[Amps] A Meeting Ground

[Tony King]

At 10:33 PM 11/5/2004, Will Matney wrote:
<snip>
>Well, the DC currents and RF currents are intermixed in the chassis 
>itself. The RF current circulates through the tank circuit to the load and 
>back to ground. It is also across the cathode and anode of the tube(s). 
>The reason for mentioning the PSU ground is the B- is at the cathode. But, 
>the tank capacitors and coil charge and discharge through the load and 
>then back. The power fed to the tank then is created by the tube(s) and 
>PSU. By the impedances being different, more RF should go to ground 
>through the wipers than through the shaft. Actually, that's how they're 
>designed to operate. It's really a simple parallel resistor circuit but 
>with mighty low resistances.
>
>>
>>  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.
>
>
>Exactly, and with the shortest connection possible.
>
>>
>>  Those circulating RF currents should not pass through the negative lead 
>> of the power supply at all.
>
>
>No they wont, they are blocked by the plate choke from doing so, and 
>filtered by the bypass capacitors. They intermix with each other through 
>the chassis only at the tube(s).
<snip>

I have to ask... with all the talk about the combined currents on the 
chassis... call that common... signal ground... chassis ground... ground or 
take your pick...  no one has said anything about skin effect... 
resistance, especially on the surface (where your RF is) of aluminum.  What 
are you doing about that? Are you treating your aluminum chassis with 
chromate?

73, Tony W4ZT