On Tue, 23 Feb 1999 20:22:16 -0800 Bob Marston <k1ta@earthlink.net>
writes:
>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 pi-network 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 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
>page AS-30-4
>
>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???
Been away so excuse the delay in replying
Sufficient details for the moment. Bill Orr might have his own comments
if you are nice to him and say please since he is often a silent AMPS
observer. Maybe we can all convince Bill to publish all those old notes.
You still fail to comment on the reams of data on how to design around a
high output C tube(s)...or are you just unaware of the subject?
A good RF designer should be able to obtain 60+ % efficiency on any HF
band. Poor efficiency is possible by poor design , a low emision pull or
a combination of both.
73 Carl KM1H
>
>73s
>
>Bob K1TA
>
>
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