I have been trying to help a fellow ham get an AL-572 tamed down via emails.
He had a tube short/arc and blow one of the 50 ohms to ground grid
resistors- the tubes were pretty old and tired anyhow so he bought a matched
set of 4 572b's from RF Parts.
Replaced the grid resistor - carefully checked all the others and also
checked all the parasitic choke elements (it has the 4 separate chokes in
the assembly with the 2 durmica series caps in each resistor leg - all
components are good )
It is working "OK" on all bands but 15 meters - but on 15 it wants to take
off .(Whether its VHF or around 21 mhz I dunno) He has not yet tried to
re-neutralize. He can get it "operational" by a fairly large change in
loading to stop arcing/spitting and at that point its about a 500 watt amp.
Other bands are an easy KW - (maybe a tad too easy on 10 which makes me
think its a littel regenerative on 10 and re-neut may be a help)
I have read , think , all of W8JI's stuff on the AL572 and AL-811 amps and
not sure of when he said what with respect to directly grounding the grids .
So other than re-neutralizing , what is the current thinking of directly
grounding the grids ? Anyone know what they are doing as shipped today ? He
is going to add the gas discharge on the filaments just as a precaution to
protect his K3 driver, and could easily do the grid grounding at that time ?
What say Ye ?
73 de Hank K7HP
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