[Amps] 2010 ARRL Handbook

[Jim Thomson]

Date: Fri, 12 Nov 2010 22:27:09 -0500
From: "Roger (sub1)" <sub1 at rogerhalstead.com>
Subject: Re: [Amps] 2010 ARRL Handbook

On 11/12/2010 9:49 PM, Carl wrote:
> Is the D7 amp the same one that was in a few years ago and got pulled 
> when the tube was  NLA?

##  Correct.  Same one as in my 2006 book.  It also uses the non existent
LGC auto tuner board as a 'tuned input'. 




 Now that its available again, at $1200, what 
> is the purpose except as a showcase for the author?

##  I paid  $1100.00  for my new Eimac  YC-243, which is the socketless
version of a 3CX-6000A7.   I paid $1200.00  for a 2nd one.  Rebuildable
till hell freezes over.  I paid $650.00  for  a new Svetlana 3CX-3000A7....and
$500.00  for a 2nd new one.





If I follow all of it, the D7 is quite different than the 8877. It uses 
the same socket as the 3-500Z, has a 5V Thoriated Tungsten filament  at 
30 A.  Same voltage and current as a pair of 3-500Zs and was designed to 
replace a pair of them.  Except for price I'd pick one over the 8877.  
70 watts of drive gives about 2 KW out with 930 watts of plate 
dissipation. Oh! The grid dissipation is 50 watts.  3rd order are -29 
and -34 dB at 3 and 4.5 KV respectively  5th order are -43 and -37 
respectively.

## 50 w of drive = 1.5 kw out on a 3x3 or 3x6.   100w of drive = 2.5 kw
150w of drive = 3.5 kw.   200w of drive = 5.2 kw...[that's all at 4.8 kv].
 600-700 w of drive = 12 kw out, on a 3x6. [6.5 kv].  Imd on a 3x3  is  -59db pep for
3rd order imd @ 5.2 kw pep out.  The imd, when run at 1.5-2.0 kw out is even better. 
That makes it the cleanest GG triode, period..limited only by the xcvr's imd.  
Grid diss is  225 w CCS... and way more, when the grid flange/grid ring is bolted
directly to the ice cold chassis. You can use the grid as a dummy load for your
FT-1000-D.  Both tubes have a 50 ohm input Z.  A simple 3agc  fast grid fuse is all
that is required for grid protection. 

##  Even Henry Radio  said a new 3x3 is only $50.00  more than a new 8877.
The 8877  is a 'throwaway' tube. The 3CX-1500D7 might be a good tube,  but
for $1200.00  ....and being yet another throwaway tube,  I'd say it's not exactly a 
good bang for the buck.  <4 kv, the smaller tubes have the advantage being able to use
a vac cap for the tune control.  But even that is questionable, since air caps  up to 9 kv
[1/4" spacing] are readily available]. 

##  IMO,  when u start spending $1200.00  for a tube, at least get a real one, regardless
of power level. 

Jim   VE7RF






OTOH "Typical operation" under 30 MHz is 5 kVdc on the plate, 0.710 A 
anode current, where 95 watts of drive gives 2400 watts out with 1220 
Watts dissipation at 3760 Ohms load impedance.

However the max ratings are for 100 MHz unlike the 8877 which will 
easily go to 2-meters IIRC.
CPI has the data sheets in pdf.

73

Roger (K8RI)