RF-301 Transceiver

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 patrol boats.

RF-301 on the HMAS ADVANCE (note the RF-302 whip tuner)

The part numbers for the complete station are:
RF-301 transceiver
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 (NATO 5935-00-801-8314)
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)

HMAS Advance

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.


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).
                                 2                                     15.24705
                                 3                                     14.24705
                                 4                                     13.24705
                                 5                                     12.24705
                                 6                                     11.24705
                                 7                                     10.24705
                                 8                                       9.24705
                                 9                                       8.24705
                               10                                       7.24705
                               11                                       6.24705
                               12                                       5.24705
                               13                                       4.24705
                               14                                       3.24705
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).
                                 0                                       6.14715
                                 1                                       6.24715
                                 2                                       6.34715
                                 3                                       6.44715
                                 4                                       6.54715
                                 5                                       6.64715
                                 6                                       6.74715
                                 7                                       6.84715
                                 8                                       6.94715
                                 9                                       7.04715
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).
                                 0                                       11.55493
                                 1                                       11.56593
                                 2                                       11.57693
                                 3                                       11.58793
                                 4                                       11.59893
                                 5                                       11.60993
                                 6                                       11.61093
                                 7                                       11.62193
                                 8                                       11.63293
                                 9                                       11.64393
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 the VFO.


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 now.

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 knob graduations.


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.


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.


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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