Okay, on to output transformers . . .
Rule of thumb #1: High quality OTs are relatively heavy compared to most low to medium quality OTs. BUT, low to medium quality OTs are not necessarily lighter than high quality OTs. Good OTs need lots of iron to keep the core from saturating at high power/low frequency operation, but they also need to be wound a certain way, called interleaving, in order to flatten the frequency response out. It's much more time consuming than conventional winding (remember, a power transformer only has to operate at one frequency: 50 or 60~), so it's going to cost more to build. Just as a f'rinstance, my Eico HF-89 OT clones (as well as the originals) have 16 different wire gauges in the primary winding, alone. Most console makers figured their customers wouldn't hear the difference between a low or medium quality OT and a high quality one--especially given the crappy speakers they were using.
Therefore, when harvesting OTs from old chassis, be cynical and skeptical of their quality (unless you know for a fact that the chassis was built by a bona fide hi fi manufacturer). Then allow yourself to be pleasantly surprised if you should happen to find a sleeper.
Rule of thumb #2: If the OT has screen grid taps, regardless of manufacturer, it's probably at least medium quality. Look for leads going to pin 4 on most octal output tubes and pin 9 on 6BQ5s. The ECL8*s are usually either 7, 9, or 3. Consult your tube manuals for details on other tubes.
Rule of thumb #3: There is no rule of thumb for color coding. For single ended transformers made in the USA during the '50s and '60s, blue was usually plate and red was usually B+. Push-pull OTs usually went with blue as the start plate, red as B+, and brown as the finish plate. Screen grid taps, if present, were usually blue and brown with a yellow or white tracer. Again, if it goes to the pins mentioned above, it's a SG tap.
Dynaco transformers are a notable exception to the above.
Virtually all console "hi-fi"s had dedicated secondaries, usually 8Ω, and the wires were generally just enamelled wire. In the case of component amps, you can pretty much count on black being 0Ω. Brown was 4Ω a lot of times, as was green for 8Ω. Yellow was popular for 16Ω, but so was orange, in which case yellow might be 4Ω instead of brown.
Another couple of ROTs before I turn the podium over to fr?re Brown for his snappy method of determining primary impedance using nothing more than smoke and mirrors: DC resistance can tell you a lot about the windings, especially the primary, in a push-pull OT. Measure from the center tap (red) to either plate lead and record the resistance. Measure from the CT to the other plate lead and note its resistance. The CT->plate resistance that's lower will be the start side. Same holds true for the screen taps. Hey SWJ, weird how things happen in bunches, isn't it?
Finally, if you should happen across a carcass made by Voice of Music (VM), kindly discard most of the rules of thumb listed above (the DC resistance one will work, but you might not know how to apply the results). VM circuits could be the electronic equivalent of the Kraft Food recipes you used to find in TV Guide back in the '70s and '80s, i.e., totally, certifiably off the wall. All bets are off concerning VM output transformers.
Okay, Ed, you're on . . .
Eric in the Jefferson State