I was curious about extra shunt capacity to ground from the filament end if
this fat assembly is placed close to chassis. The type 43 has some dielectric
constant which increases the capacitance over air by that factor. The tube must
have a Ck-g of around 40-60 pF (guessing). Of course input resistance is low so
this extra C can be figured into the matching values.
John
K5PRO
On Sep 25, 2022, 10:00 AM, at 10:00 AM, amps-request@contesting.com wrote:
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>Today's Topics:
>
> 1. suggestion/recommendation wanted for a 'tunable' 15 pf
> capacitor on MFJ 989C tuner (A Lawrence Fibich)
> 2. Re: suggestion/recommendation wanted for a 'tunable' 15 pf
> capacitor on MFJ 989C tuner (Steven Katz)
> 3. 10 kw CCS on 6M..using the 3CX-6000A7...Part 5.
> (jim.thom jim.thom@telus.net)
>
>
>----------------------------------------------------------------------
>
>Message: 1
>Date: Sat, 24 Sep 2022 16:24:11 +0000 (UTC)
>From: A Lawrence Fibich <lfibich@sbcglobal.net>
>To: "amps@contesting.com" <amps@contesting.com>
>Subject: [Amps] suggestion/recommendation wanted for a 'tunable' 15 pf
> capacitor on MFJ 989C tuner
>Message-ID: <1984878677.181227.1664036651369@mail.yahoo.com>
>Content-Type: text/plain; charset=UTF-8
>
>There is a tunable ceramic Capacitor listed as 15 pf in these tuners.
>They are on the RF output and provide power for the S Meter. Capacitors
>in the area are rated as 3 KW - I have been unable to find a 'tunable'
>micro size and wonder if simply using a 15pf? 3 KW capacitor would work
>- don't know why a 'tunable' is used and can't find one and unknown
>what voltage would work.? No response from MFJ.? ? Any suggestions
>appreciated.? Apparently with age ? and tuning up an amp destroyed this
>part.?Larry FSacramento CA areaW6EF
>
>------------------------------
>
>Message: 2
>Date: Sat, 24 Sep 2022 17:19:19 +0000
>From: Steven Katz <stevek@jmr.com>
>To: A Lawrence Fibich <lfibich@sbcglobal.net>, "amps@contesting.com"
> <amps@contesting.com>
>Subject: Re: [Amps] suggestion/recommendation wanted for a 'tunable'
> 15 pf capacitor on MFJ 989C tuner
>Message-ID:
>
> <MN2PR16MB4009A9C5D25F08DBF751622BDA509@MN2PR16MB4009.namprd16.prod.outlook.com>
>
>Content-Type: text/plain; charset="utf-8"
>
>Wow.
>
>This capacitor doesn't provide power to anything, and the MFJ-989C
>doesn't have an S meter.
>
>It would not be rated "3kW," as capacitors aren't rated that way at
>all.
>
>It's actually a low voltage variable capacitor used for compensation to
>help SWR meter accuracy. Making it adjustable is a good idea.
>
>It's a very small capacitor on the SWR bridge circuit board and one of
>these shown on this page might be similar:
>https://www.electronicsurplus.com/capacitors/variable-capacitor Even
>at 1500W applied RF power to the tuner, the voltage across that
>capacitor will never be more than about 100V assuming the tuner is
>adjusted for a match so the XMTR side of the bridge will look like
>about 50 Ohms.
>
>If you call MFJ they probably stock this component and it might be easy
>to just buy a direct replacement.
>
>-----Original Message-----
>From: Amps <amps-bounces@contesting.com> On Behalf Of A Lawrence Fibich
>Sent: Saturday, September 24, 2022 11:24 AM
>To: amps@contesting.com
>Subject: [Amps] suggestion/recommendation wanted for a 'tunable' 15 pf
>capacitor on MFJ 989C tuner
>
>There is a tunable ceramic Capacitor listed as 15 pf in these tuners.
