[AMPS] What (modern) tube to use?

[Radio WC6W]

>If one were building a new amplifier (or buying one of the new
commercial
>units) what tube or tubes in the case of a pair would one use?  

   If I was building a new amplifier, which I kinda am tinkering with...
I'd take a long hard look at transistors...which is what I'm doing.  
That leads to a whole different set of challenges...   

   Straying back on topic, tubes, I have always been partial to a single
appropriately sized tube rather than a multiple device approach.    I
will confess to building a "thing" with a pair of 813's back in the
'60's.   Contacted many faraway places with that... plus a bunch of close
in neighbor's telly-visions.


>Criteria are reliability at 1500 watts output, tube cost, availability
of 
>replacement tubes if needed in the future and overall relability of the
amplifier. 
> The 100 Amp filaments rule out a "super power" solution like the 
>4CX5000/8170 or 4CX10000/8171 and the 4-1000/8166 seems to be usable
only for a 
>homebrew solution (and then, only if one has a junk box full of them or
access to
>an old AM station <G>). 

    I just had the once in a lifetime experience of helping dispose of a
(SK) friend's large collection of power tubes.  He had everything. 
Including 4 of the 4CX5000's, a 4CX10000,  3CX2500's, a couple 3CX3000's,
some 3-500Z's, 4-400A's and about 15 4-1000A's... and let's not forget
the 4CW100000D...plus sockets chimneys... etc.   He built an amp a long
time ago with a pair of 450TH's and never replaced it... even though he
had plenty of where-with-all to do so.  

   I suppose I should mention that he had started an amp employing the
4CX5000 / 10000 but, had quit working on it about 5 years ago. 
Incidently, that unit is still available... reminds me... I need to post
another ad for it...  as soon as we cut off the lock his son put on the
garage, without first checking for a key...

    As I was re-distributing this cornucopia, I kept thinking would I
ever want to build an amp myself with any of these parts.   

    The short answer was no.   Too big, too little, too much drive
required, too much distortion, too much heat.... etc.


> The present options seem to come down to: (1) a
>pair of 3-500Z,  (2) a pair of 3CX800, (3) 3CX1200A7, (3) 8877/YU-158,
>(4) a pair of 4CX800/GU-47b, or (5) 4CX1600.

  Re-iterating my own prejudices against "couples" would eliminate most
of those.  The 8877 is likely the best of the triode solutions.  

  I am not familiar with the 4CX1600... is that a Svetlana?
   

>Whether one builds an amplifier or purchases a commercial box, the same
>general concerns apply.  A good builder will pay attention to overall
circuit design (band >switch, pi/pi-L losses, cooling, control circuits,
stability, etc.) and someone buying a >commercial amplifier should
consider the same factors.

   The commercial "amateur" designs are at the top level dictated by:

1.   What will pass muster for a FCC type approval and the way the rules
are crafted, in a vain attempt to preclude operation on 27 MHz, almost
forces a grounded grid triode solution.  

2.   What will keep the bean counters (accountants) happy and keep the
company in business profitwise.

3.   What can be easily shipped via UPS.  Note the recent increase to a
150 pound maximum weight limit.   Maybe this will help the design
process!

4.   Functioning as an amplifier probably comes in around 4th priority.


   A "home" builder can employ components such as vacuum variables
(typically obtained surplus) and larger tank components than would be
economic for a commercial builder.   
 
   I conjecture many amateur designs are (in part?) driven by which tube
happenstance bestows on them.

   In my own experience, fortune sent me a pair of 4CX1000A's in the
'60's.   I gave one to a friend who immediately found a socket & built an
amplifier with it.   

   It took me about 20 years (I wasn't looking very hard...) to find my
own socket and another couple to build the amplifier by which time I had
also acquired some 4CX1500B's one of which resides in the unit today. 
They won't  produce 1500 watts out... but 1000 really clean watts is
better than nothing!

   But, that is an "old" tube at this point in history so wandering
off-topic for the third time in this note... time to quit!

73,
   Marv  WC6W







*

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