The RF-301 radio is an HF transceiver covering the frequency range
from 2 to 15 mhz, and providing CW, AM, LSB, and USB modes.It is mainly
solid state, but also contains 5 valves. Two are used for the RF amplifier,
and three are used for the transmitter final power amplifier.The radio
has a synthesiser to generate the transmit and receive frequency. The frequency
is set by 4 knobs on the front. It cannot work on split frequencies.The transmitter
puts out 100 watts PEP CW, LSB, USB, or 25 watts AM.It can load into a normal
long wire antenna, or load into a 9, 16 or 35 foot whip using the Antenna
Coupler.The circuit and knobs are all labeled in megacycles and kilocycles
rather than megahertz and kilohertz.The radio is raised on 4 feet so that
air can be drawn in from underneath by the fan. The warm air is exhausted
through a filter on the back.The radio weighs 59 pounds. It uses a carbon
or dynamic microphone, and can use the internal speaker or a set of headphones.
There is a remote Control Assembly which has the audio in and out, and transmit
control. The RF-301 was made by RF Communications, which was taken over
by Harris.This model was used by the Royal Australian Navy on their small
RF-301 on the HMAS ADVANCE (note the RF-302 whip tuner)
The part numbers for the complete station are:
RF-302 manual antenna coupler
RF-302R remote controlled antenna coupler
RF-303 13.5 VDC internal supply
RF-304 26 VDC internal supply
RF-305 shockmount for transceiver and manual antenna coupler
RF-305A shockmount for transceiver only
RF-305B shockmount for remoten controlled antenna coupler
RF-307 remote audio control
RF-102 1 kW linear amplifier
RF-1221 morse key
P-0400 audio plug (7 pin male, push ferrule lock, cable mount) type DM9728-7P
P-0402 mains plug (7 pin female, push ferrule lock, cable mount)
type DM9728-7S (NATO 5935-00-802-5805)
These plugs were in a bag labeled DEUTSCH Electronics Components Division,
Municipal Airport, Banning, California, 92220, USA, dated 10/1/90
Microphone, SHURE type 301 (carbon type, with PTT)
There are 4 main knobs along the bottom, which are enclosed within a
line. These are labeled FREQUENCY KILOCYCLES. The left knob is marked 2 to
14 and selects the megacycles. The next 3 knobs are marked 0 to 9 and select
hundreds of Kilocycles, tens of kilocycles, and kilocycles. By using these
knobs, you can set the frequency to anywhere between 2.000 megacycles to
14.999 megacycles. The right hand kilocycles knob, can be pulled out, which
allows continuous tuning between individual kc steps. The right hand knob
is the ON/OFF switch and MODE switch. It is labeled, OFF, STBY, USB, LSB,
AM, and CW. There is a speaker in the centre of the front panel. To the right
are the knobs TRANSMIT AUDIO which sets the transmit modulation level, RECEIVE
AUDIO which is the volume control, and below this the RF GAIN control. There
are 2 toggle switches, the SPEAKER SWITCH turns the speaker ON, and the other
is used to switch on the NOISE LIMITER to ON. Located on the left hand side
is a meter that shows the signal level for receive, and the power output for
transmit. Below this are two knobs, one is the PRESELECTOR to tune the receiver,
and the other is the PA TUNE control to tune the transmitter. At the lower
left hand side is a HANDSET connector for microphone, headphones, and morse
key. On the back are two fuses, one for 28 volts DC and one for 110 or 240
volts AC. There is a screwdriver activated switch, to switch from 110v to
240 volts. There are 2 input sockets, one for AC and one for DC. There is
a REMOTE socket, and an ANTENNA socket plus a GROUND terminal. There is
also the air filter, and a protective handle on the back.
MAINS INPUT CONNECTOR
The radio is extremely easy to use. You simply select the mode, then dial
up the frequency you want, then peak the noise with the PRESELECTOR. If you
wish to tune around, you pull out the kcs knob, tune the 1 kcs range, then
advance the 10 kcs knob, and continue tuning. When you have found a signal,
you can then push the knob back in, and advance it to the correct discrete
kcs step. One thing to watch, is that when you pull the knob out, it must
be returned to that same position before it can be pushed back in. A minor
annoyance, but you get used to it. To transmit, you select CW, set
the TRANSMIT AUDIO to 70%, then set the frequency you want, tune the PRESELECTOR
for maximum noise while in receive mode, then go to transmit and adjust the
PA TUNE for maximum power reading on the meter. By using CW, there is a signal
to tune with. You should peak the PRESELECTOR first, as it is easier to tune
this way, but it is not mandatory. If you accidentally trip the ACC or ALC,
then you can set the TRANSMIT AUDIO to TUNE, or back it off to less than
70%. A possible trap, is that you can easily tune to the image frequency
on transmit or receive, so the manual advises to always tune the PRESELECTOR
from low to high frequency, to select the correct frequency.
