|
Finding the RAZ-1 -
I first saw RAZ-1 sn: 65 in 1997 at the Galena, Nevada home of W3ON,
John Ridgway. It was setting next to the SX-28 John was going to sell me (if I
could lift it off of the table,...which I did.) I asked John if he wanted to
also sell the
RAZ-1, to which he replied, "You wouldn't take a longwave receiver away
from an old Navy radioman, would you?" John was 85 years old and in
the process of was moving back to
Maryland. Over the next month, John sold me a National SW-3 receiver and
a most of his test equipment but he held onto the RAZ-1. We casually and occasionally remained in contact after his
move. John lived to the age of 93, becoming an SK in January 2006.
To my surprise, in the summer of 2006, I got a 'phone call from a
Maryland
estate agent who said that they had found a letter among John's papers
that stated that he wanted his radios and radio parts to be sent to the
"Radio Museum in Virginia City, Nevada." The agent was calling me to see
if I really wanted any of "this junk." I told them I did. The estate
paid to ship the parts and equipment back out west. The shipping of the
22 boxes was spaced out over about a six week period. In the 21st box
was the RAZ-1. Shipping had caused one small problem, one of the largest
coils had broken from its mount. The large buss wiring had kept it in
place and all that was required was to glue the mount back together and
screw the coil form back in place. I acquired the correct shock mounts
from N7ID. I did have to replace the filter capacitors in the rectifier
power unit
for quiet reception.
Circuit Description:
CRM-50092 Pre-Selector -
The antenna input has a spark gap, a 100KΩ shunt to ground and is C-coupled using a
10pf capacitor to the input coils. There are four coils that are band
switch-selected (BS) to connect as a parallel LC that is tuned with the tuning condenser and
connected to the 6SG7 grid. RF Gain is controlled by varying the cathode
to -AB (chassis) resistance utilizing a 250Ω in series with the 10KΩ variable R.
+90vdc is connected to the screen and through a 10KΩ resistor to the
plate. The output is coupled with a series LC filter to the antenna output
terminal.
CRM-20096 - Rectifier
Power Unit - The power unit uses a 5W4 as a rectifier
tube. The power transformer secondary windings supply 6.3vac 3A, 5vac 3A
and a HV winding for the +90vdc and +22vdc. The filtering is
accomplished using a Pi-filter followed by a RC filter. Three 24mfd
electrolytic capacitors are used and the RC resistor value is 1500Ω
at 5W. The +22vdc is derived from the +90vdc using a series divider with a 5000Ω
5W and a 1500Ω 5W resistors.
CRM-46092 - Radio Receiver - The antenna input has
a spark gap, a 100KΩ shunt to ground and has an air variable C (Coupling) in series
with the Antenna coils. The four BS-selected Antenna coils are parallel LC tuned
using the Tuning condenser. The Antenna coils EM couple to the BS-selected RF grid
input coils and are parallel LC tuned using the Tuning condenser. The
Trimmer is an air variable to ground on the RF grid for exactly matching
the Antenna coil LC to the RF grid coil LC. The RF amplifier tube gain
is controlled by varying the cathode bias voltage (+22vdc) using a 750KΩ
potentiometer and a 1500Ω cathode resistor. RF amplifier plate is
routed through BS-selected tuned LC plate coils that are tuned using the Tuning
condenser. The RF output is C-coupled to the grid of the Detector tube.
The Regeneration control uses the +22vdc to provide a variable Detector
screen voltage using a 750KΩ potentiometer. Four BS-selected Tickler coils
have the Detector plate voltage routed through them to provide detector
regeneration the level being dependent on the screen voltage adjustment
(Regeneration.) The Detector plate is C-coupled to the 1st AF Amplifier
tube grid. The 1st AF Amplifier screen is +22vdc and the plate is
+90vdc. The 1st AF plate is C-coupled to the #1 phone jack and to the AF
Output tube grid. The AF Output screen is +90vdc and the plate is routed
through #2 phone jack and then to the +90vdc. This allows the 'phones to
be in series between the B+ and the AF Output tube plate when #2 phone
jack is used and also why Hi-Z 'phones must be used. The "ON-OFF"
switch connects and disconnects the +6, +22 and +90 terminals from the
radio circuitry.
