Grzegorz 'gsmok' Makarewicz
"Cool" tube amplifier and rather unusual for our modern times mechanical design - everything including the charming glowing tubes is carefully hidden inside the black housing. Because there are a lot of photos of the amplifier in closed housing, I decided perversely to use as the main photo dismantled and un-retouched amplifier (dust covering elements is authentic).
Below is a photo gallery, in which I tried to capture as much detail as I could. The amplifier is not quite original. Here and there you can see some small traces of repairs. This does not change the fact that for someone who is looking for inspiration for the concept of the circuit and mechanical solution shown scenes may be helpful (at least I hope).
The amplifier offers a power of 10W and is a fragment of OTO SE amplifier circuit. Schematic diagram of the amplifier section and part of the amplifier power supply are given below.As you can see it is a two-stage amplifier, with a SRPP voltage stage on a double triode ECC83 and SE output stage based on EL84 connected in parallel.
And now the details of construction - nothing can be hidden. Electronics is located on two PCBs: a larger, on which are placed amplifier elements (both channels) and less with elements of the power supply (rectifier and filters). They are complemented by two robust output transformers and power supply transformer.
In the picture below you can see clearly all the aforementioned components. It is also seen additional screen between the power supply and amplifier PCB.
And here is the amplifier section PCB. Robust, thick laminate with thick and solid signal paths.
And now it is time for the section of the power supply with mains transformer, rectifier bridge and the filtering capacitors. White ceramic resistor is like a visitor from another fairy tale.
Two output transformers. We are dealing with an SE amplifier so transformers have gaps (shown in photo below). It is precisely these transformers which are responsible for the excellent sound of the amplifier. The manufacturer is known for the quality of its transformers. Their quality matched the very high price.
Potentiometer, like a resistor on the PSU board does not look like the original.
It's unfortunately not very successful repair. Perhaps the original potentiometer hasbeen destroyed.
At the end some pictures of the amplifier from the outside, but still with the cover removed.
I really like this amplifier. The design is not new, so you can buy used amplifier at a reasonable price. This can be a very successful investment. It is worth before buying to make sure that the amplifier has not been modified. According to me, the less reworks the better. To find an unmodified amplifier it is not easy, because these amplifiers are often subjected to various audiophile modes. I think that one reason is easy access to the interior. I have seen P1SE amplifiers with installed coupling capacitors with dimensions comparable to the transformers. Fortunately, most of these "inventions" can be removed.
Written by Grzegorz 'gsmok' Makarewicz