Maybe I need another 'scope?

Hey all youse 'scope gurus,
I'm gonna be getting a new and a used tube amplifier. The new one
is on the way and the used one is in my neighbor's garage. He still
needs to dig it out so I don't know anything about it except that has
tubes in it.
If the new one doesn't come with a schematic then right off the bat
I want to draw one so I can learn more about vacuum tube audio amp
workings. If I have to draw a schematic then I will put in the actual
values of the passives as well as the marked values. And I want to
measure the voltages in the circuit as well and put them into the
schematic. If the old one needs a schematic as well then if I can't
find one online I'll need to give it the same treatment as the new
one. If I do have schematics then all I will need to do is the
measurements and write them down. So....
I have a TEK 465B oscilloscope and it has served me well until now
diagnosing my CNC equipment. All the voltages I have needed to measure
have been below 50 volts. But looking at the 'scope it seems like at
the 10x setting on the probes the highest voltage I can measure is 200
volts. That's 4 divisions at 50 volts per division. And that's peak to
peak, not RMS. I do have one 20x TEK probe, a P5120, that I used for
measuring the mains power, but the voltages inside tube equipment go
much higher.
I have been watching YouTube videos about vacuum tube equipmet and
have learned a lot so far. "Uncle Doug" has several videos that have
taught me a lot. Maybe it's because he used to be a teacher I am
learning so much.
Anyway, do I need a different 'scope to to measure accurately what
is going on inside vacuum tube equipment? Should I just look for
different probes with even more attenuation? I certainly don't need
the 100 MHz bandwidth that the 465B has for working with audio
equipment.
If you all think another 'scope should be in my future I would love
some advice. Since this is a hobby I don't wanna spend a lot of money
on yet another toy, er tool. So a used 'scope is fine with me. I love
my used TEK 465B.
Now before everybody starts giving me advice about high voltages
and all that I need everybody to know that I am expert and know all
there is to know about working with high voltages. Don't waste my time
telling me to put down my drink before I start working around high
voltages. I always use plastic cups for my drinks when working with
high voltages. Oh, and I don't put any salt on the rims of my Bloody
Marys either. And no cans of beer either, only glass bottles. Safety
first. As an expert I know alcoholic drinks are good. They keep my
hands from shaking too much in the morning. And I don't like smoking
pot. I figure I'm just as expert as some other self professed experts
here who don't need any extraneous advice.
I just watched a video about isolation transformers, how to build
one in a proper enclosure and how to use it properly. So even though I
have the isolated variac I think I'll make a 1:1 isolation xmfr too
with a little more ampacity. And if anybody here thinks I could use
some more advice about working around high voltages I welcome it and
will certainly take heed.
Thanks,
Eric

 

[John Robertson]

On 2018/11/19 4:01 PM, etpm@whidbey.com wrote:

Hey all youse 'scope gurus,
I'm gonna be getting a new and a used tube amplifier. The new one
is on the way and the used one is in my neighbor's garage. He still
needs to dig it out so I don't know anything about it except that has
tubes in it.
If the new one doesn't come with a schematic then right off the bat
I want to draw one so I can learn more about vacuum tube audio amp
workings. If I have to draw a schematic then I will put in the actual
values of the passives as well as the marked values. And I want to
measure the voltages in the circuit as well and put them into the
schematic. If the old one needs a schematic as well then if I can't
find one online I'll need to give it the same treatment as the new
one. If I do have schematics then all I will need to do is the
measurements and write them down. So....
I have a TEK 465B oscilloscope and it has served me well until now
diagnosing my CNC equipment. All the voltages I have needed to measure
have been below 50 volts. But looking at the 'scope it seems like at
the 10x setting on the probes the highest voltage I can measure is 200
volts. That's 4 divisions at 50 volts per division. And that's peak to
peak, not RMS. I do have one 20x TEK probe, a P5120, that I used for
measuring the mains power, but the voltages inside tube equipment go
much higher.
I have been watching YouTube videos about vacuum tube equipmet and
have learned a lot so far. "Uncle Doug" has several videos that have
taught me a lot. Maybe it's because he used to be a teacher I am
learning so much.
Anyway, do I need a different 'scope to to measure accurately what
is going on inside vacuum tube equipment? Should I just look for
different probes with even more attenuation? I certainly don't need
the 100 MHz bandwidth that the 465B has for working with audio
equipment.
If you all think another 'scope should be in my future I would love
some advice. Since this is a hobby I don't wanna spend a lot of money
on yet another toy, er tool. So a used 'scope is fine with me. I love
my used TEK 465B.
Now before everybody starts giving me advice about high voltages
and all that I need everybody to know that I am expert and know all
there is to know about working with high voltages. Don't waste my time
telling me to put down my drink before I start working around high
voltages. I always use plastic cups for my drinks when working with
high voltages. Oh, and I don't put any salt on the rims of my Bloody
Marys either. And no cans of beer either, only glass bottles. Safety
first. As an expert I know alcoholic drinks are good. They keep my
hands from shaking too much in the morning. And I don't like smoking
pot. I figure I'm just as expert as some other self professed experts
here who don't need any extraneous advice.
I just watched a video about isolation transformers, how to build
one in a proper enclosure and how to use it properly. So even though I
have the isolated variac I think I'll make a 1:1 isolation xmfr too
with a little more ampacity. And if anybody here thinks I could use
some more advice about working around high voltages I welcome it and
will certainly take heed.
Thanks,
Eric

Most tube amps are serviced in our shop with a digital voltmeter...not a
scope. Really all that you need to know are correct are the plate and
cathode voltages, and if they are off then you check the screen and
grids for proper bias - after testing the tubes for proper operation.

