From: trevor@rageaudio.com.au   
      
   On 4/09/2022 10:28 am, Phil Allison wrote:   
   > Trevor Wilson wrote:   
   > =================   
   >> I am servicing a power amplifier which uses a dual, 8 pin DIP OP amp.   
   >> Unfortunately, the rail Volts on the OP amp (LF353) is +/- 22 Volts.   
   >   
   > **  That is a mistake, all versions of the Sumo 9 used nominal +/-20V rails   
   fed from series regs with 20V zeners.   
      
   **Oops. You are correct. The negative rail is fed from a 20 Volt zener   
   and the positive rail is fed from a series transistor, with the base   
   tied to a 20 Volt zener, in series with a forward biased diode.   
      
   >   
   >> I need a suggested replacement.   
   >   
   > ** Which MUST be a FET input op-amp.   
      
   **Yes. There is that.   
      
   >   
   >   
   >> And no, it is not possible to drop the rail Voltages.   
   >   
   > **Course it is, they are meant to be 19.5V each anyway.   
   >   
   >> They must remain at +/-22 Volts.   
   >   
   > ** Humbug.   
      
   **True enough. I had neglected to examine the schematic before I posted.   
   According to the schem, it is +/- 20 Volts.   
      
      
      
   --   
   This email has been checked for viruses by Avast antivirus software.   
   www.avast.com   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)