On Thursday, March 9, 2017 at 5:15:58 PM UTC+11, Jimmy wrote:   
   > HellO!   
   > I've read posting on other forum and it draws my attention.   
   >    
   > IS the DCR of the plate choke should be equal to the resistive value of the   
   plate load resistor if considering replacing the resistor with the plate choke?   
   >    
   > Example: if the current plate load resistor is 1000 ohm, should I use plate   
   choke with DCR 1000 ohm??   
   >    
   Unfortunately, you have not mentioned the tube type, or any of the operating   
   B+, Eadc, Vac conditions, so none of us can answer your question properly.   
   Please specify ALL working conditions in future.    
      
   But let us suppose you have an anode resistor of say 10k0 which has 20mAdc to   
   feed an EL84 in triode mode, where Ea = 250Vdc ( Vdc between anode and cathode   
   ) The 10k will have 200Vdc across it, and there may be Rk = 515r, with Ek =   
   +10.3Vdc, and B+ will    
   then be 10.3V+250V+200V = 460.3Vdc.    
      
   Do you understand this fully so far?    
      
   Let us assume you want the bandwidth to be 20Hz to 20kHz.    
   Now this would be easily achieved by the EL84 triode with 10k0 load only, and   
   no shunt C or L anywhere.   
      
   Let us assume you wish to replace the 10k0 with a choke.    
   The choke's dc wire resistance can be any value providing the heat generated   
   in the winding wire does not cause the choke to overheat. So a typical value   
   of Rw might be 470r, and so 20mAdc gives Pw = Isquared x R = 0.188W.   
   But the Vdc across L = 9.4Vdc, so the Ea across tube will increase to exceed   
   +400Vdc, and the Idc will increase, and soon there may be a CLOUD OF SMOKE   
   from your bench, and then you might blame us for the wrong advice.   
      
   So, DO NOT just remove the 10k0 and instal a choke; you NEED to understand a   
   whole lot more about WHY you have asked us about a choke replacing the R.   
      
   The safe way to replace the 10k0 with a choke - assuming we want better Vac   
   operation with less THD than with the R, is to keep the Ea nearly the same   
   with choke as for without it.    
      
   You need to understand the properties of the tube involved, say EL84 in   
   triode, with Iadc = 20mAdc.    
      
   Its Ra will be about 2k2. if you insist on bandwidth down to 20Hz, it means   
   the F response is -3dB at 20Hz because Ra = L reactance XL = 2,200r.   
   This means the L must be at least 17.5 Henry. This leads us to wonder about   
   core saturation and and air gap size and a whole lot of other L, C and R   
   properties of the choke and so we can safely say there could be up to 7 items   
   to be used in several    
   equations to arrive at a design for the choke which will lead to the desired   
   outcome of better result compared to having a 10k0.   
      
   The choke could have any value up to say 80H, and Rw < 500r, and then instead   
   of removing the 10k0, you can replace it with say 9k0, so that your existing   
   B+ supply remains the same.   
   The result should give slightly wider Vac swing than with a lone 10k0, and THD   
   may be slightly less, and bandwidth will be OK.    
      
   But maybe you should read my website at www.turneraudio.com.au and with luck,   
   the probability of smoke is reduced, while probability of fine music is   
   increased.   
      
   Keep well, Patrick Turner.   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)