| Performance - The RAZ-1 can be very sensitive and almost any station on LW
can be tuned in, however the very best performance (for me,
anyway) was using a homemade remotely-tuned loop antenna. I've logged a lot of NDBs with this RAZ-1 using
the homemade four foot
square, remotely-tuned loop antenna. Of course, most of this RAZ-1 and
loop listening
was over fifteen years ago when the "NDB landscape" was heavily
populated with lots of signals - quite different from today's 2022 sparse, desert-like
signal landscape where more and more NDBs are decommissioned every month. The
lack of any kind of noise limiter or output limiter is sometimes a problem if
local noise is strong but most loop antennas will greatly reduce the noise (both
natural and manmade.) To further reduce noise to an absolute minimum,
the Coupling should be set very close to zero since that will help
reduce bandwidth. The Regeneration should be right on the oscillation
point (autodyne detection) as this provides a heterodyne for NDB
detection and also will result in the best selectivity.
Then the received signals are peaked by tuning the the Pre-selector to
the received frequency. |
2007 photo showing RAZ-1 SN: 65 set
up for operation |
| The Pre-selector will appreciably amplify the incoming RF
signal and also provides more selectivity. The Trimmer control matches the RF output to the tuned detector input for the
strongest signal response. The Pre-selector gain is usually set to about
85%, the Volume is set to about 25% normally but can be advanced as
needed. These settings usually result in the best
response of signal to noise along with the greatest selectivity. I've probably logged more NDBs with the RAZ-1 than any other
LW receiver. However, that might be because it was one of the first LW
receivers that I used when I started logging NDB stations in 2006. But, it could always be relied upon to pickup whatever
was out
there as long as reasonable conditions were present,...that would be, using
my remotely-tuned loop antenna, earphones for reproducers and listening late at night during
the LW Season. See the RAZ-1 NDB Reception Log for March 25, 2022
using the Pixel Loop antenna (a magnetic shielded loop) at the end of the AR-8503 write-up. |
|
Radiomarine Corp. -
AR-8503
SN:42590
The AR-8503 was
the commercial LW receiver that the RAZ-1 was based upon. The
RAZ-1 was identical in circuit and construction to the
AR-8503. Since it was a commercial receiver, the AR-8503-P pre-selector
was optional equipment (that was only available later in
production) and wasn't always included with the receiver. Most
commercial ships in the late-thirties to early-forties operated
on DC voltage, so the RM-6 rectifier power unit
wasn't required for most installations. This write-up mainly
covers the refurbishment and performance of AR-8503 SN:42590.
|
Mar 7, 2022 - Inspection -
Today, I was
given a disassembled AR-8503 as payment for a small testing job I did for
Ham & Hi Fi (Sparks, NV.) The serial number is 42590 and that probably indicates the
receiver was built in 1942 (the first two digits usually indicate the
year of manufacture for RMCA equipment.) The receiver is about 95% complete but is missing (as
always) the small round RMCA knobs although it does have the National
Co.
"N" dial present. The four shock mounts are gone and the six binding
posts are also missing. The AR-8503 had been disassembled a long time
ago and most of the parts were supposed to be in two small fruit juice
cans inside the cabinet but, with all the recent moving around, the cans
had tipped over and screws, washers and small parts were all spilled into the cabinet (BUT, at least they
were present.)
The AR-8503 was introduced in 1937 and that's why it's in this pre-WWII
section but this receiver was almost certainly built in the early part
of WWII for commercial shipboard use on
relatively small vessels.
I've never been able to find any of the small RMCA knobs in any junk boxes
- ever! But, at a little over 1" diameter, the round Hallicrafters knobs
that were used in the late-thirties up through WWII look fairly close to the RMCA knobs and will have to do as a suitable substitute. The Halli knobs
don't have the flutes that the RMCA knobs and they lack the metal
pointers that the two bandswitch knobs have but they're still about
the closest-looking, easily-found type of knob.
