I have just gone through rebuilding two SP-600's, neither
is quite perfect yet, but close. I would like to hear the
experiences of others: problems encountered, etc.,
especially with dial calibration. My receivers are a JX-21
or possibly a JX-26 (top cover was missing) and a JX-17. The
JX-21(?) was built about 1955 judging from the dates marked
on some components. It is an R-274C built on a 1954
contract. The JX-17 appears to have been rebuilt at a
military shop some time in its life (all ceramic caps)and
has a date late in 1955 stamped on the inside of the front
panel. I've had both receivers for many years but have
recently decided to get them as close to mint performance as
I can.
I can find no specification on dial accuracy for either
model. I beleive I saw a spec of 0.25% in one Hammarlund ad,
this is not really a very tight spec and both receivers make
it. Should it be better? The design of the main tuning
capacitor is such that its adjustable and I understand that
each capacitor went through a factory adjustment proceedure
to get each section to match specs. Does anyone know
anything further.
BTW, I have visited the usual SP-600 sites on the web. In
particular the "Hammarlund Historian" and Andy Moorer's
site, both of which are quite helpful. I also obtained all
the manuals and othere material available from these sites
and from "BAMA". One of these guys is sittign about 8 feet
from me right now glowing at me:-)
This group seems to be mostly FS and WTB advertising so I
hope this post is still on topic here.


--
---
Richard Knoppow
Los Angeles, CA, USA

Richard,
I performed an electrical restoration on an SP-600 (JX-26)
last summer. The frequency accuracy was poor....WWV at
10 MHz was at 10.2 MHz (approx). What is worse IMO is the
tracking across the bands. The frequency at one end would be high,
but at the other extreme, it'd be low.

I'm sure this can be tuned out. I just haven't tried yet.

I'm in the process of bring back another JX-26 now, so if
you have any specific questions, you can write me off list.

Steve W6SSP

Well, let's see... I've done four of them, to date. Maybe I've been
lucky or something, but I haven't had too much of a problem aligning the
dials. Perhaps my spec is not tight enough? At any rate, two of the
four had tubular, vice disc, capacitors that had to be changed out. The
worst problem, but doable, are those on each of the L/C elements in the
turret and those under the RF box. Replacing the caps on the L/C
elements for the LO may be of great help in dial alignment.

"K3HVG" wrote in message
...
Well, let's see... I've done four of them, to date. Maybe
I've been lucky or something, but I haven't had too much
of a problem aligning the dials. Perhaps my spec is not
tight enough? At any rate, two of the four had tubular,
vice disc, capacitors that had to be changed out. The
worst problem, but doable, are those on each of the L/C
elements in the turret and those under the RF box.
Replacing the caps on the L/C elements for the LO may be
of great help in dial alignment.


My JX-17 had bad caps on the 7.5mc to 14.5mc oscillator
assembly. The problem was extreme instability. I replaced
the bad guy. Since this was a 1% cap of specified value I
built one of the right value from two dipped silver micas in
parallel, measuring it on a bridge. The result was just
about perfect calibration on that band and very good
stability. I may have to change others.
I am aware of he problem with the Sangamo "Black Beauty"
caps. they were all replaced with disc ceramics in my JX-17
but only in the RF deck of the JX-21, or perhaps its a
JX-26. I've replace a number of them that were obviously bad
but there nearly 60 in the receiver and not all are bad.
BTW, these ubicutous caps were originaly marketed by Sangamo
as deluxe quality replacements for wax dipped paper caps.
They are paper impregnated with Mylar in molded resin cases.
I suspect the problem is that the casing is not stable and,
as it drys out, disturbs the connection of the capacitor to
the leads and also lets moisture in causing very high
leakage. Black Beauties were used in a variety of high
quality electronic equipment c.1950s and 1960s. Sangamo also
sold dipped epoxy encapsulated versions of these sold as
"Chocklate Drops". AFAIK, these have proven to be a lot more
reliable.
But back to the calibration problem: I discovred that
molded silvered mica capacitors, once considered to be most
reliable of all, evidently suffer from a similar problem,
i.e., they become unstable with age. One symptom is a rapid
variation of capacitance sometimes called "scintillation"
and that they can change value radically. For instance, the
51uuf caps used to resonate L-34, one of the 4 mhz IF coils,
will change as the receiver heats up throwing off the tuning
of this stage. I changed this cap in both of my receivers. I
found other bad guys in the JX-17 in various places, all
molded silver mica types.
The main tuning capacitor of the SP-600 has stators which
are fastened to the frame with three screws. The stators can
move up and down and also sideways to some degree. The
should be exactly centered but the up and down movement was
evidently used in manufacture to adust the exact value of
each section to the nominal value. I am about to try this on
one of the receivers where I need to remove the RF deck
anyway. The outside plates of the rotor sections are split
but evidently plate bending was NEVER done and should not be
done to calibrate the things. Somewhere, someone probably
has the factory procedures but they do not appear to be on
the web anywhere.
I have a lot of other unanswered questions about these
receivers. So far, even after just a couple of hours I've
found at least some of what I want in this news group, for
which I thank everyone.
I should add that my JX-21 (or maybe JX-26) was bought as
junk at C&H Surplus some 30 years ago. It was very cheap
because it had wires sticking out of it. Someone had
evidently begun to modify it to a JX-17. I removed the
partial modifications and restored the original circuits. I
then did a very large number of small repairs. The RX was
missing the top cover for the capacitor compartment (I've
just recently aquired one) the shield for the crystal switch
(I made one but would like an original) and a couple of
knobs, the RF Gain knob and one of the small Xtal control
knobs. I found knobs enough like the originals to work.
Recently the main filter capacitor gave out and I decided
to really bring the thing to life along with replacing the
cap. I couldn't find an exact replacement but did find one
of the correct physical size but slightly greater
capacitance (not a problem :-) ) but discovered some
additional problem in the coarse of doing this.
The JX-17 was aquired in nearly mint condition many years
ago but was in storage for a long time. That one has come
back to life very well.
I get very frustrated by my lack of time to work on these
guys and the difficulty of obtaining parts even here in the
big city. I have gotten a liberal education about sources in
the last few months. Perhaps I've just gotten old but I am a
bit shocked at the ignorance of younger people about
component level electronics. Oh, well, enough grousing.


