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#271
07-11-2011, 11:58 AM
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You know that your power supply is working somewhat, since you have a raster on the screen and full vertical & horizontal deflection. To put roundscreen's suggestion another way, it would be useful to find out if the right voltages are being supplied to other parts of the TV (such as IF sections). The 200-something voltage supply is often called "B+," as Bill says.
If you look at your basic power supply, it delivers two such voltages, +255vdc and +210vdc:  If you look around the full schematic, there are a number of spots where a little arrow from a section points to either +255vdc or +210vdc. http://antiqueradio.org/art/temp/Majestic1600A.jpg http://antiqueradio.org/art/temp/Majestic1600.jpg The arrow means that a particular circuit draws from that part of the power supply. If you want to be very systematic, you could start from the ground up, first checking to see if those two voltages are present at the two output points from the basic power supply. (I'm guessing the answer is Yes, else you wouldn't have a full raster.) Next, you could go around the schematic, checking each place where you see the little arrow to one of those supplies. If you find the right voltages at every spot, that's great! Power is reaching all of those main take-off points. Finally, you could go to page 8 of the Sams manual, which has the voltage chart, and zero in on the voltages for each tube. The highest voltage usually goes to the tube's plate. On V14, for instance, that is pin 3. Since the video IF was suggested, you can check the video IF tubes: V3-V4-V5. On those tubes, the highest voltage is at pin 5 (also 6). For the video section, this will answer roundscreen's question whether the correct B+ voltage is getting to those tubes. For the audio section, the IF tube is V8 and its plate is also pin 5. Voltage checking is tedious and you must be careful to avoid shocks. Put one hand in your pocket when touching the voltmeter probe to any point in the live chassis. In the old days, a repair shop would have a set of "tube extenders" that plug between the tube and the chassis, exposing test points for each pin above the chassis. If you don't have tube extenders, you can set the chassis on its side and measure from underneath. If neither of those is possible, you can wrap a short piece of wire around the pin in question, re-insert the tube, and measure from that wire (slip a bit of plastic or paper between the wire and the chassis to avoid a short circuit). An experienced repairman with a shop full of specialized equipment (signal tracer, oscilloscope, etc.) could isolate your problems much more quickly, but if you're armed with nothing but a multimeter, this slow approach can be useful. Read the little notes below the voltage chart before you start, and note the line voltage setting (often 117vac). For initial checks like this, I want to see whether a voltage is in the right ballpark. If the chart says 105vdc and I measure, say, 93vdc or 111vdc, I figure that's close enough for the tube to basically operate, and I move on to the next one. Sometimes, a bad reading will jump out at you, and then you can look for a burned resistor, miswired component, etc., in that tube's circuit. If you go through all of these measurements and don't find any bad readings, you have not wasted your time. It's useful to know all of the places where your TV does have correct voltages, and that would confirm that a lot of your recapping work was successful. If measuring voltages on the live chassis isn't practical, for whatever reason, you could fall back on the resistance chart, measuring resistances on the same pins. I normally do this from under the chassis, with the tubes in place. Sorry for the long-winded reply. This is my way of avoiding work on my Capehart set, where I'm unearthing ugliness like a burned-up width control  Phil Nelson 
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#272
07-11-2011, 12:49 PM
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Hey that's a nice tutorial, Phil.
There is another 'esoteric' feature that'll inevitably be encountered that may be a puzzlement to a Noob. And that is the 'B boost' or 'bootstrap' voltage generated by the damper tube's operation. It's a by-product of that diode's anti-ringing action, and appears as rectified DC that's stacked or 'bootstrapped' on top of the regular B+ supply. Hence it's called 'B boost'. When filtered, it turned out to be quite fortuitous and handy in supplying higher voltages for certain applications. One is the plate circuit of the vert. oscillator, enabling it to make a nice linear, high level sawtooth. Another is the high level audio detector (with the quad coil) used in Zeniths, which enables the detector to drive the output stage directly, eliminating need for a 1st audio stage. (In vts1134's set, the B boost is delivered to the low end of the vert. size control. And it also supplies grid 2 of the CRT.) Last edited by old_coot88; 07-11-2011 at 12:53 PM.
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#273
07-17-2011, 06:13 PM
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Thank you for the explicit explanation Phil. I've started to go over the set from the beginning, starting at T1.
