[Amps] 2k4-hum, how to check

[Jim Thomson]

###  with a normal operating B+  supply.... with NO load, or 
very little load,  you will have no 120 hz hum.    With a full bore
dead cxr on CW mode, you will get max ripple [typ2-3%].

##  You can seer that 2-3%  ripple, [with a full bore cxr] on any
cheap  RF monitor scope !   You can also see it on the new Array
solutions  wattmeter.  On the AS  wattmeter, the last few leds on
the bargraph will..'dither' .   I thought my new AS meter was screwed
up, until I turned on the scope.. and saw the ripple.   This was only apparent,
when running >700 w , on any of my 4 x L4B's.  [ the fix was to replace
the filter caps  with new ones, at least  double or triple the original value]

## In the Henry amps, they resonate the filter choke with a small
value cap.. at 123 hz.    With a full bore cxr, on any henry amp, the
choke will drop a tiny bit in value, and resonance  goes UP a few hz. 

##  you never resonate the choke at say 118 hz,  cuz  with a full
load on it,  resonance will shift up, and as it pass's thru 120 hz,
the resonating cap in parallel with the choke  will explode! 

## Easy to check both the resonating cap.. and the big 20 uf oil
cap, with a LCR meter !  [ discharge caps 1st, temp open off one lead] 

##  probably what has happened, is the resonating cap has gone
open, or int, or bad connection,  and/or the 20 uf oil cap, has
gone way down in value.  If the resonating cap has gone down in value,
resonant freq  will have skyrocketed way up > 130 hz,  which will result
in very little  120 hz hum redux.  If the resonating cap went open, you will
get little to no 120 hz  redux.  The choke by itself is not big enough
for hum redux.  

##  Hum from  any FWB/FWD  is  2 x F [ single phase]  or  6xF [ 3phase]
IE:  120 hz in NA... and 100 hz in EU, etc. 

##  Now if  one leg of rectifier diodes has completely shorted, you will be 
pumping raw AC  into the  HV filter.... on  1/2 cycles.. which is bad news, results in
60 hz hum.  Raw AC is hard on electrolytics, and also oil caps.   

##  drive the henry amp, with a full bore cxr.. and listen on a 2nd xcvr, a few feet
away.. and tune carefully [ with 2nd xcvr on AM mode, 2nd choice is ssb]
you will hear the hum, plain as day. 

Later.... Jim  VE7RF