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Mike Rivers[_2_] Mike Rivers[_2_] is offline
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On 6/7/2018 11:45 PM, geoff wrote:
iPOD.Â* Yeah. Only Apple product I own - got it especially for
SignalSuite and Guitar Toolbax.Â* Android didn't do that back then.


I had a chat with the Studio Six guys at Infocomm yesterday and asked if
they were doing anything on Android yet. Nope, they said (as everyone
said years ago) that Androids are different enough so that they can't be
sure their software will run on the version that the user has. Same with
AudioControl, who made a really good SPL meter that works on my ZTE
Android 4.0 phone, but when I got a new phone last year because all of
my apps were telling me to upgrade - to versions that wouldn't run on
Version 4 - it wouldn't work. They've abandoned it, similarly, because
it's too difficult to reliably program for Android.

So I use my antique Radio Shack analog SPL meter and avoid buying a $700
iPhone.


--
"Today's production equipment is IT based and cannot be operated without
a passing knowledge of computing, although it seems that it can be
operated without a passing knowledge of audio" - John Watkinson

Drop by http://mikeriversaudio.wordpress.com now and then
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On 9/06/2018 12:22 AM, Mike Rivers wrote:
On 6/7/2018 11:45 PM, geoff wrote:
iPOD.Â* Yeah. Only Apple product I own - got it especially for
SignalSuite and Guitar Toolbax.Â* Android didn't do that back then.


I had a chat with the Studio Six guys at Infocomm yesterday and asked if
they were doing anything on Android yet. Nope, they said (as everyone
said years ago) that Androids are different enough so that they can't be
sure their software will run on the version that the user has. Same with
AudioControl, who made a really good SPL meter that works on my ZTE
Android 4.0 phone, but when I got a new phone last year because all of
my apps were telling me to upgrade - to versions that wouldn't run on
Version 4 - it wouldn't work. They've abandoned it, similarly, because
it's too difficult to reliably program for Android.

So I use my antique Radio Shack analog SPL meter and avoid buying a $700
iPhone.




Well I have found that there is an Android equivalent (or better) of
anything on iPhone now. And luckily have not have had the update probs
you've encountered.

geoff
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On Fri, 8 Jun 2018 00:24:16 -0000 (UTC), david gourley
wrote:

(Scott Dorsey) said...news
david gourley wrote:
Trevor said...news On 7/06/2018 1:05 AM, Scott Dorsey wrote:
In article , Tim Sprout


wrote:
On 6/5/2018 6:24 AM, wrote:
I can confirm that this type snake CAN create an ultrasonic
oscillation that can quickly damage a power amp.

How does one detect ultrasonic oscillations?

Usually by the smoke. I once saw a Phase Linear amp shoot fire three
feet
in the air due to stability issues. It was very impressive but cut

the
band's
act somewhat short.

They weren't nick-named "Flame Linear's" for nothing. :-)

The SAEs didn't seem to be far behind, either.


Agreed, and SWTPC also was famous for instability. The Phase Linear,

though,
was famous because it just had such an enormous amount of power and such
poor stability margins. The combination was bad.
--scott


Yessir, those Tigers could roar !

david

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Those darn things would break into spurious oscillation driving a
resistive load. I came up with a mod that made them stable enough that
a local rock band used them as their main amps.
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On 8/06/2018 12:12 PM, Mike Rivers wrote:
On 6/7/2018 9:47 PM, geoff wrote:
My multimeter collection, HF responses starting to drop at:
Fluke 114Â*Â*Â* 4.5kHz
Fluke 17B+Â*Â*Â* 2.5kHz
Dick Smith (OEM ?)Â*Â*Â* 10kHz


That's pretty good. My Fluke 77 goes up to about 2 kHz if I recall
correctly. I'm not near it at the moment.


Fluke 8050A benchtopÂ*Â*Â* 20kHz(+?), which is as high as my iPod Touch
with SignalSuite goes ...


The iPad is limited to 20 kHz or so due to the fact that it's going
through an A/D converter running at a sample rate of 44.1 or maybe 48 kHz.


But any decent computer-audio adapter that does 24/192 makes a great
device for measuring audio signals, oscilloscope, spectrum analyser etc.
to well above the audio band. Far better at low frequencies than nearly
all CRO's and spectrum analysers that do HF.

