From: mynamespacedbydots@xs4all.nl   
      
   "GRe"  wrote in message   
   news:4c9c6247$0$41115$e4fe514c@news.xs4all.nl...   
   >   
   > "Ian Bell"  wrote in message   
   > news:i7gi94$pf2$1@localhost.localdomain...   
   >>   
   >> I just spent some time perusing the 12AX7 data sheets in more detail,   
   >> particularly the part about RC coupled amplifiers which gives the maximum   
   >> output before the onset of grid current under various conditions. Based   
   >> on   
   >> that data I calculated the cathode voltage and also the peak input   
   >> voltage   
   >> before grid current for several values of Ra, Rk and Va. Subtracting the   
   >> two gives the grid bias at the onset of grid current and this seems to be   
   >> pretty constant at about -0.6V. It also seems that with the 300V HT I   
   >> have   
   >> there is really only one operating point that will give me the 102V peak   
   >> output swing I need without reaching grid current and that is with a 220K   
   >> anode load, 2.2K up the cathode leg and a quiescent current of close to   
   >> 0.6mA. I will try those values and see what I get.   
   >   
   > That's very close to what the "Muiderkring Electronic Tubes Handbook"   
   > (1968/p152) specifies for an ECC83 @ 300Vb and a Vo of 36Veff/102Vpp.   
   > Ra   220K   
   > R'g1 680K (load)   
   > Rk   2K2   
   > Ia   0.63mA   
   > Vout 36Veff   
   > A    36x  typo, should be 72x   
   > d    3.6% typo, should be 2.6% Rg   1M   
   >   
   > The same page specifies 11 other operating points for the ECC83.   
   > Can't find the book online but linked below is an equivalent.   
   > http://www.mif.pg.gda.pl/homepages/frank/short/054/2/288.pdf   
   >   
   > Rgds,   
   > Gio   
   >   
      
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