[Allied Knight]

FOR SALE:

TUBE TESTER - Knight model 600

Nice Knight 600 Tube Tester in good working
condition. From Allied Electronics.
Good working condition including the internal roll chart
and comes with the manual and the accessory connecting
leads. Robust, vinyl covered wooden case.
Requires 120V AC power.

Available for $65.00 plus shipping.

Picture and details at:

http://s88932719.onlinehome.us/testgear.htm

[Peter Wieck]

On Feb 25, 12:41 pm, Allied Knight wrote:
FOR SALE:

TUBE TESTER - Knight model 600

Nice Knight 600 Tube Tester in good working
condition. From Allied Electronics.
Good working condition including the internal roll chart
and comes with the manual and the accessory connecting
leads. Robust, vinyl covered wooden case.
Requires 120V AC power.

Available for $65.00 plus shipping.

Picture and details at:

http://s88932719.onlinehome.us/testgear.htm

This is a simple emissions-only tester, but has the pre-octal sockets
up through 9-pin miniature & nuvistor. It is useful for go/no-go
decisions but *not* for matching. It has an adequate "shorts" test,
but does not list a separate "gas" test.

At the price plus assuming a reasonable shipping cost, it is a
reasonable tester to have if one has none more pressing instrument
needs and the money to spend. BAMA has all the charts, updates and
operating manuals, so it is well-supported as these things go.

I am not endorsing either the tester or the seller, but one could do
much worse if it is accurately described, especially in these days of
insane prices for full GM-type testers in any sort of reasonable
condition.

Peter Wieck
Wyncote, PA

[west]

"Peter Wieck" wrote in message
ups.com...
On Feb 25, 12:41 pm, Allied Knight wrote:
FOR SALE:

TUBE TESTER - Knight model 600

Nice Knight 600 Tube Tester in good working
condition. From Allied Electronics.
Good working condition including the internal roll chart
and comes with the manual and the accessory connecting
leads. Robust, vinyl covered wooden case.
Requires 120V AC power.

Available for $65.00 plus shipping.

Picture and details at:

http://s88932719.onlinehome.us/testgear.htm

This is a simple emissions-only tester, but has the pre-octal sockets
up through 9-pin miniature & nuvistor. It is useful for go/no-go
decisions but *not* for matching. It has an adequate "shorts" test,
but does not list a separate "gas" test.

At the price plus assuming a reasonable shipping cost, it is a
reasonable tester to have if one has none more pressing instrument
needs and the money to spend. BAMA has all the charts, updates and
operating manuals, so it is well-supported as these things go.

I am not endorsing either the tester or the seller, but one could do
much worse if it is accurately described, especially in these days of
insane prices for full GM-type testers in any sort of reasonable
condition.

Peter Wieck
Wyncote, PA

This might be a good spot for Patrick to tell us (again) why he doesn't use
a tube tester. His post on this was probably a couple of years ago and
influenced me from buying one of those insane-priced testers.

west

[Peter Wieck]

This might be a good spot for Patrick to tell us (again) why he doesn't use
a tube tester. His post on this was probably a couple of years ago and
influenced me from buying one of those insane-priced testers.

There are many reasons for a person such as Patrick not to use any
commercial-grade tube tester. He is the exception, not the rule
however. That being written, there are few significant reasons to own
much of a tube tester. That I own a premier tester (Hickok 539B) does
not necessarily make me an avid advocate of the species. Especially as
90% of my testing is done on my little Simpson emissions-only tester.

However, and using the Hickok 539 series as an example, a good tester
will:

a) Give valid "Life" and "Gas" tests. Most any tester is adequate for
shorts. Few emissions-types do gas. Some GM-types do not either.
b) Enable accurate matching. Tube Testers WILL NOT give matches
without additional instruments, but they will *enable* matching to be
done with that additional information (usually a VOM with an accurate
ammeter).
c) Enable the 'rejeuvenation process'. This is of-interest to vintage
radio people mostly, not audio people.
d) Allow the direct reading of filament (heater) and plate currents
with an outboard VOM. This can be very important when choosing
transformers or replacing burnt out tranformers... WHY did it burn
out? Was it carrying too much current? And so forth. The plate current
is significant to matching.
e) Have variable bias settings, and allow outboard bias current
sources if required.

