Maxi Matcher Review

From detritu–(at)–x.netcom.com Sat Sep 12 10:38:18 CDT 1998
From: detritu–(at)–x.netcom.com(Lord Valve)
Newsgroups: alt.guitar.amps,rec.audio.tubes
Subject: The MAXI-MATCHER…a review.
Date: 12 Sep 1998 05:50:13 GMT
X-NETCOM-Date: Fri Sep 11 10:50:13 PM PDT 1998
Xref: geraldo.cc.utexas.edu alt.guitar.amps:126464 rec.audio.tubes:85482

Lord Valve Speaketh:
It’s not often that I review a piece of testgear…but this
particular gizmo is so nifty, I just can’t resist crowing
about owning one. The “Maxi-Matcher” digital tube tester
(from Maxi-Test, 6920 Roosevelt Way NE, Suite 135, Seattle,
WA 98115; phone 206-363-9915, or contact Allen Kaatz, at
ar–(at)–a.net) has become my number-one matching rig…replacing
a whole table-top full of stuff I used to use for this
purpose, including 4 meters, two tube testers (one Hikock,
one Eico) a modified Laney AOR 100 chassis, and a Variac
(OK, I’m still usin’ the Variac, but more about that later)
and some other odds and ends. The Maxi-Matcher is *small*…
about the same size as a medium phone book; 12-1/2″ X 8-1/2″
and only 2-1/4″ thick. It weighs around 10-12 pounds. It’s
a good-lookin’ little gadget, too…the control panel is
intelligently designed, and it’s a breeze to operate. (My 12
year old daughter learned to run it in less than 10 minutes.)
Some of you have already purchased tubes from me that were
matched on this device. It has 5 octal sockets…four for
testing/matching, and one marked “Short Circuit Test.”
I also ordered a set of four adaptors, which allow me to
test EL84s; other adaptors for use with the 7591A and other
non-6L6/EL34-based tubes are available.

Everything you need to know to operate the Maxi-Matcher is
printed right on the front panel. There’s a chart (all the
graphics are nicely silk-screened in a tasty maroon color,
against a cream white background) which lists the tube types,
and details the settings necessary to test each type.
There are also some “acceptable” current and transconductance
ranges listed, which I don’t entirely agree with. (I think
that the folks who developed the Maxi really didn’t have
enough representative examples on hand of all the different
tubes listed when they were brainstorming the device, since
I’ve found many tubes in the course of the matching process
which fell outside the listed ranges and still performed
flawlessly when installed in actual guitar amps.)

Tube types listed on the front panel are 6L6, 5881, EL34,
6550, EL84, 7027, and 6V6. There are four rotary switches,
a rocker-type power switch, and a 4-digit LED readout with
LARGE characters (5/8″ tall) that can be easily read even
under bright lights. Two plate voltages are available:
400 and 325, selected by a rotary switch (which also has
an “off” position.) 5 bias voltages (-60, -48, -36, -24,
and -12) are selected by another rotary switch; this one
(understandably) has no “off” position. Two more rotaries
round out the control compliment; one selects test sockets
one through four, and the other switches the LED display
between the plate current and transconductance readings. All
of the switches have that really positive “snappy” feel that
goes with quality test gear. (This gizmo ain’t cheap…
$500, and the EL84 adaptors are extra, too…) Plate current
is displayed in milliamps, with one digit to the right of the
decimal point. Of course, even with well-warmed-up tubes,
there is considerable last-digit jitter; for matching purposes,
however, this is not a problem. (The difference between 20.5
mA and 20.9 mA is completely inconsequential, in any amplifier
you’re likely to run into.) Transconductance is displayed in
“Deci-mhos,” which (I think) is Allen Kaatz’s way of saying
“We put the decimal point in a strange place, for some reason.”
Again, this doesn’t matter, for matching purposes…2.37
decimhos is every bit as useful a figure as 2370 micromhos.
(At least, I *think* that’s how it works out…) Again, there
is some last-digit jitter when taking this reading.