Quote:
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#274
07-17-2011, 06:18 PM
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Quote:
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#275
07-17-2011, 06:41 PM
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Quote:
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#276
07-17-2011, 06:49 PM
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Quote:
 
Last edited by old_coot88; 07-17-2011 at 08:30 PM.
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#277
07-17-2011, 07:27 PM
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Quote:
 I'm pointing to the location where the leads were soldered together in the picture above. The terminal the right is where the proper ground lead runs to, it's terminal is connected directly to the chassis. Does that make any sense at all?
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#278
07-17-2011, 08:01 PM
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For most tubes, one of the filament pins will be connected to the heater source and the other filament pin will connect to ground.
In the full schematic, for instance, look at the video IF amps, V3-V4-V5. For each of them, pin 4 connects to the X filament source and pin 3 connects to ground. http://antiqueradio.org/art/temp/Majestic1600A.jpg So, what I would expect to find is a line running from the X source to each of the pin 4s on those tubes. A filament presents only a few ohms resistance, so if you disconnect the X line from a tube socket and leave the tube in place, that might be mistaken for a short circuit. If you remove that tube from the socket while the X line is disconnected from pin 4, it should show infinite resistance. I don't know if that clears things up or makes them more confusing . . . . Phil Nelson
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#279
07-17-2011, 08:23 PM
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Quote:
Now on that 12AU7 video tube (V6), both heaters are lighting, right?
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#280
07-18-2011, 07:08 AM
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At the risk of seeming an intransigent fuddyduddy
, i'd like to take the occasion to air a little sumpthin'. That's regarding usage of the terms "heater" and "filament". Back in the day, it was quite a big deal to use those terms correctly.  Any tube with an indirectly heated cathode uses a heater, not 'filament'. Any tube not using an indirectly heated cathode (eg., 5U4, 1B3, 1X2, 1R5, 80, 26, etc.) uses a filament, as in a light bulb.Any techie using the terms incorrectly would come under severe admonition and demerit. 
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#281
07-18-2011, 07:19 PM
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Quote:
 )Anyhoo, just checking in with the progress so far, looks like you got quite a bit further since I last posted. (haven't posted since then since others know more about the specifics than I do)... Still got my fingers crossed for you!
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#282
07-31-2011, 06:39 PM
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I've taken a couple of weeks off from the set because I thought it was getting a little frantic. I've found that learning how to work on vintage tube electronics completely from an internet forum having no prior knowledge of the subject is quite an undertaking. I could not have asked for more knowledgeable and patient mentors and I think all of you for the efforts you have put through my hands. After two weeks of time away from the "bench" I am missing my TV time. Since starting this new obsession I've only worked on the Mighty Monarch and the radio half of an RCA 730TV1. I'd like your opinions, should I make another push on the Monarch or would it be okay to put it on hold for a bit more and start on the TV side of the 730TV1?
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#283
07-31-2011, 07:01 PM
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You gotta finish it! Don't leave us hanging, baby!
Seriously though, I have had to put things away and look at them fresh another day. Just do whatever feels right, and keeps you from being too overwhelmed. I obsessed over one project until it infuriated me and it ended up scrapped. Don't let that happen to you 
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#284
07-31-2011, 11:06 PM
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I try to tackle one (occaisionally two) projects at a time so my work space does not get too cramped. The two is for when I'm dying to work on something or when the stuff is small or easy.
That said you should do what you think is best/most fun. Tom C.
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#285
08-07-2011, 07:06 PM
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Decided on a second push with the Monarch. I performed OC's test on the video stage mentioned in post #267 again just to make sure I was doing it correctly.
 You can see M4 disconnected in the upper right hand corner of the picture and the clip lead on pin 2 of the 12AU7 towards the middle. The test produced no results. Quote:
 This is a picture of the 12AU7, lit up like a Christmas Tree. All other tubes in the set are also lit. I've also checked the voltages on several of the tubes including all of the video section. What I've noticed is that with my input voltage at 117vac my B+ is running around 15% high across the set, but it is getting to the correct pins. I have not checked the voltages on the tuner tubes. Measuring them from the bottom of the set is impossible so I will need to acquire some extenders. I'm going to bring some new tools to the party to help the second push along. I'll have a scope, and a video generator tomorrow. I'm not sure these will help in my current campaign, but they're there if needed.  I hope all of you who have been helping me along are up for a second push  .
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