Re: Premium Tubes for Hammonds & Leslies

[GOFFProf@aol.com]

To add an opinion to the *very* good tube thread that has been unravelling: 

Ted Weber, Brad and others are probably more knowledgeable on the theory
behind tube selection, but my own field experience on Premium tubes:  

The generally accepted theory behind Premium tubes is that they perform far
better than "standard" tubes or unmatched tubes.  Groove tubes, Ruby Tubes,
etc are great when used in an application where the tubes are constantly
running at or near their full output rating.  Tube output degrades with age,
so higher quality up front is certainly better. 

In the case of a Leslie 122 / 147 tube amp where a pair of 6550's is used,
they are not required to work hard, as the tubes are rated at 100 watts EACH
and the amp is only able to produce 40 watts total!  Some quick calculations
and you'll see that the tubes never develop half of their rated potential
which is very good as tube-life is far longer . 

Before the screaming responses start, there are certainly other factors to
consider in tube power factors and aging, selection etc. but  my real point
is that the *original* Leslie amp factory installed unmatched RCA, Sylvania,
GE, etc. 500 hour rated 6550 tubes usually ran for years without failure.
 The later commercially rated 6550A tubes had a larger envelope and slightly
beefier guts to withstand the military requirement of a 2500 hour rating.
 The old "Leslie" bottle tubes were 6550's made by several manufacturers but
they were also not matched!  Out of the box, then into the amp on the
production floor. 

I believe that true "hardness" matching is far more important in higher
power, higher performance amps such as guitar amps where they are driven to
75-100 watts.  The point at which tubes in this situation will distort when
you are runnniing them at or near the maximum rating is important!  Total
Harmonic Distortion (THD) is as important in either amp, but less critical in
our use.  Most tubes perform to the "average" design specification, which is
fine for a Leslie amp, but not so good for a more critical use.  The HAMMOND
factory never matched tubes in any of the organs or Leslie's.  

My own privately labelled 6550 tubes (Svetlana) were designed to our specs
specifically for use in Leslie amps. We select them in pairs by their tested
characteristics among several areas. 

The important thing to remember when any 6550 or similar power amp tubes are
replaced is to replace them in pairs. Problems quickly develop when different
brands and age (used & new) are installed!  Don't mix manufacturers, and DO
NOT use Chinese 6550 tubes ever. They fail due to the mechanical streeses
from the lower drum rotor audio  I prefer Groove Tubes to all other "Premium"
tubes and for my pro customers who asked for them (before our own tubes were
introduced), I always got 6550's in H-9 or H-10 hardness ratings.  I want the
Leslie amp loud and clean when used with a tube preamp organs, where the
preamp distortion is easily alterable and controllable. 

As information, Groove Tube founder Aspen Pittman was and hopefully still is
the proud owner of a HAMMOND Model CV and Leslie.  I have talked to him about
his organ and supplied parts.

I'm sure others will disagree on the above, but I feel that a Leslie amp
constitutes a  "mid-quality" tube need,  therefore expensive
Mazerrati-performance premium tubes aren't necessary and just waste money.
 When my brother Bill finishes a rebuild on a 122 or 147 amp for our
mail-order customers, it is *not* unusual under testing for it to produce 60
watts into our dummy load.  Before the amp rebuild and new tubes, it was
lucky to produce 12 or 15 watts!  

The #1 failure in Leslie's after the rebuilt tube amp is reinstalled ......
is Upper Driver failure in original Jensen Drivers.  Handling 15 watts from
an old amp is not so bad for the old driver to handle, but 40+ watts from a
rebuilt amp sends it to driver-Hell fast! 

Dave K., Dave B., Hugh and many other board members know this *so* well
.........
I'd be interested in what others experience is with the tube  selection issue
and "premium" tubes.  (Ken - you too. I'm NOT mad...... anymore :-)

Among all the issues facing us that could hamper older HAMMOND / Leslie
restoration, the tube issue has to be one of the ones we need to watch
closely.

Al