The receiver is a triple conversion superheterodyne, with an IF (Intermediate
Frequency) of 17.748 mcs, 11.1515 mcs and 455 kcs. There are two RF (Radio
Frequency) stages using the valves 6CD6 and 12BY7. These have a PRESELECTOR
assembly consisting of four slug tuned coils, with switched capacitors to
change bands. It is not obvious that it is changing bands. The bands are
all on the same PRESELECTOR knob and set by the MCS switch. There is a legend
on the knob to indicate approximately where you are. The bands are 2, 3-4,
5-8, and 9-14 MCS, and each band has four trimmer capacitors. There are
two cascaded tuned coils between the antenna and the first 6CD6 amplifier
valve. This also has a tuned plate coil. This is then capacitively coupled
to the grid of the 12BY7, which also has a tuned plate coil. This assembly
also has four crystals in it, which stop any spurious responses. There is
AGC (Automatic Gain Control) on these two valves. The output from this RF
AMPLIFIER board is connected to the TRANSLATOR board which has the three
mixers, and the first and second IF filters on it. There are no amplifiers
on this board. Each mixer is just one transistor. The received signal is
connected to the first mixer transistor base, and the collector is connected
to the first IF filter, which is a sealed block centered at 17.748 mcs, and
is 1 mcs wide. The synthesiser produces the injection frequency, which changes
by 1 mcs, when you change the MCS switch. In this way, any frequency between
.000 mcs and .999 mcs will pass through the filter. For example, a received
frequency of 5.500 mcs, will be in the centre of the pass band of the 17.748
mcs filter (5.500 + 12.24705 = 17.74705).
SWITCH POSITION (MCS)
INJECTION FREQUENCY (MCS)
The output from the first IF is connected to the base of the second mixer
transistor, and its collector is connected to the second IF filter, which
is a sealed block at 11.1515 mcs, and is 100 kcs wide. The synthesiser
produces the injection frequency, which changes by 100 kcs, when you change
the 100 KCS switch. In this way, any frequency between 00 kcs and 99 kcs
will pass through the filter. Using the previous example, the received frequency
of 5.500 mcs, which is now 17.74705 mcs, will be in the centre of the
passband of the 11.1515 mcs filter (17.74705 - 6.64715 = 11.0999).
SWITCH POSITION (100 KCS)
INJECTION FREQUENCY (MCS)
The output from the second IF is connected to the base of the third mixer
transistor, and its collector is connected to the third IF filter, which
is 455 kcs. The synthesiser produces the injection frequency, which changes
by 10 kcs, when you change the 10 KCS switch, and 1 kcs when you change the
1 KCS switch. In this way, any frequency between 0.0 kcs and 9.9 kcs will
pass through the filter. Using the previous example, the received frequency
of 5.500 mcs, which is translated to 17.74705 mcs, and then to 11.0999 mcs,
is now 455.03 kcs, which will be in the centre of the passband of the 455
kcs filter (11.0999 - 11.55493 = 0.45503).
SWITCH POSITION (10 KCS) INJECTION
The 455 kcs output from the TRANSLATOR board, goes to the MODE switch,
which passes the signal directly to the IF AMPLIFIER board for AM reception.
There are two 455 kcs mechanical filters, which are switched in for LSB and
USB. The USB filter is also used for CW. The IF AMPLIFIER board has four
tuned circuits and five transistors in the amplifier. There are also two
diodes that are switched in as the NOISE LIMITER and act like a clipper.
The IF signal is sampled and applied to an AGC amplifier and detector. The
AGC is applied to the IF amplifier, zero volts is maximum gain, and positive
voltage is reduced gain. This AGC is also applied to the RF amplifier. There
is a transistor used to invert this, such that zero volts is maximum gain
and negative voltage is minimum gain. The RF output from this board, now goes
to the AUDIO/MODULATOR board, which has an AM detector, and an SSB detector.
