Wrong Tubes in Set. Historical Information.

Over the years I ran into a few radios dating back just after WW2,and before, and after the war.
 They did not have the same tubes as listed on the tube chart in the radio. In fact, some were totally different.

Here are the 2 things I have found:
1. The owner just shoved the tubes into any old socket "Because they fit".   I saw this in several radios and TV sets. ("Well aren't they all the same? They fit in the same holes".)

2. This is where it gets really good and "fun".
 During and immediately after WW2 (and possibly Korea) many "common" radio tubes were not obtainable. Now you must remember this was the Age of Radio, and TV really didn't exist, except for a few experimental stations and sets.

 Since radio was the major source of news & entertainment for the populace, keeping a set going was quite important for morale. Most civilian radio production had ceased, dealers were sold out, and tubes were going to the military as a priority item. (At the beginning of WW2 the military was even requesting Ham Radio operators give their sets to the government for the war effort as there was a shortage. The government even wanted panel meters to put into new sets).

Now we all know that there are some very good subs for certain tubes that directly plug in with little to no reduction in performance of the set. These tubes disappeared rapidly as tubes in the civilian sets failed.
 
Drastic measures were taken to keep the radios going. One method was to re-wire the radio to accept a different tube than the set was designed to use. (For example most folks know that a 6N7 can be subbed by a 6SN7 or 6CG7/6FQ7, as they are the same tube in a different base, or a different pinout)
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  Another number, or even changing out the socket to use a different based tube with the same function. Some worked quite well, and some didn't. Middleton published a great set of interchangeability guides, 5 volumes I think, that gave exact, acceptable and poor substitutes for the NLA tube. Also showed the mods needed to make it work.

  Side Note of History: Now there was a black market operating during WW2 where you could obtain just about anything you needed- for a price- including counterfeit ration, tire, and gas coupons.    Tubes could also be obtained this way. (I actually have some documentation on this black market in a letter to a gas station owner that was not able to account for several thousand gallons of gas by backing it up with the gas coupons in my collection of "Ration Books and Coupons from WW2". He was in DEEP trouble with the Ration Board!).

 Also the government made available a series of tubes marked MR by the number. Maintaince Replacement. I have also seen it referred to as Material Replacement.
 The MR tubes were allegedly "fallouts" that would not meet military spec for some reason, but were good enough to use in civilian radios. In reality, some of these tubes were not "fallouts" but perfectly good tubes released as "substandard" by the mfg. per some of the articles I have read.  Even a cosmetic defect could cause a tube to be marked as MR.

So if you find a radio that has wrong tubes in it, before you try the correct ones in it, be sure to check under the chassis to see if the set was modified to use the tube in the set.

  I ran into this in my early days and let factory smoke out of parts when I put in the correct tube. I never did get the radio going, as I was self taught and had no idea tubes had been changed over because of lack of parts during the war. Nor did I have any schematics to refer to.

Now a good, competent repairman would often put a note in the radio explaining the modification, and even a circuit modification diagram as to what was actually done. If you modify a radio or TV set, you should also do this too.

Another Historical/ Hysterical side note told to me by a radio shop owner that occurred during WW2. With the tube shortage, junked radios had value as parts sets.
The story is as follows: " A couple of kids came in with some used tubes and I bought them. After I bought them and the kids left, I tested them. They all tested bad. I went out to put them in the garbage can and noticed that the old dead radio console I had put out earlier in the day had the tubes gone from it. I had just bought back the bad tubes from the garbage set".

3. (Mostly after WW2)  Now often the manufacturers would change tube types in a radio because they were able to buy a huge lot of tubes cheaply after WW2. They would not document the changes in the tube lineup chart in the set either. The demand for new sets was so great they would often use pre-war parts, cases, & knobs left over to meet the demand. I have found some eclectic mixes in radios this way. One memorable 5 tube set used an 80 rectifier, octal tubes, loctals , and a miniature. Talk about crazy! Obviously they were scraping the bottom of the parts barrel in the basement to make that set. I saw a similar one as an AA5 that used a surplus selenium rectifier with the same type mix of tubes. I think that one was late 40's or an early 50's set. Not a major name brand either.

 If you old timers remember electronics test equipment kit mfgr's. , they bought masses of Mil Surp tubes and used them in their test equipment designs, as it cut the production cost way down. Most of the eye type capacitor testers used Mil Surp  JAN 1629's  as the eye tube.