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

[James Liles]

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