Trevor.
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On 8/06/2018 4:45 PM, geoff wrote:
On 8/06/2018 2:12 PM, Mike Rivers wrote:
The iPad is limited to 20 kHz or so due to the fact that it's going
through an A/D converter running at a sample rate of 44.1 or maybe 48
kHz.



iPOD.Â* Yeah. Only Apple product I own - got it especially for
SignalSuite and Guitar Toolbax.Â* Android didn't do that back then.


How do you run those on an iPod?

Trevor.




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On 8/06/2018 10:22 PM, Mike Rivers wrote:
On 6/7/2018 11:45 PM, geoff wrote:
iPOD.Â* Yeah. Only Apple product I own - got it especially for
SignalSuite and Guitar Toolbax.Â* Android didn't do that back then.


I had a chat with the Studio Six guys at Infocomm yesterday and asked if
they were doing anything on Android yet. Nope, they said (as everyone
said years ago) that Androids are different enough so that they can't be
sure their software will run on the version that the user has. Same with
AudioControl, who made a really good SPL meter that works on my ZTE
Android 4.0 phone, but when I got a new phone last year because all of
my apps were telling me to upgrade - to versions that wouldn't run on
Version 4 - it wouldn't work. They've abandoned it, similarly, because
it's too difficult to reliably program for Android.

So I use my antique Radio Shack analog SPL meter and avoid buying a $700
iPhone.


Since it is difficult/expensive to calibrate either, you are probably
just as well off using your ears and making a guess.

Trevor.


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On 9/06/2018 4:21 PM, Trevor wrote:
On 8/06/2018 4:45 PM, geoff wrote:
On 8/06/2018 2:12 PM, Mike Rivers wrote:
The iPad is limited to 20 kHz or so due to the fact that it's going
through an A/D converter running at a sample rate of 44.1 or maybe 48
kHz.



iPOD.Â* Yeah. Only Apple product I own - got it especially for
SignalSuite and Guitar Toolbax.Â* Android didn't do that back then.


How do you run those on an iPod?

Trevor.



SignalSuite and Guitar Toolbox were IOS apps, not Android, which was
barely around (in the smartphone 'app' department at least) in those
days anyway.

Now there are Android equivalents.

geoff
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On 9/06/2018 3:08 PM, geoff wrote:
On 9/06/2018 4:21 PM, Trevor wrote:
On 8/06/2018 4:45 PM, geoff wrote:
On 8/06/2018 2:12 PM, Mike Rivers wrote:
The iPad is limited to 20 kHz or so due to the fact that it's going
through an A/D converter running at a sample rate of 44.1 or maybe
48 kHz.


iPOD.Â* Yeah. Only Apple product I own - got it especially for
SignalSuite and Guitar Toolbax.Â* Android didn't do that back then.


How do you run those on an iPod?


SignalSuite and Guitar Toolbox were IOS apps, not Android, which was
barely around (in the smartphone 'app' department at least) in those
days anyway.


Didn't know iPods ran IOS apps? Don't you need an iPad or iPhone?

Trevor.

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On 9/06/2018 6:35 PM, Trevor wrote:
On 9/06/2018 3:08 PM, geoff wrote:
On 9/06/2018 4:21 PM, Trevor wrote:
On 8/06/2018 4:45 PM, geoff wrote:
On 8/06/2018 2:12 PM, Mike Rivers wrote:
The iPad is limited to 20 kHz or so due to the fact that it's going
through an A/D converter running at a sample rate of 44.1 or maybe
48 kHz.


iPOD.Â* Yeah. Only Apple product I own - got it especially for
SignalSuite and Guitar Toolbax.Â* Android didn't do that back then.

How do you run those on an iPod?


SignalSuite and Guitar Toolbox were IOS apps, not Android, which was
barely around (in the smartphone 'app' department at least) in those
days anyway.


Didn't know iPods ran IOS apps? Don't you need an iPad or iPhone?

Trevor.


Whatever.....

Whatever it was, it was proprietary.

geoff
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On 6/8/2018 9:25 PM, Trevor wrote:
Since it is difficult/expensive to calibrate either, you are probably
just as well off using your ears and making a guess.