The SSB detector is a balanced diode bridge, which has 455 kcs input from
the SYNTHESISER board. The audio output goes to the RECEIVE AUDIO front panel
control, and then to the AUDIO AMPLIFIER board and the speaker.
The transmitter uses most of the receiver modules. There are steering diodes
in several places, and when biased correctly, the signal uses a different
path. When a diode is reversed biased, it is high impedance, and so no signal
goes through it. When a diode is forward biased, it is low impedance, and
so the signal does go through it. This makes the circuits a little hard
to understand, and fault finding more difficult. The microphone input goes
to the AUDIO/MODULATOR board, and a one transistor amplifier. There is an
input for a carbon or a dynamic microphone. The microphone has a PTT (Press
To Talk) line. For CW, there is an audio oscillator, which is connected to
the same microphone amplifier. It produces the CW and also the side tone.
In addition there is a hold circuit, which keeps the transmitter on, between
morse characters. It has about a half second timeout. The output from the
microphone amplifier, goes to the speaker, for side tone, and also to the
balanced modulator. This is the SSB detector which is for receive. It has
455 kcs input from the SYNTHESISER board. It is easy to overmodulate, and
there is a scratch on the front panel at 70% on the TRANSMIT AUDIO control,
so some operator has identified this position during use. The output goes
to the IF AMPLIFIER board, which has a single transistor 455 kcs amplifier,
and an ALC (Automatic Level Control) input. The ALC board samples the PA RF
and generates a proportional DC. This reduces the 455 kcs amplifier gain and
so reduces the PA grid drive, during speech. The 455 kcs output then goes
through the USB and LSB mechanical filters, in the same way as on receive,
and then to the TRANSLATOR board. A 455 kcs signal is added when in AM mode.
The TRANSLATOR board behaves in the same way as on receive, but in reverse
due to the steering diodes. On receive, it is RF in, mix with the synthesiser
signals, and 455 kcs out. On transmit, it is 455 kcs in, mix with the synthesiser
signals, and RF out. A clever way of doing things. The RF goes to the receiver
RF AMPLIFIER board, which is tuned by the PRESELECTOR control. The amplified
output is connected to the grids of three parallel 6146 final valves. There
is no tank coil, just an RFC (Radio Frequency Choke). The RF output goes to
a PI coupler, which has a roller inductor, and capacitors switched by the
MCS switch. It is connected to the 50 ohm output connector and the roller
inductor is used to adjust the output for maximum power transfer. It loads
into a normal half wave dipole quite well. The RF-302 external matching devices
are used for the whip aerials. Some RF is sampled to drive the power meter,
which is used for tuning. There is a preset grid bias adjustment, which uses
a press switch and the S meter to set the PA bias correctly (make sure the
transmitter is not tuned up). There is also an ACC (Automatic Carrier Control)
board, which controls the amount of carrier reinsertion during AM transmission.
In this set, the board is different to the manual, as it contains an additional
circuit that reduces the screen voltage if the PA is been driven to hard.
This set also does not have the RECEIVER PROTECTOR board fitted.
The synthesiser uses a 1 mcs FREQUENCY STANDARD, which is single block
containing a crystal in an oven. This goes to the DIVIDER AND SPECTRUM GENERATOR
board. It has three divide by 10 counters, that are constructed from discrete
transistors, set up as analog divide by 2 and divide by 5 multivibrators.
The 1 mcs, 100 kcs, 10 kcs, and 1 kcs outputs, go through clippers which
generate many harmonics. The 1 mcs output is referred to as a "pulse shaper"
and the other outputs as "keyed oscillators". This is the fixed part of the
synthesiser. The variable part consists of an oscillator for every frequency
switch. Each switch has a board on the back of it with 10 crystals (14 for
the MCS switch), so a different frequency is produced for each switch position.
The 1 mcs and 100 kcs signals go to the first and second mixers on
the TRANSLATOR board to mix with the RF signals. They also go to the 11.6
MCS ERROR board and mix with the FREQUENCY STANDARD derived 1 mcs and
100 kcs signals. This generates an error signal when compared to the FREQUENCY
STANDARD. The 10 kcs and 1 kcs oscillators go to the 11.6 MCS ERROR
board and are mixed with the FREQUENCY STANDARD error, to produce an 11.6
mcs signal for the third mixer on the TRANSLATOR board. The synthesised signals
are added in such a way, that when mixed with the received signal, it cancels
out any oscillator frequency drift. The 10 kcs and 1 kcs signals also go
to the 455 KCS ERROR MIXER board and mix with the FREQUENCY STANDARD
derived 10 kcs and 1 kcs signals. This generates an error signal when compared
to the FREQUENCY STANDARD, and produces a 455 kcs signal
for the SSB balanced modulator/detector on the AUDIO/MODULATOR board.