When screening a whole pile of ‘raw’ tubes, it’s always a given
that a few will be defective; the Maxi-Matcher has a slick
way of dealing with this…a circuit they call a “Smart Fuse”
will shut down the plate supply if the current rises above
140 mA. A red LED lights up when this happens. “Remove
bad tube to reset” is the marking by this LED; in actual use,
I found the circuit to be a little on the ambitious side. It
occasionally activates when switching from one test socket to
another; possibly a transient is generated during switching
which ‘fools’ the circuit into thinking a short exists. It
works just fine when you smack a tube to test for shorts,
though…instead of blowing the HT fuse or smoking a screen
resistor (like my homebrew modified Laney chassis does) when
a tube croaks, it just lights up the protect LED. Nifty!
One of the five octal sockets is marked “Short Circuit Test,”
and it has two red LEDs which will light (or just one of them,
depending on what’s shorted inside the tube) when a shorted
tube is plugged in. The one-page dopesheet that comes with
the Maxi doesn’t state which leakage paths are actually tested
by this socket, but it does say that it checks for leakage of
“up to 10 K-ohms resistance.”

In actual use, I found that I preferred to test Tesla 6L6s
and Sovtek 5881s with a bias voltage of -36 rather than the
specified -48, as the current readings I was obtaining with
the higher bias were all rather low. I prefer to stress the
tubes a bit when I’m testing, anyway…after all, the guys
who buy ’em are gonna thrash the crap out of ’em, right?
On the other hand, NOS Philips 7581As, Svetlana 6L6GCs, and
the new Sovtek 6L6WXT+ all gave usable readings with the
bias set to -48. ALL the 6550s (NOS GE, Svetlanas, old
Sovteks, and the new Sovtek 6550WE) liked the specified -48
bias voltage, and all of the other types listed on the front
panel tested best with the recommended settings. The ‘factory’
specs listed for the various types were 400 volts plate (with
the exception of the EL84, specified at 325) and the following
bias voltages were recommended: 6L6 = -48, 5881 = -48, EL34
= -36, 6550 = -48, EL84 = -12, 7027 = -48, and 6V6 = -36.

I took the bottom plate off (a fairly thick steel piece) for
a peek under the hood; I found a double-sided hand-soldered
PCB, with the parts accessible without board removal. Aside
>from the 40-pin (or so) display-driver chip, nothing strange
presented itself…a couple of TO-220 stye regulators, a few
diodes, an IRF380 mosfet power transistor, an LF-353 opamp,
and an RC4558. Four trimmers, all unmarked. The usual
resistors and caps. I only saw one ‘added’ (tack-soldered)
capacitor, so the board was evidently well thought out before
it went into production. The sockets appear to be first-rate
parts; it does look like it’ll be a bit of a job to replace
them when the time comes, though. Overall, the Maxi is built
like a tank. HOWEVER…

Lord Valve Bitcheth:
Yeah, I got a bitch…the HV and bias supplies are UNREGULATED.
This puts the test readings at the mercy of line fluctuations.
Allen says they will offer an upgrade for the older units (and
a factory-installed option for the newer ones) which will
include regulated supplies. For now, I have to “ride gain” on
my Variac, making sure that the incoming AC line is dead-on
120 VAC. (I’ve got one of my Flukes set up to monitor the line,
where I can see it easily.) Since I had to do this with my old
rig, I’m used to the procedure…but I’ll sure be glad when the
upgrade is available. Mr. Kaatz mentioned that the folks at
Vacuum Tube Valley tested some of the unregulated units, and
that they “didn’t find this to be a problem.” Perhaps they
don’t match ’em as tightly as I do…or perhaps they didn’t
consider that one might need to match tubes from a new batch
to some from the last batch…three months later, when the AC
line is 5 volts lower or 3 volts higher. At any rate, this is
a shortcoming that I can deal with (for now) while I wait for
the upgrade to come online.

The Nitty-Gritty:
At $500 a crack (plus an estimated $150 for the regulated HV
supply upgrade, plus whatever adaptors may be required) this
is not a toy for the hobbyist or amateur tech. For a high-end
audio shop, or a small tube-supplier like me, it’s the best
damn thing since sliced bread. Larger tech shops might want
to own this, too…buying tubes in bulk and saving the matching
fees will pay for this unit quickly. BTW, there is also a
larger unit available that loads 25 tubes at a time…but it
gives only current readings and no transconductance info.
Bottom line: I LOVE MY MAXI-MATCHER!! And, no…I don’t get
a nickle if you buy one…I hadda pay for mine like any other
slob. Dammit. 🙂

Lord Valve
Visit my website: http://www.freeyellow.com/members2/lord-valve/
Good tube FAQ for newbies. Click the e-mail link and request a
tube catalog. I specialize in top quality HAND-SELECTED NOS and
current-production vacuum tubes. Good prices, fast service.

“I’m not an asshole, but I *play* one on the Internet.” – Lord Valve