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Saturday, January 8, 2011

801A / 26 linestage with output transformer and TVC


Here some photos of a new line stage which is just finished. It uses directly heated triodes and can be configured for 801A (will also work with 10Y) or 26. Adjustment for the two different tube types is done by the simple through of a switch. It uses an external tube rectified power supply in the same style. Filament supplies are separate for each tube, employing two filament chokes per tube in passive LCL configuration.

Here it is pictured with globe shaped 10Ys.

 The capacitors are NOS Paper in Oil types. For a nicer look the caps got sandblasted and repainted with some metallic white varnish.

Note the subassemblies which are mounted to the main plate via rubber vibration dampers. This is essential in a DHT linestage to minimize microphonics.

The linestage has 4 selectable inputs and 2 paralleled sets of outputs. Connection to the PSU is via a heavy duty military grade umbilical.

All signal wiring is done with teflon insulated solid core silver.

Some adjustment of the wooden frame is still necessary. The carpenter did not do a good job and they are slightly too big. They will be redone.

The output is transformercoupled using Lundahls LL1660 in 4.5:1 for a nice low output impedance. Volume controls are autoformers. These are custom made by Dave Slagle . Volume control is in 24 steps, 2dB each.

Best regards


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