Tube Test procedure at www.koschuh.com, with the ROETEST tube tester
The ROETEST has fixed test parameters for each type of tube. For instance, the E88CC:
- 90V anode voltage (stabilized)
- -1.2V grid voltage (stabilized)
- 6.3V filament voltage (stabilized)
- after 300 seconds of forerun time: anode current "System A" is measured
- after another 300 seconds of forerun time: anode current "System B" is measured
That's it, and there is no way to cheat. Once the ROETEST finished all measurements, it sends the individual datasheet directly to the laser printer. It is this datasheet that brings you the data on each individual tube, that you seen on my website. Nothing less, nothing more.
Is there a way to cheat, you may ask? Well, not with the ROETEST. But with analog vintage test equipment, there are "possibilities". Let's stick with the ECC88 as an example. An unexperienced or dishonorable seller might tweak up the anode current:
- by raising the anode voltage (from 90.0V to an any higher voltage), which is not allowed at Koschuh
- by raising the grid voltage (from -1.20V up to +0.00 volt), which is not allowed at Koschuh
- by raising the filament voltage (from 6.30 Volt to 7V or 8V), which is not allowed at Koschuh
- by raising the AC mains voltage (on un-regulated tube testers, resulting in higher anode voltage AND filament voltage), which is not allowed at Koschuh
By using either one of these cheating methods, you can get „extremely high test results“ like 20mA or 25mA - even with faulty tubes. This will look GREAT on paper. But that's stupid. Be careful whenever you see „unexpected high“ measurement results. Espacially if the seller doesn't explain the test parameters. You are really-really interested in the anode voltage AND the grid voltage (ideally these voltages are at data sheet parameters). If either one of these specifications was missing, the complete measurement is suspicios, and so is probably the tube and it's seller.
Even worse, some sellers advertise ALL of their tubes with 25mA or more (even though such high test results are very rare and unusual, even on new tubes). They are selling all of their tubes as „ultra strong“. Unexperienced buyers might think that every ECC88 should have 25mA, but that's totally wrong. Don't fall into the trap.
Of course, high numbers look great on the paper. But they are impractically and absolutely useless. If operated under such extreme conditions (25mA or higher), the tube will be worn out after a short period of time. Also, these „test results“ are not comparable with real-life audio circuitry conditions. Keep in mind that our test results are taken exactly at the data sheet parameters: 90V anode voltage and -1.2V grid voltage. As given by the big names of the tube industry, like SIEMENS.
Our test results do not show the maximum anode current that our tubes „could“ deliver (under extreme conditions), because that's not the point. Of course, our tubes will test 25mA or higher (50mA), with stupid „alignments“. But again, don't get fooled. Don't go for the maximum anode current. Go for the electron emission under datasheet-conditions, as we do, because that's something you can really work with. From our point of view, this is the only reputable data. All of our ECC88 & 6DJ8 tubes (and longlife versions aswell) are tested under the official E88CC datatsheet parameters, using automated test equipment, with no intention AND with no possibilities to cheat.
A dishonorable seller could also tweak the "symmetrical paramaters" by:
- raising the anode voltage at the weaker triode (from 90.0V to an any higher voltage), which is not allowed at Koschuh
- raising the grid voltage at the weaker triode (from -1.20V up to +0.00 volt), which is not allowed at Koschuh
- doing the measurements at the "right time", when the anode current has the "desired figure" (explained: in the heat-up period, the anode current is rising up fast, then slowly, before it settles after a few minutes). This is why I have fixed forerun persiods. The actual forerun time is even stated on the datasheet, this could be checked by YOU.
You see, it is mandatory to have fixed values. Both in electrial terms and in time.