Most common failures are electrolytic caps, then inter-stage isolation
caps followed closely by plate resistors (they overheat with bias goes
wrong) and then cathode resistors, bias circuit, grid resistors, and
then - perhaps - a damaged output transformer.

Virtually all of that can be tested quickly with a voltmeter once you
know the average plate voltages. If the plate voltages are good then the
amp is fed a known AC signal of a set level and you then follow the AC
signal through the amp using your AC setting on the voltmeter. I check
first the input level, if good I then check the high side of the volume
control and if is on spec I then go to the output of the phase splitter
tube(s). Divide the amp in half, then halve the remaining sections to
find the problem.

If you are doing high end amp work where distortion is a factor then you
will break out a slow dual trace scope to find the issues, but for
regular tube amps like guitars and jukeboxes we usually don't bother.
Not that we don't have scopes (have almost ten in various sizes and
speeds), but they rarely help - at least for tubes!

John :-#)#

--
(Please post followups or tech inquiries to the USENET newsgroup)
John's Jukes Ltd.
MOVED to #7 - 3979 Marine Way, Burnaby, BC, Canada V5J 5E3
(604)872-5757 (Pinballs, Jukes, Video Games)
www.flippers.com
"Old pinballers never die, they just flip out."

 

[Rheilly Phoull]

On 20/11/2018 8:01 am, etpm@whidbey.com wrote:

Hey all youse 'scope gurus,
I'm gonna be getting a new and a used tube amplifier. The new one
is on the way and the used one is in my neighbor's garage. He still
needs to dig it out so I don't know anything about it except that has
tubes in it.
If the new one doesn't come with a schematic then right off the bat
I want to draw one so I can learn more about vacuum tube audio amp
workings. If I have to draw a schematic then I will put in the actual
values of the passives as well as the marked values. And I want to
measure the voltages in the circuit as well and put them into the
schematic. If the old one needs a schematic as well then if I can't
find one online I'll need to give it the same treatment as the new
one. If I do have schematics then all I will need to do is the
measurements and write them down. So....
I have a TEK 465B oscilloscope and it has served me well until now
diagnosing my CNC equipment. All the voltages I have needed to measure
have been below 50 volts. But looking at the 'scope it seems like at
the 10x setting on the probes the highest voltage I can measure is 200
volts. That's 4 divisions at 50 volts per division. And that's peak to
peak, not RMS. I do have one 20x TEK probe, a P5120, that I used for
measuring the mains power, but the voltages inside tube equipment go
much higher.
I have been watching YouTube videos about vacuum tube equipmet and
have learned a lot so far. "Uncle Doug" has several videos that have
taught me a lot. Maybe it's because he used to be a teacher I am
learning so much.
Anyway, do I need a different 'scope to to measure accurately what
is going on inside vacuum tube equipment? Should I just look for
different probes with even more attenuation? I certainly don't need
the 100 MHz bandwidth that the 465B has for working with audio
equipment.
If you all think another 'scope should be in my future I would love
some advice. Since this is a hobby I don't wanna spend a lot of money
on yet another toy, er tool. So a used 'scope is fine with me. I love
my used TEK 465B.
Now before everybody starts giving me advice about high voltages
and all that I need everybody to know that I am expert and know all
there is to know about working with high voltages. Don't waste my time
telling me to put down my drink before I start working around high
voltages. I always use plastic cups for my drinks when working with
high voltages. Oh, and I don't put any salt on the rims of my Bloody
Marys either. And no cans of beer either, only glass bottles. Safety
first. As an expert I know alcoholic drinks are good. They keep my
hands from shaking too much in the morning. And I don't like smoking
pot. I figure I'm just as expert as some other self professed experts
here who don't need any extraneous advice.
I just watched a video about isolation transformers, how to build
one in a proper enclosure and how to use it properly. So even though I
have the isolated variac I think I'll make a 1:1 isolation xmfr too
with a little more ampacity. And if anybody here thinks I could use
some more advice about working around high voltages I welcome it and
will certainly take heed.
Thanks,
Eric


An expert who has no knowledge of voltage dividers

 

On Monday, 19 November 2018 23:55:59 UTC, et...@whidbey.com wrote:

