[Heathkit] 6au6 substitutes for dx100b

[Glen Zook]

The 6AH6 definitely is the substitute.  The 6AH6 will produce a more stable frequency.  You will have to "touch up" the variable capacitors used to calibrate (do not "touch" the inductors if the calibration is correct with the 6AU6).  This is because the 6AH6 has a slightly different internal capacitance than the 6AH6.

While you are replacing the 6AH6, replace the 0A2 screen voltage regulator with an 0B2.  This drops the screen voltage and improves the frequency stability.  For less heat from the 0B2, replace the15K 5-watt resistor with an 18K 5-watt resistor.

If you feel like doing a slight modification, use the 0A2 to regulate the plate voltage of the 6AU6 / 6AH6.  This will involve adding a 7-pin miniature socket (make an "L" bracket to mount the socket).  Break the connection from the plate choke of the 6AU6 / 6AH6 to the low B+ line.  Install a 15K 5-watt resistor (removed from the 0B2) from the B+ side to pin 1 of the added 0A2.  Connect pin 5 of the 0A2 to the plate choke and connect pin 7 of the 0A2 to ground.

For more drive on 10-meters, change the 47 pf capacitor that connects to pin 8 of the 5763 with either a 180 pf or 220 pf capacitor.
 
Glen, K9STH


Website:  http://k9sth.com



On Monday, January 27, 2014 10:34 AM, Bill Cromwell <wrcromwell at gmail.com> wrote:
 
On 01/27/2014 11:07 AM, Andrew Kopke wrote:
> What is a proven 6au6 substitute that I could possibly use in the vfo of a dx-100b ? Many thanks, Andrew Kopke
>
Hi Eddy already named it. Even Heathkit and Johnson and others recommend 
it (I think).

Good luck with your DX-100

73,

Bill  KU8H

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