[AMRadio] Amp / Tube question


John Lawson jpl15 at panix.com
Wed Nov 23 01:34:15 EST 2005


   Now, be it known to all hams by these presentiments:  That I have never 
owned or operated a 'real' RF amplifier before - I've always run at 
whatever power the transmitter in use was rated for.  So forgive me for 
asking questions that might be 'obvious'.

   I got around to wiring in the 220 circuit for my 'new' Ameritron AL-80 
[note it's a plain -80, not an 'A' or 'B'] to see how much smoke I could 
make.

   I took out the tube (3-500Z) and brought it up slow on a variac and 100W 
lamp-load - got it up to full line voltage with 2600V registering on the 
meter. Checked the tube for gross shorts and fil continuity - good to go. 
Put the tube in, plate cap off - fils light, fan runs - I left it to soak 
for an hour or so.

   Shut it off, put on the plate cap, hit the power sw - BAM! as Emeril 
might say. A large blue flash went off in the tube and I welded the line 
fuse to it's cap.  And smoked the meter dropping resistor - though it's 
been replaced before, I see.

   So obviously the jug is toast - or is it? Am I missing something really 
stupid here?  I thought to ask right before I buy a nice new one and cream 
it, too...

   Finally, I have no manual for this unit, and BAMA only lists the "A" 
version, which of course is substantially different.   I have found one 
book for sale at a 'manuals' website, but if anyone has one that they'd 
like to loan me for copying  - I'll make a PDF of it and send you back the 
original plus CDR, and pay for the shippin'.

   Cheers, and Happy Thanksgiving....


John  KB6SCO




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