[SixClub] SIX Meter amps

Fri May 6 16:01:51 EDT 2005

An amp is an amp, is an amp...  Well, not quite, but virtually any modern 
tube amp can be converted to 6-meters.  I'm assuming you are still referring 
to amps for conversion.

The SB220 is so popular as they are cheap, simple, and the conversion is 
easy.
Any amp using voltages close to those of the 220 and a Pi network could use 
the same components, otherwise it's relatively simple to use the formulas in 
"the handbook" to come up with the L/C values needed. If instead of a Pi 
network it's a Pi/L then you have one more inductance value to compute.

On something like the Henry 2K4 (which I have) you'd also need to convert 
one of the input circuits to 6-meters as it uses a tuned input circuit on 
each band. These are plug in modules.  I'd modify, or preferably create a 
new one using the same L/C ratio tuned for 6-meters.  It's not necessary, 
but will reduce the drive requirements and give a slightly better match to 
the exciter.  The 2K4 definately does not have a small foot print and it is 
tall as well.  That and it weighs around 160#.

Amps, such as the readily available Alpha 76 series are now relatively 
inexpensive, but still more than the 220s.  I've seen some beautiful ones go 
all the way from $700 plus to over $1,500 with the norm being close to or a 
tad under $1,000 and tending down. Even 374s (the auto tune unit with 
8874s).

  They are very easy to drive and typically 50 to 60 watts of drive will 
give the legal limit with a pair of good tubes. The ones with three 3CX800s 
just loaf along at the legal limit.  The 76A is a bit larger than most 
tranceivers but at 65# weighs about 10# less than an SX-101A receiver <:-))

That brings me to the reason these amps are relatively cheap.  Their tubes 
are not!  The 8874 is expensive and retubing one will probably cost more 
than what the amps are selling for at present.
There are no direct replacement tubes for the 8874. OTOH the tubes in the 
3-tube version should last almost forever unless abused as they are just 
loafing along.

I've heard of them being converted to the 3CX800 which is the tube I belive 
used in current Henry  and Alpha HF models along with the 8877. Their VHF 
models were using the 3CX800 and 3CPX800.  The 3CPX800 has the same ratings 
with the exception of the capability of much higher cathode emission and can 
run close to twice the power of the 3CX800.  (The P stands for "Pulse")

If memory serves the 3CX1200 is an *almost* direct replacement for the 
3-500Z, but with an external anode.  Now that'd make for an impressive 
looking replacement and you'd never have to worry about over working them, 
plus I think the grids are capable of serving as a dummy load<:-)) with 50 
watts dissapation each.

Alpha was using the 4CX1600B in their 6-meter amps, but the tube became 
almost impossible to get and I can find no current information on Svetlana. 
Their site is up and running, but excludes US users.
I believe Radio Parts handles the Svetlana line but they have that infernal 
price of "call".  I do not know about availability.  I've seriously thought 
of picking up another 76A, (2 or 3 tube version) and converting it to 6 
meters.    Even with purchasing a nice one, buying a pair of new 3CPX800s 
and doing the conversion it'd still be about half or less the cost of any of 
the new 6-meter amps.

Strangely enough, my link to the Alpha site produces a "not found" although 
there is no 404 error so the URL must still exist.  Still strange, the Henry 
site does not list any HF, or tube type amps. They only list VHF and UHF SS 
amps.

Have I missed something?
Is no one making high power HF tube amps anymore?

The conversions basically depend on how savy the one doing the conversion.

Roger Halstead (K8RI and ARRL 40 year Life Member)
N833R - World's oldest Debonair CD-2
www.rogerhalstead.com
> Seeing all the comments re: Six Meter amps I was
> wondering if there are recommendations for new or
> recent vintage amps that are designed with six meter
> usage in mind. I always hear abour Heathket SB-220's
> and SB-1000's, is there anything a bit more "modern"
> that is as good, near to them in power output and
> perhaps with a smaller footprint? And what about ease
> of use...
>
> John Carson kd5srw
>
>
>
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