>They are on the RF output and provide power for the S Meter. Capacitors
>in the area are rated as 3 KW - I have been unable to find a 'tunable'
>micro size and wonder if simply using a 15pf? 3 KW capacitor would work
>- don't know why a 'tunable' is used and can't find one and unknown
>what voltage would work.? No response from MFJ.? ? Any suggestions
>appreciated.? Apparently with age ? and tuning up an amp destroyed this
>part.?Larry FSacramento CA areaW6EF
>_______________________________________________
>Amps mailing list
>Amps@contesting.com
>http://lists.contesting.com/mailman/listinfo/amps
>
>------------------------------
>
>Message: 3
>Date: Sat, 24 Sep 2022 22:00:50 -0700
>From: "jim.thom jim.thom@telus.net" <jim.thom@telus.net>
>To: amps@contesting.com
>Subject: [Amps] 10 kw CCS on 6M..using the 3CX-6000A7...Part 5.
>Message-ID:
> <CAB4ZMgv1-W8=SRP3C=FDw+N0oEXVBFOYu91OuXK3m6OYHObRTw@mail.gmail.com>
>Content-Type: text/plain; charset="UTF-8"
>
>10 kw CCS on 6M..using the 3CX-6000A7...Part 5.
>https://www.youtube.com/watch?v=EFgPEcMdmyQ
><https://www.youtube.com/watch?v=EFgPEcMdmyQ&fbclid=IwAR2i1mGPEdZpHa88nHgOau-I0nPQAfsm9_PB-Jnt6u2D2qITHfMkN7an4ow>
>Here the very unique method of constructing the filament choke is
>shown.
>Instead of paralleling 2 x identical 40 amp fil chokes..... (made from
>8 ga
>magnet wire on 8" long x .5" type 43 ferrite rods), a new method is
>used.
>The new method uses a string of Fair-rite ...... 'type 43 full flat
>cable
>cores' . These are oval shaped cores, that are 1.53" wide x 1.024" tall
>x
>1.126" long. Inside dimensions of the oval shaped hole are 1.03" wide x
>.51" tall.
>The max size pair of power cables that will fit inside is 1-0 RW 90
>power
>cable. (170 amp CCS, and 600 vac rated). I verified this already months
>ago, and the pair of 1-0 cables just slides in comfortably.
>For this 6M amp, double insulated 4 ga, and fine stranded wire was used
>(600 vac rated). 4 ga wire will easily handle the 79 amps of fil
>current.
>Each bead has a Z of aprx 125 ohms @ 50 mhz. 5 x cores are used which =
>625
>ohms, which is ample, considering the 3CX-6000A7's input Z is 50 ohms.
>Typ
>you want the Z of the fil choke to be quadruple the input Z. (Heath's
>SB-220 used a 9 uh fil choke = 197 ohms of XL @ 3.5 mhz).
>For lower freq operation, more cores can be used.
>The Z of each oval core per Fair-rite is as follows.
>2mhz - 25 ohms
>4 mhz - 30 ohms
>10 mhz - 75 ohms
>21 mhz - 100 ohms
>30 mhz - 115 ohms
>50 mhz - 125 ohms
>For operation down to 160m, a minimum of 8 x cores are used, which
>equates
>to a total length of 9". For larger tubes like the 3CX-10,000A7 /
>15,000A7,
>those tubes have a lower input Z, aprx 32-35 ohms...and a minimum of 6
>x
>cores are required.
>More is better of course. Typ the fil choke is oriented across the
>width of
>the chassis, between the input fil connectors at one end of the rear
>apron...and the tube at the other end. This method works good on typ
>19"/
>24" wide rack setups.
>With this 6M amplifier, the 5 x beads are flipped 90 degs, and the
>length
>to the socket is very short. Fil V is measured at the socket
>(via a pair of RF chokes). The 7.0 vac fil V at the cold end of the fil
>choke will be rectified into 8 vdc for powering the opto-isolator, used
>to
>key the myriad of vac TR relays. Fil V will be controlled via a variac,
>located in lower box #2.
>Fair-rite info.
>https://www.fair-rite.com/.../miscellaneous-suppression.../
><https://www.fair-rite.com/product/miscellaneous-suppression-cores-2643167851/?fbclid=IwAR1fruWjot5OB_h-gGq_XwiSE31jnZhwYBTcwQ3zlu3DcTtLgPkgXcWvXEY>
>
>
>------------------------------
>
>Subject: Digest Footer
>
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>------------------------------
>
>End of Amps Digest, Vol 237, Issue 19
>*************************************
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