I didn't have
six "matching" EBY binding posts. Nearly all of the large
quantity of vintage EBY binding posts I found in searching the junk
boxes had engraved nomenclature on top of the thumbnut to indicate their
intended use. I used six EBYs that were in good condition and then
removed the engraving and polished the top of the thumbnut to end up
with six non-engraved EBY binding posts. The rotating latch was missing from the tube inspection door but
it's easily made after finding a suitable metal thumb screw (found in the
vintage screw boxes.)
There wasn't a pre-selector with this AR-8503 but many of these
receivers were originally used on commercial ships without a pre-selector
(the pre-selector was actually designed a few years after the AR-8503
was introduced.)
The receiver is sensitive enough by itself (phones will be necessary) and the pre-selector
was mainly
for antenna isolation from the regenerative detector - a mandatory
requirement on Navy ships. Also, no AC power supply but many commercial shipboard
AR-8503 receivers ran on the ship's battery-generator DC supply for tube
filaments and dry cell batteries for the B+ requirements. Voltage
requirements are +6vdc, +22vdc and +90vdc. |
AR-8503 sn:42590 "as found" |
| Mar 12, 2022 -
Front Panel Clean-up
- It can't be seen very well in the "before" photo but the front
panel appeared to be stained. I tried using lacquer thinner and
this made the staining really bad (I did that on Mar 10.) That made me think that the panel
had probably been sprayed with a "clear coat" of some type and
that's what was causing the "stained look." I wondered
whether it might have been MFP but the coating didn't have the
characteristic yellowish tint so I thought it was something like Krylon Clear lacquer (a check of the National "N" dial
confirmed that the coating was something like Krylon and not MFP.)
To remove this "modern" coating I went to the old
standby, NaOH sodium hydroxide, the main component of
Easy Off Oven Cleaner. This is basically lye, that is, a caustic
solution that is good for removing some types of stains
(especially organic types.) The EOOC got rid of about 80% of the
staining (Mar 11.) I went back to the idea of "clear coat lacquer" and tried
heavy-duty paint stripper (non-methylene-choloride type.) That
removed all of the panel problems that had looked like
stains and left the textured panel looking fabulous. |
|
 |
Mar 13, 2022 - Nomenclature
Engraving Paint Fill
- The only "fallout" from the aggressive panel cleaning was that
most of the paint used for the nomenclature fill also got
"removed" in the process. Although it's tedious work, it's not
difficult to do the engraved nomenclature fill using Artist's
Acrylic paint in Mars Black. I apply a small amount of paint
using a Q-tip and work the paint into the engraving. I let the
paint dry for a couple of minutes. Then using a small, folded
paper towel piece dampened with Glass Plus I carefully remove
the excess fill paint which leaves the engraving paint fill
where it belongs (it takes some practice to do this
efficiently but it's very easy to learn and the results look
original.) The "arrows" that are on four of the control
nomenclature engravings require dabbing a small amount of paint
(using a tooth pick) into the "arrow" recess. The damp paper
towel has to be wrapped tight over a straight edge (I used a
razor blade edge) to prevent the towel from pulling the paint
out of the "arrow" recess. I used Glass Plus applied with a small short
bristle brush for clean up of other acrylic paint goofs or
excess paint that had gotten into the texturing of the front
panel. It works great as long as the paint hasn't dried
completely. Once the engraved nomenclature paint fill is
thoroughly dry (overnight is enough) the panel can be rubbed
down with a soft cotton cloth.
