Classifications of Tubes
In the descriptions on our website, tubes are classified by their test results. In general the following Q-classifications* are used:
- NOS**: tubes have NOS specs (all test results (anode current (Ia) and mutual conductance (Gm)) are better then 90% of the factory specification) and show no visual signs of use (screen print may be deteriorated).
- NOS specs: tubes have NOS specs but have visual signs of use. For dual triode tubes, we will also indicate if the sections are balanced.
- Tests Strong: tubes test between 75% and 90% of the rated value for a new tube.
- Tests Good: tubes test between the minimum for good (cq eol) and 75% of the rated value for a new tube.
- Usable: Occasionally, we offer tubes that work just fine, but don’t pass the minimum standard for “good” tubes. This is only done when the tube is highly desirable. We sell these at deep discounts.
* Unless otherwise specified in a specific testing page, eg. the testing page for E88CC tubes.
** It is almost never possible to know for sure whether a tube is really NOS (never used). Only when a tube is stil in its original sealed box; one can be sure that it is really NOS. Because very few manufacturers ever sealed their boxes (except Telefunken sometimes) it is virtually impossible to state that a tube is NOS. Only in cases were we are convinced that a tube is never used we use the rating NOS or NOS NIB. This will concern in general tubes that show no signs of use and show specs that are NOS or better. Conversely, regularly tubes that we take out of their original boxes sealed from the factory may still test just Strong or even Usable. Where manufacturers supply the specifications (range) of a new tube and end of lave data these are applied for that tube family. (for example the Telefunken specs for a NEW premium ECC83 (the ECC803S) are applied for all tubes from the ECC83 family).
Balanced Tube sections
For double triodes we also rate the balance between the two triode sections. When the test results for both anode current (Ia) and transconductance (Gm) of both sections do not differ more than 10 % we rate the tube as platinum grade. With a maximum difference of 20% we rate the tube as gold grade.
Matched Tube Sets
Tubes are matched according to test results for both anode current (Ia) and transconductance (Gm) at test conditions that represent typical operation found in audio equipment. This helps ensure that tubes that are matched will actually perform as a matched set in your equipment. The operating conditions that we use for testing and matching are specified in the category pages of a product.
Our goal is to provide as much information as possible to help you choose the right tube for your application. For that purpose we test all tubes thoroughly. In general tubes posted on our website are checked for the following:
- Transconductance cq mutual conductance (Gm)
- Anode current (Ia)
- Section balance (where applicable)
Our standard test results are measured using laboratory grade equipment at test conditions as specified by tube manufacturers. Where no manufacturers test data are available the testing data given in AVO Valve Data Manual 23rd edition 1981 are used. Where manufacturers specify a testing method for their tubes we prefer to use this method.
The general testing is done with our calibrated Utracer3+ with two external precision heater supplies (Korad KA3005P programmable power supply) or with an AVO Mk4 tubetester, both with a stabilized mains supply (RFT stabilized power supply). Test conditions are controlled with a Keithley 2700 and Fluke 145 (3x).
The Utracer3+ features include the following:
- Tests tubes at real-world power levels, up to 400V @ 200mA
- Curve tracing:Ia1, Ia2 and Gm versus Va, Vs and Vg.
- Fixed bias tests: Ia, Gm, R and Mu.
- Accuracy and Stability: ± 1 % for heater voltage, ± 1 % for plate, screen, and grid voltage, for mutual conductance (Gm) and plate current (Ia) measurements
For specific tests, like the tests with a cathode resistor as described by Telefunken for ECC8803S, ECC802S, ECC801S and E88CC, we use in addition a Philips 1532 precision high voltage supply, high precision resistors, Fluke 145 (3x), a Bang & Olufsen Low Distortion Oscillator TG8 and a Keithley 2700 61/2 digit laboratory DVM.
Shorts and gas tests are checked with an AVO Mk IV.
For tubes that do not comply to the Utracer3+ specs and for specific tests, we use an AVO Mk4 with the AVO Valve Data Manual 23rd edition 1981.
Test conditions of individual tests
The test conditions for individual tubes are specified in the category page for the tube family or in the tube description.
Validity of test data
The specified test data like anode current en Gm are what I obtained with the test equipment and methodology as specified. I DO NOT guarantee that you will see those numbers on your tester. Different (vintage) tube testers usually give different readings depending on their calibration, measuring principle and test conditions (You will find a lot of information about this topic on the web). I only guarantee that these tubes will test good, with no shorts, or gas, on a decent calibrated tester. I don’t guarantee or imply anything else.
Return policy and additional notes
All customers are requested to read these delivery conditions and notes before buying from me !
If anything you buy from me is less than satisfactory, please send me a message immediately. If you want a return for any reason, I will give you back 100% of your purchase and any shipping you paid to me; if returned within 7 days after delivery and and subject to the limitations below.
Sound quality is tremendously subjective. For tubes returned for “noise” or “sound quality of any kind” you pay for the shipping, we refund the purchase. So we refund the price of the item NOT the shipping costs. If we have sent the wrong tube we will of course pay for return shipping.
For any tubes that are ‘broken on arrival’ we require that you send a us a picture of the shipping box to show us the damage. We test EVERY tube sent out and none should be ‘dead on arrival’ unless broken in shipping.
PLEASE NOTE: Tube silkscreen (lettering on the tubes) is very fragile. It can be wiped off and destroyed VERY easily. If you wipe off the silkscreen while handling the tube you diminish their value by up to 40%. DO NOT handle or hold the tubes from the cylinder. ALWAYS hold them by the BASE. If you are returning tubes and they are not in the same condition cosmetically as when shipped, I cannot give you a full refund. THIS IS VERY IMPORTANT.
Preferable wait for us until we invoice you the correct amount. If you have bought more than one item, we have to calculate how much the shipping will be. Shipping will be HIGHER due to insurance and shipping methods needed for expensive item totals. If you are buying only one item this will not be an issue.
Under no circumstances will we state on shipping documents a declared value of lower than the selling price.