[Elecraft] Time for the KPA-1500

[Jim Brown]

On 2/20/2012 9:27 PM, Guy Olinger K2AV wrote:
> Are transistors really ready for 1500 watts brick-on-key with oodles of
> dissipation headroom.  What is the price/point analysis of an absolute
> brick-on-key 1500 W transistor solution that will suck up 3:1 SWR without
> folding or faulting?

I have three Ten Tec Titan 425s for my SO2R station. One is a spare.   
If I can believe the various power meters around my shack (I have two 
Birds and several lesser ones), they put out 1500 watts without 
breathing hard, using a pair of 3CX800A7 tubes,  which last decades if 
you don't do stupid things. Yes, THREE very good  legal limit amps for 
less than the cost of ONE used Alpha! I bought all three used for an 
average price of about $1600.

They have a manually tuned Pi-L network output stage that needs to be 
tuned when you change bands or antennas, but the network can match a 
fairly wide range of load impedances, AND when you write down the 
settings for your antennas and bands, you can return quite close to 
those settings when changing bands during a contest .I've learned to do 
that with one amp while making QSOs on the other band.

They are very tolerant of abuse, like things happening in the connected 
antenna that cause the load to be vastly different from how they are 
tuned. I remember a CQ160 SSB contest several years ago when a lot of 
wind was causing my TX vertical to do the dipsy doodle all night, often 
letting it short out to the mounting plate for the radials. The red LED 
on the Titan would flash RED indicating excessive grid current, and I'd 
stop TX for a second or two, then keep on going. Three years later I'm 
still using those tubes, and they're no worse for the wear  And any 
contester will tell you that it's easy to transmit into the wrong 
antenna, especially when you're tired halfway through a long contest, or 
keep track of QSOs flying by you on two radios, one in each ear.

My ham neighbors will tell you that they are also pretty clean in terms 
of spectral purity. .

So don't tell me about tubes are dead, or "old technology."  Sure, it's 
possible to design for high reliability operation with solid state 
devices, but I bought these 30 year old legal limit rigs (25 years old 
at the time) for 20% less than the cost of a KPA500 in kit form. Do I 
love the KPA?  You betcha. But it's unlikely that my Social Security 
check is gonna let me buy ONE KPA1500 (should it appear in my lifetime), 
let alone two. :)

73, Jim K9YC