[ARC5] [Milsurplus] 6AQ5 Tank

[jmfranke]

But he wanted the Xc to be constant! To do that you have to increase C by a 
factor of 6. And if you increase C by 6 and L by 6, you get the factor of 
36.

John  WA4WDL

--------------------------------------------------
From: "J. Forster" <jfor at quik.com>
Sent: Wednesday, July 20, 2011 7:27 PM
To: "jmfranke" <jmfranke at cox.net>
Cc: "David Stinson" <arc5 at ix.netcom.com>; "ARC-5 List" 
<arc5 at mailman.qth.net>; <milsurplus at mailman.qth.net>
Subject: Re: [Milsurplus] 6AQ5 Tank

> If you want to change the frequency by a factor of 6, you need to change
> the LC product by 36. If the L stays constant, you have to increase the C
> by 36x -->  36 * 40pF = 1440 pF.
>
> Best,
>
> -John
>
> ================
>
>
>> John,
>>
>> Yes, you are correct about the coil. I was working the capacitance issue
>> and
>> arrived at the same number as you for the capacitor. And, having changed
>> the
>> capacitance by a factor of 6 the coil inductance would have to increase 
>> by
>> a
>> factor of 6 for resonance. Working on maintaining the same reactance
>> values
>> for the coil and/or the capacitor should and does bring us both to the
>> same
>> point. Ignoring any change in resistive elements, Q would be maintained 
>> by
>> maintaining the same reactance values as the frequency is changed.
>>
>> John  WA4WDL
>>
>> --------------------------------------------------
>> From: "J. Forster" <jfor at quik.com>
>> Sent: Wednesday, July 20, 2011 7:04 PM
>> To: "David Stinson" <arc5 at ix.netcom.com>
>> Cc: "ARC-5 List" <arc5 at mailman.qth.net>; <milsurplus at mailman.qth.net>
>> Subject: Re: [Milsurplus] 6AQ5 Tank
>>
>>>> Ok all you smart people-
>>>> I'm looking at a 6AQ5 Pierce crystal oscillator/tripler
>>>> with a plate tank circuit which outputs at 24 MC.
>>>> The plate tank capacitor is 40 pFd.
>>>> The capacitive reactance at 24 MC is only 166 ohms.
>>>
>>> You have to multiply by the Q. If the Q=100, it will look like 16.6K
>>>
>>>> This seems low for a tube tank.  Output capac.
>>>> of 6AQ5  is 6 pFd,  so that doesn't change the picture much.
>>>
>>> Agreed.
>>>
>>>> I was looking at changing the tank to output at 3.9 MC,
>>>> but if Xc = 166 ohms is correct, the tank cap
>>>> at 3.9 MC would be 6.7 uFd.  That can't be right.
>>>
>>> Let's see:
>>>
>>> The frequency scales as the SQ. RT. of LC
>>>
>>> 24 MHz / 3.9 MHz = about 6, so the C needs to be 6*6 *40 pF = 6*240 =
>>> 1440
>>> pF.
>>>
>>> This is probably still too large. I'd increase the number of turns on
>>> the
>>> coil by about 6 and the C to about 240 pF.
>>>
>>> Best,
>>>
>>> -John
>>>
>>> ================
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>>> What's up with this?
>>>>
>>>>
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>>
>>
>
>
>