photo left:
Close-up of the tube access door and the engraved data |
| Mar 14, 2022 -
Reassembly - This was accomplished without any
problems since I had previously sorted all of the various types
of fasteners and insulators that had been in the fruit juice
cans. The front panel was mounted first using the seven 8-32 OH
dress screws. The front panel is also secured using the mounting
nuts for the various controls. The COUPLING air variable has to
be mounted with shouldered insulating washers since it's in series between
the antenna and the tuning condenser. Also, the two phone jacks
have to be insulated using fiber washers and shouldered mounting
nuts. There isn't a flexible coupler between the "N" dial and
the tuning condenser so it has to be centered and connected to
the tuning condenser shaft before the dial base mounting
screws are tightened. The "N" dial didn't have the internal
mounting screws installed but the proper screws were among the
sorted fasteners. I mechanically set the "N" dial to "0" with
the tuning condenser at full mesh. The remaining controls were
mounted in the normal fashion with dress washer and mounting
nut. The remaining knobs were then temporarily installed. |
Quick Testing - I
hadn't modified the EBY binding posts yet so the voltages required
were connected to the lugs that would normally mount to the proper
binding post. I used test clip-leads for the connections. For a
power supply I used the CRM-20096 from the RAZ-1 set. The
AR-8503 receiver was out of its cabinet for the testing. The
initial test used the 162' EFW antenna and the reproducers were
Hi-Z TRIMM phones. I started with Band 4 at the AM-BC band and tuned KPLY
on 630kc, a local (Reno, NV) station with a very loud signal. A
few other AM-BC stations were also heard just below KPLY but
since it was about 4PM in the afternoon they weren't DX
stations. Next, I switched to Band 2 and tuned around for WWVB
60kc which should have been at 58 on the dial - it was on 57.
But, the WWVB signal is pretty broad so it was easy to find and
it was a strong signal. Next, I switched to Band 1 and looked
for NLK 25.8kc from Jim Creek, WA and it was coming in strong.
So was NPM 21.8kc from Hawaii. Both of these USN MSK stations
were tuned in very close to the dial settings shown in the
manual. For daytime listening, the AR-8503 seemed to be working
fine and I was surprised at the receiver's sensitivity when used without
a pre-selector. This AR-8503 seems
to do a pretty good job just by itself. But,
more evening testing will be required. I'll probably use the EFW
antenna first and then compare those results with another reception
test
using the Pixel Loop antenna. |
|
Mar 14, 2022
Reception Test - 2200hrs to 2220hrs PDT
MW 408kc - Moses Lake, WA
MOG 404kc - Montegue, CA
PNA 392kc - Pinedale, WY
CNP 383kc - Chappell, NE
MEF 356kc - Medford, OR
XX 344kc - Abbotsford, BC, CAN
RYN 338kc - Tucson, AZ
DC 326kc - Princeton, BC, CAN
Using 162' EFW antenna - Hi-Z TRIMM phones
Conditions good. Best DX is probably CNP 383kc in Nebraska.
These aren't difficult NDBs, in fact, they're all pretty easy
ones. But, the AR-8503 is out of the cabinet and connected to
the PS by test clip leads and it is the end of LW season,...so
not too bad, considering. |
Mar 15, 2022 -
Refurbishing the "N" Dial - The "N" dial had been
sprayed with some type of clear coat lacquer (not MFP) and some
of the lacquer was laid-on so thick it was on the verge of
running (there were even bubbles in the coating.) I disassembled
the dial to prevent the stripper from getting into the vernier
mechanism. I used heavy-duty stripper (not methelyne-chloride)
and that removed the lacquer coating easily. The index scale and
the upper and lower part of the base assembly also needed to
have the spray lacquer removed. The entire stripping process
only took about 15 minutes to complete. The dial pieces were
washed in water and then washed again with Glass Plus. After
drying, the "N" dial was reassembled and remounted.
