I'll be a contrarian and ask, Do you really need a tester?

I have restored many tube radios, including some boatanchors. I own a couple
of testers, but don't use them often. Usually, the tester only tells me
something I could find out another way ("That's a dud -- duh").

As Colin mentioned in another post, marginal differences between tubes may
not make any noticeable difference in how the radio performs. Many times, I
have replaced a "weak" tube with a new one, only to find that the radio
performs exactly the same.

There are exceptions, of course. The horizontal and vertical circuits in a
TV may be fussier about tube condition than the circuits in a simple,
consumer-grade radio.

One case where a tester is very useful is if someone gives you hundreds of
loose tubes. It can quickly sort out the duds from the keepers.

The best test of all is in a working circuit for which that tube was
designed.

You can test tubes without a tester if you have some working radios and
known-good tubes in the house.

For example, you can test a suspect tube by putting it in the same type
application in a working radio. If the radio still works, the tube is
"good."

You can also do the reverse. That is, substitute a known-good tube in your
subject radio and see whether the radio works better. If so, the suspect
tube was "bad." If not, it was "good" (or at least you have ruled out that
tube as the *sole* problem -- many unrestored tube radios have multiple
problems such as leaky capacitors.)

So, ask yourself, Is this something that I really need and will use often?
Or will it just be another Thing cluttering up my life?

If you're determined to get one, I'd buy a cheap emission type tester and
try it out for a while. You can always buy a fancy tester later, if that
seems necessary.

Just my $0.02 :-)

Phil Nelson
Phil's Old Radios
http://antiqueradio.org/index.html

Behold, Phil Nelson scribed on tube chassis:

I'll be a contrarian and ask, Do you really need a tester?

Hi Phil,

I do no repairs, but design from scratch, so yeah, it'd be handy ;-)

I have over 1,000 tubes with many onesies, so I can't really sub too
easily. Example, a tube regulator drove me nutz. It was a bad 6AU6,
'cause when I rewired for a 6CB6, it worked :-)

Cheers!

--
Gregg "t3h g33k"
http://geek.scorpiorising.ca
*Ratings are for transistors, tubes have guidelines*

Switching tubes in a radio is a good simple test, but still requires some
basic organization. I remember using a radio to test a batch of 6CB6 tubes.
I tested about ten old unboxed tubes and found two of them were bad.
Unfortunately, I had grouped the tubes into different groups of similar
performance. A couple bad, a couple very hot, some middle of the road and
so on. When I got done, I had forgotten where the bad tubes were, so had to
start over again.

Before a friend died, he requested that I purchase his collection of 14,000
used tubes - which I did. Fortunately, my wife was away and I got them home
and stored before she got home. It was weeks before she figured out there
was something new in my collection.

But, having 15,000 tubes (I had 1,000) is something like a curse. The last
time I needed a particular tube, I could not find it and had to buy one.
Found it 2 months later.

73, Colin K7FM

Hi,
Colin wrote:

Incidently, one of my close friends
designed many of the circuits in the 585, and single handedly designed the
519 and 130, and I have a row Tek scopes and other Tek equipment.

The 130 L-C meter? Great little instrument: I still have one on my
bench, and examples of both the old and newer models.

Alan

Yep, the 130 L-C meter. Cliff needed something like that for a project and
there was nothing available, so he whipped one up. It was so useful, the
other engineers soon wanted one. Then Product Design got ahold of it.

I have his personal 575, too.

Colin K7FM

The RCA Tube Manuals have an excellent summary of tube testers.

Many transconductance tube testers test the tube under static conditions,
using dc on the grid. This is a simpler technique, but not as accurate as
tests made under actual conditions. That is the reason that the best test
is to install the tube in the circuit and see if it works properly. Some of
the very expensive tube testers, like the Western Electric card tester, will
test the tube under conditions likely to be seen in the actual circuit. The
problem with one of those testers is that the tester is one large heavy
suitcase and the cards used in the tester is one large heavy suitcase.

The dynamic tube tester uses ac on the grid and an ac ammeter of the
dynamometer type. Transconductance is equal to the ac plate current divided
by the input-signal voltage.

The summary of the RCA text is as follows:

"The tube tester, therefore, cannot be looked upon as a final authority in
determining whether or not a tube is always satisfactory. Actual operating
test in the equipment in which the tube is to be used will give the best
possible indication of a tube's worth."

Colin K7FM

COLIN LAMB wrote:
The RCA Tube Manuals have an excellent summary of tube testers.

Many transconductance tube testers test the tube under static conditions,
using dc on the grid. This is a simpler technique, but not as accurate as
tests made under actual conditions.

I have never seen a DC transconductance tester. All of the Hickok units
that I am aware of are "dynamic mutual conductance" testers.

That is the reason that the best test
is to install the tube in the circuit and see if it works properly. Some of
the very expensive tube testers, like the Western Electric card tester, will
test the tube under conditions likely to be seen in the actual circuit. The
problem with one of those testers is that the tester is one large heavy
suitcase and the cards used in the tester is one large heavy suitcase.

Agreed, but I'd sure love to have one anyway.


The dynamic tube tester uses ac on the grid and an ac ammeter of the
dynamometer type. Transconductance is equal to the ac plate current divided
by the input-signal voltage.

That is the method used by all of the testers based on the Hickok designs.
Testers designed by Hickok, but made by others, include, I177, TV2, TV7,
and I believe the RCA suitcase testers.

The summary of the RCA text is as follows:

"The tube tester, therefore, cannot be looked upon as a final authority in
determining whether or not a tube is always satisfactory. Actual operating
test in the equipment in which the tube is to be used will give the best
possible indication of a tube's worth."

That is, of course, the reason why any tube tester is basically a luxury. They
do a good job of showing when a tube deviates drastically from the norm, but
say nothing about whether the tube will/won't work in an actual circuit. Tektronix
warns technicians not to replace tubes just because they test weak, but rather
to replace tubes that prevent the scope from meeting alignment specifications.

-Chuck

Hi,
The static transconductance test is more commonly known as the
grid-shift method. It's very old, dating from the 1920s, but can be
extremely accurate, depending on the amount of grid shift (easy with
modern digital meters). Grid-shift went out of favor in the US in the
1930s but most of the British AVO models use it, except with rectified
AC on the plate instead of DC.

The Hickok AC-47 from 1930 had a dynamometer movement (6.25mA F.S.)
and is actually a very fine instrument but was dropped in the mid-30s
because of expense and the difficulty of keeping it up to date with
adapters. Other than one Sensitive Research design, the last
dynamometer model was Hickok's "laboratory model" 700. That beast was
obsolete the day it appeared in 1951.

The Hickok Cardmatic models---123, military USM-118B, Western
Electric KS 15874---can measure either emission or transconductance,
sometimes both (on TV sweep tubes for instance where extra cards are
provided for each test).

Alan