The iron shouldn't blow a fuse often enough to worry about accessibility.

It took 50 years for this one to pop.....I'd install a chassis mount fuse holder wherever it will fit. 

Better check the RS-50 schematic: there is one 2N3771 in the rear that is used to drive the 8 pass transistors - 4 per heat sink mounted on each side of the supply. A 2N3906 small signal transistor on the regulator board sets the crowbar threshold voltage and drives the SCR.


** To KD7YZ:  If in fact you shorted the case of the single 2N3771 mounted at the rear to ground (the power tranistor that is mounted to the chassis and not one of the side mounted heat sinks), then you likely caused CR1 and/or CR2 to fail - not CR101 or CR102.

CR1 and CR2, along with capacitor CR6 provide a dedicated low current DC source for the regulator and drivers, Q2 a TIP29 and the lone 2N3771 on the chassis which I refer to above.

CR101 and CR102 provide a dedicated high current DC source to the pass transistors which should not be involved, unless CR1 and CR2 failed shorted, causing the LM723 to fail, then the drivers and possibly the pass transistors - but I highly doubt this occurred.

This would also explain why the fuse didn't blow which is rated to handle the full output current of the supply plus margin for start up current, etc.

One step at a time - isolate CR1 and CR2 and check them using a DMM with a diode test mode or use a Simpson on the X1 ohms range.

The 3771's are pass transistors - the crowbar is an SCR located inside the supply.

Could be a lot of things, including audio starting from the mic.

 I managed to find my December 1982 copy of QST and sure enough on page 39 is the Universal T-R Controller.
 
 As K8AC points out, this device will take care of #1, 2 and 4 on your list, but if you want chirp-free keying, you still need to make the grid blocked keying modifications to the transmitter and VFO.
 
Also, while running through the schematic of the T-R Controller, I noticed a few shortcomings of the circuit that are easily fixed:

 - The 1N914 switching diodes on the negative keying output are only rated for 100 volts PRV which is marginal, especially for keying a boat anchor. I would change them to 1N4005's, 1N5061's or better.

 - The power transformer T1 is rated 24 vac with a bridge rectifier which can create 34-37 vdc at the input of the regulator lightly loaded, which depending on line voltage (nominal to high line) could exceed the input voltage limit of the 7812 regulator. A better choice would be a 16 or 18 vac transformer which will keep the voltage within the limits of the regulator and drop the regulators power dissipation by almost 50%.
 
..WA1RNE

 
 Actually what you want to do is use grid block keying. A grid blocked keying circuit turns on the VFO several microseconds before the oscillator and PA turns on, allowing the VFO to stabilize before being applied to the transmitter.

Here's the modification that Johnson published to add grid blocked keying to the Viking 122 VFO. Notice the 12AU7 keyer tube V201 that accomplishes the grid bias switching. Today, I would go solid state with an equivalent circuit, or keep it "boat anchor period correct" with tubes.

 Here's the scheme I would use to accomplish this:

 1) For grid blocked keying of the transmitter, copy the circuit fundamentals from a transmitter/VFO combo like the Johsnon Viking II or the Heath DX-60. Instead of the current configuration where the key simply shorts the cathodes of the oscillator and PA to ground, the key removes/applies cut-off grid bias to these tubes AND the VFO in the correct sequence.

 2) For the receiver muting and antenna changeover, add a circuit that picks up the change in grid bias from the key line that:

    a) mutes the receiver. You could use a MOSFET, HV transistor or some combination.

    b) drives the antenna relay. You can set up your timing with RC delays and discrete parts or use a combination with 555 timers, flip-flops, etc. There are many ways to do it.


 Not an over night task but a good project that should work very well.

 ..WA1RNE

 If you're looking at the service manual that KA4POL recommended, it provides the assembly view that you need on page 8-4.

The compressor switch is on "Switch D" board "SW-D". After removing the front panel (faceplate) which I understand you already did, remove ONLY the shaft nut for the "Mode" switch which fastens the entire board to the chassis. Also remove a single philips head screw at the top of the chassis just above board SW-D.

   The board should now pull right out toward the back.

I've owned this rig for 28 years and never had a copy of the service manual until now - thanks Dieter.  

On the other hand, never needing it is probably a testament to ICOM's design.

...WA1RNE

Most bang for the buck, I'd take a look at a Hy Tower Jr. Works 80-10 with full quarter wave elements and cage loading on 75/80. You should be able to base load it on 160, though I haven't actually heard of anyone trying it. There's also no reason why 17 and 12 meter stubs can't be added to cover all HF bands. Not including radials, $350 isn't a bad deal for a trap-less all band vertical.

...WA1RNE

 
 It's not his problem, but I maintain that the spirit of cooperation IS a worthwhile precedent, especially once the problem is solved. His neighbor will likely tell his friends about the issue, how his new ham friend took an interest and had the technical know-how to solve the problem.

 BTW, nobody recommended that G7IVJ buy the ferrites - he can simply recommend a solution and offer his assistance.

 ...WA1RNE

 There's a very good chance that some mix 43 snap-on ferrites will calm things down.

 However, don't forget to add at least 1 to the PC speaker INPUT cable which may be the real cause for the RFI. If you go this route, make sure you buy types that are large enough to allow at least 2-3 turns to pass through the core, significantly increasing the impedance.

 ...WA1RNE

 You don't need to use a twist lock plug/receptacle for this application.

 A 6-15 or 7-15 series plug/receptacle is more than adequate, is much cheaper and mounts easily in a standard wall box.

As others have recommended, 240 volts is overkill for everything except the amplifier.

 
   Also, making modifications at your service panel is serious business. Shut down main power first, take your time and double check your work.


 ....WA1RNE

 
 Without a watt meter - which would allow you to properly assess power output versus power input, you are feeling your way around in the dark.

 You would also be able to make a direct correlation to low line voltage as a cause for not being able to obtain full plate current, or 500 ma. as well as any metering issues, i.e. low grid current. You may still have a problem but you don't have enough data yet to tell.


 ...WA1RNE

 Should you decide to install an external SWR bridge/Wattmeter, there is no advantage to installing the meter after a tuner. Being 50 ohm devices, SWR/Wattmeters are rated for RF voltages up to  ~300-500 volts max. At the output of a tuner, depending on the impedance mismatch and power level  - especially if you add an amplifier - the meter could be exposed to much higher voltages and possibly flash over at the sensor.

Install the meter at the input of the tuner and adjust the tuner for an impedance match at the lowest power level that allows you to read SWR or reflected power. Using a 100 watt transceiver, 25% is about all you need to start adjusting the tuner.

Once the SWR or reflected power is adjusted for lowest reading, start increasing output, check forward power and if it's increasing normally toward maximum, go back and check reflected power, adjust the tuner if necessary, check forward power, etc. until you obtain nominal output under matched conditions.


 ...WA1RNE

 

 The SWR is under 1.5:1 across 80% of the band - hardly a reason for concern.

 I'd get on 6 meters and start using it, as-is.


 ...WA1RNE

  The RF field is probably very strong but RF feedback is unlikely to be an issue if the mic grounds and shields are properly connected.

  You never did reply concerning my suggestion to check the grounds inside the mic connector where it plugs into the mic base, as well as the connector pins themselves which may be oxidized.

 After that, you could try adding an RC filter at the preamp output. Try 100 ohms in series w/ the preamp output and a 0.005 uF ceramic disc capacitor after the resistor to ground.

 ..WA1RNE