Xindak MT-3 amplifier

Grzegorz 'gsmok' Makarewicz

   A tube amplifier with the so-called middle shelf. Traditional circuit solution with non-traditional, rarely used ability to switch between triode and pentode modes. I was encouraged to post a short description and a not-so-short set of photos by the information appearing in many places that it is an automatic polarity amplifier that does not require the adjustment of the quiescent current of the output tubes. Well, it is not true and I warn users of this amplifier against a lighthearted approach to this important issue.

   The first photo shows the amplifier which heats up during the procedure of adjusting the quiescent currents after replacing the electron tubes in the amplifier's power stage.

   Looking for information about the XINDAK MT-3 amplifier, I was surprised to find that despite a large number of sales offers and positive opinions, there is practically no detailed data on its SAFE operation. Replacing the electron tubes in a tube amplifier is not the same as changing a toothbrush. It must be approached in a thoughtful and, above all, safe manner. And here I come back to the introduction. In one of the audiophile magazines (not Polish, fortunately) I found an opinion expressed by an "expert" on the subject that due to the automatic polarity of electron tubes, this amplifier is a particularly good proposition for those who like to experiment with electron tubes. They can replace them at will without the need for any regulations. I have very little hair left on my head, but this remnant was brought to attention when I read about it. As an example of the dangers related to the replacement of electron tubes, let us use the fact that after replacing the tubes in the amplifier, which I present here without any regulation, the measured currents were from 35mA to 80mA for individual tubes.

    I would like to congratulate our national focus groups. I found threads in which the participants are aware that the amplifier requires regulation of the quiescent currents. Unfortunately, it ends there. Most statements boil down to advice that these currents should be adjusted to the so-called ear. The electron tubes are to serve the owner, not themselves. Dear Audiophiles, who push for this type of opinion - "by the ear" an audiophile died in the hospital (it was a friend of a peasant who died by eye). If the amplifier does not work with correctly set quiescent currents, change the amplifier to another one that will play for you and do not cry, that the electron tubes for which you set the operating points "by ear", within which you exceed the admission power by 50%, only a dozen or so work hours. Well, enough of these complaints.

    Now I am going back to the beginning, which is the photography from the overview to the details. Delight your eyes with beautiful views, because there is something to see. The amplifier is really well-made and has a well-thought-out design. There was only one "flaw" in it - the cables connecting the motherboard with the transformers were too short, which made servicing a bit difficult - but it's really a trifle.

    On the market you can find several varieties of this amplifier model that differ in terms of housing (there is a version with wooden elements - really nice) and equipment (gain control and input selector). The example shown here is the "poorest" version. The technical specification is common to all versions. Here it is (manufacturer data):

Technical Specifications

Tubes EL34×4, 12AX7×1, 6SN7GT×2
Output power 2×18W (Triode mode), 2×40W (Pentode mode)
THD Distortions 0.2%
Frequency response 10Hz - 70kHz
SNR 89dB
Input voltage 400mV
Input impedance 50K
Output impedance 4 i 8 ohms
Power consumption <300W
Dimensions 356 (W) x 321 (D) x 197 (H) mm
Weight 18.5kg

Grzegorz 'gsmok' Makarewicz