--
---
Richard Knoppow
Los Angeles, CA, USA

"Richard Knoppow" wrote in message
ink.net...

[snip]

I am aware of he problem with the Sangamo "Black Beauty"
caps. they were all replaced with disc ceramics in my JX-17
but only in the RF deck of the JX-21, or perhaps its a
JX-26. I've replace a number of them that were obviously bad
but there nearly 60 in the receiver and not all are bad.
BTW, these ubicutous caps were originaly marketed by Sangamo
as deluxe quality replacements for wax dipped paper caps.
They are paper impregnated with Mylar in molded resin cases.
I suspect the problem is that the casing is not stable and,
as it drys out, disturbs the connection of the capacitor to
the leads and also lets moisture in causing very high
leakage.

[snip]

If your capacitors are anything like the oil-filled Sprague Black Beauties,
I'd replace all of them on sight. It might just be my bad luck, but the
oil-filled Black Beauties seem to short even harder than the wax paper caps.
However, if the later paper-mylar Black Beauties are like the early series
of paper-mylar Orange Drops, they should hold up well.

I think the all the oil-filled Black Beauties had one of the wires soldered
into a ferrule and the paper-mylar Black Beauties had both of the leads come
out in the standard way.

The paper-mylar Black Beauties seem much less common than the older oil
filled Black Beauties. As far as I know, paper-mylar was around only in the
late 50s to the late 60s.

Frank Dresser

I'll second what Frank suggests about replacing ALL of the black
beauty caps. I'm doing that now on the SP-600 I'm restoring.
While none were a dead short, most showed some leakage,
about 100K ohms. In many circuits, that won't cause a problem
but in some its a big deal. About 1/3 had cracked cases.

Steve

Steve wrote:
I'll second what Frank suggests about replacing ALL of the black
beauty caps. I'm doing that now on the SP-600 I'm restoring.
While none were a dead short, most showed some leakage,
about 100K ohms. In many circuits, that won't cause a problem
but in some its a big deal. About 1/3 had cracked cases.

Steve

Two things make the Sprague Black Beauty caps a problem,
and both relate to their losing oil.

The cap is molded out of a black plastic, with a small
brass filler tube on the banded end. The capacitors were
filled with mineral oil through this tube, and the lead was
placed in the hole, and crimped. They then sealed the capacitor
by adding a little bit of solder.

So far, so good. Well, when the capacitors are installed, very
often the banded lead is close to the lug that is being soldered,
and it will carry the heat to the solder seal, and to the oil in
the cap. The slight pressure increase in the cap will softly
blow the solder out of the seal joint, and the oil will begin to
seep out of the capacitor. Note: the oil is the dielectric, not the
paper.

Also, most all plastics will shrink over time, and the plastic the
Black Beauties are made from is no exception. When it shrinks, the
leads, and the filler tube do not, and you get a small crack, and a
leak.

If the oil is allowed to seep out, and the moisture is allowed to
seep in, the capacitor will be compromised and become leaky. Also,
without the oil, the WV of the capacitor is lowered, because the oil
is the dielectric. Capacitors that are used near their WV will often
arc over, and become shorted.... with catastrophic results for the
rest of the circuit.

-Chuck

Steve wrote:
I'll second what Frank suggests about replacing ALL of the black
beauty caps. I'm doing that now on the SP-600 I'm restoring.
While none were a dead short, most showed some leakage,
about 100K ohms. In many circuits, that won't cause a problem
but in some its a big deal. About 1/3 had cracked cases.

Steve

Ditto on the Black Beauties, especially the ones with the little brass
tube, they seem to leak like crazy. More on the average than wax
capacitors many decades older.

Also bad news are those pea-green molded caps with the color bands.
Many Trans-Oceanics have around two dozen of those, all leaky.

I havent seen any major problem with postage-stamp or dipped
silver-micas, maybe it was just one manufacturer's kind that is getting
flaky? There is the problem of the silver migrating on silver-micas
with considerable DC voltage across them.

Ancient_Hacker wrote:

Also bad news are those pea-green molded caps with the color bands.
Many Trans-Oceanics have around two dozen of those, all leaky.

I havent seen any major problem with postage-stamp or dipped

There is one variety of capacitor that looks like the silver mica
"postage stamp" type of capacitor with all of the dots, but isn't
a mica at all. It is just a paper capacitor. They are usually
dark brown in color, and fail at about the same rate as normal wax/paper
capacitors.

-Chuck

Black Beauties,
I'd replace all of them on sight.

Kill 'em all. They are junk by now, just like earlier wax/paper caps, for
any serious application.

It takes less time to simply replace one than it does to pull it out, test
it, and either re-install it or replace it.

You won't regret it, and you have nothing to lose. Unless you're one of
those vintage electric guitar nitwits who wants to find an original
"bumblebee" cap or two to provide that tasty "period" sound (i.e.,
distortion resulting from badly leaking capacitors, which certainly wasn't
what the guitar sounded like when new).

Regards,

Phil Nelson
Phil's Old Radios
http://antiqueradio.org/index.html