In case you don't know, this is a oldey-timey CRT oscilloscope used by the USN back in the 20th century. It doesn't have an accurate timebase, and the triggering options are primitive, but it does have a 3 inch CRT that lets it do something these nifty digital scopes don't usually do well at all: X-Y mode! OK, I'm sure you can spend enough and find a digital O-scope that does a decent X-Y mode, but I don't think anything less that a kilobuck will do it. So I have this OS 8, and there's my dual-channel signal generator, and it struck me that it'd be fun to drive it in X-Y and make some 'lissajous figures'.
Problem #1: The carrying-case top latches to the case bottom against a rubber gasket. This gasket has done a heroic job of excluding incursions of arthropods and humidity, but the last time it was asked to 'let it go' was probably 1998, and the thing had turned into something more like epoxy. It used to be soft and white and squishy. Some leverage was required to pry the case top loose, and revealed the gasket had turned brown and somewhat crystalline looking. That'll need a replacement. Probably a section of old 23mm bicycle inner tube will have to do for now.
Problem #2: The CRT has this nice shroud-piece that you can slide in and out, which is just a felt-lined cylinder around the face of the CRT, that you can use to combat glare on the glass face. The fit is a little snug, I suppose so that the shroud will stay wherever you slide it to. For storage you need to push this all the way in, but in operation, you almost always want to pull it out part way. So I went ahead and pulled on this ever so gently ... and the shroud and the CRT both slid forward. Not Good. Didn't think I could possibly have pulled hard enough to un-seat it from the 12-pin socket. Well, it was already at full extension and was offering no change in resistance, so I slid it all the way out. OH BOY. There at the base of the CRT, where you'd expect the black bakelite tube base, was nothing but the bare end of the CRT with 12 springy steel wires sticking out. The tube had separated from its own base. Let that be a lesson, kids: when drawing the shroud out, keep your other hand on the face of the CRT and provide just enough force to balance the pull you're putting on the shroud. Fortunately, those big fat pins on the tube base actually have open ends, they only look solid b/c usually those wires are soldered into it. I managed to clear the old solder from the openings, and by some combination of persistence and luck, to get all ten (*) of those wires to fit back into their pins, and solder the lot. Remeains to be seen if this works.
Starting to make sense of the Transoceanic's "coil tower". Basically you have three adjustable band-pass networks in there. Each network has a section of one of the seven front-panel's band switches, so that's why there are 21 switches. Still haven't managed to grok those switches, but that level of detail is not necessary to an overall understanding. So you have three networks, which fwiw seem to include the main tuning capacitor. First is the 'antenna' section, that filters between the antenna and the 1st stage, the RF amp. The next section filters between the RF amp output and the 1L6 'converter' input, which on the schematics is refered to as the 'detector coils'. (In what way these detect anything, idk.) The last group is used by the bottom two grids of the 1L6, which is in line with calling it the 'oscillator coil' section. The happy news here? Those three sections appear to function independently, insofar as each has a clear purpose within the set. There aren't any confusing interconnections between the three parts of the coil tower. Now, they're not of course totally independent; each makes use of part of the main tuning capacitor, and the same band-switches, so they work in concert (super-het!), but electrically they're independent.
Had another idea about how to maybe breathe life into the old Y600 (turns out, it's probably a 'Y' owing to the 6T40Z chassis), which is this: use a BJT to perform Local Oscillator (LO) duties, and re-wire the 1L6 socket to take a 1T4 to function purely as a mixer. Frankly I like this idea better than bypassing everything.
Some have mentioned that these 1-volt tubes don't even glow. Supposedly they are really quite sensitive to filament current, and e.g. a 1L6 that oscillates with 1.3V across its filament might not with just 1.25V -- don't quote me on those values, I only intend to illustrate how finicky these things are. For tubes that don't even glow, they have some attitude. Now I really want to get this Y600 in action, to see if these low-voltage wonder tubes even get warm.
Which brings me to another of my throw-a-semiconductor-at-it ideas: an LM317 could be made into a nifty 50mA current source for that filament string.
Finally, I'd like to mention that the coil-tower/band-switch apparatus in the TO is an absolutely diabolical piece of work. If someone on antique radio forums should happen to know the theory on that, pls DM justjeff over there, would you? Thaaaanks. Seriously, I get it's essentially a load of different band-pass filters, I get what 'antenna coils' and 'oscillator coils' would do, but what the heck does a 'detector coil' do?! There are no fewer than 21 switches behind those seven band select buttons, many of which reconfigure 5 or 6 lines. Heck, they can't even make a schematic using normal switch symbols, they have to resort to depicting the physical shape of the slider and its relation to the contacts! How did anyone ever design a thing like that? Then there are a dozen-ish lines off that coil tower, tied into things like L2 and L4, and a pile of spaghetti between all that and all the grids on the 1U4 RF amp and the 1L6 converter. I know what a super-het does, just, dang if I can make sense of how the Y600 gets its super-het on.
Fun with a Zenith Trans-Oceanic T600, and the dreaded open filament 1L6. If you do come into possession of one of these TO sets, I'd recommend first thing, pull the 1L6, and put a continuity tester on pins 1 and 7 (the two adjacent to the gap), b/c if that tube is blown, your project just got a whole lot more complicated and or expensive.
See, they never made very many of those, the youngest ones date from 1962 or so, and NOS are fetching $100/ea. Worse, it's a vacuum tube peculiarity known as a pentagrid converter, which combined an oscillator and a mixer using vacuum state voodoo, making drop in replacement a dicey proposition. How is it that cheap pocket radios do this same 'converter' with just a single BJT? If I figure that one out, maybe I'll share..
I did have this perfectly horrible idea: what if I were to bypass the entire hollow state signal train? Make use of the mechanical marvel band switched tank circuits, and the IF cans, but craft a tiny little transistor equivalent of the tube sections, and tuck it under the chassis where it wouldn't be seen? I don't mean to trick anyone, I just want this lovely old radio to operate again. Not to worry, probably never happen. There just aren't that kind of free hours in a day.
Also have an R392, the indestructible army radio that some well meaning person rendered destructible, and which is now in need of serious TLC, so that may feature here in future.