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Tuesday, April 1, 2014

801A Drives 801A, Part 1


Power amps which use the same tube in the driver and output socket have been a major theme on my blog during the recent months. Starting with the 211/211 amps which are still in progress and then followed by two versions of 45/45 amplifiers. Such a line up of amplifiers would not be complete without a 801A/801A.

The construction technique and chassis layout is similar to some of the amplifiers shown recently. The amps are monos with separate power supplies. But the PSU is a bit more elaborate due to the different voltage requirements of driver and output tube. The inside of the PSU chassis with two filament transformers, one for each tube, two filament chokes and 4 high voltage smoothing chokes:

The main high voltage transformer resides on the top plate along with the oil caps and rectifier tubes:

Inside the amp section there are another 4 chokes, a smoothing cap and the input transformer:

The top plate of the amplifier section with all the signal wiring in place:

The transformers used are Hirata Tango NC 20 interstage and FC20-14S output transformers. These are from my stock of transformers which had been salvaged from old amplifier projects. They have some scratches:

So they had to go under some transformer covers:

Stay tuned for part 2 which will show the complete amps.

Best regards



  1. How about use for preamp output tubes?And using 14k preout transformer.

    1. Hi!
      See all my posts about 10Y preamp. The 801A can be used in those as well