Holy craapp! I get bent out of shape when I need to mow my own lawn. I need to be grateful that I have a lawn to mow. I feel like an idiot...
Sysco, at least I can say this about you and 99% of the regulars in here. We all range from just getting by, to fairly comfortable income, home and family life wise. But the reality of it is, whatever our story, these 99% will be the first to reach out to help those who are up against it. Whether it is fixing someone's TS9 Pedal, offering to buy a guitar or amp etc to infuse some funds into a low funded member's need, or tech help on amps, cars, houses, health issues etc, we have a pretty knowledgeable, resourceful and good bunch here.
Having read his situation, plus his experience with his JCM800, I would express my biggest word of advice to Bluesman regarding his Jonesing to use the amp vs. getting it fixed right.......
First, My advice is the same as AMPMAD said. DO NOT play the amp until it is fully checked and gone over by Tech of choice. No matter how good the new Tubes make it sound NOW, you run the risk of ruining them and other more costly fixes to the amp. In doing so, you set yourself up to risking more of your already thin finances.
2nd, I know you say it has been 6+ years...
In 16+ years time for me, I have owned my 1972 Marshall JMP 50 watt head, and in my lack of experience/amp education, I did the thing I knew best to do. Asked a more experienced guitar playing friend who to go to for repairs here in Maryland. The guy had a decent reputation but some things about him during the initial consult and subsequent repairs rubbed me wrong. In the end I feel as if I lost a perfectly good OEM transformer that later became his stash or sold for profit,,,, because the amp still failed me after his 2 repair trips and even my own later learned amp checks and setting things right that he missed.
Ya see, after the amp still acted up on me once he " fixed" it, I decided to take a step back and see what I could learn to fix it myself or find a more knowledgeable and thorough tech to do it right. That is when I found some really sharp members here and on the Marshall amp forum. These guys can look at pictures and see things even better than I can looking in person with my untrained naked eye. They also know how to make sense of the schematics, expected values and specs of the components and how to test and verify that things are either within spec, or on their way out or already failed.
Third, I took the time I really would have loved to be playing the amp to learn as much electronics and amp theory, testing, study as I could immerse myself in till I got to the point of understanding what our " experts" were telling me.
You see, a 72 JMP that works as it should is a wonderful thing, but a dead amp or dead me was the downside I wasn't wanting to see happen. In all my learning, I stress safety as number 1. ( it troubles me that 218 221---- 220K etc statement you made.) This is because how do we know you were in your amp as safely as possible if their was any confusion as to what reading you were actually getting?
This is why I stated that in my own amp diagnosing sessions, I would proceed to make any test lead connection, any Multimeter setting, any tubes in- tubes out, fuse blows etc scenarios ONLY after confirming that I understood precisely what the experts were telling me and they understood what I was proposing to do.
In fact one member here even brought up such a level of concern that I was pretty sure I had covered. I cannot stress this was the most important concern and surely glad he voiced his thought for me to verify my equipment with him.
He said he wanted to make sure my test leads and the Volts ratings of them plus my Meter could handle the potential volts amps put out. He said to be safe in a live amp that needed to be like 600V.
Having said all that, I am sure I will come up with other advice. BUT that is a good start other than to say LISTEN to Ampmad. He will not steer you wrong, and if you want to stretch your skills before you get a complete understanding, I would only do so on useless sacrificial and non lethal components such as Scrap electronics, scrap pcb boards etc. DO not RISK your LIFE or RUIN a perfectly good JCM800 by your own limits of experience, patience or ability to fully concentrate and be organized in your repair bench/tool setup, and physical dexterity with test tool or hot soldering iron.