From: not.here@invalid.invalid   
      
   On Thu, 14 Apr 2011 14:55:54 -0700, Big Bad Bob wrote:   
      
   > On 04/14/11 11:13, mick so wittily quipped:   
   >>> /me ponders microcontroller running the power supply.  At ~$17 per   
   >>> controller board (unassembled), it would make things VERY interesting.   
   >>   
   >>   
   >> Should be fairly reasonable to do - with a PIC at least. Use a PWM   
   >> output, RC filter to give Vref into op-amp/transistor current source.   
   >> Then ramp or step the PWM signal to give whatever warmup speed you   
   >> like. You don't need precision so software-driven PWM would be ok. You   
   >> could use an 8-pin, something like 12F675, and write the software in   
   >> GCBASIC ('cos it's free). You don't need a clock crystal, it's all on-   
   >> board. Just stick it on a piece of veroboard with the other bits.   
   >>   
   >> Of course, once you have a chip in there you start to get other ideas   
   >> too...  ;-)   
   >>   
   >> You can do a rampup with a LM317 (or similar) regulator - it's shown in   
   >> the data sheets. It's constant voltage though, not current. Should be   
   >> easy enough to add another transistor/resistor to get a fixed max   
   >> current limit though.   
   >>   
   >>   
   > yeah all kinds of possibilities exist.  total cost of hardware +   
   > long-term reliability would be the driving factors.  If micro-C is cheap   
   > but fails before tubes then it's kinda dumb.  On the other hand if a   
   > simple CCS charging a cap makes your rampup work then it's under $1.  I   
   > would actually sequence more than that since you want bias first, then   
   > heaters, and after heater rampup, a quicker rampup for B+ lines (maybe 1   
   > second).  That way you don't get a 'pop' when you apply B+, you don't   
   > apply B+ without reasonably warm cathodes, and you don't apply B+ unless   
   > there's a bias supply already charged.  It's a bit more than I   
   > considered before looking at the 'Gettimg the Most Out of Vacuuum Tubes'   
   > (Tomer) book I recently found on-line.   
      
      
   I just grabbed that book. Good isn't it?   
      
   Let's see...   
   opto-isolator fed from bias supply: input into PIC   
   No further action without bias   
   PIC ramps up heater(s)   
   Allow some warm-up time   
   Close a relay to allow B+ via a resistor   
   Another delay   
   Close second relay to short out B+ resistor & allow full supply   
      
   owzat?   
      
   --   
   Mick                      (Working in a M$-free zone!)   
   Web: http://www.nascom.info   
   Filtering everything posted from googlegroups to kill spam.   
      
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