[Hallicrafters] Hurricane HV connector

[James Liles]

Good evening Paul:

Congratulations on your acquisition.  I'm an avid SR-2000 collector and like 
to gather the serial numbers and owner info for these great radios.

I have not replaced that connector in 35 years but have found it to be 
problematic.  If you should find one, be sure to replace the metal locking 
screws with nylon as the connector has a tendency to develop a static arc 
causing a ticking when HV is enabled.  Can't tell you where to find one but 
would like to head you off at the pass regarding replacing the paper caps. 
Please read the following info which is not directed to you but speaks to 
the capacitors used in the SR-2000 and why certain caps were used and where. 
There are five what look to be paper caps in the SR-2000 but they are not 
paper but high quality poly film made by General Instruments.  Four are 
likely as good today as when they were installed.  The fifth was under rated 
and if it is not defective today, it will be at some time.  That cap is the 
.0022uf TC cap from the suppressor/2nd control grid of the 6GX6 to 
ground --- replace it with a 600v film cap.

Please read the following which is a general service note that I wrote 
several years ago regarding the capacitors used in the SR-2000.  Hope you 
find it interesting.

-----------------------------------------NOTE -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
“There are several old paper capacitors under the chassis, should I replace 
them?”

The answer is absolutely not because they are not paper capacitors but 
expensive very high quality non-inductive film capacitors manufactured by 
General Instruments.  The SR-2000/400/400A/150 transceivers implemented 
poly-film capacitors that resembled paper caps.  They were used in analog 
circuits rather than ceramic capacitors, e.g. the source and sink for the 
balanced modulator, key click filter, and other circuits where linearity and 
stability is of concern.  Their capacity does not vary with applied voltage 
or age as do the popular class 2 (X7R) or class 3 (Z5U) ceramic caps.  The 
capacity of class 2 and class 3 ceramic capacitors begins to increase at 
less than 1vac and by 3vac can be 5% and 10% higher for the class 2 and 3 
respectively.  After 3vac, they begin to drop as the voltage is further 
increased to as little as 50% at the max voltage rating.  The varying 
capacity of ceramic class 2 and class 3 capacitors in the presence of more 
than a fraction of a volt AC will create distortion and is an inappropriate 
choice for analog design.  Every research paper written has substantiated 
this behavior of ceramic class 2 and 3 capacitors.

Ceramic capacitors used in other locations were; the X7R class2 caps to 
bypass cathode, screen, and the plate circuits because their capacity does 
not drop as radically in the presence of DC voltage as the class3 Z5U caps. 
Note, the SR-2000 uses 280v on most plate and 120v on most screen circuits. 
If they had used the Class 3 Z5U, the capacity would have been as much as 
40% lower at 280vdc which in most cases would be inconsequential, however, 
is that what the designer expects --- 60% to 80% of the indicated capacity?

In the final compartment, they used Class 1 and 2 --- no class 3 caps.  The 
coupling from the plate to pi-section is a high level Centralabs class 2 
X5U.  The AC voltage swing through that capacitor is nowhere near that of 
the caps that participate in the circulating current of the tuned circuit, 
making a high voltage class 2 cap an appropriate choice.

For the 3.5Mc and 7Mc caps that are switched in with the tuned circuit, a 
class 1 100pf N750 door knob is used.  Yes, a class 1 cap.  Class 1 caps 
include the C0G, NPO, and temperature compensating caps.  They used a class 
1 cap because the voltage swing is over 2000v in the tuned circuit and the 
capacity in class 1 caps does not vary with applied voltage.  A class 2 or 
class 3 cap would have added unacceptable distortion and harmonic content 
into the final pi-section; remember, the capacity of class 1 caps does not 
vary with applied voltage.

The 50 ohm, antenna side of the pi section sees approximately a 225v swing 
with a good match and maybe 400v with a poor SWR.  Here they use the high 
level, high voltage X5U Class 2 cap, again because the voltage swing as 
compared to the 5000v rating of the cap is insignificant.

Do not arbitrarily grab a ceramic capacitor from your stock to replace a 
paper or what looks like a paper capacitor thinking it has to be the right 
choice.

