Whoa! The 12-tuber is the oldest version. Has three relays. The later 10-tube versions had only two relays.
Looks like what's posted at CB Tricks is only the later 10-tube versions. They are a bit easier to service, since they used a 12-VOlt relay and transistor keying circuit.
The relay between the coax sockets on the rear panel, and the high-voltage relay alongside the four driver tube sockets are in all versions. The third relay is the one directly under the tubes, between the drivers and finals. ALL your RF power goes through this one, and the tuneup is a bit bizarre. Two knobs on the front function ONLY on low side. This is because that third relay bypasses the eight final tubes on Low side. The far-left lower knob peaks the driver tubes ONLY on high. The main Load control , the upper large left-most knob, is active on low side, too. You have to tune it up on High, to get that knob where it belongs, and then switch to Low side. Then, those two knobs on the bottom will work.
The High/Low relay always fails. Always. Since High side goes through the Normally-Closed contact points, those tend to fail first. Never hurts to clean them off before replacing that relay, but wear and tear will have pitted the contact surfaces so much that cleaning almost never helps.
And if either the HV or Antenna relay turns out to be only a 35-year item, they'll have to go, as well.
The tube-type keying circuit tends to require a lot of carrier drive from the radio to make it key. The SSB delay almost never works right. Some units were made to use a 12AQ5 keying tube. Yep, has a 12.6-Volt heater. Others were built to take the more-common 6AQ5 tube. The heater is on pins 3 and 4. One of those pins will be grounded, usually pin 3. The other one of those two has a wire on it, that is either solid green or green with a yellow stripe. As a rule, the yellow stripe indicates the 6.3-Volt 6AQ5, and the solid green wire for a 12AQ5. Not a big deal to change it from one to the other, if you don't have the version of the keying tube it's built to take. And if you plug a 6.3-Volt tube into a socket wired for 12.6 Volts, it will key as soon as it warms up, and destroy the keying tube. But usually not before the rest of the tubes cherry up and fail. Always wise to keep a close eye on one of these while it warms up.
I have a 350k Jpeg of that diagram, but I need to find someplace to host it.
If the filter capacitors are original, they are a time bomb. Or, maybe like a grenade with the pin pulled? We always add a bleeder resistor across EACH of the replacement filters. This version has only two sets of three in series, six total. The factory used a single 1-Meg 2 Watt resistor as a bleeder, but it's not effective. A separate bleeder across each filter also serves to divide the 950 Volts evenly across all three capacitors in series. Without adding them, you can't count on that. Just because the factory got away with leaving them off, doesn't mean that you can. The value isn't critical. We use 240k 2 Watt, but up to 470k is alright, just so long as they are ALL the same resistance value. Makes it marginally less suicidal to reach you hand into later, besides.
Or, you could choose a cheaper, simpler restoration project, like a 1970 Plymouth Road Runner.
Well, maybe not cheaper, but there's a resemblance. And if you have to buy tubes, that makes the car look a little cheaper in comparison.
Uh, okay. I uploaded this to imageshack. Rather than make a dial-up user wait for this thing to display, try this hyperlink and see if you can't access the file that way.
img212.imageshack.us/img212/6162/phat5003ww.jpg
Right-click on the link above and "Save As" is probably better than just left-clicking on it. Tried it with "preview", and it worked for me.
73