Hallicrafters Knobs as RMCA
Substitutes - As mentioned, these knobs that were
used on a lot of Hallicrafters equipment from the late-thirties
through WWII are a pretty good match as substitutes for the
missing RMCA
knobs. They have a similar design and are only slightly smaller
than RMCA knobs. One thing I needed to do was to make a white
index "dot" on the knobs like the RMCA knobs would have. This
required drilling a shallow hole towards the rim of each knob
and filling the hole with off-white paint. White is usually way
too bright so I mix in a little light brown and a small dab of
black to end up with a manila-color for the fill that will look
"aged." The two RMCA bandswitching knobs had metal
pointers that would have been difficult to make and since these
were only "substitute knobs" I just went with the "dot"
indicator to match the other Halli knobs.
|
|
 |
License Tag
- The "license" tag that mounts on the
top of the cabinet and definitely ties the AR-8503 to commercial
shipboard use with its reference to "contract of sale"
in the wording. The tag was in a slightly oxidized and dirty
condition. I have good cleaning results by performing a very
light "going-over" the tag with 0000 steel wool and WD-40. Light
pressure is all that's required to clean the oxidation and leave
the lettering in perfect condition. The tag was bent and needed
some bodywork to straighten. Photo to the left shows the cleaned
tag. |
| Cabinet Cleaning, Bodywork,
Painting and Shock Mounts - I used Glass Plus and brass brushes to
clean the wrinkle finish paint. The top of the cabinet was bent
and needed a little bodywork to straighten. The exterior paint
was in fair condition so all that was needed was to do a "wash."
For this process, I mix Artist's Acrylic to match the original
cabinet color and
then thin that paint mix with water until it's about as thick as
a thin milk shake. I then use a sponge to apply the paint in a
dabbing technique. Also, some touch-up was required before the
wash to cover a few of the larger bare metal spots. The shock
mounts were threaded 1/4-28 so mounting only required machine
bolts and lock washers. These
mounts were olive drab and the missing originals were silver but
I painted them grey with the same touch-up paint I used on the
cabinet. Tube Access
Door Latch - The tube access door latch really only required a suitable
metal thumbscrew, a washer, two nuts and a metal "arm" that's
mounted to the thumbscrew shaft. I modified a spring contact arm
I found in the junk box to work as the door latch arm. Very
simple but it works fine. |
Mar 17, 2022 - EBY Binding Posts
- Six of these were required. I found one vintage original that
was unused and didn't have any engraving on the thumbnut. I had
a dozen or so more that I found digging through the junk boxes but
all of them had the engraved thumbnuts. I just chuck-up the threaded rod
end into a hand-drill and then use an emery board (works better
on bakelite than a file) to remove the
engraving and retain the proper shape of the thumbnut head. Then
the thumbnut is polished with 0000 steel wool. Wenol's can be
used for a high polish. If done carefully the end-result looks
somewhat original,...maybe a bit worn but still acceptable.
Reassembly
Completed - Mar 20, 2022 - The shock feet were
mounted and the license tag installed onto the cabinet. The
tubes were finally tested and to my surprise the RF amplifier
tube was a 6J7 instead of a 6K7. Although these tubes are almost identical, the 6K7 is a remote cut-off pentode and the
6J7 is a sharp cut-off pentode (different grid structures for
AVC control or Manual control.) While these two tubes behave almost the
same in this receiver the correct tube, the 6K7, allowed the
VOLUME (RF gain) control to function better. The other tubes were correct
and tested good. The receiver chassis was then installed into
the cabinet (luckily, all 15 RH 6-32 machine screws were in the fruit
juice cans.) |
| Disappointing
Results when Testing with the
Pixel Loop Requires Further Investigation - To my surprise the Pixel Loop didn't
work well at all with the AR-8503. As with any loop, the signal
levels available will be less than a large outdoor wire antenna.
But, the AR-8503 response level seemed to be very low - I
couldn't even hear any AM-BC signals. I thought it might be an
impedance mismatch but that didn't seem likely.
To confirm that the AR-8503 was functioning differently than
the RAZ-1, I needed to operate the CRM-46092 receiver without
the CRM-50092 preselector. Before doing that though, I checked
the schematic for both receivers to confirm that they were
indeed identical component for component (they are, or they
should be.)
The Pixel Loop operating with the CRM-46092 was quite
different. Lots of strong signal levels with KPLY 630 "blasting" in
requiring the VOLUME to be reduced to about 10%. The available
sensitivity allowed tuning in the NDOT road conditions station
on 530kc. Since it was daytime I was limited to the AM-BC for
testing. The Pixel Loop will only go down to 150kc and actually
begins to drop off response beginning at about 300kc.
