High Class-A Stereo Amplifier
Ultralinear, 8 x KT88, 2x 70 W
The basic design criteria for amplifier JJ 828 were as follows:
Our designers have chosen this solution:
For the first time, tube ECC 99 is used as a driver for KT 88. This is a tube specifically developed by JJ Electronics for application as a unique linear driver for high power tubes KT88 and 300B. Concertina with ECC 82 parallel was chosen as a phase inverter in front of the ECC 99.
There are two feedbacks in this design: one is a global feedback from OT (–6dB) and the second is from the KT88 cathodes through OT (5dB).
Output transformer is based on C-core made from 0.13-0.15 mm sheets, with air distance 2 x 0.05 mm. The air distance provides linearization of electrical parameters within the entire power range. The manufacturing of C-core, similarly as in the case of the JJ 322 amplifier, is under complete control of JJ Electronic. There are two OT coils: each has four primary, four bifilar secondary and two feedback windings. This OT design yields 3mH at Lp 35H lsp.
|Tube Complement||8 x JJ KT88
2 x JJ ECC99
4 x JJ ECC82
|Circuit type||Push-Pull Ultra Linear AB with CFB|
|Output power||2 x 70 Watt RMS|
|Load impedance||4 Ohm, 8 Ohm|
|Input impedance||25 000 Ohm|
|Input sensitivity||0,775 V for full output|
|Input sensitivity||20 Hz - 25 000 Hz (-1 dB)|
|S/N Ratio||- 88 dB bellow full output|
|Input connectors||5 x Line (unbalanced)|
|Output connectors||Tape out: For tape recording|
|Power Supply||230 V (120 V, 100 V) AC 50/60 Hz|
|Power Consumption||400 W max.|
|Dimensions||480 x 350 x 180 mm|
|Finish||chasis: black, gold antique or silver antique (pulver lack)
top plate: gold or silver (pulver lack)
cover: gold or silver (pulver lack)
wood: brown, natural (glossy) or black (dull)
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