[AMRadio] Valliant 1

[RABRUNER at aol.com]

AL,
866's are rectifier tubes, not regulators.  They require a little care in 
their use, but are generally reliable.  They must be aged in when first 
installed without HV on them, then they must be carefully pre heated each 
time you light up the transmitter, before applying HV.  Also, mercury vapor 
tubes are sensitive to mounting position. Operating them with the transmitter 
in a non standard position, may allow the filament to sag and cause the 
result you experienced.  Putting B+ on them cold can also blow them up. 
Download a data sheet and get familiar with what you've got there before you 
light it up again.  3B28s are a non mercury vapor tube that can usually be 
plugged into the same socket and don't require quite so much skill in their 
use.  But you have to find out what took out the 866 before you put anything 
else in there. Was it operating conditions or a problem in the load on the 
rectifiers? You could have a choke that is arcing, or a filter capacitor 
shorting. You will just be blowing up solid state diodes or 3B28s instead of 
866s.  The 866 is a rugged reliable tube when used properly and it should not 
have shorted just because it was having a bad day.
    It seems like you are having a lot of trouble in other sections of the 
transmitter.  Try to make sure the power supply is solid as a stand alone 
unit, filter caps, good, etc.  Then troubleshoot the transmitter section by 
section, perhaps at lower plate voltage using another power supply.  
Otherwise, you can go through a lot of difficult to locate and replace 
classic radio parts.
Bob Bruner
WB4TAJ/9