Alex Eban wrote:
> The grid dissipation is not so much of a factor, since it is inherent in
> high u tubes. That's what you pay for high gain. As long as you keep to
> class AB1 operation, you shouldn't have grid dissipation problems. The
> mishaps happen usually with non ALC controlled transmitter chains, that
> can't control the amplitude of the driving signal. It isn't much more
> complicated to implement an ALC circuit than installing grid protection
> circuits.
> as for the other complaints, they are certainly true! But what can
> you do? Install a $100 switch? A copper tube tank coil? Use a CCS rated
> power transformer? These things will bring up the price at non competitive
> levels, something a a manufacturer cannot afford these days.
> This is why such a thing, with a little forethought will always be better
> when home built than when bought. For a one off you can afford the best you
> consider adequate.
>
This is why a company like Ameritron has a line of amps from economy to
well...not quite so cheap although I consider the entire line to be
economy from construction to packaging. I'm not calling them poor amps.
To me they appear to be a good value for the cost.
OTOH as you say, building a truly bulletproof amp would put it out of
the reach of all but a few hams making it an uneconomically viable
commodity. Plus stateside the manufacturers are limited to a series of
regs that limit gain and some other parameters including the amp must be
externally keyed. (Is 10 still off limits?) Those who really want the
best, "to them" either build, or have an amp custom built. Yes, you can
get the 3 and 4 CX 3000 and 5000 pulls are reasonable prices, but you
don't find pulls in new amps. OTOH a yc-156 pull at $385, or a yc179
pull at $575 is really a bargain for a custom built or home brew amp and
you really don't have to move to the farm so you can install a 3-phase
power supply. Although a good, well regulated, low ripple 3-phase supply
is easier to build than a single phase. I'd really like to have amps on
HF and 6 meters like that, but I'm afraid some one would notice. I'm
probably (strike that probably) more afraid of my wife noticing the cost
than the FCC noticing the signal<LOL> BUT either a yc156 or 179 with a
reasonable PS and close to a 100 watts drive will run the legal limit
with only a little overhead, but the tubes have outstanding IM
characteristics and should last forever.
I have to admit, that even if all the drive you have available will just
give the legal limit, opening the hood to show off an amp that has a
tube with handles would be kinda good for the ego and it'll put out a
very clean signal. AND if you build it, there is absolutely nothing
illegal about it far as I can interpret the regs. So what if I had an
amp capable of 8000 watts out, if I had that much drive (I have
neither), in addition to the lack of drive I don't have an antenna on
the place that would handle much more than the legal limit...if that,
and a number that would be hard pressed to handle the legal limit in any
thing other than SSB. Nor do I have the coax connectors that would
handle that kind of power. So, sure I could put a yc-189 on and still
be legal as long as I didn't push the output into the illegal realm if I
haven't read the regs wrong.
Engineering, like all amp usually consists of a bunch of compromises.
Having been a project engineer I can appreciate the compromise angle
from both the engineers and management's perspective. It boils down to
selling not only what the customers want, but what the customers will
purchase. The automotive industry made the mistake of building what
people wanted, not what they'd purchase.
With an amp, you have to build something that will deliver the desired
power, that is rugged enough to keep the complaints to a minimum, and
that includes the packaging. As for the ALC option, I haven't had an
amp in the last 20 years that did not have an alc line back to the
transmitter. Some of todays not only have that, but those running AB1
have their own ALC. The solid state amps from a KW up tend to be a tad
pricey, but they have protective circuits, auto band switching, and ALC
that would have made manufacturers jealous 10 or 20 years ago. My old
Heathkit and Hallicrafters amps don't, or didn't even have an ALC
connector. IIRC my Dentrons didn't either, but I'd not guarantee that.
A couple of us "locals" were recently talking about building amps that
would be rugged, provide a reasonable overhead for reliability, and look
like it was built by some one who knew what they were doing. That meant
sending the panels out although we both have the capability and skill to
do the metal fabrication. BUT by the time we each purchased the parts
for a "one off" amp, including the panels we could get what we wanted
commercially for the same price or even cheaper than doing it yourself.
Now these are legal limit amps that could run digital at the legal limit
24 X 7 and although desktop I'd not call them either small nor light.
73
Roger (K8RI)
> Alex 4Z5KS
>
> -----Original Message-----
> From: amps-bounces@contesting.com [mailto:amps-bounces@contesting.com] On
> Behalf Of Jim Thomson
> Sent: Wednesday, March 24, 2010 3:56 AM
> To: amps@contesting.com
> Subject: [Amps] Good engineering
>
> ORIGINAL MESSAGE:
>
> On Mon, 22 Mar 2010 19:31:09 -0700, "Jim Thomson" <Jim.thom at telus.net>
> wrote:
>
>
>> ## I wouldn't be holding Command or anybody else up as any kind of
>> 'standard of engineering excellence.' If these ham amps were built
>> right, they would all have individual, adjustable bias for each tube,
>> plus mating metering, real bandswitch's and real tank coils, and plate
>> xfmrs... and maybe toss in a real tube..... and not something with a floozy
>>
> 4 watt delicate grid.
>
> REPLY:
>
> Any fool can overbuild a product. Good engineers know when to stop, and good
> engineers get paid good money to get it right.
>
> 73, Bill W6WRT
> ## Bill , got any idea what 3 x NEW EIMAC 3CPX-800A7's cost these days?
> ##That's the tube line up used in the HF-2500E.. really smart. The 12 ga
> wireroller inductor,used in the 10 kw palstar ant tuner is a joke, along
> with SO-239's,and the mickey mouse balun on the INPUT of the tuner.. which
> will explode. Toss in undersized tank coils, bandswitch's, mickey mouse
> tune/load padding schemes,t/r relays that hot switch, and you wonder why
> the HB amp builder gets into designingand building his own stuff. Ten tec
> brags abt the 3.5 kva CCS xfmr used in the centurion,and sez it's good for
> 7 kw.."IVS" [int voice service], yet it barely does 1.3 kw pep
> out....[almost legal limit]. A buddy accidently had his cat fall asleep on
> his footswitch for 2 hrs.His 87-A was pumping out a 1.5 kw FM cxr on 29.650
> mhz. He had the optional cooling fan.The RF deck had turned into molten
> glop ! Alpha tech tells him..... " don't believe the hype"The home builder
> has the luxury of using what
> ever components he wants.. and can get hishands on. Typ ham amps have cut
> every corner there is. 1/4"-3/8"-1/2" cu tubing is cheapat home depot... so
> why melt airdux ? Ceramic vac caps are readily available, so I use em
> fortune and load. If something is marginal... I re-design it. Who's the
> fool ? later... Jim VE7RF
> _______________________________________________
> Amps mailing list
> Amps@contesting.com
> http://lists.contesting.com/mailman/listinfo/amps
>
> _______________________________________________
> Amps mailing list
> Amps@contesting.com
> http://lists.contesting.com/mailman/listinfo/amps
>
>
_______________________________________________
Amps mailing list
Amps@contesting.com
http://lists.contesting.com/mailman/listinfo/amps
|