From: phil_a@tpg.com.au   
      
   "Iain Churchus"   
   >   
   > Enjoyed. Many thanks. I will try to reciprocate with   
   > some docs on the Radford STA 100B (B=balanced input)   
   > aother fine British valve/tube amp also used by the BBC.   
   >   
   > Meanwhile, schematic here:   
   >   
   > http://ampslab.com/vintage_radford_sta100.htm   
      
      
   ** Hmmmmm  -  two UL output stages powered from a common 600V DC supply with   
   only simple cap filtering.   
      
   With just 100uF effective capacitance, the peak to peak ripple at idle is   
   about 18 volts or 3 % of the 600 rail.   
      
   That 18 volts of ripple will rise to 45 or more at full output, or about 8%.   
      
   Good balance in the output valves will prevent any audible hum, but has no   
   effect on the 100 /120 Hz amplitude modulation the constantly varying screen   
   supply voltage causes.   
      
   Means there is a heck of a lot of work for the NFB loop to do.   
      
   A filter choke in the PSU and two more caps would fix it completely.   
      
   Was Arthur Radford a " penny pincher " ???   
      
   Hmmmmmm........   
      
      
   ....  Phil   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)