Hey all youse 'scope gurus,
I'm gonna be getting a new and a used tube amplifier. The new one
is on the way and the used one is in my neighbor's garage. He still
needs to dig it out so I don't know anything about it except that has
tubes in it.
If the new one doesn't come with a schematic then right off the bat
I want to draw one so I can learn more about vacuum tube audio amp
workings. If I have to draw a schematic then I will put in the actual
values of the passives as well as the marked values. And I want to
measure the voltages in the circuit as well and put them into the
schematic. If the old one needs a schematic as well then if I can't
find one online I'll need to give it the same treatment as the new
one. If I do have schematics then all I will need to do is the
measurements and write them down. So....
I have a TEK 465B oscilloscope and it has served me well until now
diagnosing my CNC equipment. All the voltages I have needed to measure
have been below 50 volts. But looking at the 'scope it seems like at
the 10x setting on the probes the highest voltage I can measure is 200
volts. That's 4 divisions at 50 volts per division. And that's peak to
peak, not RMS. I do have one 20x TEK probe, a P5120, that I used for
measuring the mains power, but the voltages inside tube equipment go
much higher.
I have been watching YouTube videos about vacuum tube equipmet and
have learned a lot so far. "Uncle Doug" has several videos that have
taught me a lot. Maybe it's because he used to be a teacher I am
learning so much.
Anyway, do I need a different 'scope to to measure accurately what
is going on inside vacuum tube equipment? Should I just look for
different probes with even more attenuation? I certainly don't need
the 100 MHz bandwidth that the 465B has for working with audio
equipment.
If you all think another 'scope should be in my future I would love
some advice. Since this is a hobby I don't wanna spend a lot of money
on yet another toy, er tool. So a used 'scope is fine with me. I love
my used TEK 465B.
Now before everybody starts giving me advice about high voltages
and all that I need everybody to know that I am expert and know all
there is to know about working with high voltages. Don't waste my time
telling me to put down my drink before I start working around high
voltages. I always use plastic cups for my drinks when working with
high voltages. Oh, and I don't put any salt on the rims of my Bloody
Marys either. And no cans of beer either, only glass bottles. Safety
first. As an expert I know alcoholic drinks are good. They keep my
hands from shaking too much in the morning. And I don't like smoking
pot. I figure I'm just as expert as some other self professed experts
here who don't need any extraneous advice.
I just watched a video about isolation transformers, how to build
one in a proper enclosure and how to use it properly. So even though I
have the isolated variac I think I'll make a 1:1 isolation xmfr too
with a little more ampacity. And if anybody here thinks I could use
some more advice about working around high voltages I welcome it and
will certainly take heed.
Thanks,
Eric

200v limit sounds most unlikely.
Enjoy frying yourself. It sounds like you will at some point.


NT

 

[Ralph Mowery]

In article <d_WdnYzCwa0jzm7GnZ2dnUU7-QXNnZ2d@giganews.com>,
spam@flippers.com says...

Most tube amps are serviced in our shop with a digital voltmeter...not a
scope. Really all that you need to know are correct are the plate and
cathode voltages, and if they are off then you check the screen and
grids for proper bias - after testing the tubes for proper operation.

I agree. Forget about the scope if you want to just measure voltages.
I have the same scope and would never try to make accurate voltage
measurments with it.

You can always get a 100 to 1 probe. However, you can get one of the
'free' Harbor Freight meters and do better for what you want.

For just DC measurments you can just make your own 100:1 voltage
devider.

 

[Phil Allison]

John Robertson wrote:

Most tube amps are serviced in our shop with a digital voltmeter...not a
scope.

** Wow, that is contrary to how most audio amplifier techs do it.

With a scope probe, you can check DC levels and AC waveforms at the
same time - so the first step is to connect an audio generator and
dummy load and see if there is any clean output.

Really all that you need to know are correct are the plate and
cathode voltages, and if they are off then you check the screen and
grids for proper bias - after testing the tubes for proper operation.

** OK, maybe having a good tube tester changes how you do things.

Most common failures are electrolytic caps,

** I see amplifiers from the 1960s up to a year or so old and faulty
electros are not the most common parts to be replaced - faulty tubes are.
Electros always get replaced if my ESR meter says they are bad or there are visible problems like leaking electrolyte.

then inter-stage isolation caps followed closely by plate resistors ...

** Only rarely need replacing, IME.

If you are doing high end amp work where distortion is a factor then you
will break out a slow dual trace scope to find the issues, but for
regular tube amps like guitars and jukeboxes we usually don't bother.

** I find I use the scope and DMM in combination until the amp is all working properly. This will usually take longer on an unfamiliar example where no circuit is available.


