Why not a 1:4 un-un and a 200 ohm swamping with a 3db pad between the
exciter and the un-un
Don W4DNR
Quoting Carl <km1h@jeremy.mv.com>:
> 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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>
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