The synthesised signals are added in such a way, that when mixed with the
received signal, it cancels out any oscillator frequency drift. When the
1 kcs knob is pulled out, it turns on a VFO (Variable Frequency Oscillator),
which is for variable tuning. A crystal oscillator is also turned on in the
455 KCS ERROR MIXER, as local oscillator drift is irrelevant, when using
MODULATOR BOARD AT RIGHT
I had two RF-301 transceivers to repair, so there were many faults. It
appeared as though these two units ahd been used as parts donors, with good
boards swapped out to repair other units, and bad boards put in these units.
One unit had a tag saying "UNSERVICEABLE: AN/URC-58, U/S power supply,
bare wire around switch, blown diodes, blows fuses continuously, return to
stores". The other unit had a similar tag saying "U/S". I had a unit on display
at the Central Coast Field Day in February 2008, and a gentleman said he
had "worked on those in the Navy, and they were horrible things." I suggested
he had put a few faults in them and agreed he probably had.
The rear rotary switch is used to select 110/240 and is extremely close to
the chassis. One wafer was broken. I repaired it with epoxy, and rearranged
the wires, so that they were as far from any earth points as possible. I
also covered the switches and the fuses with insulating tape, while working
on them. I did not have the correct mains or microphone connectors, so I
hard wired in the mains cord until I sourced the connectors from a friend.
One unit had a loud transformer hum when initially switched on. I investigated
this, and eventually decided that the encapsulated transformer must have
some resonance, or loose laminations, or was lacking in whatever was inside
the sealed case. It never got hot, so I left it alone. Someone else had also
investigated this, as all the rectifier diodes on the transformer secondary
had been removed. I put back the four low voltage diodes for the relays
and the transistors. They worked without any problem, but the 12 VDC regulator
had a broken wire. I fixed this and the receiver came to life. I then put
in the two diodes for the 220 VDC supply for the RF amplifier, which had
a short circuit, and a resistor started smoking. I straightened a bent pin,
and the RF amplifier appeared to work. I fitted the High Voltage diodes and
the 900 VDC appeared. I fitted High Voltage diodes to the unit that
had them missing, and they immediately stared smoking. I found the large
4 MFD capacitor was a dead short. This is a 4 inch high oil filled capacitor.
I found a similar sized one in my junk box. It appeared to be a motor start
capacitor, as it had AC ratings as well as DC ratings. I painted it grey
to match the RF-301 and wired it in, replacing the High Voltage diodes again.
The 900 VDC appeared. The power supplies in both units appeared to working
They were receiving signals now, but not very well. One had a loud crackling
noise, which turned out to be a noisy capacitor in the 455 KCS ERROR MIXER
board. This produced noise on the 455 kcs signal which was injected into
the balanced modulator. It was quite now.
The IF AMPLIFIER needed alignment, but it cannot be done in place, as
you cannot get at the coil slugs, the relay board is in the way, and there
is 240 VAC on the switch in front of it, and 900 VDC on the chassis mounted
choke terminals. The board needs to be removed, which involves undoing 2
screws down on the chassis. These are hard to get at, and require the 455
KCS ERROR board and the AUDIO/MODULATOR board on the top of the chassis to
be removed first, as the bolts go through. Chassis mounted nuts would be
easier. The board can now be mounted on one of its brackets on top of the
chassis. One IF amplifier aligned properly, but the other was unstable, and
oscillated all the time with hand proximity. After a very long time and many
efforts to stabilise the board, it was discovered that there was a wiring
error on the external terminal strip, and the board had 14 VDC on it, and
not the 12V DC it required. This is probably a technician installed fault.
A broken slug was replaced and the board aligned properly. The AGC did not
work and so two faulty transistors were replaced.
The VFO was not working when the knob was pulled out. It was suspected
that the microswitch hidden underneath the switch was fault and not supplying
power to the VFO board. This switch is extremely difficult to get at, and
you cannot measure the voltages on it. To get this switch out, remove the
speaker switch, push it aside, then remove the VFO card, and loosen the connector.
Then remove 2 screws, and push aside the 455 kcs mechanical filter
assembly. Remove the knob and undo the FUNCTION switch and push it aside.