Which comes down to a quantum-leap in superiority over an emissions-
only tester as actual tube quality may be discerned to a greater
degree. Emissions-only testers are valid for go/no-go decisions, no
more.

I do some audio work. That justified me paying $100 for a surplus,
recently calibrated 539B from the GE Re-entry Systems Division in
Philadelphia some 10 years ago (through a local jobber). That it had
all the books, updates and an additional roll-chart helped. It would
not justify me spending the +/-$1000 that I could get for it today. I
paid $35 for the Simpson tester ($50 including shipping), also well-
documented roughly two years ago. That is about right. For vintage
radios, it is more than adequate 95+% of the time.

The best test of any tube (after shorts are ruled out, anyway) is the
circuit it lives in. No tube-tester will be able to duplicate that
test.

Peter Wieck
Wyncote, PA

[Patrick Turner]

Peter Wieck wrote:

This might be a good spot for Patrick to tell us (again) why he doesn't use
a tube tester. His post on this was probably a couple of years ago and
influenced me from buying one of those insane-priced testers.

There are many reasons for a person such as Patrick not to use any
commercial-grade tube tester. He is the exception, not the rule
however. That being written, there are few significant reasons to own
much of a tube tester.


Back in the days of 1960 when nearly all the electronics was tubed.
And there may have been 30 tubes in a colour TV, so having a tube tester
to test the triode-pentodes and
other multigrids of a complex nature was sensible. You could find out if
a tube was dead or not
from an IF strip without much effort trying to measure IF gain.

But now ALL the tubed electronics is either AM radios, or audio amps,
with perhaps 0.00000001% being an FM tuner that is tubed.

So while probing around an AF circuit, one not only finds out if a tube
is crook or not, but
whether something else nearby is stuffed, such as a resistor or coupling
cap.

You sure as hell don't need a tube tester these days. They were built to
sell
to repair workshops wanting to reduce the time taken for repairs.

But don't let me prevent anyone from having fun with a tube tester which
you may want, but don't need.

Nearly all the guys I know who have scrambled to get a tester then got
another, because the first
one had serious switch and burnt resistor faults, AND, they didn't and
still don't have a clue about the inner
basics of how a tube works, how to measure and observe for low noise and
microphony which are things
a tube tester won't tell you, and they sure dunno how to fix the broken
tester from 1960.
Many of these guys could not design a one triode gain stage if their
life depended on it.

They place faith in a tester when their brain is empty of real
knowledge.

That I own a premier tester (Hickok 539B) does
not necessarily make me an avid advocate of the species. Especially as
90% of my testing is done on my little Simpson emissions-only tester.

However, and using the Hickok 539 series as an example, a good tester
will:

a) Give valid "Life" and "Gas" tests. Most any tester is adequate for
shorts. Few emissions-types do gas. Some GM-types do not either.
b) Enable accurate matching. Tube Testers WILL NOT give matches
without additional instruments, but they will *enable* matching to be
done with that additional information (usually a VOM with an accurate
ammeter).

What's wrong with setting up the two output tubes for matching in the
same PP circuit
and measuring applied Eg with the same Ik?
This leaves the ac matching, easily done by ensuring Vg signal is equal
to each output tube,
and then measuring the ac at the cathode of the output tube while in
class A.
This tests the active gm and Ra of both tubes.
It also tests the amp you have in front of you so with the tube test,
the driver stage balance is tested and the
output tubes, OPT continuity, and many other things as you probe around.
The tube tester wastes time.....

c) Enable the 'rejeuvenation process'. This is of-interest to vintage
radio people mostly, not audio people.

Find a new tube, plug it in.
Rejuvenation is like sewing patches on grandad's undies to make them
last an extra 3 mths.
Tubes WERE expensive in 1960, but not now.


d) Allow the direct reading of filament (heater) and plate currents
with an outboard VOM.

The data is usually correct enough about heater/cathode currents.


This can be very important when choosing
transformers or replacing burnt out tranformers... WHY did it burn
out?

