the controls.  And I think it will
be nice to have Tektronix 2445B embossed on the front.

If any of you have done this and could share an STL file.  If not, I'll
share mine when I've done it.

john ferguson








!DSPAM:609ac495112981552110542!
--
Paul Amaranth, GCIH | Manchester MI, USA
Aurora Group of Michigan, LLC | Security, Systems & Software
paul@AuroraGrp.Com | Unix/Linux - We don't do windows


front cover for 2445B

John Ferguson
 

I've only seen one of these things and all too briefly.  It was on a 2465B in a stack and not easily removed for inspection.

I want to 3D Print a couple of them. I can do it in two parts glued together.  Not having seen one in detail means I get to design it myself.  It looks like it ought to press-fit/latch over the flange which runs around the plastic front plate on the scope.

It then needs to be deep enough to clear the controls.  And I think it will be nice to have Tektronix 2445B embossed on the front.

If any of you have done this and could share an STL file.  If not, I'll share mine when I've done it.

john ferguson


Re: Unusual use for a Tektronix scope?

 

Would it be possible to use a pulse generator as a scope?

:-)
Martin


Re: Wanted - Tektronix 305 Oscilloscope Knobs and Caps

 

The SEC/DIV and VOLTS/DIV look very similar to the knobs from the 7A18A, though the part numbers are different.

I am working on casting hard-to-find or commonly damaged knobs. If you could take some measurements of the knobs you need (specifically knob height, and diameter of the shafts) I can check how they match up to the 7A18A knobs. Maybe I can make a set of replacements that will work for you.

-- Jeff Dutky


Re: Looking for sensitive audio RMS meter

 

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: Looking for sensitive audio RMS meter

 

I'm looking to measure noise, but not THD.

I don't want to use a sound card as those generally cannot be calibrated.

The ones that can be calibrated cost much too much.

I see the points with the excess bandwidth making the measurement less
sensitive.

I'm looking to measure noise at least up to 30 kHz, but 22 kHz might
be fine too.

Perhaps the suggested 3456A or, as Liam suggested, 3457 are a good idea.

If I had money to blow I'd buy an Audio Precision box. My budget is in
the low $xxx for this.

On Tue, May 11, 2021 at 12:35 PM Marian Beermann <public@enkore.de> wrote:

I have two 3400A's (with nuvistor frontends), their noise-floor is around
60 µVrms, but they do have 20-25 MHz -3 dB bandwidth (so their noise is a
factor ~14 higher due to excess bandwidth). These have tons of gain (like
250-300x) after the input amplifier (which is a nuvistor plate follower
with unity gain on the lowest range, and 1:1000 attenuation at 1 V and
above), which is not conducive for ultra-low-noise performance.

Your best / cheapest bet is a "gain box" and a sound-card as others
mentioned.

Cheers, Marian

Am Di., 11. Mai 2021 um 05:06 Uhr schrieb Kerry Burns <
kburns@netspace.net.au>:

Hello Chris



I have an older 3400A. It works well for most audio measurements ( and
beyond, up to 10 MHz), but the lowest range is 1mV so probably not
sensitive enough for sub 1uV work.



Kerry



From: <TekScopes@groups.io> on behalf of bhome1959 <bhome@sympatico.ca>
Reply to: <TekScopes@groups.io>
Date: Tuesday, 11 May 2021 at 12:41 pm
To: <TekScopes@groups.io>
Subject: Re: [TekScopes] Looking for sensitive audio RMS meter



Hi Liam,

I would love a 3457A!



Anyone have a HP 3400A? That would completely suit Bob's requirements.
BTW, I am also looking for one of those that works. I bought one on
fleabay and it has serious problems.



-Chris






















Re: 465 Capacitor Refit Adapters

Bill
 

Thank you!!
Bill


Re: 465 Capacitor Refit Adapters

Michael W. Lynch
 

On Tue, May 11, 2021 at 08:37 AM, Bill wrote:


I have received my Capacitor Adapters 15.5mm triangle from CUOG on Ebay. How
are the pin headers used to make up the ground connections?

Getting close to installing them.
The pin headers solder into the vias of the adapter boards, Once the caps are soldered onto the boards, The ground connections are made by traces in the adapter boards themselves. I made a small soldering jig that would hold all 4 pin headers and allow them to be soldered easily and perfectly perpendicular to the adapter boards.

--
Michael Lynch
Dardanelle, AR


Re: 465 Capacitor Refit Adapters

n4buq
 

I did something a bit different:

https://groups.io/g/TekScopes/album?id=64929

It's not the prettiest, but if those caps ever need to be replaced, it won't involve soldering on the main board (provided snap-in caps are still available at that point).

Thanks,
Barry - N4BUQ

----- Original Message -----
From: "Dave Peterson via groups.io" <davidpinsf=yahoo.com@groups.io>
To: TekScopes@groups.io
Sent: Tuesday, May 11, 2021 9:41:48 AM
Subject: Re: [TekScopes] 465 Capacitor Refit Adapters

Bill,

I put up some photos of my recap job in the folder:
 https://groups.io/g/TekScopes/album?id=258720

There are examples of the new caps with the adapters on (these are pre-snap
in sized adapters), and a view of the board with the caps soldered in. I had
to trim the leads of the snap-in caps to fit the adapters. Plenty of
material left to make good solid electrical and mechanical attachment.

I backed up the large holes with a piece of foil tape. The thick aluminum
foil used to seal duct work (not duct tape!). I used a hole punch to make
nice round patches, then stuck the lead through the middle. The adhesive
melts right away, but the foil did a good job of not allowing the solder to
overflow onto the backside of the board. I didn't fight too much to fill the
large holes entirely. The electrical connection is beyond established, and
the mechanical connection is also very solid. The caps are significantly
smaller and lighter than the originals.

Hope the pics help.
Dave


On Tuesday, May 11, 2021, 06:37:52 AM PDT, Bill via groups.io
<ko4nrbs=yahoo.com@groups.io> wrote:

I have received my Capacitor Adapters 15.5mm triangle from CUOG on Ebay.
  How are the pin headers used to make up the ground connections?

Getting close to installing them.

Bill











Re: 465 Capacitor Refit Adapters

Dave Peterson
 

Bill,

I put up some photos of my recap job in the folder: https://groups.io/g/TekScopes/album?id=258720

There are examples of the new caps with the adapters on (these are pre-snap in sized adapters), and a view of the board with the caps soldered in. I had to trim the leads of the snap-in caps to fit the adapters. Plenty of material left to make good solid electrical and mechanical attachment.

I backed up the large holes with a piece of foil tape. The thick aluminum foil used to seal duct work (not duct tape!). I used a hole punch to make nice round patches, then stuck the lead through the middle. The adhesive melts right away, but the foil did a good job of not allowing the solder to overflow onto the backside of the board. I didn't fight too much to fill the large holes entirely. The electrical connection is beyond established, and the mechanical connection is also very solid. The caps are significantly smaller and lighter than the originals.

Hope the pics help.
Dave

On Tuesday, May 11, 2021, 06:37:52 AM PDT, Bill via groups.io <ko4nrbs=yahoo.com@groups.io> wrote:

I have received my Capacitor Adapters 15.5mm triangle from CUOG on Ebay.  How are the pin headers used to make up the ground connections?

Getting close to installing them.

Bill

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