Now remove the knob and the 100 KCS switch and push it aside. Now you can
access the micro switch. However, it was not faulty, so I reassembled everything.
There was a broken wire on the bottom of the VFO connector. I soldered that
back on. It now worked. I adjusted it so that it tracked the synthesiser
VIEW OF THE MICROSWITCH
One unit had pulsing audio and the other had audio flutter. I started on
one unit which had a low negative 36 VDC supply. This is used for the transmitter
grid bias and also the AGC for the RF amplifier. This voltage was only negative
24 VDC and had 50 hz ripple on it. I replaced the 2 resistors as they were
high, but that changed nothing. I also replaced the diode, but no improvement.
I noticed one of the electrolyics had been replaced, so someone else had
been working on this section, probably chasing the same fault. I then noticed
the electrolytic was in upside down, this is a negative supply so the positive
terminal should go to earth. I replaced both electrolytics and put them
in the correct way. The supply voltage was now correct and the ripple was
gone. Another technician installed fault was removed. The audio flutter
was still there, despite these improvements.
The audio flutter and pulsing proved hard to isolate. I swapped cards between
the 2 units, but got no definite indication where the fault was. It also
seemed worse when it heated up. The heat gun and freeze did not help isolate
the fault. I went through the audio, the IF, the RF, and the translator boards
and nothing would fix it. I began to suspect the synthesiser, as the 455
kcs injection into the balanced modulator appeared different between the
units, and roughly correlated to the symptoms. Also the 1 kcs and VFO changed
it and the 10 kcs switch seemed to have some effect as well. So I looked
at the error mixer boards but could see nothing definitely wrong. I
looked at the oscillator output from the frequency switches, and there seemed
to be some correlation but not a lot. I looked ta the 1 MCS FREQUENCY STANDARD
which is different on both the units. One is chassis mounted and one is
mounted on the DIVIDER AND SPECTRUM board. There is a special section on
how to align this card, so I decided to follow it. The dividers use multivibrators,
and RC (Resistor Capacitor) networks for the timing and these have adjustments.
I used an oscilloscope and followed the diagrams in the manuals. I noticed
that one divider would divide by 10 for three counts, and then divide by
11 for one count. I adjusted this for proper division and the flutter disappeared.
I then adjusted the other unit and it was dividing properly but I could
adjust out the pulsing audio, with the controls, even though I could see
no changes on the oscilloscope.
RIGHT HAND SIDE BOARDS
I aligned both receivers and they worked very well. One had a broken trimmer
in the RF box which had to be replaced.
One transmitter gave 100 watts output at 10 mhz, but not much else across
the frequency range. The other did not work at all. I traced it to the IF
amplifier which had the AGC still turned on during transmit, it should be
disabled with a relay. I tracked it down to a wiring error which was another
technician installed fault. I did follow the circuit for a while, trying
to identify where the MODE switch changes the AM/CW line, but the units were
different, and the faulty unit did not have these wafer contacts fitted.
The transmitter now worked.
One unit overmodulated, when the TRANSMIT AUDIO control was advanced beyond
70% CW rotation, but after a lot of investigation, this turned out to be
normal. The other unit was low in modulation. It was difficult to measure
the output of the balanced modulator as it was very low. I finally tracked
it to a physically broken disc ceramic capacitor on the IF AMPLIFIER board.
They both now overmodulate at the same point.
The transmitter alignment proved very difficult. I thought that if it was
right for receive, then it would be right for transmit. It is the other
way around. I followed the method in the manual several times, but could
not get an even power over the whole range. And occasionally I thought the
PA would take off, as I could hear the power supply groan. I would shut it
all off and wait for the whole thing to cool down. I eventually permanently
connected the screen drive to the ACC tripped state, and aligned for a maximum
power output of 10 watts into a dummy load. This was due to the fact that,
the ACC would trip and give me uneven results that required releasing the
PTT and starting again. I could not use the fully CW (clock wise) TUNE position
of the TRANSMIT AUDIO control as it over modulated. Also I could be damaging
the 6146 valves with no drive conditions. I tried using the sweep generator
in several different ways, but could not get consistent results. I eventually
just tried to get the 2 mhz range correct. When I finally achieved that
(after many attempts), I then did the next range (3-4 mhz). If I couldn't
get that right, I redid the 2 mhz range, with the slugs in different positions.
Then worked up to the next range. I finally got even power across the whole
frequency range. I then reconnected the ACC and was getting 100 to 150 watts
across the range. The receiver seemed a little better as well. It was a
marathon effort over a month.