I went back to the AR-8503 just to verify the different
performance and the only signal that could be heard was KPLY
630kc and that was with the VOLUME at about 75% advanced. |
AR-8503 Problems -
First, I verified that all of the ERIE resistors were the correct
value, or at least close. ERIE resistors can drift in value
depending on the circuit. All resistors were close in value.
Schematic Error -
Checking further I discovered that the AR-8503 schematic that's
in the Sterling Radio Manual had the VOLUME pot and the
REGENERATION pot values at 750KΩ each. The actual values are
75KΩ each and those values are shown correctly in the RAZ-1 manual
schematic and parts list. Both pots checked at about 75KΩ in the
AR-8503. Solder Problem
- Luckily, in checking the pot values I found that the buss wire
connection to the ground terminal on the VOLUME (RF gain) pot
had a broken solder joint. This was repaired. Further checks
didn't reveal any other problems.
Switch Contacts, Tuning Condenser Contacts and Spark Gaps
- I used DeOxit and a small paint brush to clean the band
switches and the grounding contacts on the tuning condenser. I
also hadn't installed the antenna spark gap so those two pieces
were mounted on the ANT and GND terminals. A quick test (out
of the cabinet) using the Pixel Loop and KPLY 630 was tuned in
with a very strong signal requiring the VOLUME control to be reduced down to about 10%.
Several other AM-BC stations were tuned in from 650kc down to
530kc. Any further differences between the AR-8503 and the
CRM-46092 can probably be attributed to the differences in the
tubes. |
| Nighttime
Check - Mar 27, 2022 - The AR-8503 was still out of the cabinet
but still connected to the power supply and to the Pixel Loop. I
was tuned to about 400kc and MOG 404kc was coming in and with
some adjusting of the controls the reception improved
significantly. Further tuning found GC 380kc in Gillette, WY,
RPX 362kc in Roundup, MT and RYN 338kc in Tucson, AZ. I only
listened for about five minutes since it was 2215hrs and this
was just a test to see that the reception using the AR-8503 and
the Pixel Loop had improved dramatically. It's also the end of
March and the conditions are slowly deteriorating as we get
further into Spring. Some lightning crashes were heard and that's
a sign that LW Season is coming to an end. AR-8503 Wrap-up
- In looking at the photo to the right showing the completed AR-8503,
note the Halli knobs and how at a casual glance or from a
distance they look fairly close to the RMCA knobs that should be
installed. The shock mounts are also fairly close but not
exactly like the originals. This was a "refurbishment" that
resulted in the AR-8503 looking good and performing quite well.
The receiver is certainly a nice enough example that IF
seven RMCA knobs became available I'd replace the Halli knobs
"in a minute" and same goes for the shock mounts.
The AR-8503 does receive all LW signals very well when using
an antenna that is similar to what was used onboard the ship.
That would be about a 200ft end-fed wire. That type of antenna
will produce strong signals but also will produce quite a bit of
noise. The shielded magnetic loop will not produce strong
signals like a large outdoor wire antenna can, but the greatly
reduced noise allows the listener to hear much weaker signals -
a better signal to noise ratio. If possible, that is, if you're
in a RFI-quiet area, use a large outdoor wire and the AR-8503
will respond well. But, in RFI-noisy areas, a shielded magnetic
loop will allow receiving some LW signals. |
Radiomarine Corp.
- Model AR-8503 Radio Receiver SN: 42590
|
|
RAZ-1 with
Pixel Loop - March 2022 TESTING INFORMATION |
|
Mar 25, 2022 - 2215hrs
to 2225hrs PST
MOG 404kc Montegue, CA
PNA 392kc Pinedale, WY
AA 365kc Fargo, ND
RPX 362kc Roundup, MT
MEF 356kc Medford, OR
YXL 346kc Sioux Lookout, ON, CAN
XX 344kc Abottsford, BC, CAN
OIN 341kc Oberlin, KS
RYN 338kc Tucson, AZ
RAZ-1 set, Pixel Loop, TRIMM 'phones,
cndx good.
