At 01:50 PM 2/21/99 -0500, email@example.com wrote:
>>Secondly they have a fairly high output
>>(36pf) So even though they have a max freq spec of 110Mhz your not
>>match them up with a pi-network on 10 Meters.
>And why not?
I dug out my W6SAI Amateur Service Newsletters just for you. And all the
subscribers to the Amps List. BTW These notes are a treasure trove of
amplifier design info. From Pi Pi-L Networks to Intermodulation Distortion
to Forced Air Cooling to the Original Article on the Stanley Steamer Bill
Orr has packed quite abit into the 49 Notes that I have. I'm missing a few,
AS-13 Understanding Tetrode Screen Current, AS-22 Reference Index-- Eimac
Tubes in Amatuer Service, and AS23 External Anode Tetrode Tubes. If there
is interest I would consider obtaining permission to reprint them from
Eimac/W6SAI and posting them on the net.
To the matter at hand. First what has to be determined is the input
resistance at the desired operating voltage.
R= Plate Voltage
2x Plate Current
Assuming 50% efficiency 1500 watts out yields 3000 watts in.
At 3kv this yields 1 Amp of plate current > 1500 ohms
At 4kv this yields .75 Amps > 2700 ohms
At 5kv this yields .60 Amps > 4100 ohms
at a tank Q of 10 the Capacitive Reactance for the Tuning Cap is Figure 3
150 ohms for 1500
270 ohms for 2700
410 ohms for 4100
this yields a TOTAL Cin of
Cin = Ctube + Cstray + Ctuning cap
Ctuningcap = Cin - (Ctube + Cstray)
Ctube is 36pf
Cstray is 5pf
Ctuningcap = 38 - (36 + 5)
Ctuningcap = -3pf
Well that rules out a design Q of 10
Now to a design Q of 20
the capactive reactance for the operating conditions sited above are:
205 ohms respectively
and a capacitances of
3kv is easily do able if you don't mind retuning every 20 khz. The best
Vacuum Variables have a minimum capacitance of 5 pf + 36pf + 5pf = 46pf.
4kv and above ain't going to work.
Initial reports from some who have worked with this tube on 10 indicate an
efficiency on the order of 40%.
That's marginal to poor in my book
Is that enough details???
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