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Old 10th April 2008, 10:59 PM   #1
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Default Original schematic without feedback

It was one dispute, what solid amplifier canít 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.
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Old 11th April 2008, 10:09 PM   #2
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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
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Old 11th April 2008, 10:43 PM   #3
KSTR is offline KSTR  Germany
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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
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Old 11th April 2008, 10:50 PM   #4
bigwill is offline bigwill  United Kingdom
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I bet it sounds nice
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Old 11th April 2008, 11:42 PM   #5
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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
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Old 12th April 2008, 07:23 AM   #6
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bigwill, yes it has sound likes very good triode PP amplifier in class A, but without tube's colour.

Parameters of transistors:
2Ō903
power disipation - 6W
max ds voltage - 20V
S=50-60mS (Id = 50mA)
Cgd=13pF
Cgs=15pF

2Ō926A (SIT, triode characteristics)
power disipation - 50W
case - TO-3
max Uds - 450V
Ri = 270 Ohm
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Old 12th April 2008, 08:22 AM   #7
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The inductors/transformers, we can buy them or we have to DIY?
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Old 12th April 2008, 06:40 PM   #8
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Output transformers and interstage inductors we made in our laboratory (www.lampovik.ru). 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.
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Old 15th April 2008, 12:53 PM   #9
h_a is offline h_a  Europe
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My congratulations! What an exotic amp!

All the best, Hannes
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Old 15th April 2008, 03:12 PM   #10
KSTR is offline KSTR  Germany
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... 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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