on 1/3/02 6:27 AM, Mike McCarthy, W1NR at w1nr@eecorp.com wrote:
>
> Why does everyone insist that the 4-1000 needs in excess of 5kV to run legal
> limit? I have built several that easily put out 1500W with only 4-4.5 kV
> and 100W from a solid state rig. Am I just using good tubes vs. ones near
> the end of life? Probably.
Who knows. I've read similar things and built my amp using about 6 KV on
the anode (about 5.2 KV under load). I get an easy 1500 Watts out with less
than 100 Watts of drive.
I had problems with the original design of the amp (I rebuilt someone
else's) and after reading all the stuff about needing high plate voltage, I
decided to build it that way since I had the PS capacity. It's no problem
for me to lower the anode voltage, so I could try that and see what happens.
I just may do that and report back to everyone.
In fact, lowering the voltage a bit will make the tank circuit easier since
you'll be lowering the anode's output impedance.
There are a lot of other factors why the view is probably expressed. For
one, a lot of people think the B&W 850 tank coil is designed for use with
the 4-1000A. It isn't. In fact, it's no where close to what you need for a
tank circuit coil if you do the math. It's what I used (since it was there
by the original builder) and if I had to build another PA, I wouldn't use
it. I think the reason for this particular myth is that a lot of the old
designs out there use that coil. However, those old designs were all done
when the FCC had the 2KW input power limitation so those amplifiers didn't
have to worry about putting out 1500 Watts.
I've also noticed that on 80 meters and 40 meters, I have a whole heck of a
lot more gain than on the upper bands. It's probably related to either my
input circuit design of my tank circuit (I think it's likely both but the
majority is the latter). On 80 meters I only need to run 60 Watts to get
full legal limit. On 15 meters (the worst band), I need to run about 95
Watts.
I really don't have a lot of desire to go back and mess more with mine since
it more than meets my needs. I get full legal limit on 80 through 10 with
less than 100 W drive and it would be too big of a headache to mess with.
I would say that if you have a good layout, good design and good tank
circuit, no, you probably don't need the monster voltages. The technical
docs from Eimac on the tubes capabilities certainly show that you don't need
6 KV for 1500 Watts out.
73,
Jon
NA9D
-------------------------------------
Jon Ogden
NA9D (ex: KE9NA)
Member: ARRL, AMSAT, DXCC, NRA
http://www.qsl.net/ke9na
"A life lived in fear is a life half lived."
--
FAQ on WWW: http://www.contesting.com/FAQ/amps
Submissions: amps@contesting.com
Administrative requests: amps-REQUEST@contesting.com
Problems: owner-amps@contesting.com
|