[Amps] A Meeting Ground

[Dennis12Amplify at aol.com]

In a message dated 11/5/04 4:57:10 PM Central Standard Time,  craxd1 at ezwv.com 
writes:

Dennis,

Well they probably would somewhat but I would think the  currents in the 
face plate would be reduced a good degree this way. If the  negative from 
the power supply is attached directly to the chassis pan  like most are, 
the the electrons will flow towards the capacitor, It the  wiper lead is 
attached to the pan, and the current passed it first, they  should tend 
to follow it more. The reason being is there's two mechanical  
connections between the chassis and the cap through the  faceplate


----------------------------------------------
 
 Will,
 
 I agree with you that more wiper contact is better, especially when  there 
are large amounts of circulating RF currents (High Q) in the  tank.
 
But......
 
 I believe that in your analysis you may be confusing the DC  plate power 
supply currents with the circulating RF currents in the tune and  load caps.
 
 Since a part of tuning capacitance is the internal capacitance of the  tube, 
the best possible scenario would be to have both the tune and load cap  
frames or wipers going to a single point ground at the tube RF  ground location.
 
 Those circulating RF currents should not pass through the negative  lead of 
the power supply at all.
 
 Your wiper direct idea is nice because I have seen poor connections  between 
the wipers and the frames, the ball bearings and the frames, and the  frames 
to the chassis via the mounting screws, cause all kinds of strange  problems.
 I even had a small fire once caused by RF currents heating the ball  
bearings of an old load cap hot enough to ignite the bearing grease. (At least  it 
showed me where the intermittent tuning problem was coming from, and taught  me 
an important lesson about the magnitude of the circulating RF currents  in any 
high Q tank circuit!)
 
 At the very least, I solder short lengths of wire, (or flat braid  like 
solderwick if I have it handy), to the frames of both the tune and load  caps, and 
then tie the wires together and solder them to the chassis between the  two 
caps.  This does two things for me very cheaply, (the key word here  being 
CHEAPLY),...It eliminates the possible grounding problem between the  frames and 
the chassis, and it removes that 'tingle' one sometimes gets when  they 
accidentally touch the set screw of their tuning knob when the tune cap is  not 
properly grounded.
 
 This technique probably would not work as well at UHF frequencies,  but I 
have successfully applied it from 160 to 6 meters.
 
Regards,
 
Dennis O.