[Hallicrafters] Black Beauty capacitors Beware

[Jim Liles]

Hi Greg,

Exactly!  They were as good as film and legions better than ceramic.  That’s why you still see paper defined on the schematics not ceramic caps.

I still would replace the paper because as they dry out or begin to leak the Q goes to the devil.  Won’t effect the .5Kc position because it doesn’t use them but when you use the higher band widths, especially the 1Kc, they will widen because of the denigration of the Q.  May not be obvious but if you sweep that filter system it’s obvious.  The band center skew jumps out at you when using the ceramic caps.

In any case the paper at their worst will out perform ceramic unless they are shorted or open.

One measure is, you should be able to tune in an SSB signal in the 5Kc position and dial right down through 1Kc and still clearly copy that conversation without touching the BFO and tuning to peak for clarity.  The best definition that describes what you have to do when incorrect caps are installed is “You have to be a human I.F. shift mechanism”  You have to tune an SSB signal then tune slightly back and fourth for peak strength while adjusting the BFO for clarity.  You don’t want to go there, let the radio do it for you. 

One thing that I didn’t mention is the 390 ohm resistor will be well above 420 ohms.  Those resistors are very critical.  Get it right on or 5% below not above or the 5Kc position will droop excessively.

Kindest regards Jim K9AXN







-----Original Message----- 
From: Greg Gore 
Sent: Saturday, March 07, 2015 8:15 AM 
To: hallicrafterssr2000 at k9axn.com ; hallicrafters at mailman.qth.net 
Subject: Re: [Hallicrafters] Black Beauty capacitors Beware 

Thanks Jim, 

Is this why you don't see much improvement replacing black beauties in the selectivity circuits of Hallicrafters 50KC systems? The capacitance of the molded capacitors has not changed much over the years while leakage at high voltages is almost always excessive and dangerous.

Regards, Greg



-----Original Message-----
From: Jim Liles <hallicrafterssr2000 at k9axn.com>
To: hallicrafters <hallicrafters at mailman.qth.net>
Sent: Fri, Mar 6, 2015 12:26 pm
Subject: [Hallicrafters] Black Beauty capacitors Beware


The ER article regarding Black Beauty capacitors has an assumption that needs attention. All of the 50 Kc I.F. systems in the Hallicrafters receivers beginning from day 1 used Paper or Plastic film capacitors except one, the flagship SX-115 which used Ceramic disc Z5U capacitors. This was a disaster that only becomes worse year after year. The selectivity circuits in the SX-117 using film handily outperform the SX-115. We talked about the reason for this in an earlier post so won’t repeat all here. I have never seen a schematic drawn by the Hallicrafters Co. that referred to a film or plastic capacitor, just Paper, even though they switched to plastic film well before the SX-100 was built. The reference to paper is to assure that Ceramic is NOT used in the noted circuit. You will find paper and ceramic of the same value in these radios so why distinguish? There is a notion that the paper capacitors had some peculiar property when used in the 50 Kc I.F. system or any other circuit that would enhance the performance of the radio. The purpose of the capacitors in the 50 Kc selectivity circuits is but one. Move the band pass center away from the 50Kc carrier to a point where widening the band pass with resistors would not require shifting the BFO. Nothing more. In the SX-115, using Ceramic Z5U capacitors resulted in shifting the band pass centers to anywhere but where they belong and it gets worse over time. Why the problem with the SX-115? Find out for yourself. Measure the capacitors. The .01uf caps will be approximately .0082uf. That’s because Ceramic disc class 3 capacitors loose 5% of their capacity every decade. Take it a step further. The Z5U has a +20 –56 temperature coefficient. If you heat the caps to 20 degrees C over room temperature which is the expected temp deviation in the radio, the capacitor will end up at about .0072uf to .0074uf. The paper or film will be .01uf. Result, the band passes are significantly misplaced. Alas, lost in space looking for GPS coordinates! In audio circuits the notion that paper has some magic and mirrors in comparison to film is campfire talk. In comparison to ceramic class 2 and 3, it is no longer campfire talk but irrefutable fact. Kindest regards Jim K9AXN ______________________________________________________________ Hallicrafters mailing list Home: http://mailman.qth.net/mailman/listinfo/hallicrafters Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Hallicrafters at mailman.qth.net? List Administrator: Duane Fischer, W8DBF ** For Assistance: dfischer at usol.com ** This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html