Never because of a tube having slightly high Ik, or Ih.
A tube filament or cathode is always either OK, or its a short
to a grounded cathode or grid, or its open, and applied voltage won't
heat the tube.
No need for a tester again.

Was it carrying too much current? And so forth. The plate current
is significant to matching.

Full circuit analysis and appraisal and possible
re-design/re-engineering
is the answer to what is needed to replace an existing tranny that went
hot.
The tester tells us SFA about overall circuit workings.


e) Have variable bias settings, and allow outboard bias current
sources if required.

Biasing can all be measured and tested and often varied for a tube while
it in the amp
where it has to work.
Don't work without the analysis.
Tube testers entice techs to work without the time spent on analysis.
hobbyists and diyers risk keeping faulty circuits with their fauls
surround the tube
intact, and a replacement of a tube without checking the circuit out is
a fool's occupation.

What if the grid coupling cap is leaky?



Which comes down to a quantum-leap in superiority over an emissions-
only tester as actual tube quality may be discerned to a greater
degree. Emissions-only testers are valid for go/no-go decisions, no
more.

Emissions are usually there, or not there, but many tubes fade with age,
and emission goes low
gradually, and insidiously the power at clipping which should be always
measured
goes low, and is distorted, and tube testers don't do THD, or power
measures.
pentodes or beam tubes with heat warped screens will show horrid THD and
high Ig2.
This is easily spotted in routine probing. Not so easy with a radar set
from a
navy ship, but who has one now?



I do some audio work. That justified me paying $100 for a surplus,
recently calibrated 539B from the GE Re-entry Systems Division in
Philadelphia some 10 years ago (through a local jobber). That it had
all the books, updates and an additional roll-chart helped. It would
not justify me spending the +/-$1000 that I could get for it today. I
paid $35 for the Simpson tester ($50 including shipping), also well-
documented roughly two years ago. That is about right. For vintage
radios, it is more than adequate 95+% of the time.

Well, don't let me spoil the fun. I have I think about 3 testers,
all rather stuffed and without accompanying
books, schematics, data et all, and they can gather dust.
People said "this is really good..." But alas they were not.



The best test of any tube (after shorts are ruled out, anyway) is the
circuit it lives in. No tube-tester will be able to duplicate that
test.

Now you are talking real sense.

In audio amps, its the best place to test the tube, and all the things
around it while you are there.

And BTW, some output tubes begin conducting more Ia with the same Eg as
time ages them.
Popping out the output tubes into a short test does not reveal the
ageing unless the tube is left for an hour in the tester
so that the presence of positive grid current at idel can be detected.
During this time a tube could fail to becoming saturated, or shorting
and thus damage the tester.
Its one reason why so many testers I have seen are stuffed. The other
reasons are because the wrong
switch settings have been used for the tube under test. Humans regularly
stuff equipment up.
A typical "healthy-ish " KT66 may have +1V across the 680k biasing R in
a Quad-II amp after being on for an hour.
In the amp you may find that after turn Eg will be slightly negative in
a brand new tube, but after some time
it may gradually become 0V, then start being +ve, and +0.25V isn't
unusual 10 minutes afer switch on.
an hour later its perhaps +1V.
Then with some tubes you measure +10V, and the Ek has risen a few volts,
and Ia is also high,
and you know you have a tube just about to die, and perhaps also fuse
1/2 the OPT primary as it does so
without the owner knowing anything. This same tube also doesn't have a
high +Eg at turn on either,
and must be observed over time. It seems the phenomena is because of
positive gas ions gathering at the grid,
or a leaking mica support
allowing I flow from screen to grid and sometimes the tube has become
detectably noisy.
Using 50k for the bias resistor
reduces the +Eg1, and hides the problem, and prevents thermal runaway
for slightly longer.
The effect must not be confused with a leaky coupling cap which gives
the same symptoms.
So disconnect the coupling caps to find out!

Input tubes such as 6SN7 with a typical 470k bias Rg should have
slightly -ve Eg1,
but as they age the Eg1 will become positive, and invariably the tube
becomes noisy,
maybe nothing to worry about in a power amp, but something you don't
want in a preamp.
Not all these problems are reduced with loop NFB, especially if there
isn't any NFB.