It's difficult to calibrate to the standards required by the Music
Police for writing tickets, but with a loudspeaker, pink noise source,
and a hardware SPL meter (all of which I have) you can make a rough
calibration that will be good enough to let you know, after listening
all day and your ears are getting dull, if things are getting too loud.
The AudioControl app (that doesn't work on my present phone) tracked my
calibrated SPL meter quite well.

I can calibrate any of the other SPL phone apps at a single point and
they're repeatable at that SPL, but because the AGC isn't disabled,
lower levels are boosted and higher levels are sat on before they get to
the meter app, so everything comes out at about the same reading. The
Kewelsoft SPL meter app allows you to calibrate it at three points and
it creates a calibration curve, but that doesn't help in this situation.


--
"Today's production equipment is IT based and cannot be operated without
a passing knowledge of computing, although it seems that it can be
operated without a passing knowledge of audio" - John Watkinson

Drop by http://mikeriversaudio.wordpress.com now and then


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On 6/8/2018 11:35 PM, Trevor wrote:
SignalSuite and Guitar Toolbox were IOS apps, not Android, which was
barely around (in the smartphone 'app' department at least) in those
days anyway.


Didn't know iPods ran IOS apps? Don't you need an iPad or iPhone?


Signal Suite is an audio signal generator. For Android (and maybe iOS)
the Keuwlsoft Dual Channel Function Generator app is very flexible and
works on all of my Android devices. It's a little tricky to get the hang
of how the signals are assigned to the left and right outputs, but no
worse than a digital mixing console.

Of course the problem with using your phone as a signal generator is
that all you have for an output is a phone jack (or virtual one) and you
can't drive an input to +24 dBu with that if you want to find out how
much headroom the equipment or system you're testing has. Most line
level inputs have enough sensitivity so that you can run a frequency
response check or put noise into a room to look for problem spots, so
it, with the proper test leads, can be a handy tool for field work.

The input side, though, is a different story. If you want to measure
actual signal level, you need to disable the AGC (and also you need to
calibrate it).


--
"Today's production equipment is IT based and cannot be operated without
a passing knowledge of computing, although it seems that it can be
operated without a passing knowledge of audio" - John Watkinson

Drop by http://mikeriversaudio.wordpress.com now and then
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geoff wrote:
On 9/06/2018 6:35 PM, Trevor wrote:
On 9/06/2018 3:08 PM, geoff wrote:
On 9/06/2018 4:21 PM, Trevor wrote:
On 8/06/2018 4:45 PM, geoff wrote:
On 8/06/2018 2:12 PM, Mike Rivers wrote:
The iPad is limited to 20 kHz or so due to the fact that it's going
through an A/D converter running at a sample rate of 44.1 or maybe
48 kHz.


iPOD.* Yeah. Only Apple product I own - got it especially for
SignalSuite and Guitar Toolbax.* Android didn't do that back then.

How do you run those on an iPod?

SignalSuite and Guitar Toolbox were IOS apps, not Android, which was
barely around (in the smartphone 'app' department at least) in those
days anyway.


Didn't know iPods ran IOS apps? Don't you need an iPad or iPhone?

Trevor.


Whatever.....

Whatever it was, it was proprietary.

geoff


The iPod touch is an iPhone without the phone bits. It runs iOS.

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Mike Rivers wrote:

geoff wrote:
My multimeter collection, HF responses starting to drop at:
Fluke 114Â*Â*Â* 4.5kHz
Fluke 17B+Â*Â*Â* 2.5kHz
Dick Smith (OEM ?)Â*Â*Â* 10kHz



That's pretty good. My Fluke 77 goes up to about 2 kHz if I recall
correctly. I'm not near it at the moment.


** To me it seems strange that instruments intended for engineers and service techs to use for all kinds of electronic work have such poor AC response..

Most analogue multimeters cover at least the audio band and beyond, so if you can hear a sound coming from a loudspeaker, the meter will measure the signal
level for you. It can substitute for a VU meter if need be and test line voltage PA installations.

In the 1950s and 60s, the standard bench instrument for professional techs and engineers was a VTVM like this one:

https://www.radiomuseum.org/r/rca_se...st_wv_98c.html


Typical specs we

11Mohms input impedance on DC volts.

1.5 V to 1500V AC or DC in 7 ranges.

3 to 5 MHz bandwidth on AC readings.

100 ohms to 1000 Mohms FSD in 7 ranges.

10 ohms at centre on lowest ohms range with 100mA of SC current.

