Testing and Miscellaneous info....
Preamp tube testing and batch power tube testing.
We took possession of our first Amplitrex AT1000 on 06/16/08 and our second Amplitrex in 2012. We simply call these machines the last word in tube testing. It is the most well thought out and precise tester we have ever used. In short, a thoroughly amazing piece of gear! In the past we had found the VTV Characterizer very helpful in allowing us thru experimentation to find certain grades and characteristics that worked very well with different amps but the extraordinary accuracy and available data that the AT1000 offers has taken our in house testing and grading to new levels.
As you can see in the second picture we are actually bumping up the internal audio level with an outboard amp and then literally placing a headphone speaker right on both sides of each tube to check for noise and microphonics. Most will consider this excessive but that's the way we are!
In the third pic you can see Michael using an old Sencore where we pre-heat each tube before running them thru the AT1000 which runs them at real world voltages.
So major kudos' to Chris Terraneau for brining the AT1000 to market! If you would like to check out his site here is a link: Amplitrex
Power tube matching.
April 10th 2012,
matching power tubes, it all comes down to two things: Regulation and
consistency. If this cannot be maintained, a proper match can be difficult to
obtain and a repeatable grading scale can be very difficult to develop.
piece of equipment in today’s tube resale industry for testing/matching power
tubes is the Maxi-Matcher. Built by Maxi Test in Seattle Washington. We’ve
used these units since day one (1998) and up until recently maintained what we
would call a small fleet of them to keep up with our matching needs. They have
served us well but as any mechanic will tell you, there’s nothing like having
that perfect tool for the job. The Maxi-Matcher is a nice piece of kit but it
doesn’t take long before any user starts to get a sense for its quirks and
cumbersome temperament. After using these units for years we often discussed one
day having matchers that would be the definitive “last word” in supplying
all necessary data and ultimate accuracy.
Kamna. Matt has been present in the local audio community in and around the
Portland Oregon area for quite some time. His passion is HIFI as well as most
things tube related with a particular knack for “myth-busting”. His
background gives him a unique insight into our industry. After spending years
working in some of the largest US based Electronics firms he went rogue.
done some free-lance design work for us in the past and with dreams of the
perfect power tube matcher in sight, we knew he was the best man for the job.
for our new matcher was pretty simple, but not easily obtainable. Unlike the
Maxi-Matcher which has two options for plate voltage (325VDC and 400VDC) we
wanted the plate voltage to be continuously adjustable from 300VDC to 500VDC.
This setting also needed to be regulated to within a tenth of a volt under
normal line conditions (115-130VAC).
alone would be one the biggest hurdles but one of the most crucial, as the
Maxi-Matcher features no active regulation (which is its biggest pitfall). This
means that even a 1VAC change in line voltage had a measurable effect on the
test result of the Maxi-Matcher. Since we started using Maxi-Matcher’s in 1998
we’ve had to regulate our line voltage to less than half a volt to hold
consistency in our grades.
Maxi-Matcher heats up four tubes at a time, it only applies high DC plate
voltage to the tube that’s been selected to test, leaving the remaining three
tubes in “stand-by”. This design allows Maxi Test to get by with a very
small power supply since they’re only effectively running one tube at a time
aside from the filaments. But this power supply is in fact so small that even
when running a single higher output power tube (like a KT88) the B+ rail sags
under normal test conditions. We had to compensate for all of these variables to
create a solid matching system and to insure a consistent grading scale.
matcher features individual readouts for each socket and each socket is fully
active during the duration of the matching process which includes testing for
current, transconductance and individual audio tests (covered later). This means
that a very stout power supply was needed and the regulation circuits had to be
capable of dissipating some pretty serious wattage under severe circumstances.
To get an idea of what this means you’re looking at a 5lb Maxi Matcher vs.
