Three 801-As PSE 17W amp

Three 801-As PSE 17W amp

1) Introduction
This three 801-As PSE amp is designed and built by adopting the idea from "801-As parallel single ended
stereo amplifier" appeared in "Radio gijyutsu"a Japanese Audio Magazine on September, 1979 written by
Mr. Takesue Kazuma. He was regarded as a top leader of amateur amp builders in Japan. The purpose of
assembling 801-As PSE amp is to provide the reference amp for my other 3 sets of amps being employed
the regulator tube drive method together with using various zero bias transmitting tubes. There fore, I need
a good quality ordinary amp: Three 801-As PSE amp with no NFB under the conventional minus bias
configuration. So far, I have made the said three 801-As PSE amp in 1997 and re-built it again from scratch
basis in year 2007.

Points of major modifications:
- Stereo amp to mono-block construction.
- Pair of 801-As to three 801-As in parallel connection.
- Output power increased from 12W to 17W.
- Output transformer changed from Tango to Magunequest.

2) 801-A
The 801-A(VT-62) has been developed rather old; in year of 1934 / 1940 according to the data seat of RCA.
It was used various purpose such as RF power Amplifier, AF power amplifier, Modulator.

- Plate dissipation: 20W, Filament: 7.5V (1.25A), Amplification factor: 8.
- Maximum plate voltage 600V (30mA) and Plate resistance of 4.3K ohms.
- Unique inherent linearity of average plate characterrist.
However, using 801-A single in A class single ended operation, one must, in principle accept its high plate
voltage, limited plate current flow and higher plate resistance resulting difficult to use. This PSE amp used
three 801-As in parallel, reducing plate resistance to 1/3 and achieved 17W of output. It is feasible solution to
employ three tubes in parallel connection approach to widen selection of output transformers remaining its
uniqueness of 801-A inherent linearity.

3) Others
- The output transformer is Magnequest FS-007 (6K ohms) .
- The plate current of each 801A can be measured separately by Test-points on chassis top plate.
- Adjustment of potentiometers for high voltage and grid bias of power tubes can be done from chassis top plate.
- For Firlaments of 801A is used ripple filter with transistor circuit which was also Mr.Takesue developed in nineties.

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