From: info@turneraudio.com.au   
      
   Phil said....   
      
   " The Deluxe Reverb is a re-issue."   
   ** But no Fender amp is called that.   
    Kindly post the name printed on the face plate.   
   ....  Phil   
      
   The front plate on amp chassis has Deluxe Reverb in written white lettering.   
   Silver cloth face has "Fender"   
   Black cabinet, 12" speaker.   
   The schematic has '65 Deluxe Reverb' and created and plotted dates on   
   schematic are February and July 1993.   
      
   Lord valve calls us all "poor wankers" and I shall leave him confused.   
      
   Amp has wear and tear and looks 20 years old, but it sure ain't from 1965.   
      
   John Stewart asks me what was the F of the RF oscillations. I don't know,   
   I didn't measure the F, but appeared to be over 50kHz, or "super sonic"   
   aka low RF. HF oscillations in audio amps with NFB can be from say 10kHz to   
   5MHz, depending the amp type and devices and how the circuit is when such   
   oscillations are measured.   
      
   The Fender here did not appear to oscillate at RF, super sonic, whatever, when   
   the original 820r + 47r GNFB network was in place and which gives 2dB GNFB.   
      
   This tiny amount of NFB does hardly anything to flatten the signal at the   
   speaker. The signal response at has a 6dB peak at 100Hz and +6dB at 2kHz,   
   relative to 1kHz level. So the Vo merely outlines the speaker Z which is to be   
   expected because the amp Rout is a much higher ohm value than the speaker at   
   300Hz where speaker Z is the minimum, probably about 8r.   
      
   Phil implies moving grid stoppers 1k5 at PCB to tube sockets might do   
   something, because Fender did it in the past, but such a move would do SFA.   
   Maybe **increasing** grid stoppers to say 4k7, 6k8, 10k0 *might* have an   
   effect.   
   But what I done loads the 6V6 with 9.4k a-a above about 30kHz, thereby   
   stopping the oscillations.   
      
   Possibly this amp could be converted to use EL34, with adjustment of bias and   
   the connection of pin 1 to 8 so suppressor grids are biased at earthy volts.   
   I dunno if it would make the perceived harsh tone of this particular amp sound   
   any better. Perhaps an Alnico magneted speaker would be better. I have no clue   
   what further mods I could might improve tone. I need to move on to other   
   projects.   
      
   BTW, many amps use pin 6 ( not used in octal power tubes ) to bring feed from   
   driver stage coupling caps to OP tubes, AND also the grid bias voltage. Then   
   the stopper R is between pin 6 and   
   grid pin 5.   
      
   If pin 1 is used instead of pin 6, and Summ Eadiot plugs in EL34, watch for   
   smoak, as results could be uncertain, because g3 are being driven like g1.   
      
   As the old sage mite siegh, Cood be Farr Khan interress sting.   
      
   Patrick Turner.   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)