40lbs for the new matcher. Almost all of this difference comes from the power
supply where we had to use separate transformers in each aspect (bias voltage,
B+ and filaments).
aspect was the bias circuit. The Maxi-Matcher is pretty versatile in this
regard. They give you a bias voltage range that’s stepped from -12VDC to
-60VDC in five pre-set increments. Once again we wanted this aspect to be
continuously adjustable and with a slightly wider range of about -10VDC to
-60VDC. The point of making the plate voltage and bias voltage continuously
variable is that we can now replicate real world situations. If you have a fixed
bias amp that runs a quad of EL34’s with 455VDC on the plates and the grid
voltage is fixed at -37VDC we can replicate that. This allows us to approach
things in a completely different manner than any other piece of test equipment
would allow, and we can actually find the perfect grade of tube for a fixed bias
amp if these parameters are known.
prototyping process we observed how much a small variance in any aspect of the
power supply affected the tubes performance and thus the quality of the match we
were able to achieve. One thing that caught us by surprise was the filament
supply. We discovered that a 5% change in filament voltage changed the tubes
plate current output by at least 1.5mA. We ended up using a separate transformer
for the filament supply along with a 10 amp regulator so we know whether we’re
running EL84’s or KT88’s, the filament supply will stay at exactly 6.3
twist we had to throw in was an audio circuit. It almost seemed silly to go
through all of this trouble and not whip out a stethoscope during the
physical… Matt got straight to the point by employing a solid state
amplification circuit that we can insert directly into the cathode connection
for performing audio tests on each tube separately. Now all power tubes undergo
the same little “hammer test” and microphonic test that our preamp tubes go
We refer to
our new addition as the “Kamna Matcher”. It is a one off “one of a kind”
machine, with about 75% of its chassis being massive heat sinks. However
underneath its industrial and “prototypish” exterior it is pure “state of
the art” precision, and our new standard.
we wish to acknowledge that we have depended on a fleet of Maxi-Matcher’s for
fourteen years, and with skilled men at the wheel and highly regulated line
voltage, we gained a stellar reputation for critical matching.
would like to extend our profound thanks to Engineer “Par Excellence” Matt
Kamna for making our dream machine matcher a reality!
We can now say that the matching supplied by Eurotubes is unsurpassed and
Click to enlarge
All power tubes have a 24 hour burn and we grade all of our power tubes right down to the milliamp so that we can supply future orders to customers that will exactly match the originals.
We still occasionally use our Hickok TV2 for certain tubes and we also have two of the VTV Preamp tube Characterizers that we can use if you're looking for a specific grade of tube that you have used in the past that was spec'ed out on a VTV. Otherwise we will be using our Amplitrex AT1000 for all preamp tubes as we have found it to be a far superior unit in every way.
We also offer graded, balanced and matched preamp tubes for an additional charge listed in the online store which is very nice for HiFi applications and phase inverters in guitar amps. We also offer hand picked high gain preamp tubes, especially for you players who can never get quite enough gain! The high gain tubes are an increase of between 10 to 15 percent.
We very much enjoy talking or corresponding directly with each customer. So we encourage you to call or email us about the tone and sound your looking for. We're always happy to talk tubes!
A special note for players ordering EL84’s for Peavey Classic Series amps, VHT Pitbulls, Mesa, Carvin or any of the fixed bias EL84 amps, please specify your playing style or styles such as Rock, Blues, Jazz etc. Also indicate whether the amp is played at mostly low, moderate or high volume. This will help me choose EL84’s that will either break-up earlier for a Blues style or provide more headroom as preferred by Jazz and Country players.
Phone 503-659-7401 / FAX 503-659-7385
We warranty all tubes for a full six months from the date of purchase for manufacturer defects. In other words if a tube simply stops working and is physically in tact we will replace it. We will not warranty tubes that are broken during the installation process. Even with all the testing we do we see about one in three hundred tubes fail which we feel is exceptional. It will be up to our discretion as to whether or not we want a failed tube to be returned. If we need the tube to be returned the shipping cost is the responsibility of the customer. We will of course pay any shipping on a tube that we send out under warranty.
We will NOT cover failed power tubes if the amp was not biased properly (this applies to adjustable bias amps), or if the tubes were not installed properly, or the sockets were not cleaned properly, or tubes that were simply burned up due to problems with components in an amp. If you take your tubes to a tech to have them installed we will not warranty them unless the afore mentioned parameters were meet. We reserve the right to void the warranty at our discretion if a third party installs your tubes. There are a lot of very competent techs out there and we sell tubes to quite a few of them, but unfortunately there are also a lot of techs who are neither competent nor trustworthy, so beware.
We cannot accept returns on tubes that have been used. It would be nice if we could offer a "buy - try - return" policy on tubes but this would mean that we would be sending out "used" tubes to other customers and we will not do this. Unused tubes may be accepted if authorized, at our discretion for store credit and subject to a 20% retesting and restocking fee if the tubes and boxes are returned in perfect condition.
We cannot warranty tubes that are broken after arrival. Please read about the proper handling and installation of tubes on our FAQ page.