[Milsurplus] 6AQ5 Tank

[J. Forster]

Check the OP. He was questioning the huge C to resonate the same inductor,
IMO.

The best answer is to up the L and C by about 6x each.

Best,

-John

==============


> 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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>>>>
>>>>
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>>>
>>>
>>
>>
>>
>
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