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RE: Heathkit W-6

Posted by Eli Duttman (A) on April 6, 2015 at 09:52:43

In Reply to: RE: Heathkit W-6 posted by mark.korda@myfairpoint.net on April 5, 2015 at 21:29:11:

The B+ PSU in a W-6M is a "full wave" voltage doubler, not a 4 diode bridge rectifier. The diodes are series wired pairs, to increase PIV capability.

That topology is cost effective and can be HIGH performance. It's found in some McIntosh models, the Harman/Kardon Citation 2, and the Marantz 8B. :>D While nothing more need be said, superior bass behavior is a big benefit of SS rectified B+. The better amps employ a choke between the doubler stack and the reservoir position. The W-6M is cheaper.

Only vacuum rectifiers with cathode sleeves, like the 5AR4 and 5V4, exhibit a "soft" start. Directly heated types like the 5U4 and 5R4, turn on almost as quickly as SS diodes do.

I see some obvious areas of improvement in the W-6M.

Extra heater current is available. So, rewire pins 4,5, and 9 of the I/P 12AU7 socket and install the much more linear 6CG7/6FQ7.

Replace the OEM B+ diode pairs with 2X 600 PIV/2 A. Schottky diodes. Install a CL-130 inrush current limiter in the line between the rectifier winding and the center of the doubler stack. Increase the value of the doubler stack capacitors. Install a low DCR 1 H. choke between the doubler stack and the reservoir position. Increase the capacitance in the reservoir position. An additional B+ PSU refinement is inserting a "hash" filter between the doubler stack and the main filter choke. Increases in the decoupling capacitance value could also be of benefit.

Improve the bias supply by installing a 4X Schottky diode bridge and CRC filtering the rail.


Eli D.

• Heathkit W-6M Schematic   (Open in New Window)

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