[ARC5] [Milsurplus] 6AQ5 Tank

[J. Forster]

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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