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Kostya-M 10th April 2008 10:59 PM

Original schematic without feedback
2 Attachment(s)
It was one dispute, what solid amplifier cant be made without feedback in signal path. After several tests I devised balanced topology that works well. I made more then ten copies of such amplifiers with different power supplies, servo and variations. My last variant has no any servo. But it demand of accurate selection of transistor in pairs.

Kostya-M 11th April 2008 10:09 PM

2 Attachment(s)
I add several information
Max output power of this amplifier is 20-25 W
Damping factor = 4
Frequency response 5 Hz - 67 kHz by -3 dB
1% harmonic distortion is reached on 7 W
Harmonic level and spectrum is not depend on frequency.
THD level as function of frequency on different levels represents on figure

KSTR 11th April 2008 10:43 PM

Nice tube-style amplifier!

Can you give some details on VT5 & VT6? Are those really high-voltage high-power JFETs? And the FETs in the driver stage, what are their specs?

- Klaus

bigwill 11th April 2008 10:50 PM

I bet it sounds nice :)

Kostya-M 11th April 2008 11:42 PM

2 Attachment(s)
VT5 and VT6 are static induction JFET with max drain voltage 450V.
VT1 and VT2 are middle power HF JFET

And photo of the amplifier

Kostya-M 12th April 2008 07:23 AM

bigwill, yes it has sound likes very good triode PP amplifier in class A, but without tube's colour.

Parameters of transistors:
power disipation - 6W
max ds voltage - 20V
S=50-60mS (Id = 50mA)

2926A (SIT, triode characteristics)
power disipation - 50W
case - TO-3
max Uds - 450V
Ri = 270 Ohm

lumanauw 12th April 2008 08:22 AM

The inductors/transformers, we can buy them or we have to DIY?

Kostya-M 12th April 2008 06:40 PM

2 Attachment(s)
Output transformers and interstage inductors we made in our laboratory ( Power transformers and power inductors made in Russia by order. Input transformer-attenuator made in Moldova by Vorobiev, it's analog of Sowter 9335. Transformer after attenuator for variable output is Sowter 3575.

h_a 15th April 2008 12:53 PM

My congratulations! What an exotic amp!

All the best, Hannes

KSTR 15th April 2008 03:12 PM

... and take a look at the other great projects of these guys! Big bottled tube stuff, tesla coils, all beautifully handmade and packaged... impressing....

- Klaus

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