(enough to make a loud click in a speaker and/or see which way the cone moves).


BTW:

Ever try to test the resistance of a speaker in a noisy room with a DMM ??


..... Phil












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On 6/9/2018 6:29 PM, Phil Allison wrote:
** To me it seems strange that instruments intended for engineers and service techs to use for all kinds of electronic work have such poor AC response.


I'm sure that there are still laboratory-grade digital multimeters that
cover the audio band, but for service applications, mostly of your AC
measurement requirements aren't for loudspeaker power, but for line
power, and maybe to check out a (line frequency) transformer. I have an
H-P 400D and 4300 analog voltmeters for audio measurements. Their scales
are logarithmic, in dB, cover from millivolts to shocking volts. I paid
less than $25 for each of those and have had them for years. I also have
an NTI Minilyzer that's digital but I think its maximum input level is
+18 dBu, so if I want to check out a devices with a specified maximum
output level of more than that, I have to go the analog route. And the
Digilizer cost a few hundred bucks.

Most analogue multimeters cover at least the audio band and beyond, so if you can hear a sound coming from a loudspeaker, the meter will measure the signal


True, but a decent one is more expensive than a digital multimeter, and
a cheap one may not make as accurate measurements. Depends on what you
need and why you're making the measurement. I wrote an article in
Recording magazine about multimeters and making audio level
measurements, and the bottom line was that you could use a budget priced
meter to calibrate the audio interface for your computer (that you
probably already have) at a frequency that you can rely on the meter to
measure accurately, then use your interface as a "meter" to measure over
the full audio range.

In the 1950s and 60s, the standard bench instrument for professional techs and engineers was a VTVM like this one:
https://www.radiomuseum.org/r/rca_se...st_wv_98c.html


I have one of those on my workbench, and it still works.

For my article, I was reluctant to suggest buying a 50 year old analog
meter that could handle the full audio range, for fear that I'd soon
have to write an article about repairing antique test equipment.



--
"Today's production equipment is IT based and cannot be operated without
a passing knowledge of computing, although it seems that it can be
operated without a passing knowledge of audio" - John Watkinson

Drop by http://mikeriversaudio.wordpress.com now and then
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On 10/06/2018 12:48 PM, Mike Rivers wrote:
On 6/9/2018 6:29 PM, Phil Allison wrote:
In the 1950s and 60s, the standard bench instrument for professional
techs and engineers was a VTVM like this one:
https://www.radiomuseum.org/r/rca_se...st_wv_98c.html


I have one of those on my workbench, and it still works.


The AVO meters were the most common in places I worked. Still have my
AVO model 8. If you don't fry them, no reason they won't outlast the user.

Trevor.



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Mike Rivers wrote:

Phil Allison wrote:
** To me it seems strange that instruments intended for
engineers and service techs to use for all kinds of electronic
work have such poor AC response.



I'm sure that there are still laboratory-grade digital multimeters that
cover the audio band,


** It's a basic requirement that analogue multimeters can all do.


Most analogue multimeters cover at least the audio band and beyond,
so if you can hear a sound coming from a loudspeaker, the meter
will measure the signal



True, but a decent one is more expensive than a digital multimeter,



** No, they can all do it.

Makers decided to "penny pinch" early DMMs, simply not mention the limited AC bandwidth and got away with it. So called True RMS models are usually no better for the same reason.



In the 1950s and 60s, the standard bench instrument for professional techs and engineers was a VTVM like this one:

https://www.radiomuseum.org/r/rca_se...st_wv_98c.html


I have one of those on my workbench, and it still works.


** Excellent.

For my article, I was reluctant to suggest buying a 50 year old analog
meter that could handle the full audio range, for fear that I'd soon
have to write an article about repairing antique test equipment.



** The only hard to get / repair item is the moving coil meter itself.

12AU7s and 6AL5s are cheap & readily available, the 10uF PSU electro and selenium rectifier might need replacing.


BTW:

Ever try to test the resistance of a speaker in a noisy room with a DMM ??

Do you know what happens?



..... Phil
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On 10/06/2018 12:11 AM, Mike Rivers wrote:
On 6/8/2018 9:25 PM, Trevor wrote:
Since it is difficult/expensive to calibrate either, you are probably
just as well off using your ears and making a guess.