..... Phil

 

[Phil Hobbs]

On 11/19/18 7:01 PM, etpm@whidbey.com wrote:

Hey all youse 'scope gurus,
I'm gonna be getting a new and a used tube amplifier. The new one
is on the way and the used one is in my neighbor's garage. He still
needs to dig it out so I don't know anything about it except that has
tubes in it.
If the new one doesn't come with a schematic then right off the bat
I want to draw one so I can learn more about vacuum tube audio amp
workings. If I have to draw a schematic then I will put in the actual
values of the passives as well as the marked values. And I want to
measure the voltages in the circuit as well and put them into the
schematic. If the old one needs a schematic as well then if I can't
find one online I'll need to give it the same treatment as the new
one. If I do have schematics then all I will need to do is the
measurements and write them down. So....
I have a TEK 465B oscilloscope and it has served me well until now
diagnosing my CNC equipment. All the voltages I have needed to measure
have been below 50 volts. But looking at the 'scope it seems like at
the 10x setting on the probes the highest voltage I can measure is 200
volts. That's 4 divisions at 50 volts per division. And that's peak to
peak, not RMS. I do have one 20x TEK probe, a P5120, that I used for
measuring the mains power, but the voltages inside tube equipment go
much higher.
I have been watching YouTube videos about vacuum tube equipmet and
have learned a lot so far. "Uncle Doug" has several videos that have
taught me a lot. Maybe it's because he used to be a teacher I am
learning so much.
Anyway, do I need a different 'scope to to measure accurately what
is going on inside vacuum tube equipment? Should I just look for
different probes with even more attenuation? I certainly don't need
the 100 MHz bandwidth that the 465B has for working with audio
equipment.
If you all think another 'scope should be in my future I would love
some advice. Since this is a hobby I don't wanna spend a lot of money
on yet another toy, er tool. So a used 'scope is fine with me. I love
my used TEK 465B.

Everybody should have another scope now and again. I have 11 at the
moment, which is none too many.

(On average I pay about 3 cents on the dollar, which makes new scopes an
easier sell.)

Cheers

Phil Hobbs


--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com

 

On Tuesday, 20 November 2018 06:18:38 UTC, Phil Hobbs wrote:

On 11/19/18 7:01 PM, etpm@whidbey.com wrote:
Hey all youse 'scope gurus,

Anyway, do I need a different 'scope to to measure accurately what
is going on inside vacuum tube equipment?

no

If you all think another 'scope should be in my future I would love
some advice. Since this is a hobby I don't wanna spend a lot of money
on yet another toy, er tool. So a used 'scope is fine with me. I love
my used TEK 465B.

Everybody should have another scope now and again. I have 11 at the
moment, which is none too many.

(On average I pay about 3 cents on the dollar, which makes new scopes an
easier sell.)

Cheers

Phil Hobbs

If you're going to get one you don't need, consider making it a pocket scope. Quite handy, even with modest specs.


NT

 

[pfjw@aol.com]

Find a mirror. Put it at eye level and stare into it for one (1) full minute. Then repeat ten (10) times:

I don't need a scope to service tube amps.

Repeat as necessary.

Your isovariac will be adequate for the work. That, reasonable caution, common sense, understanding of what tubes are and do (and do not), and patience. None of which are common characteristics.

On tube testers:

YES, they are handy if you have a good one that tests for shorts and gas. And if you are going "full audiophile", one that allows you to match is also useful. But the brute fact of the matter is that there are few testers out there that actually give information that is both good and useful. That a tube has no shorts and is not gassy is good to know, but not particularly indicative of its function-in-use. I keep two - one a fairly simple Simpson emissions tester, good for about 90% of my needs, and a Hickok 539B, which is allows proper matching with additional equipment (2 x VOM). Sadly, tube testers that have been restored, calibrated and are reliable are getting scarce and expensive. The amount of *stuff* that crosses my bench in a given year justifies the need.

I also keep a very good scope - that I have used twice in five years to find that niggling problem, and that was on solid-state devices. If I ever get another scope, it will be a "pocket" device as they take up a LOT of real-estate otherwise.

Peter Wieck
Melrose Park, PA

 

[Tim Schwartz]

Eric,

I'd suggest using a voltmeter (analog or digital, whatever you
prefer)for the DC voltage measurements. I like my old Heathkit VTVM for
troubleshooting, as you are unlikely to cause any serious damage to the
meter, as could happen with a digital.

The scope you have is all you need, as what you need it for is the AC
part of the waveform. Set the scope to AC coupling at the input and
you'll be looking at the ripple on the supply. If the ripple exceeds
400 volts (8 divisions at 5 volts each is 40Vp-p and with a 10x probe
that gets you to 400Vp-p) then something is seriously wrong with your
power supply or measurement technique, or you don't have a good ground
between the amp and the scope.

Regards,
Tim



On 11/19/2018 7:01 PM, etpm@whidbey.com wrote:

Hey all youse 'scope gurus,
I'm gonna be getting a new and a used tube amplifier. The new one
is on the way and the used one is in my neighbor's garage. He still
needs to dig it out so I don't know anything about it except that has
tubes in it.
If the new one doesn't come with a schematic then right off the bat
I want to draw one so I can learn more about vacuum tube audio amp
workings. If I have to draw a schematic then I will put in the actual
values of the passives as well as the marked values. And I want to
measure the voltages in the circuit as well and put them into the
schematic. If the old one needs a schematic as well then if I can't
find one online I'll need to give it the same treatment as the new
one. If I do have schematics then all I will need to do is the
measurements and write them down. So....
I have a TEK 465B oscilloscope and it has served me well until now
diagnosing my CNC equipment. All the voltages I have needed to measure
have been below 50 volts. But looking at the 'scope it seems like at
the 10x setting on the probes the highest voltage I can measure is 200
volts. That's 4 divisions at 50 volts per division. And that's peak to
peak, not RMS. I do have one 20x TEK probe, a P5120, that I used for
measuring the mains power, but the voltages inside tube equipment go
much higher.
I have been watching YouTube videos about vacuum tube equipmet and
have learned a lot so far. "Uncle Doug" has several videos that have
taught me a lot. Maybe it's because he used to be a teacher I am
learning so much.
Anyway, do I need a different 'scope to to measure accurately what
is going on inside vacuum tube equipment? Should I just look for
different probes with even more attenuation? I certainly don't need
the 100 MHz bandwidth that the 465B has for working with audio
equipment.
If you all think another 'scope should be in my future I would love
some advice. Since this is a hobby I don't wanna spend a lot of money
on yet another toy, er tool. So a used 'scope is fine with me. I love
my used TEK 465B.
Now before everybody starts giving me advice about high voltages
and all that I need everybody to know that I am expert and know all
there is to know about working with high voltages. Don't waste my time
telling me to put down my drink before I start working around high
voltages. I always use plastic cups for my drinks when working with
high voltages. Oh, and I don't put any salt on the rims of my Bloody
Marys either. And no cans of beer either, only glass bottles. Safety
first. As an expert I know alcoholic drinks are good. They keep my
hands from shaking too much in the morning. And I don't like smoking
pot. I figure I'm just as expert as some other self professed experts
here who don't need any extraneous advice.
I just watched a video about isolation transformers, how to build
one in a proper enclosure and how to use it properly. So even though I
have the isolated variac I think I'll make a 1:1 isolation xmfr too
with a little more ampacity. And if anybody here thinks I could use
some more advice about working around high voltages I welcome it and
will certainly take heed.
Thanks,
Eric

 

[Tim Schwartz]

Eric,

I'd suggest using a voltmeter (analog or digital, whatever you
prefer)for the DC voltage measurements. I like my old Heathkit VTVM for
troubleshooting, as you are unlikely to cause any serious damage to the
meter, as could happen with a digital.

The scope you have is all you need, as what you need it for is the
AC part of the waveform. Set the scope to AC coupling at the input and
you'll be looking at the ripple on the supply. If the ripple exceeds
400 volts (8 divisions at 5 volts each is 40Vp-p and with a 10x probe
that gets you to 400Vp-p) then something is seriously wrong with your
power supply or measurement technique, or you don't have a good ground
between the amp and the scope.

Regards,
Tim


On 11/19/2018 7:01 PM, etpm@whidbey.com wrote:

Hey all youse 'scope gurus,
I'm gonna be getting a new and a used tube amplifier. The new one
is on the way and the used one is in my neighbor's garage. He still
needs to dig it out so I don't know anything about it except that has
tubes in it.
If the new one doesn't come with a schematic then right off the bat
I want to draw one so I can learn more about vacuum tube audio amp
workings. If I have to draw a schematic then I will put in the actual
values of the passives as well as the marked values. And I want to
measure the voltages in the circuit as well and put them into the
schematic. If the old one needs a schematic as well then if I can't
find one online I'll need to give it the same treatment as the new
one. If I do have schematics then all I will need to do is the
measurements and write them down. So....
I have a TEK 465B oscilloscope and it has served me well until now
diagnosing my CNC equipment. All the voltages I have needed to measure
have been below 50 volts. But looking at the 'scope it seems like at
the 10x setting on the probes the highest voltage I can measure is 200
volts. That's 4 divisions at 50 volts per division. And that's peak to
peak, not RMS. I do have one 20x TEK probe, a P5120, that I used for
measuring the mains power, but the voltages inside tube equipment go
much higher.
I have been watching YouTube videos about vacuum tube equipmet and
have learned a lot so far. "Uncle Doug" has several videos that have
taught me a lot. Maybe it's because he used to be a teacher I am
learning so much.
Anyway, do I need a different 'scope to to measure accurately what
is going on inside vacuum tube equipment? Should I just look for
different probes with even more attenuation? I certainly don't need
the 100 MHz bandwidth that the 465B has for working with audio
equipment.
If you all think another 'scope should be in my future I would love
some advice. Since this is a hobby I don't wanna spend a lot of money
on yet another toy, er tool. So a used 'scope is fine with me. I love
my used TEK 465B.
Now before everybody starts giving me advice about high voltages
and all that I need everybody to know that I am expert and know all
there is to know about working with high voltages. Don't waste my time
telling me to put down my drink before I start working around high
voltages. I always use plastic cups for my drinks when working with
high voltages. Oh, and I don't put any salt on the rims of my Bloody
Marys either. And no cans of beer either, only glass bottles. Safety
first. As an expert I know alcoholic drinks are good. They keep my
hands from shaking too much in the morning. And I don't like smoking
pot. I figure I'm just as expert as some other self professed experts
here who don't need any extraneous advice.
I just watched a video about isolation transformers, how to build
one in a proper enclosure and how to use it properly. So even though I
have the isolated variac I think I'll make a 1:1 isolation xmfr too
with a little more ampacity. And if anybody here thinks I could use
some more advice about working around high voltages I welcome it and
will certainly take heed.
Thanks,
Eric