Tsting for noise is done by amplifying the anode signal with the grid
grounded with a short link.
The amplifier can be a normal low noise amp with flat response and
gain = 66dB over a tailored bandwidth of 20Hz to 20kHz, -3dB points.
A good 12AX7 with its halves cascaded and with NFB used to reduce the
open loop gain from
about 3,500 to 1,000 will usually be fine, as it is in a microphone amp
where the mic has output above about 5mV.

The results can be shown on a CRO, and the equivalent input noise
of the tube = amp output signal / amp gain / tube gain .
So you may see 30mV of noise, easily measured at the preamp output, the
tube tested has a gain
of say 15, and preamp gain = say 1,000, so total equivalent input noise
= 0.03 / 1,000 / 15 = 2 uV, which is quite a good measurement, and
typical for a good 1/2 6SN7.
There should be no slow "sputtering," or pop corn noise, or hum any
greater than the other kinds of noise.
The CRO and an amp&speaker to see and listen to the tube noise helps you
to understand.
Microphony can be seen/heard when you tap the tube under test, and
compared with a known good one.

Gain of the tested tube can be measured with two different AC loadings,
and since gain = µ x RL / ( RL + Ra ), you get two equations for gain
with two RL,
so the µ and Ra can be worked out agebraically.
If you are a tech who didn't complete high school, then the math will be
difficult, so learn the math,
the brain won't fall out.

Patrick Turner.


Peter Wieck
Wyncote, PA

[robert casey]

Back in the days of 1960 when nearly all the electronics was tubed.
And there may have been 30 tubes in a colour TV, so having a tube tester
to test the triode-pentodes and
other multigrids of a complex nature was sensible. You could find out if
a tube was dead or not
from an IF strip without much effort trying to measure IF gain.

But now ALL the tubed electronics is either AM radios, or audio amps,
with perhaps 0.00000001% being an FM tuner that is tubed.

So while probing around an AF circuit, one not only finds out if a tube
is crook or not, but
whether something else nearby is stuffed, such as a resistor or coupling
cap.


Back in 1960, most any few year old tubed consumer device that developed
a problem could usually be fixed by finding and replacing a worn out
tube. Most everything else in the set hadn't aged enough to go bad yet.

Now jump forward to 2007. This is plenty of time for things like wax
paper caps to be definitely bad, whether if the set was used or just sat
around unused all those years. Tubes only wear when used, but will last
forever if they never see heater voltage or B+ (and anything else too).
So the old wisdom of "check the tubes" no longer makes much sense. In
a restoration project, the first thing to do is replace all wax caps,
and don't bother to test them, they are all bad or soon will be. Vacuum
tubes nowadays would be lower on the list of suspects when a circuit
doesn't work right.

[Peter Wieck]

On Mar 2, 3:39 pm, robert casey wrote:
Back in the days of 1960 when nearly all the electronics was tubed.
And there may have been 30 tubes in a colour TV, so having a tube tester
to test the triode-pentodes and
other multigrids of a complex nature was sensible. You could find out if
a tube was dead or not
from an IF strip without much effort trying to measure IF gain.

But now ALL the tubed electronics is either AM radios, or audio amps,
with perhaps 0.00000001% being an FM tuner that is tubed.

So while probing around an AF circuit, one not only finds out if a tube
is crook or not, but
whether something else nearby is stuffed, such as a resistor or coupling
cap.

Back in 1960, most any few year old tubed consumer device that developed
a problem could usually be fixed by finding and replacing a worn out
tube. Most everything else in the set hadn't aged enough to go bad yet.

Now jump forward to 2007. This is plenty of time for things like wax
paper caps to be definitely bad, whether if the set was used or just sat
around unused all those years. Tubes only wear when used, but will last
forever if they never see heater voltage or B+ (and anything else too).
So the old wisdom of "check the tubes" no longer makes much sense. In
a restoration project, the first thing to do is replace all wax caps,
and don't bother to test them, they are all bad or soon will be. Vacuum
tubes nowadays would be lower on the list of suspects when a circuit
doesn't work right.

