On 5/25/2011 3:04 PM, Bill Fuqua wrote:
> On HF a 4-1000A should run a good 1.5kW , even more, continuously.
> Red glowing plate is normal. In fact when in idle with 5500 V on plate in
> GG they glow
> brighter than when driven to 1.5kW output. Unless there is some reason why
> the efficiency is low, they should operate 24/7 with a full gallon output.
> 73
> Bill wa4lav
>
If the tube has enough emission to run it, a 1000 watt plate dissipation
at 60% efficiency should be capable of 1.67KW out without exceeding the
plate dissipation. As Carl said, cooling is important and if efficiency
is below 60% it's time to get it back up there. Just divide the plate
dissipation rating by the percent. IOW for a 1500 watt tube dissipation
the tube should be capable of 1500/0.6=2500 watts. But there are tubes
like the 4CX1500B which I understand will not come near the 2500 out due
to lack of emission.
Now I have a FU728F with only a 1200 watt dissipation rating, BUT it's
capable of 2500 PEP out. As SSB has a duty cycle of only 20% this is no
where near hitting the 1200 watt dissipation. The tube is capable of a
2KW nominal output. At 60% efficient that works out to an input of 3,333
watts - 2000W = 1333 watts dissipation. which is 133 watts over the
listed plate dissipation. Boost the air flow a bit (might get a bit
noisy) and you are still within the capability of the tube. How well
it'd hold up running that much emission I don't know.
I've never used a 4-1000A, but am looking at picking up a pair of good,
tested ones locally along with a stack of 813's and 3-500s. I think a
4-1000A should be capable of, or close to, matching anything a "pair" of
3-500s can do.
Except I had forgotten how little the 3-500s look when compared to a
4-1000A<:-)) I haven't heard what the club plans yet, but a few of them
are likely to show up at the next swap if club members don't take them
all. As there are few of us running QRO I think there may be a few
available. I'll know more in a couple weeks.
BTW at work (in the old days) we used to run a pair of Amperex tubes
that looked like 3-500s on steroids (bout the size of a 4-1000A but with
a graphite plate). They were a low Mu triode, convection cooled with a
tad over 6KV on the plate running about 6 KW, link coupled into a wide
range of impedances.
One of the locals pulled the guts out of one of those and built up a
4-1000A in it. He used to claim he may not have had the most powerful
amp, but it was likely the largest and heaviest KW around. <:-))
73
Roger (K8RI)
> At 11:58 AM 5/25/2011 -0400, w3hvq wrote:
>> Gents/Ladies,
>> Just a suggestion if running a 1-1000A and the bright red plate
>> bothers you as it does me. I know, many think that this tube should
>> always run with a plate red because its built for it. All I know is that
>> my HB amp's tube is still in perfect condition after 15 years of mostly
>> "black-plate use" here at station W8OHT.
>> My suggestion is based on my happy experience in the recent Volta
>> RTTY contest. For good results in this DX contest, as is in most, almost
>> full RF output is required from the amplifier when using a 4-1000A linear
>> into a poor-man's inverted ell on 40 meters at night, for example. My
>> tube's biasing is fixed at about 10 vdc as I recall.
>> When my homebrewed Pi loading control (ex-HRO-receiver variable with
>> all sections-in-parallel) was set the same for RTTY as for SSB or CW, my
>> tube's plate went from black to full red (not yellow) by the time my
>> longest contest exchange macro had completed its canned message: (his
>> call 599 Q# Q# - 05 05 his-call). Since I couldn't allow my favorite pet
>> tube to undergo such treatment, I reduced the drive from the K-3 to about
>> 11 watts. A cheap old RF watt meter on the antenna line indicated about
>> 300 watts to the antenna (with no appreciable reflected power). Due to
>> noisey nitetime conditions on 40m this output signal was enough to get
>> DX, but only with frequent repeats.
>> So I made an effort to see if I could lighten the loading control to
>> result in more RF voltage on the plate of the subject tube and thereby
>> get the same output with less DC plate current. The HRO loading control
>> had been indicating a reading of 200, but now I could put amplifier in
>> tune and use more drive power (45 watts), yet experienced no RF voltage
>> break downs (frying sounds) in the amplifier's output circuit (the HRO
>> loading dial now indicated 25 (a much higher output pi loading capacity,
>> i.e., lighter loading). Now turning the tuning capacitor always yielded
>> a much easier-to-adjust dip and there was only slight-redness in the
>> plate at the very end of contest transmissions. Now the output RF meter
>> indicated 850 watts output to the antenna and the longest sending macro
>> for the contest resulted in plate redness only during the final second of
>> these hundred-percent-duty-cycle transmissions. So "Mission
>> accomplished". No more contest messages had to be repeated.
>> FYI,
>> John, W8OHT
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