Is there any evidence of damage to the wiring, leaking of caps both electrolytic and paper, burned resistors, frayed wiring anywhere?  I don't like the variac method, it can mask problems that come up later. 

Pull all tubes then power it up, if it blows a fuse, then you need to know why.  If it doesn't then you can install all tubes to see if the filaments light.  If they do then you should replace the filter and bypass caps.  Then check and replace out of tolerance resistors before applying full power to the entire set. 

Think it through and look at what each switch does.  I may be cautious but it is cheaper than a choke or transformer rewind.  Remember Harbach is no longer in the Amateur transformer business so that leaves only one source.

Dynamic Mutual conductance is nothing more than a fancy emission tester, mostly Jackson,  Find a good Hickok mutual conductance if you must have one.  Remember they all have their limitations and advantages.

Should you be planning to do more receivers I would look for a function generator at the next hamfest.  Be sure it covers to at least 1 megacycle and has a sweep function.  The one I have cost me all of 10 bucks and is solid state with button activation of all functions including the sweep.  Frequency coverage for it is from 5 cycles to 10 meg which covers all the IF possibilities and the lower bands for RF.

Then using it with an oscilloscope you can sweep align the IF sections which is much easier and better than using a VTVM across the output or the S meter.

There is a service note about replacing the mica variable caps in the oscillator section with small Johnson air variables to improve the stability.  Would require a bit of work but a nice change.

Spell check ...ABC is supposed to be AGC tube 6AH6.  I am referencing a small tubular cap between the 3rd IF 6BA6 to the grid of the 6AH6.

The placement of the coupling cap from the last IF to the ABC tube is critical.  Move it to the best location.

It is also based on commercial operation of 24/7 where they monitor the number of hours because they don't want to be caught with a failure.  So they establish a basis on which to change them from the manufacturer's recommendation.  In life critical situations it may be more often than the manufacturer's specs or in a broadcast situation it may be what is specified.  In almost all cases when a tube is retired, it works very well in amateur service where the transmit time is 10 mins. on and 20 off.

This line is the key to any final amp tube replacement.  Any time you change finals, no matter the designation, you should neutralize them.  If I recall correctly the problem the Collins transmitters experienced could be fixed by changing or adding to the neutralizing cap. 

So you are the one that keeps tuning your rig on top of our conversations?

Not only that Allen but the individual circuits for every stage in the 500 is in the old handbooks.  Norm you should find one before you begin to work on the modulator deck, the build may very well be different than the diagram you have and what is there is straight out of the handbook.  The pin numbers will be correct there.

What futher complicates things is people mixed decks from different models to make a complete transmitter.  They would find a 500A missing the modulaton deck and then locate a B modulator deck to go with it.  You may have a 500 power supply with a 500C modulator then a 500A RF deck or any combination thereof.  Given the popularity of these things it happened quite frequently in the past 10 years.  Add to that an RF deck from the factory marked 500A that has a B model oscillaor.

As I mentioned in your other thread, things may be mixed.  Your deck could have had a 6sj7 or a 6ag7.  Compare different diagrams.

The specification for the Globe King 500 A, B and C plate transformer for HV are CCS not ICAS. 

My modulation deck was marked with 5514 also but had 811As installed because the filament transformer was 6.3 not the 7.5.  If you need 5514 then look for my call on the Call Search here and pick up the direct address then send me a message. Couple of other tips, be careful of all manuals for WRL stuff.  They are full of mistakes mostly pin numbering on tubes and such none the less check carefully.  WRL didn't waste anything and you may find mis-markeded chassis in the transmitter.   I am restoring a Globe Champion 300A that all sorts of modifications to enhance the audio.  In the repairs I found the cathode bypass electrolytic cap on the second stage installed in reverse.  That killed the audio out of the second stage to the driver.  Not finding the FACTORY mistake someone put 811s in place of the 809s to get enough modulation and made other modificatons  in the audio.  I don't know how they missed that but be very careful going through the thing.

As for the capacitors I don't recommend spending a lot of money for higher value caps.  It accomplishes nothing but drive up the cost, and in the case of cap input filters which the bias supply on the RF deck is, can damage that transformer if you use caps that are too large.  I used the closest value I could find, ie. 33 for 30, etc. throughout for filters and all others

Check all the resistors.  You probably will find near 80 percent of them of the wrong value.  Also carefully inspect the postage stamp caps.  Some are mica and some are paper.  If they look suspicious at all, replace them  I have seen bad mica caps like that.  You might want to check with Gary/WZ1M about that transformer you lack.  If the core and size is correct for the one you have, he may rewind it for you to WRL specification at less cost than buying a new one or casting about for a long time looking.  Anytime you have one rewound, specify the primary for 120-125 volts.  That helps with stress and heat.

There are other issues on the 500A that should be addressed but this has gone on long enough

Return the RF to design specifications and you then can determine if it needs other help.  Return the modulation deck to original for the same reason.  I have a 500A that will modulate properly up to 100% positive and about 95% negative.  That is really all you want, especailly in the negative. 

If you need 5514s then let me know, I have a boat load.  Replacing plate and modulation transformers is an expensive process.  When you finish you will have more invested in the transmitter than the monetary value, but it is a good piece of equipment.  Not only that, if you have good transformers, chokes and such it is easy to repair if necessary.

The transformer you have found that uses 220-240 volt will require you carefully balance the rest of the load on the primary.  The rest of the transformers requires 115 volts to run the bias, filament, low plate voltage and relays.  There are some 500s out there that has the transformers that you can find.  Look at other venues and ask around.

That modulator and RF deck was designed around 1800 volts at the plate of the final.  If you run less power then the tank circuit sees a different load impedance and your harmonic suppression will suffer.  Also the modulaton transformer wants to see the impedance presented to the secondary with 1800 volts at the rated current in your manual.  Anything different changes that ratio and your audio may suffer.  Most changes like this are not good and affect the transmitter in negative ways.  IIRC the Q of that tank circuit is 10 which is bare mimimum.  Any change to it could cause that figure to fall dramatically