[Hallicrafters] Orande dip, yellow tubular, and disc ceramic capacitors

[Peter Bertini]

Hi Jim

My only concern would be the bypassing effectiveness of most caps at UHF or
VHF frequencies. This is usually not an issue at HF, but for those instances
where high gain tubes are used (6EH7,  etc.) a .01uF disc is probably going
to be much more effective at preventing unwanted parasitics in an RF or IF
stage. I've notice that most transmitters only use disc ceramics for
bypassing screens, etc.
Temperature stability usually isn't a big issue for bypassing. Hammarlund
used large value discs for audio coupling--but I wouldn't because of the
Piezo electric issues.

73

Pete k1zjh

On Fri, Dec 31, 2010 at 1:01 PM, James Liles <james.liles at comcast.net>wrote:

>   Hi Pete:
> Both the Orange dip and yellow tubular come in polyester and
> polypropylene.  The polypropylene range from < .001uf to < .01uf and are
> designed for R.F. applications as are the class 1 ceramic caps.  The
> polyester and class 2, 3, and 4 ceramic are designed for lower frequencies.
> Usually come in values  => .01uf.
>
> For my peace of mind, I use only NPO or G0D disc ceramic caps for bypass
> ops, the others or those with no attribute descriptors are unpredictable.  I
> also would use nothing but disc ceramic caps to preserve the historic nature
> of the radios that I work with but it’s a bit difficult to find reasonable
> NPO caps.
>
> Thanks for the response Pete, good to hear from you.
>
> Kindest regards Jim K9AXN
>
>
>
>  *From:* Peter Bertini <radioconnection at gmail.com>
> *Sent:* Friday, December 31, 2010 9:34 AM
> *To:* James Liles <james.liles at comcast.net>
> *Cc:* hallicrafters at mailman.qth.net
> *Subject:* Re: [Hallicrafters] Orande dip, yellow tubular, and disc
> ceramic capacitors
>
>   Jim
>
> You might also consider that the "Orange Drops" come in different flavors.
> Both polyester and propylene dielectrics were used. Specs and prices are a
> bit different.
>
> I'd still opt for disc caps for RF bypassing apps.
>
> Pete
>
>
> On Fri, Dec 31, 2010 at 11:55 AM, James Liles <james.liles at comcast.net>wrote:
>
>> We’ve been using all of the above capacitors in restoration for years and
>> haven’t had a situation where one appeared better than the other.  My
>> preference is the yellow tubular caps only because they are pleasing to the
>> eye.  The following information represents the result of testing the
>> components to enable practical, unbiased choices.  Assume measurement
>> accuracy to be +/- 5% to 10% with consideration for component variations,
>> lead lengths, and lead form.
>>
>> The .01 mfd capacitors:
>> Ceramic disc ------  Self resonant at an average 8.0Mc
>> Orange drop ------- Self resonant at  an average 10.0Mc
>> Yellow tubular ----- Self resonant at  an average 9.0Mc
>>
>> The .001 mfd capacitors
>> Ceramic disc -----Self resonant at an average 29.0Mc
>> Orange drop ----- Self resonant at an average 26.0Mc
>> Yellow tubular --- Self resonant at an average 24.0Mc
>>
>> See no reason to measure the ESR because the frequencies that these
>> components service expect a minimum resistance of approximately 4 to 6 ohms
>> which is very likely above the ESR.
>>
>> Things to consider.  Ceramic disc capacitors come in class 1, 2, 3, and
>> 4.  Class 1 disc ceramic caps are the only group recommended for use at 30Mc
>> +.  They can be identified by the NPO or C0G stamp.  The others can be
>> unpredictable, lossy, and because the ceramic disc has Piezo properties can
>> go off and do their own thing.
>>
>> The Orange dip and yellow tubular caps are not made like the old paper
>> tubular caps.  The connection to the old paper caps was at the end of the
>> roll of each plate whereas the new cap connections are to the entire edge of
>> each roll significantly reducing the inductive properties.  The inductance
>> including 1” leads for the Yellow tubular and Orange dip is somewhere around
>> .04 uh of which a good part is lead length and shape.
>>
>> Another thing to consider is that self resonance in these caps is SERIES
>> not parallel.  That means that as you move up the frequency scale to self
>> resonance, the reactance drops to 0 ohms leaving only the resistance of the
>> conductors.  From that point, say 24Mc using the .001 uf yellow tubular cap,
>> as the frequency is increased, reactance begins to increase but will be
>> inductive in nature.  The apparent inductive reactance at resonance will
>> begin at 0 and increase not exceeding the original capacitive reactance
>> until well above 30mc.  With this in mind, any of the .001 uf caps can be
>> used at 30Mc for coupling or bypass operation with no measurable reason to
>> choose except personal preference.
>>
>> If you are interested in the technique used to measure self resonance in
>> these caps drop a note ---- needs a schematic to explain.
>>
>> Hope this helps to choose the appropriate cap when you reach for the box
>> of parts.
>>
>> Kindest regards Jim K9AXN
>>
>>
>>
>>
>>
>>
>>
>>
>>
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