At 01:50 PM 2/21/99 0500, km1h@juno.com wrote:
>>Secondly they have a fairly high output
>>capacitance
>>(36pf) So even though they have a max freq spec of 110Mhz your not
>>going to
>>match them up with a pinetwork on 10 Meters.
>
>And why not?
>Details please.
>
OK Carl
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 PiL 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,
AS13 Understanding Tetrode Screen Current, AS22 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
page AS304
150 ohms for 1500
270 ohms for 2700
410 ohms for 4100
this yields a TOTAL Cin of
38 pf
20 pf
13 pf
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:
75 ohms
135 ohms
205 ohms respectively
and a capacitances of
80 pf
40 pf
25 pf
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???
73s
Bob K1TA

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