Nine stations in ten minutes listening. No doubt that
XYL 346kc in Sioux Lookout, Ontario, CAN was the best DX. |
RAZ-1 with the Pixel Loop
- I never had operated the RAZ-1 with the Pixel Loop. I had very
good results with my homemade remotely-tuned loop so I
wanted to see if a shielded magnetic loop would also
perform well. If the Pre-selector RF
Gain is is set too high, it will affect how the
receiver regeneration functions. But, as expected, the
receiver Coupling, Volume (receiver RF Gain)
and Trimmer also interact somewhat. Although "touchy" to
adjust, I was able to get good results with the Pixel
Loop and the RAZ-1 set. The reception log to the left
are the results of a ten minute listening test. I set up the RAZ-1 in the afternoon and tried the
Pixel Loop on AM BC. The results were what was to be
expected in that KPLY 630kc (Reno,NV) was extremely strong. Tuning
was relatively easy since the signal was so strong. A
little fine tuning and I picked up a weak AM BC station
probably around 560kc. I used a RF signal generator for
a signal source in the NDB range setting up for 404kc
(for MOG.) Although the sig gen was easy to tune in with
the RAZ-1, when
that signal was removed, MOG's carrier could be heard
but not MOG's MCW ID (this is normal reception of MOG
during the daytime.)
The test at night showed that the Pixel Loop can be
used with the RAZ-1 set because the CRM-50092
Pre-selector is providing ample signal gain ahead of the
RF amplifier in the CRM-46092 Receiver. The RAZ-1 and
Pixel Loop combination is a bit "touchy" and requires
constant small adjustments to the COUPLING, the TRIMMER,
the REGENERATION and the VOLUME on the receiver. But,
once the Pre-selector RF Gain is set to about 70 and the
VOLUME (receiver RF gain) is set to about 50%, then the
adjustments become less frequent. Also, it's very
helpful to use both hands and tune the Pre-selector AND
the Receiver simultaneously. It was very difficult to
adjust the Pre-selector's RF Gain correctly. Lots of
scratchy, intense noise with each movement of the gain
control. So, more problems,... |
|
| Other RAZ-1 Issues
CRM-46092 Receiver,
for many years now I've noticed that the +90vdc terminal was
very loose. Since 15 panel screws have to be removed just to be
able to slightly pull the receiver out of the cabinet to tighten
up the nut, I put off doing it. Also, the RAZ-1 had been relegated
to "display status" for quite a while now so there wasn't any
urgency to tighten the loose nut. Well, since we're testing the RAZ-1
everything should be repaired, so 15 panel screws were removed, the
receiver slid out of the cabinet a few inches, then all of the
5/16 hex nuts on all of the terminals were tightened and the
receiver slid back into the cabinet and the panel
screws reinstalled. Further testing has shown the the
Regeneration pot is very worn. It might clean up but if not the
value is an odd one,...75KΩ. (Found one in the "pot box"
- replaced Mar 29, 2022 - Regeneration now easy to control.)
CRM-50092 Pre-Selector
- The Pre-selector RF Gain control had always been very "noisy" so I thought it
probably just needed cleaning. It was a style of potentiometer
with a tandem ON-OFF switch. These types of pots are easy to
disassemble for thorough cleaning. However, when disassembled
the actual problem became painfully apparent - the carbon track
had severe gouges, like a sharp tool had been used to create this
half-inch long "canyon" in the carbon track. No amount of cleaning
was going to fix this problem. The schematic and parts list
indicate a value of 10KΩ, but, finding a 10KΩ pot with
tandem switch wouldn't be too easy. The closest I could find in
the potentiometer junk boxes was a 25KΩ (linear taper) with tandem switch.