It's difficult to calibrate to the standards required by the Music
Police for writing tickets, but with a loudspeaker, pink noise source,
and a hardware SPL meter (all of which I have) you can make a rough
calibration that will be good enough to let you know, after listening
all day and your ears are getting dull, if things are getting too loud.
The AudioControl app (that doesn't work on my present phone) tracked my
calibrated SPL meter quite well.


Is it really currently calibrated to any national standard? Or just a
sheet that came with the instrument and completely useless for any legal
purpose?


I can calibrate any of the other SPL phone apps at a single point and
they're repeatable at that SPL, but because the AGC isn't disabled,
lower levels are boosted and higher levels are sat on before they get to
the meter app, so everything comes out at about the same reading.


:-) Exactly, and the vast majority of users don't even have a way to
check them at ANY level, yet still think they have a useful measurement.
:-(

Trevor.

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On 10/06/2018 2:36 AM, Ralph Barone wrote:
The iPod touch is an iPhone without the phone bits. It runs iOS.



Oh, obviously I haven't been keeping up with Apple products.
(never bought anything they make, I doubt I ever will)
I wonder how big a market there is for a crippled iPhone though? Sort
of an iPad with too small a screen to be useful by the looks. But too
big and expensive for the people that usually buy music players.
Everybody that wants to use a phone size player already has a phone that
does that I would think. And in the Android world you can just plug a
huge micro SD card into most phones for unlimited storage. (swapping
cards if really necessary, not something Apple allows because they make
so much money on selling memory at hugely inflated prices.)

Trevor.



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In article , Trevor wrote:
On 10/06/2018 12:48 PM, Mike Rivers wrote:
On 6/9/2018 6:29 PM, Phil Allison wrote:
In the 1950s and 60s, the standard bench instrument for professional
techs and engineers was a VTVM like this one:
https://www.radiomuseum.org/r/rca_se...st_wv_98c.html


I have one of those on my workbench, and it still works.


The AVO meters were the most common in places I worked. Still have my
AVO model 8. If you don't fry them, no reason they won't outlast the user.


I hope I never, ever have to use a VTVM ever again. I spent more time
balancing and zeroing than taking measurements, it seemed. Modern
high-impedance DMMs make my life so much easier.

I do keep a Simpson 260 on my bench and I use it often. It lets you see
trends, count capacitor discharge curves, and so forth. The comparatively
low impedance means it won't get false measurements through leakage. But
it's just a coil of wire inside a magnet, there's no active electronics in
there.
--scott
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Scott Dorsey wrote:

Phil Allison wrote:

In the 1950s and 60s, the standard bench instrument for professional
techs and engineers was a VTVM like this one:
https://www.radiomuseum.org/r/rca_se...st_wv_98c.html

I have one of those on my workbench, and it still works.


The AVO meters were the most common in places I worked. Still have my
AVO model 8. If you don't fry them, no reason they won't outlast the user.



I hope I never, ever have to use a VTVM ever again. I spent more time
balancing and zeroing than taking measurements, it seemed.


** Once the tubes in the meter have warmed up, DC balance should be steady.

Zeroing the ohms ranges is needed with VOMs too.


Modern high-impedance DMMs make my life so much easier.



** The single biggest time saver is the auto-ranging feature.

However, most are poor at in-circuit testing resistors and semi junctions.


I do keep a Simpson 260 on my bench and I use it often.



** I have a similar Japanese made multimeter that I use occasionally.

Taut band, 20kohms/V, 100kHz response plus dBm scale.

The ohms x 1 range will reliably forward bias semiconductor junctions while in circuit.



..... Phil







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On Sun, 10 Jun 2018 17:03:41 -0700 (PDT), Phil Allison
wrote:


I do keep a Simpson 260 on my bench and I use it often.



** I have a similar Japanese made multimeter that I use occasionally.

Taut band, 20kohms/V, 100kHz response plus dBm scale.

The ohms x 1 range will reliably forward bias semiconductor junctions while in circuit.

For in-circuit testing I find it useful to have an ohms range that is
of low enough voltage that it can't forward bias a junction. I have a
separate range that does provide forward bias, and reads out a voltage
rather than a resistance.

d

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Don Pearce wrote:


Phil Allison


I do keep a Simpson 260 on my bench and I use it often.



