[Fox_Tango] 6146 mod

[Dr.Gerald Johnson]

Shouldn't be too hard on the power supply if you keep the output 
down to 6JS6 ratings, not 6146B ratings. Be sure to use a mod that's 
made for the tubes. 6146B take significantly different neutralization 
values than 6146 or 6146A. But a set of 6146B running at 6146 ratings 
should have an extremely long life.

Getting 130 watts pep out of a pair of sweep tubes is pushing 
them beyond reason and has a lot of splatter because they aren't 
nearly as linear as 6146.

Most recent QST articles are indexed on the ARRL website, possibly 
for members only though. But search www.arrl.org for the article 
reference.

Its conceivable that a poorly done 6146 mod could oscillate. First 
thing it to be sure to use adequate bypass capacitors for cathode 
and screen, high voltage disk ceramics with very short leads. By 
short, I mean none exposed between the capacitor body and the 
lowest hole on the tube socket pin and the lowest hole on the 
ground lug. Bolt down several ground lugs close to the tube 
socket, don't depend on the tube socket mounting screws and 
mounting rings for grounds. Then make sure the plate circuit 
parasitic suppressors match the needs of the 6146 and the radio 
should work beautifully. Using polyester capacitors instead of disk 
ceramics for screen and cathode bypass would tend to let the 
tubes oscillate and to have poor output above 10 MHz.

73, Jerry, K0CQ

-- 
Entire content copyright Dr. Gerald N. Johnson, electrical engineer.
Reproduction by permission only.