What is a "Run Number"? Is it Important?

When looking for a radio or TV schematic be sure to look for a "Run Number" on the chassis, in the cabinet, glued onto the chassis on a paper tag, or even stapled to the bottom of the cabinet.
 Why is this so important?
 Because it is! Ok - Remember your parents saying that to you ? LOL

Seriously, the Run Number indicates a change in the production run of a device.
 It can be a parts change, cabinet change, function/band change,  different tubes, transistors, you name it.

 Often it is a change from tube types. Like using octals or miniature tubes in place of Loctals, a change in fuse value, or a safety issue that needed to be resolved.
 Possibly there was a  circuit change to enhance the products performance. (Like Zenith doing the 4 legged capacitor in the System 3 TV sets upgrade to keep the HO xistor from failing). 

 This was the bane of working on TV sets, especially the early ones. The factory would make a production change in parts, locations, values, or omit parts. Now if you were an ASC for that brand, you subscribed to the OEM service literature. Zenith, RCA, etc. would send out a production change notice , schematic revision or a notice to change part values in a set. At times it was for a bad original run of parts IE: out of tolerance, mis-marked, change in knob or cabinet style or color and such.

I actually saw and worked on a set, where the company had totally revised the chassis enough that it was a totally different chassis, bearing no physical likeness to the original chassis in the previous production runs, except it fit the exact same cabinet as in the previous sets. Same model number, different Production Run Number and different schematic,

 Sams Photofacts would issue a PCB  (Production Change bull.)for some sets indicating production changes, or Sam's goof up in printing the schematic; BUT ONLY IF YOU HAD THE POM SUBSCRIPTION! Yup. You had to $ub$cribe to the monthly $chematic $ervice. (POM= Photofact Of the Month).

In later years companies like Sears would order "X" number of sets from a mfgr. with specific requirements. A Low end set, a mid grade set and the high end set.
 Bet you didn't know the chassis for many of these sets were identical, but parts were added or subtracted to meet the buyers price point.

 I worked on enough PCE/Magnavox sets that had huge vacant spaces on the PC boards. The holes were there, just no parts in them. It was possible to upgrade a set by adding the missing parts to bring it up to a higher level set. I never knew anyone who did this, as it was not cost effective. 

 Upgrades could add audio & video inputs and outputs, HDMI, DVI, RGB, and such mods, as well as better picture processing, better color, and such.
 So unless you had a model, chassis, and run number you could chase your tail trying to find the correct schematic.

So hopefully this sheds a bit of light as why a RUN number is important.