Hi End tube pentode amplifier on Generali Electric 6AU5GT and 6Zh7

Sold a unique amplifier - fully pentode single-cycle on tubes 6AU5GT General Electric and 6Zh7.

The amplifier sounds up to goosebumps naturally.
Technically - this is the best Hi End solution on the territory of Ukraine in this direction.
The price corresponds to the sound.

Features:
- Output stage on original 6AU5GT General Electric beam pentodes in "native" inclusion.
- Schematic of the author's design. Successful design, when the output stage on a shielded tube works well with multiband loudspeakers.
- Pre-amplification 6Zh7.
- Power system 5Ts4C x 2 + SG3C.
- Output power 2 x 7 watts.
- Works with 4 or 8 ohm speakers without switching.
- Relay switching of two inputs.
- Weight - 19 kg
- High-quality power transformers (description read further)
- The size of the case (with a block-"hood" transformers) 36 x 33 x 21 cm.

Audiophile chat: t.me/papatubeaudiotalk
Site with tube amplifiers: papatube.audio

The amplifier is designed by Dmitr Afanasiev, known for unique and quality projects in the field of audio engineering.
He uses a variety of circuitry and unique tubes, including rare models, which provides high quality sound.
All projects of Dmitr Afanasiev are characterized by high quality and uniqueness, comparable to the works of leading developers of tube amplifiers.
The amplifier has the appearance of a standard design, with quality matte coloring and classic design.
Equipped with kenotrons for voltage rectification and input driver tubes for stability and sound quality.
Includes gas-discharge voltage stabilizers to improve the performance of the output tubes.
Open design: the circuit and components are available for self-build, but you can also purchase a pre-built amplifier.
The amplifier is compatible with both 8-ohm and 4-ohm speakers without the need to switch.
Built with industrial components to ensure availability and high sound quality at a reasonable price.
A principled approach to design - prioritizing ideas and build quality over component cost.
The sound of the amplifier is characterized by brightness and richness, especially when combined with Delta Sigma and PCM DACs.
The amplifier has a deep and textured bass thanks to quality output transformers.
The project confirms that sound quality does not depend on the cost of components, but on the correct circuitry and operating modes.

Output transformer on OSM-0,063 core
I should note that the transformer will turn out to be "close to the limit" in terms of capabilities.
Calculation for 6P13C mode: Ua = 170-190V, Ia = 80 mA. Ra = 2k, Rn = 1,2 Ohm and 4-5 Ohm.

Core Ш24х25, window 44х15 mm, winding dimension at good quality frame 40 х 13 mm. The average winding length is approximately 15 cm.

Primary winding: wire 0,22 mm on copper (0,26 on varnish). 2800 turns - 20 layers of 140 turns per layer.
Secondary winding: wire 0,45 mm on copper (0,5 on varnish). 75 turns - 4 layers - 2 layers in two sections.

Winding order:
- two layers of secondary winding - 75 turns each in parallel
- 2800 turns of primary winding in one section (20 layers)
- two layers of secondary winding - 75 turns in parallel.

For 1,2 Ohm load (6GDR-1) both sections of the secondary winding should be connected in parallel.
For 5 Ohm load (4 - 5 Ohm) connect the secondary winding sections in series.

Interlayer insulation - oiled capacitor paper (from carefully disassembled KBG-MN or similar, we cut the tape into strips and divide the paper into layers, as the paper comes in two layers on the sides of the foil).

Mode 6Zh8
Ea = 190 V, Ra = 22 kOm, Rk = 390 Ohm, Ua = 85 V, Ug2 = 100 V, Ik = 5 mA.

The transformer on the OSM-0.25 core for the external power supply version was as follows.
1. Primary winding 3220 turns of 0.25 mm copper wire (0.29 mm lacquer) - 14 layers (2 sections of 7 layers each), 230 turns per layer
2. Secondary winding 87 turns of 0,67 mm wire in three sections; the first and the last ("extreme" - inner and outer) sections in three layers in parallel, the middle section (between the sections of the primary winding) in 6 layers (3 layers in parallel - i.e. two independent "sub-sections");
- for 1.2 ohm load, connect in parallel the "outermost" sections and one "sub-section" (3 layers) from the middle section.
- for 4 ohm load, in series with the mentioned combination for 1,2 ohm, we connect the 2nd middle "sub-section" (to take into account the winding direction, it is checked by connecting the primary winding to 220 volt network and measuring the voltage on the connected secondary)
- for 8 ohm load it is necessary to wind 2 more layers in the "extreme" windings and these "extras" to parallelize and connect in series with 4-ohm configuration.
3. The gasket in the core is 0.13 mm (it is the gasket in three parts between the interlocking surfaces of the core horseshoes), the calculated value of the gap is 0.26 mm.