I couldn't assemble a "parts" pot-switch to create a 10KΩ with
switch because internally the pot has to have the tab that
actuates the switch and a standard pot doesn't have that
internal tab. Since
the original pot still had continuity it could be measured for
value and it was a surprising 18KΩ! It's certainly possible that
the gouge could also have some fractures associated with it that
might have increased the total R somewhat. But, since the
potentiometer is connected as a variable R for adjusting the RF
gain by varying the cathode R, the maximum R of the pot
shouldn't be too much of a problem as it will just result in a
somewhat reduced range of adjustment (25KΩ to 250Ω instead of 10KΩ
to 250Ω with the 250Ω being maximum gain.) So, the 25KΩ pot should
function fine as the Pre-selector RF Gain control (a variable
cathode resistance.)
No issues with the pot installation. Both the receiver and
pre-selector were reassembled, connected together and connected to the
AC power supply. I pre-tuned to the top of Band 4 and as the
RAZ-1 warmed-up, I could hear KPLY 630kc. An incredible
difference! Now I could adjust the Pre-selector RF Gain just
where I wanted it without the intense "scratchy-crackle" - just
silently increasing the RF Gain. Of course, this also made the
adjustment of the receiver much easier since the Pre-selector RF
Gain could be exactly what was needed rather than a just a few places on the
pot that happened to work. Next, is another nighttime test with the Pixel
Loop. |
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| The Final Test - Mar 28,
2022 - Rather than doing all of these reception tests
that attempt to compare performance differences between the
AR-8503 and the RAZ-1 by tuning in NDBs on different nights with
all of the variables that could be experienced with that type of
testing, I decided on a test that would be consistent as far as
the signal level. I decided to use the HP-606B RF Signal
Generator to output a measured signal that would be the same for
both receivers. The set up used the CRM-50092 Pre-selector with
both receivers. The same Pixel Loop for both receivers and the
same CRM-20096 power supply for both receivers. The only change
was using either the AR-8503 receiver or the CRM-46092 receiver.
The HP-606B output was connected to a ten foot long wire and the
Pixel Loop was located in another room upstairs with a distance
of about 35 feet between the Pixel Loop and the HP-606B
"antenna." This testing can be performed during the
day, in fact, it's better if it's performed during the day (no
more waiting until 2200hrs for testing.)
"Signal Level Reception Test"
- The AR-8503 was tested first. The HP-606B was set to 388kc.
This frequency was chosen because it's in the NDB portion of the
MW band and it happened to be a frequency that was clear of any
daytime switching noises. The test was to first tune in the
signal with the HP-606B output at about .030mv rms to the ten
foot long wire. Once the signal was found, the receiver and
pre-selector were further fine tuned and adjusted for maximum
sensitivity. Then the HP-606B output was reduced until the
signal couldn't be heard in the receiver 'phones.
AR-8503 - The received signal using the Pixel Loop was easily
heard with the output level at .003mv rms. Also, easy to hear at
.002mv rms.
Barely heard at .001mv rms and the signal disappeared into
the noise below .001mv rms. Probably .0008mv rms from the HP-606
fed into the ten foot wire produced a signal was at the
threshold of signal detection (just above the
noise) using the Pixel Loop.
RAZ-1 - Interestingly, the CRM-46092 with the Pixel Loop
performed exactly the same with the same results of "barely
heard at .001mv rms" and disappeared below .001mv rms.
NOTE: This
isn't a "sensitivity measurement" of the receivers. What it does
is to provide a known signal level with a specific radiator
that's a specific distance away from the receiving antenna. The
test setup is consistent and repeatable and that will help to
evaluate the reception possibilities of a particular receiver
using the Pixel Loop for the antenna.
This type of test doesn't depend on
receiving conditions that change from night to night. Also,
sometimes our perception of a "really great performer" might be due
to great conditions rather than the receiver itself.
Additionally, testing like this can be performed at any time
during the year and that's especially advantageous during the
summer months when LW reception is very poor. I think I'm
going to include this type of test in each LW receiver write-up
from now on. I'll also retro-test some of the other LW receivers
and include the test data in those write-ups.
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