 

On Tuesday, 20 November 2018 12:24:49 UTC, pf...@aol.com wrote:

On tube testers:

YES, they are handy if you have a good one that tests for shorts and gas. And if you are going "full audiophile", one that allows you to match is also useful. But the brute fact of the matter is that there are few testers out there that actually give information that is both good and useful. That a tube has no shorts and is not gassy is good to know, but not particularly indicative of its function-in-use. I keep two - one a fairly simple Simpson emissions tester, good for about 90% of my needs, and a Hickok 539B, which is allows proper matching with additional equipment (2 x VOM). Sadly, tube testers that have been restored, calibrated and are reliable are getting scarce and expensive. The amount of *stuff* that crosses my bench in a given year justifies the need.

I also keep a very good scope - that I have used twice in five years to find that niggling problem, and that was on solid-state devices. If I ever get another scope, it will be a "pocket" device as they take up a LOT of real-estate otherwise.

Peter Wieck
Melrose Park, PA

Maybe it's time to make some new tube testers.

While we're here, an iso won't help if you connect an earthed scope to the thing. It will bite you if you touch, and that's how HT is.


NT

 

[Ralph Mowery]

In article <45a5d682-139d-4aaa-9ca2-b4d9243ea05e@googlegroups.com>,
tabbypurr@gmail.com says...

Maybe it's time to make some new tube testers.

While we're here, an iso won't help if you connect an earthed scope to the thing. It will bite you if you touch, and that's how HT is.

It is usually easier to just pop in a good tube instead of testing
unless looking for a matched set.

I have bought a $ 300 Hantek scope. It is suppose to be good to 200 MHz
and rated for 600 volts peak. Good thing about it, you can set the
screen up for waveform and digital volt meter. YOu see the waveform and
good resolution of voltage at the same time.

Sometimes it may be better or easier to just isolate the test equipment
from the ground and not the unit under test. I don't know how much the
solid scope draws without going to check, but it could probalby be
powered by 2 transformers of 24 volts at 2 amps or so placed back to
back.

 

[John-Del]

On Tuesday, November 20, 2018 at 9:28:22 AM UTC-5, tabb...@gmail.com wrote:

On Tuesday, 20 November 2018 12:24:49 UTC, pf...@aol.com wrote:

On tube testers:

YES, they are handy if you have a good one that tests for shorts and gas. And if you are going "full audiophile", one that allows you to match is also useful. But the brute fact of the matter is that there are few testers out there that actually give information that is both good and useful. That a tube has no shorts and is not gassy is good to know, but not particularly indicative of its function-in-use. I keep two - one a fairly simple Simpson emissions tester, good for about 90% of my needs, and a Hickok 539B, which is allows proper matching with additional equipment (2 x VOM). Sadly, tube testers that have been restored, calibrated and are reliable are getting scarce and expensive. The amount of *stuff* that crosses my bench in a given year justifies the need.

I also keep a very good scope - that I have used twice in five years to find that niggling problem, and that was on solid-state devices. If I ever get another scope, it will be a "pocket" device as they take up a LOT of real-estate otherwise.

Peter Wieck
Melrose Park, PA

Maybe it's time to make some new tube testers.

There's plenty of them out there, and they're very simple circuits. I probably have half a dozen or more, the only one that's kind of a dead end is a very nice one that checks the four pin tubes that has a dead meter. Otherwise, the standard recap and check for off value resistors and maybe replacing a selenium rectifier. But very simple to restore.

These testers are very handy and I do use them, but the best way to check any tube is to observe it's behavior and measure it's performance in the circuit itself.

 

[pfjw@aol.com]

On Tuesday, November 20, 2018 at 9:28:22 AM UTC-5, tabb...@gmail.com wrote:

Maybe it's time to make some new tube testers.

While we're here, an iso won't help if you connect an earthed scope to the thing. It will bite you if you touch, and that's how HT is.


NT

http://amplitrex.com/

This is one of several currently available. They are not cheap. If one is into tubes at a level to justify a new tester at this level, I would posit that the need is beyond the hobby level.

I tripped over my 539B when an old friend closed his business. The Simpson I found at a garage sale in Tamaqua, PA.

"Popping in" a new tube is OK for those of us with a couple of thousand tubes in a closet. Not so much for those working on operating inventory only. I do, also, like to screen tubes prior to installation.

