[Moon-net] 70cm 4cx250b amp question.

Jordan outposter30 at shaw.ca
Fri Nov 7 16:16:48 CET 2008


I've received several replies, with several different suggestions which I'll 
have to sort out....Thanks for your input...!

It looks like I'll need a big resistor in the grid cavity... I didn't think 
a wire-wound power resistor would be a friendly thing in there, but at 10w 
dissipation, do I have an option...? I could parallel some 2w carbons, but 
that would also end up being a sizeable lot of 5 resistors....

I'd like to have 10mA on idle, so with 360v it looks like 36K @ 10w will 
do....

I've heard differing opinions on the use of MOVs/VDRs etc.....

I'll also be refurbing a 1kw 2m amp that uses a pair of 250Bs... I have a 
nice pair of SK600/610 sockets, that have the 1100 pf screen caps built into 
the socket, so I'll replace the current sockets, and I'll have to rebuild 
the plate connection rings, as the original rings are only meant to connect 
to the small center HV connector as opposed to the entire plate collar.....

I'll be sharing a power supply between amps, with separate filament 
transformers for each amp.... The screen and bias V's can be handled with a 
rotary switch, but what is a practical method of switching the 2200V B+...? 
I will be using PL-259 connectors for the 2200V , and RG-8 cable to bring 
the B+ to the amps.....Would a ceramic switch work out alright with the 
proper spacing...?    I have a large 2+KW rf rated ceramic switch I could 
use.....Ideas...???

73...Jordan VE6ZT 


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