** I have a similar Japanese made multimeter that I use occasionally.

Taut band, 20kohms/V, 100kHz response plus dBm scale.

The ohms x 1 range will reliably forward bias semiconductor
junctions while in circuit.



For in-circuit testing I find it useful to have an ohms range that is
of low enough voltage that it can't forward bias a junction. I have a
separate range that does provide forward bias, and reads out a voltage
rather than a resistance.


** The diode check range ?

Limited current ( typ under 1mA) makes them near useless for in circuit and other work.


** FYI:

If you connect say a 100 ohm pot wired as a rheostat to the ohms x 1 range of an analogue multimeter, plus monitor the voltage across the probes with another meter ( say a DMM) you can arrive at DC voltages corresponding to various ohm readings.

Then you can carefully mark another scale just above the ohms one- in my case up to about 2.2 volts. Checks Ge and Si diodes, BJTS & Darlingtons and LEDs except with blue or white ones.

----------------------

When repairing an amplifier suspected of having blown BJT outputs & drivers, plus various small signal types and diodes in the SOA limiter - I found a meter that reliably forward biases junctions is needed to find the bad ones.

BJTs can fail with junctions shorted or open, plus C-E shorts - an analogue meter gives unambiguous readings with these conditions while a DMM gives mostly ambiguous ones, when testing in circuit.

Even if the DMM has a "diode check" range, the current is limited to under 1mA.
Either this is insufficient to bias the junction/s or a low value resistor in parallel the draws all the current.

Darlington power transistors read like single BJTs devices with "diode check" due to inbuilt resistors bridging B-E junctions.

High voltage BJTS ( eg horizontal defection ) have 30 to 100ohm resistors across the B-E junction internally.

Early Phase Linear models had output BJTS with inbuilt 70 ohm B-E resistors as well as 10 ohms across parallel sets on the PCB.


..... Phil
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On 10/06/2018 10:06 PM, Scott Dorsey wrote:
In article , Trevor wrote:
On 10/06/2018 12:48 PM, Mike Rivers wrote:
On 6/9/2018 6:29 PM, Phil Allison wrote:
In the 1950s and 60s, the standard bench instrument for professional
techs and engineers was a VTVM like this one:
https://www.radiomuseum.org/r/rca_se...st_wv_98c.html

I have one of those on my workbench, and it still works.


The AVO meters were the most common in places I worked. Still have my
AVO model 8. If you don't fry them, no reason they won't outlast the user.


I hope I never, ever have to use a VTVM ever again. I spent more time
balancing and zeroing than taking measurements, it seemed. Modern
high-impedance DMMs make my life so much easier


You could say that about digital CRO's Vs analog ones too. Spent a lot
of time adjusting CRO's before you'd even attempt to use it.


I do keep a Simpson 260 on my bench and I use it often. It lets you see
trends, count capacitor discharge curves, and so forth. The comparatively
low impedance means it won't get false measurements through leakage. But
it's just a coil of wire inside a magnet, there's no active electronics in
there.


To be fair the AVO's were not VTVM's, just a meter, multipliers and
shunts. But you did need a VTVM/SSVOM or CRO when loading was a problem.
Not something people often worry about these days with modern digital
multi-meters, even when they should. 10Mohm is a lot better than
20kohm/volt in most cases, but if you are working with Megohm plus
impedances, you still need to know about loading. Amazing how many
people get caught out still.

Trevor.


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Trevor wrote:




I hope I never, ever have to use a VTVM ever again. I spent more time
balancing and zeroing than taking measurements, it seemed. Modern
high-impedance DMMs make my life so much easier


You could say that about digital CRO's Vs analog ones too. Spent a lot
of time adjusting CRO's before you'd even attempt to use it.


** The exact opposite is true.

Analoge scopes ( CROs to some) are easy and quick to use, no ambiguous stuff on the screen to worry about. With a DSO, one fiddles about with the controls and menus for ever.



To be fair the AVO's were not VTVM's,


** VTVMs waayy outperform AVOs when it comes to electronics, especially with high impedance or valve circuitry.

However, they shine with electrical gear like motors, relays, transformers lighting etc. Old school.


But you did need a VTVM/SSVOM or CRO when loading was a problem.
Not something people often worry about these days with modern digital
multi-meters, even when they should. 10Mohm is a lot better than
20kohm/volt in most cases, but if you are working with Megohm plus
impedances, you still need to know about loading. Amazing how many
people get caught out still.


