[Amps] Dedicated RF / tube query

[Jim Thomson]

Date: Mon, 30 Jul 2012 12:56:56 +0930
From: "Leigh Turner" <invertech at frontierisp.net.au>
Subject: Re: [Amps] Dedicated RF / tube query

Hi Dan,

Not that it matters much, but are you absolutely certain that the current
3CX800/3CPX800A7 tube products sourced from CPI are not of Chinese origin
and instead supplied to CPI under an OEM outsourcing supply agreement with
bespoke Eimac labelling / badging done by the China tube factory?

Also I'm curious about the rationale for using two little puppies in
parallel instead of a single 3CX1500A7/8877 tube...it sounds like you have
given this key decision a lot of thought?

Leigh
VK5KLT

##  Point well taken Leigh.  A single chinese  8877 would make more sense...and far less expensive
than a pair of Eimac  3CPX-800A7’s.    You don’t  put 2 engines under the hood of your truck,
you put one big mother in there. 

##  On another note, it chokes me to spend $10K on an amp with AIR variable tune + load caps ! 
Dunno where Dan is getting his 28 kv rated vac caps  from, but I like em.  


20 kV (working limit) / 28 kV (test limit) vacuum capS
Custom-built edge-wound tank roller inductor (1/16" x 3/8" silver plated 
Beryllium)
Toroidal HV transformer with 97% efficiency + or -
Remote display head
etc, etc


##  Now does  this mean vac tune AND load caps..or just the tune cap. 
Dunno why you require a 28 kv cap for a rinky dinky  3CPX-800A7 tube.
Heck, my 15 kv rated vac tune cap is plenty for my 3CX-6000A7. 
A 5 kv cap is plenty for the vac load cap. 

##  IMO.... I wouldn’t  go the all the trbl of building an amp with vac tune + load
caps..then stuff a pair of small tubes into  it.   Why spend $1400.00   on a pair
of 3CPX-800A7’s.... when you can get a 3CX-3000A7 for less...even an Eimac. 
The 3CX-3000A7  is the  real deal.   The Eimac version is rebuildable !  That tube has
a  50 ohm input, instant on, 4 kw CCS anode diss, and a 225 watt grid diss.  You can use
the grid  as a dummy load for your  yaesu 1000-D !   Since the grid is bonded to the chassis,
the grid diss is actually higher.    A simple fast grid fuse is all the grid protection you require. 
50 watts in = 1500w  out.   100w =2500w  150=3500  200 =5200w.   The chinese 3x3 is cheap too. 

##  at 5200w pep out, the IMD3 is  -59db pep.   What more do you want. 
Dans idea of a remote control head is slick....  stick the amp in another room, and
let its blowers make all the racket they want.    Dans  use of a 20 kv cap is great....
if the tube is a 3CX-20,000A7  with the full 10 kv on it.  

Later...  Jim  VE7RF