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## [AMPS] YC-156

 To: [AMPS] YC-156 k1ta@earthlink.net (Bob Marston) Tue, 23 Feb 1999 20:22:16 -0800
 ```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??? 73s Bob K1TA -- FAQ on WWW: http://www.contesting.com/ampfaq.html Submissions: amps@contesting.com Administrative requests: amps-REQUEST@contesting.com Problems: owner-amps@contesting.com Search: http://www.contesting.com/km9p/search.htm ```
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