Check the DC voltage at the zener's cathode with a meter.  If it is solid and within the proper voltage range, someone may have back to backed two good diodes or -- bad practice -- tacked a good diode across a bad one in a quick and not so smart repair.  

As for the cherry red tubes, first thing to check is electrolytic filtering in any bias circuit.  AC leakage here can cause that and is common.  Likely the zener is in the bias circuit but haven't looked at the skat before typing this.  Jumping the electrolytic with a known good one is the fast troubleshoot, if things settle down, and the odds are good they will, replace the cap.  

You might want to replace the zener with one that is proper while you are in there.  I would.  

Constant voltage drop across them.

For silicon diodes, Vf = 0.6 V, varying a bit from lot to lot, but two rectifiers from the same lot will be very close indeed, much more precise than using resistors.  

Can't find the schematic quickly right now, but such back to back rectifiers are commonly used in circuits for low level AC overvoltage protection, matching of common mode between two devices, creating a common point that is a constant level above actual ground, which can eliminate common mode noise, things like that.  Not uncommon for them to actually cover more than one of those parameters at the same time and at low cost, too.  

Someone who has been inside the 2500 more than I will likely come along and pinpoint their usage and possible failure modes here exactly.  

You might detail the history of soccer and nontelevised soap operas, both of which predate the advent of radio communications by just a wee bit.  

Or you might just smile knowingly and wave at them...

TS940 doesn't use tubes.  

Solid State Power Amp, with "unobtainium" for driver transistors, if the drivers are shot, board may not be repairable.  

Are you sure that's a '940?

Must be too much lead in their tubes, too...

>>.........Is there any concern for me voltage wise? or am i not in that area of the amp.<<<

There is always a safety concern when working with 120/220 VAC Line Current circuits, as well as the secondary high tension circuits.  

While you only have to be concerned with making sure that the DUT is not connected to the AC mains when working on those primary connections, because there won't be any capacitors that will charge up and keep the AC input side of the transformer at high potential after disconnecting from the mainline, you should still be aware that the secondary side of the circuit may have charged capacitors in there.  Most amplifiers physically separate the two areas and provide a way to get to the 120/220 changeover strip without opening the side that contains the high tension voltages, but it is still paramount to be aware of what you are dealing with here.  

220VAC can be lethal if you make a mistake.  

But don't be unduly afraid here, check things twice, slowly, carefully, good idea to unplug from wall and roll the cable up such that it cannot be inadvertently reconnect until you are ready.  Some wrap a bit of tape over the plug or pigtail end to remind them while the DUT is open on the bench.  

Typewriters make copying faster.  

Handwriting isn't even possible past a certain speed, which McElroy was well past.  

Thumbing throught the manual to find the page is such a chore...

A shorting stick with an appropriate resistance in it can keep you from becoming the guy who welded the screwdriver to the chassis or punched a spotweld into the tube cap.  


And trusting the screwdriver handle only can indeed be a recipe for life threatening disaster if you hand should slip...

I'd recommend leaving the ALC hooked up and first start with conservative settings on the mic and RF output on the rig.  Like around 70W of drive power output and then set the mic gain down low and very gradually increase it in tiny amounts until the hams at the other end tell you that you are nice and clear.  

~70W drive level is what I use all the time, barefoot or amplified.  

You should follow the manual for the rig to set its ALC and then follow the manual for the amp to set the amp ALC after that.  


KE3WD

Not being able to examine the amp and that switch circuit, I'm not going to even try to tell you explicitly what that added switch is really doing in there or how it is wired.  (!)  

*Might* be switching the relay, might not, we have no way of knowing from here.  

The only surefire solution would be tracing the circuit and maybe even drawing it out.  

Logically, it should most likely be switching the relay coil, but there exists the possibility of some kludge installed by someone somewhere...


KE3WD

Seriously reconsider the "helpful advice" about using 572b's in there.  

Doing so will not solve your original problem, which is what lunched the 811s in the first place.  

There could be a situation where, if you do the same thing again with the stouter 572b's in there that much more expensive damage will occur to other components in the amplifier instead of just losing the cost of 3 8lls.  

Your amp, your call.  

Many will likely come out of the woodwork and say that this is nonsense.  Many others are likely lurking here just awaiting the possibility, with firsthand accounts of having switched to the 572 without problem, too.  But over the years I've even seen folks tell others that they have run for years without grounded antennas, understand?  


KE3WD

Be advised that sometimes attempts to power LEDs from the old AC filament supply can be problematic, even when using a half wave rectifier in series with the LED along with the proper current dropping resistor.  

Peak Inverse Voltage of the LED can still be exceeded here, check the PIV in such circuits carefully.  

Even then the half wave solution is still more or less a kludge that appears to work but may not be the best thing for the LEDs lifetime without adding additional circuitry such as coil and cap suppression to avoid fast peaks in the switching transient.  This is "unseen" if you don't look for it with a 'scope, but each cycle can be making the poor little LED scream ouch on ya.  

Besides that, the warm glow of the filament bulb won't be there anymore.  

That trick mentioned above, placing a rectifier (1N400x) in series with each standard filament lamp, will run the lamps off of the AC half cycle and extend their lifetime indefinitely.  Is a good one for the older rigs, softer glow, easier to read meters and such in many circumstances, give that one a try.  


KE3WD

Antenna is not long enough for the Shortwave bands.  

You are most welcome.  

And thank YOU for reporting back with the final on this one, may help others who come across it.


KE3WD