[Amps] LF oscillation caused by defective plate choke?

[Jim Thomson]

###  points well taken.   The typ 50 uh choke will resonate at aprx 35 
mhz...so no worry about series resonances in ham bands.
That’s actually a good design.   I have no clue how much rf Voltage..is too 
much ?    But with tubes with handles etc, we are dealing with way
more than 2000 V...so the simple extra LC would be of a great benefit...and 
easy to implement.

Jim  VE7RF


-----Original Message----- 
From: peter chadwick
Sent: Wednesday, October 09, 2013 4:03 AM
To: Jim Thomson ; amps at contesting.com
Subject: RE: [Amps] LF oscillation caused by defective plate choke?

>###   250 uh is fine for the plate choke.     Instead of the 1000 pf bypass 
>cap,  use 2-3 x 4700 pf disc ceramics.     That combo makes for an 
>excellent lower freq bypass cap.
Then wire 1-3 x  500pf ceramic doorknob caps in parallel with the 4700 pf 
caps.   The 500 pf caps make for an excellent higher freq bypass cap.<


You will have about 1 volt across that combination on 80m. Using 1 4700 pF 
cap and 1 500 pF cap in parallel will give 3 volts: then a 50 microhenry 
choke and another 4700 pf will drop this to 27mV and you have saved 1 or 2 
500 pF caps and 1 4700 pF cap and got a better result. Just adding 
capacitors gets to a state of diminishing returns.

73

Peter G3RZP