** Say you have an audio triode valve with 250V on the anode fed from a 470kohm resistor. Both a VTVM and a modern DMM will show 5% or more low on the actual anode voltage. So will a 20kohm/VOM set to its 500V range.


..... Phil

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Those darn things would break into spurious oscillation driving a
resistive load. I came up with a mod that made them stable enough that
a local rock band used them as their main amps.


so what was the mod?

m



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so what was the mod?

m

I did these mods back in the 1970s and then I had a near photographic
memory so I didn't document it. It consisted of installing pico value
caps in various locations. I can't remeber the locations or values of
the caps.


there is some interesting info in this book

file:///C:/USER/DOWNLOADS%20go%20here/elebda3.net-gh-238.pdf

especially Chap 17, the section on electronic overload protection.

If done correctly it looks like a modern design should be immune to damage, even if it does go into osc.



m

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On 12/06/2018 5:37 AM, wrote:
there is some interesting info in this book

file:///C:/USER/DOWNLOADS%20go%20here/elebda3.net-gh-238.pdf


Do you actually expect everybody to have access to your hard drive?

Trevor.


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Trevor wrote:
On 12/06/2018 5:37 AM, wrote:
there is some interesting info in this book

file:///C:/USER/DOWNLOADS%20go%20here/elebda3.net-gh-238.pdf


Do you actually expect everybody to have access to your hard drive?

Trevor.


Just the NSA...

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In article ,
Scott Dorsey wrote:
In article , Trevor wrote:
On 10/06/2018 12:48 PM, Mike Rivers wrote:
On 6/9/2018 6:29 PM, Phil Allison wrote:
In the 1950s and 60s, the standard bench instrument for professional
techs and engineers was a VTVM like this one:
https://www.radiomuseum.org/r/rca_se...st_wv_98c.html

I have one of those on my workbench, and it still works.


The AVO meters were the most common in places I worked. Still have my
AVO model 8. If you don't fry them, no reason they won't outlast the user.


I hope I never, ever have to use a VTVM ever again. I spent more time
balancing and zeroing than taking measurements, it seemed. Modern
high-impedance DMMs make my life so much easier.

I do keep a Simpson 260 on my bench and I use it often. It lets you see
trends, count capacitor discharge curves, and so forth. The comparatively
low impedance means it won't get false measurements through leakage. But
it's just a coil of wire inside a magnet, there's no active electronics in
there.
--scott
--

Scott, I'm surprised at your comments about VTVM's. I have several RCA
WV-97A's and one WV-98C; and all have been plug-n-play bulletproof since
I got them up to snuff about 25 years ago.

The VTVM's that gave grief (of those I've dealt with) were the H-P 400
series AC RMS meters. Those were built with vitamin noise, and while I
chased down and cured several, I never was satisfied. Big problem was
ground lugs rivetted to aluminum. I may sound prejudiced because I
worked for Tektronix in the 1960's, but a lot of H-P stuff was rather
poorly made. A 200CD audio oscillator was very nice---after you
replaced all the postage stamp capacitors and carbon resistors. I added
either terminal strips or Tek ceramic strips (pirated from junk K plug
ins) for mounting the central electronics. One exception is the h-P
412A DC VTVM. Once working, those are rock-solid. But for AC RMS, a
Ballantine 300 beats the H-P 400 all day, even if they look archaic.

For passive VOM's, my treasures are a Triplett 630-NA (the model with
the double sensitivity switch) and Simpson 260-8. I bought the 260-8
new because it has a 25 volt range suitable for automotive use. Had to
wait for the Ojibwas, who make them now, to come back from pow-wow and
refill the pipeline, but it was well worth the wait. Both reside in
padded cases, also well worth the cost. I have a couple of cheap analog
"beater meters" as well, but the 630-NA and 260 are crown jewels around
here.

DMMs? I just plain don't like them. If I'm chasing intermittents, a
DMM doses me with spinning numbers, while an analog meter pointer
movement doubles as a poor man's low-frequency oscilloscope. And I
don't like being foxed by autoranging.

I have to wonder, what were the VTVM's that gave you so much grief.
One reason I have for so many RCA's is that when I am bringing up a Tek
530-540 series scope for the first time, I have a meter on every power
supply ready to read the moment the time delay closes.

