[Elecraft] Solid State Amps

[n2ey at aol.com]

-----Original Message-----
From: Lee Buller <k0wa at swbell.net>

>I see there is now a
>great interest in solid state amps.

>I thought that these amps were...well...not as efficient as tube amps 
thus not
>being attractive to hams.

>So, what has
>changed?  Have the SS Amps gotten more efficient?

In the case of truly *linear* amplifiers (not Class E or Class D), I 
don't think the SS amps have gotten much more efficient than they were 
years ago.

What *has* changed is this:

First, the cost of a tube amp keeps increasing because the tubes 
themselves and the parts around them are low-quantity items. You can 
still build a tube amp for cheap *if* you don't insist on 100% new 
parts. Rig manufacturers have to use all-new parts, though. Meanwhile, 
the cost of SS keeps going down. I also think the dollars-per-watt cost 
of RF transistors has gone down and the watts-per-device has gone up 
over the years.

Second, under the old rules of way back when, we hams measured power by 
DC input, so efficiency was a big deal, since at the legal limit, 
higher efficiency meant more watts to the antenna. But since the rules 
changed 20-odd years ago to output, DC-to-RF efficiency takes a back 
seat.

The difference between a legal-limit amp that's 66% efficient (2250 
watts input gives 1500 watts output) and one that's 50% efficient (3000 
watts input gives 1500 watts output) is 750 watts at the DC input. That 
seems like a lot, but consider that with SS there are no heaters to 
keep warm 100% of the time and that the 750 watts difference is only 
needed when actually transmitting.

Third, switching power supplies.

Fourth, things like no fans, no tuning and easy remote/computer control 
have become more important to a lot of hams, as well as less expensive 
in the overall picture. Consider a K3, KPA1500 combo - won't *that* be 
a sweet setup? Yet in inflation-adjusted dollars, it will probably cost 
less than an S-line of 40 years ago.

Fifth, in the old days it was common for contesters to have separate 
amps for each band so they didn't have to lose time retuning. With an 
SS no-tune amp, computer-controlled and integrated into the rig, one 
amp can be just about as flexible as the old stack of them.

IOW, it's evolutionary, not revolutionary.

And the evolution has been going on a long time.  I still remember, as 
a relatively-new ham, when a QST arrived that showed a legal-limit 
all-HF-bands all-solid-state linear amplifier on the cover. Full 
homebrewing details, too - you could build one from the article.

Back then I thought "well, we won't see tubes in ham shacks for much 
longer, because now even the high-power folks don't need tubes in their 
rigs."

That QST issue was for April 1976...

73 de Jim, N2EY

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