[Hammarlund] Possible solution for 6C4...

[Glen Zook]

The 6AH6 is inherently more stable than the 6AU6.  Heath found out with the Apache VFO.  The first "run" of the transmitters had VFO frequency instability whereas replacing the 6AU6 with a 6AH6 (direct substitution) solved the problem.

Also, replacing the 6AU6 with a 6AH6 greatly stabilizes the Heath VF-1 (the same VFO is in the DX-100 and DX-100B), Johnson 122 (and the same VFO is in the Ranger, Valiant, Navigator, Five-Hundred, etc.).

The only thing is that the inter-electrode capacitance of the 6AH6 is slightly different from the 6AU6 and that may require "touch up" of the variable capacitors used in the calibration.  Just the capacitors, not the inductance.

Glen, K9STH

Website:  http://k9sth.com


--- On Thu, 6/9/11, James A. (Andy) Moorer <jamminpower at earthlink.net> wrote:

Anyone have a clue as to why the 6AH6 should be any more stable? Is it just the presence of the screen grid?
 
Any why the 6AH6, which is more of a power tube? Why not our old friend, the 6AU6?
 
Unclear on the concept, as usual.