From: peterca@ento.csiro.au
Subject: Re: Tube sources
Originator: tjk@csd4.csd.uwm.edu
Organization: University of Wisconsin - Milwaukee
Date: Thu, 3 Sep 1992 13:08:14 GMT


Dan Kester asks various questions about tubes.  I am fairly new to this too
but will pass on what I have gathered.
>
>Having recently bought a hybrid-tube preamp (Counterpoint SA-1000 with 3 tubes)
>I have started to pay attention to ads for tubes.  What I'm wondering is how
>different are the different tubes?  What is a good source of tubes that netters
>have been satisfied with?  
I have been impressed with PM Components. Selectron House, Springhead
Enterprise Park, Springhead Rd., Gravesend, Kent,England, DA118HD.  
Tel.(0474)660521.  Telex No. 966371 TOS-PM G.   Fax. (0474)333762
I have faxed orders to them with a credit card no. and recieved the goods
in Australia in under two weeks. They will send you a price list of
commonly used audio valves including the two you have.  They list around a
dozen versions of each ranging from their own TEONEX brand for less than 2
pounds to fancy military versions with ruggardised construction or low
noise/microphony selections for up to 8 pounds which is still less than
some of the US prices I have seen.  They claim to be able to get any valve
available.  They will do selections as above as well as matching halves of
dual valves and matching sets as pairs quads etc.  They also have real old
valves EG. I got some for my power amp which had "BBC valve section checked
OK 1952" stamped on them.
>The tubes in the preamps are 6DJ8 and 12AX7. 
Some synonyms may be worth knowing.  For European numbers: 6DJ8 = ECC88,
12AX7 = ECC83.  Various high spec military types can be substituted
also-see PM Component list. 
[For example, 6922 for 6DJ8 and 6057 for 12AX7. BIG difference. -tjk]
>
>Is there a difference between 12AX7 and 12AX7A?
I'm told it is a small internal mechanical improvement- not something to
worry about.
>
>Is it worthwhile to try different tubes in a hybrid preamp?
Its always worthwhile to have a spare set so why not buy some and try.
>
>Are there specific versions (manufacturers/sources) of these two tubes that
>anyone would recommend? 
In my limited experience I have certainly noticed big differences in the
noise from different valves but not other differences.  However most of the
valves I have used were already selected types for low microphony or made
other claims to audio superiority. 
>
>Any advice on how to tell if a tube is running as well as possible?
Tell me too!
>
>Is it desirable to mechanically isolate a tube preamp (as compared to other
>components)?  
I am assured it is but I have not noticed any obvious microphony problem
(subtle ones maybe).  I tried using sorbothane damping rings.  These didn't
do anything obvious except for melt on my line level valves.  I now have
some "army damping cans" (one pound from PM Components) which couldn't do
any harm.  They are metal tubes which slip over the valves with a spring
metal sheet between them.  This sheet has many little springy fingers which
alternately contact the metal tube and the valve.  If you have interferance
problems you could use them as shielding by connecting them to earth.  I
didn't notice any difference and left them in place.
>
>Any other good advice for a new tube user? 
>
>Thanks for all comments!
>
>Dan Kester
>kester@mte.ncsu.edu

----------------------------------------
Peter Campbell
C/O Div. Entomology, C.S.I.R.O.
Box 1700 Canberra A.C.T. 2601
Australia  (peterca@ento.csiro.au)
Ph.61-6-2464158 (w), 61-6-2516213 (h)
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