Bypassing a screen, or plate rf cold side with a class 2 or 3 ceramic cap is 
ok because there is no voltage swing to speak of as the cap provides a low 
impedance path to ground for RF.  One caveat, a .01uf Z5U 400v used as a 
bypass for a circuit that has 280vdc will likely result in a .006uf to.008uf 
capacitor, not .01uf.  The X7R will vary far in a way less than the Z5U.  If 
that satisfies the design criteria all is good.  You will NOT find a class 2 
or 3 cap used in a tuned circuit for all of the above reasons.

A common example of paper capacitor terror is the replacement of the band 
pass caps with ceramic in the 50kc I.F. systems e.g. the SX-100.  Bad 
choice, use film.

Polypropylene caps do not have the frailties inherent to ceramic caps.  The 
capacity varies insignificantly with voltage and they do not age like the 
class 2 and 3 ceramic caps.  The notion that the polypropylene dielectric is 
lossy at high frequency is not what you think or have been told.  The 
manufactures data sheets for polypropylene caps specifically state that they 
are non-inductive and can be used to their self-resonant frequency.  The 
inductance that they present is close to that of a straight length of wire. 
A one inch length of #22 wire exhibits about 18nh of inductance.  If you 
short the leads of a capacitor using a 1/8 inch wide flat copper strap to 
minimize the connection inductance on a .001uf film cap, it is self-resonant 
at approximately 65MC.  This represents approximately 6.0nh ---- the total 
inductance of a 1/3rd inch length of #22 wire.  Several .001uf ceramic caps 
shorted in the same manner are also series resonant at approximately 65Mc. 
Measuring the Q at 65Mc for both gives the polypropylene caps a 130/100 
advantage over the ceramic caps.  The polypropylene dielectric outperforms 
the ceramic class 2 and class 3 capacitors regarding stability and Q to well 
above their series resonant frequency where BOTH, the ceramic and film caps 
become inductors.  A 500pf polypropylene cap is series resonant at 
approximately 105Mc and continues to display a higher Q than ceramic caps.

Here is an interesting story.  Everyone has heard about the carbon dating of 
some object.  We also know that the resistances of vintage carbon 
composition resistors are universally quite high.  What we tend not to know 
is that ceramic capacitors age as well.  The class 2  X7R age at 
approximately 2% per decade and the class 3 Z5U approximately 5% per decade. 
Don’t believe this?  Clip a cap out of an SR-2000/400/400A or any vintage 
radio and measure the capacity.  You will find them down from 10% to 25%+ 
depending on the age and class.  Check your inventory.  Take it a step 
further and restore them to their original state.  Place them in a coffee 
cup and bake them at 300 degrees for 1.5 hours, let them cool for 24 hours 
and re-measure.  The crystalline structure is now recovered and their values 
are as new.  One caveat, the aging process begins again.

Note the Class 1 NPO/C0G or temperature compensating ceramic caps do not 
display varying capacity with applied voltage or the aging problem as do the 
class 1 and class 2 ceramic caps.

Seems to require a million words to express a concept and it’s easy to warp 
the meaning of the written statement as you have read in the frequent 
diatribes on this and other reflectors.  The fundamental reason for this 
post is the flawed notion that any time you find a tubular capacitor in a 
vintage radio, replace it with a ceramic cap ---- careful what you wish for.
--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
I am currently four to six weeks from the completion of an SR-2000 
restoration.  If the above statements have generated contradictions, please 
read any of the dozens of research papers regarding ceramic capacitors and 
if necessary I’ll record a video that demonstrates the instruments, setup, 
procedures, and results to verify the above information when I finish the 
restoration project.

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Paul, Hope this is useful and again congratulations on your radio.  Please 
let me know as you bring the radio up how you like it. 
Kindest regards Jim K9AXN

-------------------- ORIGINAL NOTE --------------------------------

Message: 1
Date: Sun, 29 May 2011 12:26:47 -0400
From: Paul W4QG <w4qg at bellsouth.net>
Subject: [Hallicrafters] Hurricane HV Connector
To: Hallicrafters at mailman.qth.net
Message-ID: <4DE273C7.8020508 at bellsouth.net>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed

Hello All,

I just acquired a Hurricane with matching power supply. I will be
rebuilding the supply as well as going through the standard stuff with
the RF deck (paper caps, checking resistors, cleaning sockets etc...)

The radio/ps looks to be complete and original with the exception that
the high voltage connector has been removed from the end of the power
supply cable. I believe it is J5 Hallicrafters P/N 035-000095.

Any guru's on the list happen to have a source for this connector?

Any help would be appreciated.

73,
Paul W4QG