Re: tube choice for Leslies

[bpb@bpbsn.cca.rockwell.com (Brad Baker)]

Ben Jacobs wrote:

   > One last question.  Sovtek (and maybe others) sell a solid-state
   > plug-in replacement, ostensibly suitable for all 5Y3, 5U4, 5AR4
   > type rectifier applications.  Any comments on what to expect from
   > SS rectifier in a Leslie, as opposed to tube component?

To which, and in addition to some other stuff, Al Goff responded:

  > SOLID-STATE RECTIFIER --- The VR-105 (OC3) rectifier tube in a 122
  > / 147 Leslie amp may not a suitable candidate for a solid-state
  > replacement.  It may work, but be sure that the replacement is
  > exactly for an OC3, not a 5U4 or other rectifier tube.  If you're
  > going to go to this trouble and expense, why not get rid of the
  > tube entirely and replace it with a good quality 105 volt Zener
  > diode?  (Don Leslie did not have such an animal available when the
  > amp was designed.)  The zener diode is not as rugged as the OC3
  > tube in the event of tube failure, etc., but they can be easily
  > changed, and they are cheap.  Some other components can also be
  > removed if the change to a zener is made.  I do not necessarily
  > recommend that this change be made, only that it is possible and
  > will work.  I personally install the tube rectifier as per the
  > original design.

the rectifier replacements ben mentioned, for 5y3, 5u4, etc., are
solid-state replacements for the tube type rectifiers mentioned. the
leslie already has a solid-state rectifier so those particular types
of replacements don't really apply to the leslie amplifier.

the oc3 regulator drops 103 to 116 volts (that's what the book sez
anyway), and provides among other things, the screen supply. the
6550's screens draw maybe 30-40 ma with signal. it looks like that
zener would have to dissipate more than three watts, so you'd probably
put in a 10 watt or greater unit for reliablility and bolt it into the
chassis somehow to dissapate the heat (that is unless, as al sez,
there is a direct, pin compatible, oc3 solid-state replacement, which
would then be sticking up into the bass rotor's prop wash). it seems
easier to just stick with the stock oc3.

brad baker
bpb@cca.rockwell.com