Depends. 80+% of what I do is slanted towards vintage radios, with
most of that further slanted towards pre-war (WW-II) multi-band units.
These radios were never cheap, and as noted tended to last a good
while and see constant use. After the War, when the great amalgamation
of the American Populace took place, these radios were carefully (in
most cases) put away and replaced with more modern stuff. Or, if they
failed, rather than being repaired, they were stored, again. It has
been my experience over several thousand radios over the last 25 years
that about half-or-more of them were put away because something failed
or broke. Of that half, perhaps 2/3 were due to failed tubes or the
consequences of failed tubes. So, a method of rapidly screening tubes
is very useful to *my* particular path in this hobby. And, most of us
in the vintage radio end of the hobby do not use tubes in modern
production... when is it that Sovtek last made a 6A8G? And we
generally shotgun-recap anyway (and also check the resistors for
drift, as it happens).

This does NOT mean a these-days-$1000 Hickok lab-grade tester, as I
have written on many occasions. My little Simpson does all that just
fine.

HAVING the Hickok, however, does allow me to do some few things that I
could not do easily otherwise, given that this is a HOBBY, not
production. I do not have permanently installed tooling, jigs or test-
beds but pretty much clear the (quite small) bench out before each new
project. So, I can appreciate what I can learn at short-notice from a
good tester. It ain't nohow the be-all and end-all of tube screening,
but it can save time when hobby time is disproportionately
valuable.

And also as it happens quite a bit of tube-audio has crossed my path
in the last six months from a McIntosh tuner to a Fisher 800B to both
a Dynaco SCA-35 and ST-35, to a couple of FM-3s and more. The McIntosh
had two flat-out failed tubes (filament lit, 0 GM, 0 emissions), the
Fisher one, the Dynaco amps were fine, the FM-3s one each. Of those,
two types I did not have in stock. They were cheap-enough to get, but
knowing I had to get only them helped.

Peter Wieck
Wyncote, PA

[Ian Bell]

robert casey wrote:
So the old wisdom of "check the tubes" no longer makes much sense. In
a restoration project, the first thing to do is replace all wax caps,
and don't bother to test them, they are all bad or soon will be. Vacuum
tubes nowadays would be lower on the list of suspects when a circuit
doesn't work right.

My own experience bears this out. I restore a lot of valve wireless sets and
I have lost count of the red hot af output tubes caused by leaky wax
coupling caps.

Ian

[Patrick Turner]

robert casey wrote:

Back in the days of 1960 when nearly all the electronics was tubed.
And there may have been 30 tubes in a colour TV, so having a tube tester
to test the triode-pentodes and
other multigrids of a complex nature was sensible. You could find out if
a tube was dead or not
from an IF strip without much effort trying to measure IF gain.

But now ALL the tubed electronics is either AM radios, or audio amps,
with perhaps 0.00000001% being an FM tuner that is tubed.

So while probing around an AF circuit, one not only finds out if a tube
is crook or not, but
whether something else nearby is stuffed, such as a resistor or coupling
cap.


Back in 1960, most any few year old tubed consumer device that developed
a problem could usually be fixed by finding and replacing a worn out
tube. Most everything else in the set hadn't aged enough to go bad yet.

Now jump forward to 2007. This is plenty of time for things like wax
paper caps to be definitely bad, whether if the set was used or just sat
around unused all those years. Tubes only wear when used, but will last
forever if they never see heater voltage or B+ (and anything else too).
So the old wisdom of "check the tubes" no longer makes much sense. In
a restoration project, the first thing to do is replace all wax caps,
and don't bother to test them, they are all bad or soon will be. Vacuum
tubes nowadays would be lower on the list of suspects when a circuit
doesn't work right.

When fixing anything old, the older it is the wider your eyes need to be
open.

Patrick Turner.

[Peter Wieck]

On Mar 2, 9:12 pm, Patrick Turner wrote:
When fixing anything old, the older it is the wider your eyes need to be
open.

Damned Straight.

Peter Wieck
Wyncote, PA