Hank



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On Tuesday, June 12, 2018 at 2:45:24 AM UTC-4, Trevor wrote:
On 12/06/2018 1:50 PM, Ralph Barone wrote:
Trevor wrote:
On 12/06/2018 5:37 AM, wrote:
there is some interesting info in this book

file:///C:/USER/DOWNLOADS%20go%20here/elebda3.net-gh-238.pdf


Do you actually expect everybody to have access to your hard drive?


Just the NSA...


:-)
I doubt they bother to read this group though. You'd need to use the
words they auto flag. Oh wait, maybe your use of "NSA" did that already.
:-)

Trevor.


whoops sorry about that
try this

http://www.kelm.ftn.uns.ac.rs/litera...gnHandbook.pdf

or google power amplifier design handbook, there is a newer edition out there.
m
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wrote:



there is some interesting info in this book


** You did a Google word search to find that - right ?


file:///C:/USER/DOWNLOADS%20go%20here/elebda3.net-gh-238.pdf

especially Chap 17, the section on electronic overload protection.


** That is all in Chap 13.

If done correctly it looks like a modern design should be immune to
damage, even if it does go into osc.



** ********.

The Chap does not even mention the topic of positive feedback amplifier oscillation.

Google can't know things that and neither do you.


..... Phil
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In article , Trevor wrote:
On 10/06/2018 10:06 PM, Scott Dorsey wrote:
I hope I never, ever have to use a VTVM ever again. I spent more time
balancing and zeroing than taking measurements, it seemed. Modern
high-impedance DMMs make my life so much easier


You could say that about digital CRO's Vs analog ones too. Spent a lot
of time adjusting CRO's before you'd even attempt to use it.


I disagree. I spend forever fiddling with the damn menus on the DSO. I like
the DSO for a lot of things, especially for very low frequency stuff and the
ability to get power spectra, but I'll take an analogue scope any time for
making quick qualitative measurements.
--scott

--
"C'est un Nagra. C'est suisse, et tres, tres precis."


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In article , Trevor wrote:
On 13/06/2018 12:19 AM, wrote:
http://www.kelm.ftn.uns.ac.rs/litera...gnHandbook.pdf

or google power amplifier design handbook, there is a newer edition out there.


Yes, thanks for that. Have an old printed edition myself, never bothered
to look for a newer edition on-line before.


Are we talking Doug Self's book here?
If so, you should buy the printed edition instead of bootlegging it, because
Self is a good fellow and deserves your support.
--scott

--
"C'est un Nagra. C'est suisse, et tres, tres precis."
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On 13/06/2018 11:31 PM, Scott Dorsey wrote:
In article , Trevor wrote:
On 10/06/2018 10:06 PM, Scott Dorsey wrote:
I hope I never, ever have to use a VTVM ever again. I spent more time
balancing and zeroing than taking measurements, it seemed. Modern
high-impedance DMMs make my life so much easier


You could say that about digital CRO's Vs analog ones too. Spent a lot
of time adjusting CRO's before you'd even attempt to use it.


I disagree. I spend forever fiddling with the damn menus on the DSO. I like
the DSO for a lot of things, especially for very low frequency stuff and the
ability to get power spectra, but I'll take an analogue scope any time for
making quick qualitative measurements.


Fair point, adjusting settings via menu's can be a pain. I was thinking
of the fact you no longer have to adjust beam focus, vertical position
etc. But you still have to adjust probe compensation I guess. So you're
probably right.

Trevor.


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On 13/06/2018 11:35 PM, Scott Dorsey wrote:
In article , Trevor wrote:
On 13/06/2018 12:19 AM, wrote:
http://www.kelm.ftn.uns.ac.rs/litera...gnHandbook.pdf

or google power amplifier design handbook, there is a newer edition out there.


Yes, thanks for that. Have an old printed edition myself, never bothered
to look for a newer edition on-line before.


Are we talking Doug Self's book here?
If so, you should buy the printed edition instead of bootlegging it, because
Self is a good fellow and deserves your support.


As I said, I already have a printed copy. Just wanted to see what may
have been added in a newer edition. Certainly no real need for me to buy
a new printed copy these days, not doing that design work any more. I
have far too many copies of the same books in various editions as it is.
:-(

Trevor.

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