Considered the exponential progression of the historic valves prices we believe we have to give more guarantees to investors in this particular segment.
Since the inception of the webshop all valves "new old stock" or "new in box" sold by Audiogears are tested and priced based on measured performance and matching.
From now on, this selection is pushed to the extreme level that the equipment in our possession allow us, and we believe we are the only worldwide retail outlet that offers the tubes with the system described below.
All tubes proposed by Audiogears will have a unique code that will allow us to locate them in time and retrieve the test done before the sale even after many years
The results collected will be printed on a label on the box of each tube together the factory codes basic measures and the unique code Audiogears.
The tubes will be selected individually, in pairs or multiples, and all parameters will be reported online. The selection will be made by the method which you can read below. The photos will refer ALWAYS commissioning tube for sale. Basically what you see in the image will be what you are really buying.
The expenditure of time is huge but we believe it's worth it. The valves from Audiogears definitely cost a few euro more than the competition, but you will have the absolute guarantee that you are going to buy.
To better relate to our competitors we made sample purchases both by the most popular eBay resellers who by the most accredited independent competitors and we had incredible surprises, in the negative.
Of course in the description you can see the year of production (where this can be determined) and the actual tube manufacturer which is not always the brand printed on the glass.
Proposals tubes are all NEW and classified as NOS (new old stock) or NIB (new in box) the difference among these is the presence of the original box (NIB) or not (NOS)
There may be some cases where, since the extreme rarity of the item, there is a certain degree of use, in this case also be clearly stated, whether it is virtually impossible to estimate the number of hours of use.
To get a first idea of quality level it will be indicated under the initials of the tube the fundamental fact: the Mu for triode preamp and GM for the power tubes. Below we will see why.
Then opening the valve page to which you are interested you will find all other parameters
Method of tubes selection
To proceed with the selection of the valve and matching we note the following parameters
also it is checked:
Loss of grid
almost all of historic valve retailers (exceptions can be counted on the fingers of one hand) proposed as a method of selection the only Ia: the anode emission.
In fact this has a relative weight if linked to the matching process
The reason that the Ia is the most widely used reference is that most of the sellers is equipped with tube testers able to give an indication of the type "good" or "bad" while in the best cases precisely detect the anodic current.
Very few historians testers are capable to detecting the transconductance and as we will see later is a fundamental fact to derive a key value into pairs of preamp tubes: the Mu ie the gain.
Mu, Gm and Rp that is to say the basic parameters
Mu (voltage gain), GM (transconductance) and Rp (plate resistance) are the three basic electrical characteristics for a vacuum tube.
Mu is the product of two data: GM and Rp
What does GM? incremental variation of plate current / incremental variation of the grid voltage to a specific working point and is the primary measure to detect the gain of the tetrodes and Pentodes. The GM decreases with the aging of the tube, is therefore an important fact to get a first rough idea of the fact that our valve is new or not (but is not an absolute certainty)
In triode two fundamental parameters: GM and Rp will produce a third Mu. These parameters are in a relationship such that knowing any two you will get the third. Just as Ohm's law. In the case of triodes, Mu = Gm x Rp. GM is measured in mhos, (micromohms) and Rp is measured in ohms between them is obtained by multiplying the MU, a Mu of 30 means that what enters the valve comes out in principle 30 times more great.
Triodes are mostly used for voltage amplification in our preamplifiers. Here the Mu (voltage gain) is the most important parameter to be measured and the one that most directly effects what we're going to listen.
So let's say that if you get two triode combined using as a parameter the only GM there is no guarantee that these pipes will have an equal voltage gain.
But the Rp is hardly ever measured, the value that the passionate search is normally the anode output (Ia). Our tube tester, Amplitrex AT1000, can measure each parameter as those cited above we are therefore able to propose matched tubes and, in the case of double triode, with sections balanced as it should be.
Some famous tester, Hickock for example, are sought after for their ability to measure the Gm, but if it is not able to detect the Rp as well will not be possible to calculate the Mu with a simple multiplication. The reason that almost never gets the data from Rp valve suppliers is that it is difficult to measure, and with the old commercial tester has never disclosed this parameter.
Many of you are buying pairs of tubes because the seller says they are matched, if you look on popular online sales sites or on ebay you will notice that almost all vendors offer their matchate valves only according issuance anode. Very very rarely you find Gm and practically never the MU
then is FUNDAMENTAL into pairs of preamp tubes that, both the two inner sections (in the case of double triodes), and between the tube and tube there is a given Mu as similar as possible.
Typically in the case of the most thrusts selections this should be below the 5%
Audiogears will put on sale the triode with MU values significantly unbalanced to the lowest figures of the average market value. Keep in mind that much of what you buy at full price by the majority of sellers does not take any account of this fundamental fact.
PENTODES, tetrodes etc.
The pentodes are an entirely different matter. For pentode, such as those used in the output stages of the amplifiers, the Gm is actually essential for good performance. So to match our pentodes we will have to rely on this data.
Pentodes in the Rp assumes less importance as related to the output transformer. So the GM is the parameter to be considered in the matching But even in this case the old meters are not all'atezza of the situation because they can not detect this parameter (the few who are able to do so) under the actual working conditions to ' internal of the circuit.
Amplitrex once again is able to do so.
Couples or quartets that you will find here are paired taking as the main parameter precisely the transconductance.