At one stage I was tuning one transmitter, and smoke came out of the other,
even though it was on receive. An oscilloscope lead was picking up RF and
it was amplified by one of the valves and destroyed a resistor in the coil
area, R2. I had to replace that. I kept the other receiver off, and no leads
connected to it. Another time, I lost transmit audio, and tracked it down
to a broken wire on the TRANSMIT AUDIO control. My oscilloscope clip had
broken it off. These two faults were due to the units being on the bench
for a long time, constantly being tested and turned over and over, pulled
apart, and powered up.
I started on the second transmitter. It was equally difficult, but occasionally,
would give power out at the wrong PRESELECTOR setting. It was oscillating
and the neutralisation had little effect. I found the roller inductor was
loose, but this changed nothing. I used the GDO (grid dip oscillator) on
the PI coupler, but this was resonating properly with no spurious resonances.
I tried the GDO on all the coils in the RF section to see if that helped,
but it gave no consistent results. I finally got consistent power out across
the frequency range. If I avoided tuning the PRESELECTOR above 10 mhz while
operating below 5 mhz, it did not oscillate. This was not the correct solution.
Now that the transmitter was correct, I noticed the receiver would occasionally
oscillate. So I started chasing this. The neutralisation seemed to have
some effect but not much. I checked all the capacitors on the RF amplifier
board. I checked all the resistors, and changed one which might have been
inductive. I changed the valves. It was hard to determine which one was
oscillating, the 12BY7, the 6CD6, or the 6146. They all seemed to have an
effect. The 12BY7 has no valve shield, so I decided to fit one, I found one
and slid it on, and it changed the oscillation frequency. There was no earth
connection, so I decided to screw a flying lead to it. Perhaps a better way
would be to wrap some metal around the valve base, and then the shield can
use that. Why not take a metal base off a 9 pin socket and use that. I got
a 9 pin valve base out of the junk box. I decided to change the whole socket.
When I removed the RF AMPLIFIER board and looked at it, it had 10 pins! So
it appears it did originally have a shielded socket (the tenth pin was earthed)
and it had been removed. Another technician modification. I fitted thesocket
and the shield, and put it all back together. No change, it still oscillated.
RF BOARD WITH NEW SOCKET
The circuit showed two feedback capacitors, a 39 pf 1000 VDC capacitor near
the roller inductor. Also a 7.5 pf 3000 VDC capacitor but I had
been unable to locate this one. I started looking in the RF coil box, and
found it on a standoff insulator. But it went nowhere. It was actually a
feed through, and the wire which connected it to the bottom of the 12BY7
plate coil, was missing from the other side. I connected a wire in, and the
oscillation went away. Another technician fault fixed.
The 3 and 9 positions on the 100 KCS switch gave low transmitter output.
I looked at the filters and RF coils for a problem with the alignment, but
could find nothing. I eventually measured the oscillator output and noticed
it was lower for these two positions. It needs two new crystals as they are
low in output. This is a minor problem.
I cleaned the two units up, gave one back to the owner and now use the
other one on the air.
It is nice to use, and sends good stable AM and CW.
The block diagram is a little hard to follow, and the manual could be
written more clearly. One thing to watch, is that when you pull the
1 kcs knob out, it must be returned to the same position before it can be
pushed back in. A minor annoyance, but you get used to it. A possible
trap, is that you can easily tune to the image frequency on transmit or receive,
so the manual advises to always tune the PRESELECTOR from low to high frequency,
to select the correct frequency. If you accidentally trip the ACC or ALC,
then you can set the TRANSMIT AUDIO to TUNE, or back it off to less than the
70% position. The IF AMPLIFIER needs to be uncovered to make the coils accessible
for alignment. If the relay board was relocated to cover the 900 VDC on the
chassis mounted choke terminals, and the 240 VAC on the back of the switch
had a cover, it would be easier. Chassis mounted nuts would make it easier
to remove the board. The board needs to be redesigned so that the IF coils
are near the top edge and easy to get at. The radio sits easily on the Left
Hand Side as it is a blank panel. The right hand side has an exposed board
on it which you have to be careful not to crush. The AUDIO/MODULATOR and
455 KCS ERROR boards are hard to get at. If the panel they are on was hinged,
it could fold down, and give easy access for servicing, and also grant access
to the VFO board. The fan is a little noisy and could be quieter.
copyright Ray Robinson
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