[Hallicrafters] Hurricane HV connector |
James Liles
james.liles at comcast.net
Mon May 30 22:32:06 EDT 2011
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.
------------------------------------
END -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
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
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