[Heath] Heath Digest, Vol 94, Issue 9

[ChrisIwata]

Wow, you came in pretty close.  I'm guessing, the hardest part for 
accuracy was to measure the thickness of the wafer.

The IF cans on the AR-2 have different part numbers (52-4 & 52-5), but 
they are pretty much the same.

Chris, KL7DM

On 10/21/2018 9:55 AM, Al Skierkiewicz wrote:
> Chris, both of the i.f. cans in the AR3 are the same part number.  To
> calculate the capacitance, I simply measured the dimensions of the screened
> silver areas, subtracting for the circular area and then pulled out the
> reference books on calculating capacitance based on the thickness of the
> mica sheet.  I calculated the larger area to be 0.086238 in.sq. and the
> smaller to be 0.0689 in.sq.
>  From the Handbook C (pf)=.224((dielectric constant x area)/spacing between
> plates)  I chose 5.4 for the dielectric constant of mica and using a
> calipers, I measured the thickness of the sheet at 0.001 in.  So C=.224((5.4
> x .08638)/.001)=104.3pf for the larger cap and substituting 0.0689 I
> calculated 83pf for the smaller cap.
> Al
>
>
>
> -----Original Message-----
> From: Heath [mailto:heath-bounces at puck.nether.net] On Behalf Of
> heath-request at puck.nether.net
> Sent: Sunday, October 21, 2018 11:00 AM
> To:heath at puck.nether.net
> Subject: Heath Digest, Vol 94, Issue 9
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>     1. Re: Heath Digest, Vol 94, Issue 7 (ChrisIwata)
>
>
> ----------------------------------------------------------------------
>
> Message: 1
> Date: Sat, 20 Oct 2018 17:36:46 -0700
> From: ChrisIwata<chrisiwata at aol.com>
> To:heath at puck.nether.net
> Subject: Re: [Heath] Heath Digest, Vol 94, Issue 7
> Message-ID:<5BCBCA1E.60807 at aol.com>
> Content-Type: text/plain; charset=windows-1252; format=flowed
>
>
> Good result!
>
> My AR-2 had the same problem with the IF cans.
>
> Calculating the capacitance from the surface area and the width of the mica
> wafer must have been hard:  How did you do the measurements?
>
> For those who don't have an inductance meter to measure the coils with the
> internal cap disabled,  the value for the caps is around 110pF.  It will be
> slightly different for primary vs secondary winding, and 1st vs 2nd IF can.
>
> You might be able to pinpoint which cap(s) is bad by wiggling each IF can
> solder lug successively.  Do this with the radio ON and an insulated wand.
> The mica wafer is physically attached to the solder lug.  Anyway, that's
> what worked for me.  Thus, I didn't have to replace all 4 caps.
>
> Chris, KL7DM
>
> On 10/20/2018 1:31 PM, Al Skierkiewicz wrote:
>> Guys,
>> I have just finished restoring an AR-3.  It was a labor of love as I
>> my first ham receiver AR-3.  I had purchased it used for $15 from
>> George at the Radio TV Lab in Chicago.  I saw this one at the hamfest
>> in Oak Creek, Wisc for $25 and just wanted to get it going.  My cap
>> was not frozen but very stiff.  I just shot some Lubriplate white
>> grease into the ball bearings that make up the reduction.  I waited
>> for a day and just started moving the shaft until the grease got
> distributed.  Worked wonders.
>> I had more problems with the fact that the kit wasn't fully correctly
>> wired and that the silver mica caps in the i.f. transformers were all
> noisy.
>> (Thunder syndrome)  If you tap on the cans and you hear tons of
>> crackling and thunder, then you have the same problem.  I removed the
>> mica wafers and replaced the caps with dipped silver micas.  I
>> calculated the values from the area of the mica that was plated with
>> silver.  The fact that there were wiring errors meant that the radio
>> had never been aligned.  A RF signal generator is kind of necessary
>> for alignment of this box.  Although I got it working, I also bought a
>> Q multiplier that wouldn't work at all.  Turns out, that the i.f. was
>> 50kHz low.  Once I got everything correctly tuned, the Q mult worked great
> as well.
>> Al
>> WB9UVJ
>>
>>
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