That 1000 Ohms is for 1.5W of drive.
Carl
KM1H
----- Original Message -----
From: "pfizenmayer" <pfizenmayer2@q.com>
To: "Carl" <km1h@jeremy.mv.com>; "Bill, W6WRT" <dezrat1242@yahoo.com>;
<amps@contesting.com>
Sent: Friday, August 10, 2012 11:48 AM
Subject: Re: [Amps] 4CX1500B project - swamped grid
> Thought he was talking about no grid current - but even with grid current
> what other sort of input network would be any better over the swing with
> regard to match? I would think , without doing the detailed calcs , that
> 50 ohm shunt is pretty well gonna hide any change in grid input impedance
> as far as match over the cycle is concerned. One EIMAC $CX1500B data sheet
> I saw suggests 1000 ohms swamping if gonna run into grid current so 50
> ohms should surely eliminate that issue ????
>
> 73 Hank K7HP
>
>
>
>
> ----- Original Message -----
> From: "Carl" <km1h@jeremy.mv.com>
> To: "pfizenmayer" <pfizenmayer2@q.com>; "Bill, W6WRT"
> <dezrat1242@yahoo.com>; <amps@contesting.com>
> Sent: Friday, August 10, 2012 5:49 AM
> Subject: Re: [Amps] 4CX1500B project - swamped grid
>
>
>> Id be concerned at how well the match holds over the full input cycle.
>>
>> Carl
>> KM1H
>>
>>
>> ----- Original Message -----
>> From: "pfizenmayer" <pfizenmayer2@q.com>
>> To: "Bill, W6WRT" <dezrat1242@yahoo.com>; <amps@contesting.com>
>> Sent: Friday, August 10, 2012 1:12 AM
>> Subject: Re: [Amps] 4CX1500B project - swamped grid
>>
>>
>>>I looked at 50 ohms shunted by 80 pfd -- 2 - 30 mhz - --- series L of 271
>>> nhy and shunt C of 71.5 pfd at input gives better than 23 db return loss
>>> from 2 to 30 mhz.
>>>
>>> I was wondering why Alpha did not look at that for the 8410 but the
>>> 4CX1000
>>> is 77 to 90 pfd input so a pair is something like 2X the 4CX1500 or
>>> about
>>> 160 pfd.
>>>
>>> If I add another LC section to the 4CX1500 I get virtually no
>>> improvement -
>>> but if I add some series L to the 50 ohm shunting resistor it gets
>>> incredibly good , better than 30 db return loss 2 to 30 mhz.
>>>
>>> The network becomes the 80 pfd tube , 50 ohms with 53.7 nhy in series
>>> with
>>> it to ground and then the L net of 245 nhy series L , 59 pfd to ground
>>> at
>>> input .
>>>
>>> One would want to be a bit careful about lifting the grid off the 50
>>> ohms
>>> too much but 53 nhy may be Ok . Actually I suspect you might want to use
>>> a
>>> pair of 100 ohm 50 watters .
>>>
>>>
>>> 73 Hank K7HP
>>> ----- Original Message -----
>>> From: "Bill, W6WRT" <dezrat1242@yahoo.com>
>>> To: <amps@contesting.com>
>>> Sent: Wednesday, August 08, 2012 11:15 PM
>>> Subject: Re: [Amps] 4CX1500B project
>>>
>>>
>>> ORIGINAL MESSAGE:
>>> On Wed, 08 Aug 2012 21:50:42 -0700, you wrote:
>>>
>>>>
>>>>Because as I understand it, the tubes are essentially the same except
>>>>for a
>>>>slightly
>>>>larger anode cooler which accounts for the additional dissipation. The
>>>>parameters for
>>>>typical operation on the 4CX1500B data sheet are based on a load line
>>>>closer to class A
>>>>than those on the 1000 sheet -- they call for lower bias and screen
>>>>voltage
>>>>and more
>>>>idling current. The intention is to produce much less IMD. Since I'm a
>>>>CW
>>>>operator, I
>>>>would rather have full legal output than reduce IMD.
>>>
>>> REPLY:
>>> Ok, but "typical operation" is just a starting point. Don't feel bound
>>> by
>>> that.
>>>
>>> If you want max output and max gain, put the screen voltage close to max
>>> (400
>>> VDC) and set the bias for a small amount of idle current, say 100 mA or
>>> less.
>>>
>>> The higher the screen voltage, the higher the gain. The lower the idle
>>> current,
>>> the higher the efficiency but the higher the IMD too. For CW, as you
>>> imply,
>>> IMD
>>> doesn't matter.
>>>
>>> One thing to be aware of when using swamped grid design: This tube has
>>> a
>>> fairly
>>> high input capacitance in grounded cathode mode, aprox 80 pF. You will
>>> no
>>> doubt
>>> have an SWR problem on the higher bands so you may have to switch in a
>>> parallel
>>> resonant circuit to compensate. Or if your transceiver has a good
>>> antenna
>>> tuner,
>>> or if you have an external one, that may take care of it. Just something
>>> to
>>> keep
>>> in mind when you're doing the layout. Leave room for the parallel
>>> resonant
>>> circuit and switch if you need it. Better yet, breadboard it first and
>>> check
>>> the
>>> SWR with an MFJ SWR analyzer or the equivalent.
>>>
>>> 73, Bill W6WRT
>>>
>>>
>>> _______________________________________________
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>>> Amps@contesting.com
>>> http://lists.contesting.com/mailman/listinfo/amps
>>>
>>>
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>>
>>
>
>
>
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