Peter Wieck
Melrose Park, PA

 

On Mon, 19 Nov 2018 16:22:22 -0800, John Robertson <spam@flippers.com>
wrote:

On 2018/11/19 4:01 PM, etpm@whidbey.com wrote:
Hey all youse 'scope gurus,
I'm gonna be getting a new and a used tube amplifier. The new one
is on the way and the used one is in my neighbor's garage. He still
needs to dig it out so I don't know anything about it except that has
tubes in it.
If the new one doesn't come with a schematic then right off the bat
I want to draw one so I can learn more about vacuum tube audio amp
workings. If I have to draw a schematic then I will put in the actual
values of the passives as well as the marked values. And I want to
measure the voltages in the circuit as well and put them into the
schematic. If the old one needs a schematic as well then if I can't
find one online I'll need to give it the same treatment as the new
one. If I do have schematics then all I will need to do is the
measurements and write them down. So....
I have a TEK 465B oscilloscope and it has served me well until now
diagnosing my CNC equipment. All the voltages I have needed to measure
have been below 50 volts. But looking at the 'scope it seems like at
the 10x setting on the probes the highest voltage I can measure is 200
volts. That's 4 divisions at 50 volts per division. And that's peak to
peak, not RMS. I do have one 20x TEK probe, a P5120, that I used for
measuring the mains power, but the voltages inside tube equipment go
much higher.
I have been watching YouTube videos about vacuum tube equipmet and
have learned a lot so far. "Uncle Doug" has several videos that have
taught me a lot. Maybe it's because he used to be a teacher I am
learning so much.
Anyway, do I need a different 'scope to to measure accurately what
is going on inside vacuum tube equipment? Should I just look for
different probes with even more attenuation? I certainly don't need
the 100 MHz bandwidth that the 465B has for working with audio
equipment.
If you all think another 'scope should be in my future I would love
some advice. Since this is a hobby I don't wanna spend a lot of money
on yet another toy, er tool. So a used 'scope is fine with me. I love
my used TEK 465B.
Now before everybody starts giving me advice about high voltages
and all that I need everybody to know that I am expert and know all
there is to know about working with high voltages. Don't waste my time
telling me to put down my drink before I start working around high
voltages. I always use plastic cups for my drinks when working with
high voltages. Oh, and I don't put any salt on the rims of my Bloody
Marys either. And no cans of beer either, only glass bottles. Safety
first. As an expert I know alcoholic drinks are good. They keep my
hands from shaking too much in the morning. And I don't like smoking
pot. I figure I'm just as expert as some other self professed experts
here who don't need any extraneous advice.
I just watched a video about isolation transformers, how to build
one in a proper enclosure and how to use it properly. So even though I
have the isolated variac I think I'll make a 1:1 isolation xmfr too
with a little more ampacity. And if anybody here thinks I could use
some more advice about working around high voltages I welcome it and
will certainly take heed.
Thanks,
Eric



Most tube amps are serviced in our shop with a digital voltmeter...not a
scope. Really all that you need to know are correct are the plate and
cathode voltages, and if they are off then you check the screen and
grids for proper bias - after testing the tubes for proper operation.

Most common failures are electrolytic caps, then inter-stage isolation
caps followed closely by plate resistors (they overheat with bias goes
wrong) and then cathode resistors, bias circuit, grid resistors, and
then - perhaps - a damaged output transformer.

Virtually all of that can be tested quickly with a voltmeter once you
know the average plate voltages. If the plate voltages are good then the
amp is fed a known AC signal of a set level and you then follow the AC
signal through the amp using your AC setting on the voltmeter. I check
first the input level, if good I then check the high side of the volume
control and if is on spec I then go to the output of the phase splitter
tube(s). Divide the amp in half, then halve the remaining sections to
find the problem.

If you are doing high end amp work where distortion is a factor then you
will break out a slow dual trace scope to find the issues, but for
regular tube amps like guitars and jukeboxes we usually don't bother.
Not that we don't have scopes (have almost ten in various sizes and
speeds), but they rarely help - at least for tubes!

John :-#)#

Thanks for the reply John. I think my tongue in cheek "expert" comment
fell flat but you saw through my poor attempt at humor. Since I will
be interested in looking at the AC signal through to the speaker to
see how it changes, when clipping starts, a scope will be necessary.
From what you say it looks like using a VOM for the DC and a scope for
AC would be a good way to see how the amp is working.
Thanks,
Eric

 

On Tue, 20 Nov 2018 08:21:51 +0800, Rheilly Phoull
<rheilly@bigslong.com> wrote:

On 20/11/2018 8:01 am, etpm@whidbey.com wrote:
Hey all youse 'scope gurus,
I'm gonna be getting a new and a used tube amplifier. The new one
is on the way and the used one is in my neighbor's garage. He still
needs to dig it out so I don't know anything about it except that has
tubes in it.
If the new one doesn't come with a schematic then right off the bat
I want to draw one so I can learn more about vacuum tube audio amp
workings. If I have to draw a schematic then I will put in the actual
values of the passives as well as the marked values. And I want to
measure the voltages in the circuit as well and put them into the
schematic. If the old one needs a schematic as well then if I can't
find one online I'll need to give it the same treatment as the new
one. If I do have schematics then all I will need to do is the
measurements and write them down. So....
I have a TEK 465B oscilloscope and it has served me well until now
diagnosing my CNC equipment. All the voltages I have needed to measure
have been below 50 volts. But looking at the 'scope it seems like at
the 10x setting on the probes the highest voltage I can measure is 200
volts. That's 4 divisions at 50 volts per division. And that's peak to
peak, not RMS. I do have one 20x TEK probe, a P5120, that I used for
measuring the mains power, but the voltages inside tube equipment go
much higher.
I have been watching YouTube videos about vacuum tube equipmet and
have learned a lot so far. "Uncle Doug" has several videos that have
taught me a lot. Maybe it's because he used to be a teacher I am
learning so much.
Anyway, do I need a different 'scope to to measure accurately what
is going on inside vacuum tube equipment? Should I just look for
different probes with even more attenuation? I certainly don't need
the 100 MHz bandwidth that the 465B has for working with audio
equipment.
If you all think another 'scope should be in my future I would love
some advice. Since this is a hobby I don't wanna spend a lot of money
on yet another toy, er tool. So a used 'scope is fine with me. I love
my used TEK 465B.
Now before everybody starts giving me advice about high voltages
and all that I need everybody to know that I am expert and know all
there is to know about working with high voltages. Don't waste my time
telling me to put down my drink before I start working around high
voltages. I always use plastic cups for my drinks when working with
high voltages. Oh, and I don't put any salt on the rims of my Bloody
Marys either. And no cans of beer either, only glass bottles. Safety
first. As an expert I know alcoholic drinks are good. They keep my
hands from shaking too much in the morning. And I don't like smoking
pot. I figure I'm just as expert as some other self professed experts
here who don't need any extraneous advice.
I just watched a video about isolation transformers, how to build
one in a proper enclosure and how to use it properly. So even though I
have the isolated variac I think I'll make a 1:1 isolation xmfr too
with a little more ampacity. And if anybody here thinks I could use
some more advice about working around high voltages I welcome it and
will certainly take heed.
Thanks,
Eric


An expert who has no knowledge of voltage dividers

I know what a voltage divider is and have used them for some DC stuff,
but I don't know enough about AC signals to know if one would affect
the way the signal looks on a scope.
TYhjanks,
Eric

 

On Mon, 19 Nov 2018 23:02:22 -0500, Ralph Mowery
<rmowery28146@earthlink.net> wrote:

In article <d_WdnYzCwa0jzm7GnZ2dnUU7-QXNnZ2d@giganews.com>,
spam@flippers.com says...


Most tube amps are serviced in our shop with a digital voltmeter...not a
scope. Really all that you need to know are correct are the plate and
cathode voltages, and if they are off then you check the screen and
grids for proper bias - after testing the tubes for proper operation.



I agree. Forget about the scope if you want to just measure voltages.
I have the same scope and would never try to make accurate voltage
measurments with it.

You can always get a 100 to 1 probe. However, you can get one of the
'free' Harbor Freight meters and do better for what you want.

For just DC measurments you can just make your own 100:1 voltage
devider.

Thanks Ralph.
Eric

 

On Tue, 20 Nov 2018 06:28:19 -0800 (PST), tabbypurr@gmail.com wrote:

On Tuesday, 20 November 2018 12:24:49 UTC, pf...@aol.com wrote:

On tube testers:

YES, they are handy if you have a good one that tests for shorts and gas. And if you are going "full audiophile", one that allows you to match is also useful. But the brute fact of the matter is that there are few testers out there that actually give information that is both good and useful. That a tube has no shorts and is not gassy is good to know, but not particularly indicative of its function-in-use. I keep two - one a fairly simple Simpson emissions tester, good for about 90% of my needs, and a Hickok 539B, which is allows proper matching with additional equipment (2 x VOM). Sadly, tube testers that have been restored, calibrated and are reliable are getting scarce and expensive. The amount of *stuff* that crosses my bench in a given year justifies the need.

I also keep a very good scope - that I have used twice in five years to find that niggling problem, and that was on solid-state devices. If I ever get another scope, it will be a "pocket" device as they take up a LOT of real-estate otherwise.

Peter Wieck
Melrose Park, PA

Maybe it's time to make some new tube testers.

While we're here, an iso won't help if you connect an earthed scope to the thing. It will bite you if you touch, and that's how HT is.


NT

See that's exactly the kind of advice that I can't be told often
enough. Even though I did already know about this. My isolated variac
does not have an isolted ground so I bought one of those plug/socket
adapters that doesn't pass the ground through but instead provides a
tab to connect to ground.
Thanks,
Eric

 

>"Sometimes it may be better or easier to just isolate the test equipment from the ground and not the unit under test. "

"Floating the scope" is not good practice and may be illegal in a commercial setting. I do it but I am the type who works on live wiring and all that, there is specific and unmitigable set of rules for that which I will not attempt to list here. You have to REALLY know HOW to respect electricity, ESPECIALLY with tube equipment.

Pretty sure all scope manufacturers advise against it, some might try to void the warranty, maybe. Thee are other dangers, such as any ground fault in the test equipment you float can damage the DUT.

It most certainly can create insidious shock hazards as well, not just the ground and metal case of the scope, but ANY and ALL other test equipment connected to the same circuit(s).

I'll do it but I do not recommend it. Save that for when you have no choice..