[Amps] Air Variable Spacing Question

[Carl]

Oren Elliott Products, the primary supplier of bread slicers in the USA.
http://www.orenelliottproducts.com/

Carl
KM1H




----- Original Message ----- 
From: "Mike" <mikek4gmh at gmail.com>
To: "Jim Garland" <4cx250b at muohio.edu>
Cc: <Amps at contesting.com>
Sent: Friday, December 07, 2012 4:22 PM
Subject: Re: [Amps] Air Variable Spacing Question


> Okay, guys, what's an "OEP" capacitor?
>
>  73,
>  Mike, K4GMH
>
> On Thu, Dec 6, 2012 at 1:15 AM, Jim Garland <4cx250b at muohio.edu> wrote:
>
>> Thanks for your note, Gerald. Your calculations are right on the mark.
>> Sounds like my .080" cap would have enough safety margin for my
>> application.
>> It's a nice Cardwell capacitor, but only about 250pF maximum, which I 
>> would
>> pad for use on 160m. I just need enough capacitance range to tune the
>> entire
>> band, and 250pF should be more than adequate. Carl KM1H suggested a 0.1in
>> custom OEP capacitor, and that's a reasonable approach also. I have a
>> couple
>> of nice OEP caps on hand, though they're not right for this application. 
>> I
>> suppose I could use the .080 cap, but leave enough room for a larger 
>> custom
>> cap if the need arises.
>>
>> 73,
>>
>> Jim W8ZR
>>
>>
>>
>> From: TexasRF at aol.com [mailto:TexasRF at aol.com]
>> Sent: Wednesday, December 05, 2012 1:16 PM
>> To: 4CX250B; Amps at contesting.com
>> Subject: Re: [Amps] Air Variable Spacing Question
>>
>>
>>
>>  Jim, with a little reverse engineering and thinking through this: 2500v 
>> /
>> 1.88A = 1330 / 1.8 = 739 ohms (approx).
>>
>>
>>
>> One would hope for 60% efficiency so power generated = 2500v X 1.88A = 
>> 4700
>> (w input) X .6 = 2820w.
>>
>>
>>
>> The voltage at 739 ohms = sqr( 2820 X 739) = 1444 rms. Peak voltage would
>> be
>> 1444 X 1.414 = 2042 v.
>>
>>
>>
>> If the capacitor has a peak voltage rating of 3200 v then there would be 
>> a
>> safety margin of 3200 - 2042 = 1148 v peak. Or, room for a vswr mishap 
>> that
>> would cause an increase of about 56% of the transformed impedance.
>>
>>
>>
>> While not bullet proof, it seems if you were to take care that the
>> amplifier
>> would always have a reasonable load this would work just fine. It 
>> probably
>> is a good idea to roughly calibrate the tune and load settings vs 
>> frequency
>> to prevent a tuning situation allowing the plate load impedance to rise 
>> to
>> a
>> damaging level.
>>
>>
>>
>> So, in my mind the plate load impedance is very important.
>>
>>
>>
>> If my numbers are off I am sure an eagle eyed reader will catch it!
>>
>>
>>
>> 73,
>>
>> Gerald K5GW
>>
>>
>>
>>
>>
>> In a message dated 12/5/2012 3:03:42 A.M. Central Standard Time,
>> 4cx250b at muohio.edu writes:
>>
>> Hi All,
>>
>> I'm trying to decide which air variable plate tuning cap to use on my
>> forthcoming 160m monoband amplifier. The one I'd like to use has .080"
>> plate
>> spacing, and I've tested it and it works up to 3200 VDC on my tester 
>> before
>> sparking across the gap. My question is whether that's enough of a safety
>> margin to use with 2500V plate voltage on three GU-74Bs? Not that it
>> matters
>> particularly, but the plate impedance of the three tubes is about 740 
>> ohms.
>> There'll be no DC voltage on the cap.
>>
>>
>>
>> I also have several air variables with .075 in spacing, and one with 
>> .140"
>> spacing. The latter I've tested to 6kV, but want to save it for a 
>> different
>> project. In principle, I'd like to use one of the .075" caps for my
>> monobander, because of their convenient size, but I think that's cutting 
>> it
>> a bit close for 2500V. Whaddya think?
>>
>> 73,
>>
>> Jim W8ZR
>>
>> _______________________________________________
>> Amps mailing list
>> Amps at contesting.com
>> http://lists.contesting.com/mailman/listinfo/amps
>>
>> =
>>
>> _______________________________________________
>> Amps mailing list
>> Amps at contesting.com
>> http://lists.contesting.com/mailman/listinfo/amps
>>
> _______________________________________________
> Amps mailing list
> Amps at contesting.com
> http://lists.contesting.com/mailman/listinfo/amps
>
>
> -----
> No virus found in this message.
> Checked by AVG - www.avg.com
> Version: 10.0.1427 / Virus Database: 2634/5446 - Release Date: 12/08/12
>