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

[Carl]

----- Original Message ----- 
From: "James Liles" <james.liles at comcast.net>
To: <hallicrafters at mailman.qth.net>
Sent: Friday, December 31, 2010 11:55 AM
Subject: [Hallicrafters] Orande dip, yellow tubular,and disc ceramic 
capacitors


> 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


The self resonances you measured appear way off.


>
> 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.


 ESR measurements is for electrolytics.


>
> 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.


Wow, Ive heard tall tales before and this is right up there.

1. Any disc can be used for general purpose bypassing as it is not frequency 
dependent. Going by your pronouncement even a .01 to .05 uF cathode, screen 
or plate bypass has to be NPO in a SX-42/43/62/71/73 and others that dare to 
go above 30 MHz.
2. NPO is fine for frequency determining circuits, not needed elsewhere in a 
general purpose radio.
3. The piezo effect is something dreamed up by the audio end of the world. 
There may be some truth to it when used in a big amp but normal folk have 
been using them in manufacturing since the 50's without going off and doing 
their own thing as you so elequoently stated.
4. Except for speciality caps there are no commonly avalable and economical 
.001 or higher NPO discs in the above 200V category making them generally 
useless in tube radios.


>
> 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.



Thats rather significant at 10M. If they were so good you would see them in 
general RF use...like discs.

In some 30's era consumer type radios the old paper cap foil was used to act 
as a shield between input and output. When modern caps replaced them the 
stage takes off requiring parasitic suppression techniques. The more stable 
and easier to tame are the ones with disc ceramics. Film type are very 
critical of placement plus require parasitic suppression and many of the 
radios already had warnings about lead dress.


>
> 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.



I'll remember that the next time I need a cap for a tuned input or RF plate 
blocking in an amp. Gee, I wonder how long an Orange Dud would last. Why not 
try it in a SR-2000?

Just about any HB of the late 60's forward lists the self resonant frequency 
of various discaps. The .001 is around 50 MHz with 1/2" leads, 18 MHz for a 
.0047 and 13 MHz for a .01. Construction hasnt changed so Ive no idea where 
you are generating your info from.

You might also want to dry an Orange Dud on a Q Meter.


>
> If you are interested in the technique used to measure self resonance in 
> these caps drop a note ---- needs a schematic to explain.

You dont need a schematic to use a GDO which gets very close. I suppose I 
can fire up the HP Q Meter or VNA tomorrow if I really care about that sort 
of accuracy but not on New Years Eve. As soon as my 3 sons get back from the 
Celtics game were heading out with the rest of the family.


>
> Hope this helps to choose the appropriate cap when you reach for the box 
> of parts.
>
> Kindest regards Jim K9AXN


I hope others seriously consider what you posted before chosing and dont 
foolishly spend money.

Carl
KM1H


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