[Amps] powersupply/grid current query

[Steve Thompson]

Sean Williams wrote:

>Hi All,
>
>As a follow on from the Gi7 144meg amp I have a query.
>
>I am still having problems with grid current, although not as serious as before.
>
>  
>
Did I miss some posts about grid current? The last thing I recall was 
about a 480MHz hoot - did you fix that, and how?

>My question is would low HT cause a rise in grid current? I ask this because as I approach higher drive levels 30 - 40 watts grid current soars, and output does go up, but not a great deal, however the power supply sags from 2.4Kv offload to 1500v on load at 800mA?
>
>  
>
Yes, it can. When the anode volts swing too low, grid current tends to 
rise. With that much swing on the dc volts, I reckon you've either got a 
dead rectifier, or a transformer that's not up to it - maybe one 
intended for choke input operation.

>The amp has masses of loading (120pf) but this is obviously crazy.....
>
>  
>
What's the format of the output coupling? If it's still the tuned link, 
then it needs adjusting. With that much capacitance it's not tuned, just 
an inductive link - being non adjustable, you're going to struggle to 
get the loading right.

Steve