[Amps] 2010 Handbook

[Roger (sub1)]

On 11/16/2010 7:11 PM, Hsu wrote:
> I do not know why ARRL stiill published so old article,
They do have  some new topics of which I am particularly fond. <:-))
>   as you know, the 4CX1600B is rare and expensive part.
The 4CX1600B is not only rare, as I understand it is no longer 
produced.  It was, in  my estimation, a great tube, but apparently there 
wasn't enough demand to justify continued production along with economic 
difficulties in the producing country.
>    It is bizarrerie, why few person using 4CX1000A?
> It has  legal power.
I can guess of a few reasons although they may not be valid I think they 
exist.
1:     The tube has zero grid dissipation.  With a proper circuit that 
is not a problem with a tetrode, but it carries a stigma and one I 
believed for a while.
2.    It only has 1000 watts plate dissipation, yet that is more than 
enough to get the US legal limit. Alpha uses a pair of them in the 
manual tune amp.
3.    It was used in the 30S-1 and associated with only about 1200 watts 
max out even if that amp was designed to the OLD US specs.
4.    It uses an oddball socket, although it is the same socket as the 
4CX1500B uses and basically the same as the             Chinese FU728F 
socket except for the size of the centering pin. (easily fixed if you 
want to exchange tubes)
         Maximum frequency for full power is only 110 MHz, but I believe 
it will operate at 144-147 MHz at reduced ratings and a pair in PP will 
easily run more than the legal limit.  Basically the three tubes 
mentioned are interchangable except for the filament voltage and that 
centering pin.
5.    maybe the most important, the 4CX1500B will do almost anything the 
4CX1000 will do and it's more rugged.
6.    The Chinese FU728F will do most any thing the 4CX1000A will do for 
about half or less than half the price.
7.    4CX1500B tubes seem to be readily available.
8.    A single 4CX1000A is good for for about 2000 watts out while the 
4CX1500B is good for roughly 2600 watts out (PEP). So is the FU728F even 
though it is officially rated at 1200 watts plate dissipation.

One thing I like about these tubes is they will operate in any position, 
not just vertical with base up or down. At least the two US tubes will 
and I believe the Chinese tube will as well.

One other point, here in the US Triodes are the configuration of choice 
and Tetrodes and not all that popular.
Part of this has come about due to the FCC regulations with gain 
limitations or drive power that were in effect for several decades.

Another is that a number of triodes from the 3CX800 through the 3CX3000 
to CY156 are available as pulls at reasonable prices and will operate at 
higher frequencies at full power. Although the CY156 has a very long 
warm up time when used any where near amateur power levels the things 
should last for generations.  I happen to like both the 3CX3000 and the 
4CX3000A7 as well. The 3CX3000A7 operates at reasonable voltages, is 
rebuildable, and is capable of substantial output power at good IM 
products as is the 4CX3000A7.  OTOH the sockets for the 3CX3000 are 
cheaper and currently readily available.  The sockets for the 4CX3000 
are *EXPENSIVE*! which is probably why the tubes are available at pretty 
reasonable prices.  BTW the 3 and 4CX3000 tubes are Thoriated Tungsten 
which makes them almost instant on.  The 4CX version is rated full power 
to 150 MHz.

Guess that covers far more than the original question.

73

Roger (K8RI)
>      73!Hsu