Anyone Familiar with the Knight KG-625 VTVM?

Hy Chantz chantz at WELL.COM
Wed Aug 29 18:37:25 EDT 2007

Speaking of KnightKits, every forty years or so, I try to resuscitate 
some failed summer kit projects from my past.

I'm "currently".. working to see what went wrong with my Knight 
KG-625, whose lack of success has haunted me lo these many years.

Basically, it's a standard VTVM circuit which  uses a meter as a 
Wheatstone Bridge between the two plate circuits of a 12AU7A.

My problem is that is seeems to work only on the .5 DC +Volts position,  
if that.

At any other range,  say 1.5 volts DC, it WHACKS to one side for plus + 
, and WHACKS to the other side for minus -.  The zero and ohms control 
don't have enough authority to bring the meter to zero.  The AC and Ohms 
are similarly non-functional.

Of course, I've traced my (own) wiring umpteen times, and done a bit of 
resistance work.  The plate voltages and plate resistances seem about 
50%  below what's called for in the manual.  But I'm darned if I can 
find where I mis-wired the function or ranges switches, or any shorts to 
ground.  I've carefully looked at the wafer switch sections and can't 
find any stray traces or bent fingers.   The calibration and wafer pots 
seem OK.

As I recall, I had a buddy with the same problem who inferred that these 
things often NEVER worked, but I find that hard to believe!  I would 
hate to give up the potential of this fine handcrafted instrument 
and (gasp!) go to a DMM for further boatanchor activities.

Any suggestions are most welcome! Thanks!

Best 73s,


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