49258648   
   From: nasadowsk@usermale.com   
      
   In article   
   <7f520899-2099-4bbb-aa60-201415bbcb8f@w30g2000yqw.googlegroups.com>,   
    Corvette Bob  wrote:   
      
   >  I've looked at mine and while   
   > they look fairly new, I can't see any visible glow in them.   
      
   Sometimes the glow can be dark.  But if there's no glow, you do NOT have   
   voltage.  There needs to be about 180 volts or so across this tube to   
   'light' it.  Check the voltage at the plates of the 6X4 - you should see   
   -400, according to the book. +- a few volts is ok, but if it's rally   
   close to 0 or far higher, something's wrong.   
      
   >  I noticed   
   > the 2050 tube is not firing when I make a selection.   
      
   It pops when the machine finds a selected record.   
      
   >  The 6X4 tube is glowing   
   > nicely which tells me I'm getting proper voltage to it.   
      
   (!)  Only the heater on the 6X4 should glow!  If the plates are glowing   
   then you are burning up your transformer!  You can ID these parts of a   
   tube, right?  The plate's the black part.  Glowing here = very bad.   
   There's a central part that at the ends (top, base) of the shiny   
   cylinder, there might be a redish-orange glow.  That's the heater.   
   It'll glow whenever there's 6.3 volts to it.  That's needed, but doesn't   
   mean the tube's getting any other voltages.  This tube is a rectifier   
   diode - it's just like the solid state one only it gets warm :)  It   
   should not get excessively hot - that poor little 6X4 can't put out much   
   current like a 5U4 can.  If you can't touch it without burning your   
   fingers after a minute or two or operation, something's wrong with the   
   circuitry...   
      
   > Is is possible   
   > to pull each OA2 tube separately and test for proper voltage on the   
   > pins?   
      
   No.  The OA2 is like a Zener diode.  it's a 150 volt Zener, really,   
   though it needs 185 volts to activate and glow (it then regulates to   
   150).  Put a volt meter across the pins and see what the voltage is.  I   
   bet it's not 150.   
      
   >  Do I risk doing damage to other components if I try this?   
      
   Maybe, but I don't think so here - it looks like it's wired to unplug   
   from the circuit in a way that won't kill anything (they put jumpers in   
   it for this purpose)   
      
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