With the repair bench ready, I am starting to revamp my test equipment. 1st on the list is the Precise 111M tube tester. This one is a little different than most I have seen. It must be a later version, since it has sockets for the newer compactron type tubes. Since I will be working on TV's as much as radios, this one appealed to me since it has sockets going back to the 4 pin tubes as well. No adapter needed! The major drawback (to me) is that there are more knobs to set than for a Hickok. But, it does look like a more thorough tester too, so it has its place.
I have gone through the calibration procedure with my other 111, but this one is a little different. I don't have the manual or much of any updated tube charts. Bama has manuals for the older versions, but so far, I haven't had any success in finding info on this "M" model. It is the same as a Radio Shack (Realistic) 113. Any help in this area would be greatly appreciated.
This tester appears to have very little, if any use at all on it. There is absolutely NO wear anywhere on it! It has never even had screws put into the cabinet! I kind of wonder if it ever worked right. My first test revealed a 'bouncy' meter, and inability to set the 'line'. It does test tubes, but I am sure it's off. My 1st step is to recap, then attempt a calibration. This one also has a transistor tester. It could complicate things, since I don't have any assembly/calibration instructions. Any info, insight, advice or comments welcome.
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The insides remind me of that sea creature from old legends.....the one with lots of tentacles.
Or of Medusa Gorgona.
Looks intimidating.
Yea, looks like spaghetti in there. This one is worse than the 111, since it has the transistor checker in it also. I may have figured out why it wasn't used any or very little:
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This 2nd pic is a switch from a 111 without the transistor tester function. This is S2, the "test" switch. I may be saved since what I think is the "tube" part of the switch nearest the chassis looks ok. I may be able to use it with the broken switch. But, if not, any ideas on how to repair? It only has contacts on the top side. I have an idea, but before I attempt, has anyone dealt with something like this before? Or does anyone have a 'parts' unit that I could obtain the switch from?
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The 3rd pic I found interesting for obvious reasons.
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So far, I have found a broken NE51 shorts bulb, a cracked meter, (very small), and I don't think it will affect anything. I am getting ready to start the recap and try to locate a bulb. I don't have any schematic or assembly instructions. If anyone here has this and is willing to help, could you PM me please.
Progress:
Removed broken wafer. Any ideas on how to repair?
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The rest of the switch looks identical to the 111 switch. Without a diagram, looks like that part is for the tube testing part.
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maybe,,,some JB weld,--on the waffle switch
I could try that. Is JB weld conductive? I was thinking of some type of epoxy. Still open to ideas.
After thinking about this for awhile, I have started a repair attempt. I tried to wrap a wire around it as was mentioned. I didn't have any success, so I made a "jig" for the wafer to hold things in place, then used a small amount of epoxy to start off with where it was broken.
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I tried to make the wafer as straight as I could, and used the screws to apply pressure to force it together. It turned fairly well in the jig, and had continuity when in a 'test position'. This is step one. I hope this will stick things good enough to move on to step 2.
looking good so far!!
I finally had some time to advance on this project. I used clear epoxy to repair the switch. It seemed very strong, although I am sure if it gets bumped hard again, it will break. Been trying to come up with a way to protect it, but haven't found anything practical as of yet. A well shot picture saved the day in rewiring the switch. Love those digital cameras!
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I started the recap. Here are a few shots of the progress.
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I hope to attempt calibrating this weekend. I guess this till tell me where I am in the electronic part of this restoration. I found and repaired a broken lead on a resistor on the meter switch, but I don't know if I broke it or if it was already this way. There was a correction on the build sheet to add a .01 mf disc cap across 2 and 9 of the screen voltage control. I added this, since it hadn't already been done. I also found a 220K resistor out of spec on the test switch, so I replaced that too.
I had a switch on my Precision that was broken in three pieces. I used expoxy after wrapping the switch with tape to hold the pieces in place. It was not removed. All came out well except the 2.5V setting on the switch (filament select). It takes a little rocking and rolling in to get it to fire up. I wouldn't use JB weld as at least the one I used for another project was rather conductive.
Jerry
OK,,,I not the smartest!!!!,, But wye a electrolytic capacitor between the terminals on the meter ??? I would not think that would BE the cass,,,,when there looks to be a regular capacitor there ????
Kenneth, here it the shot of the cap that was across the meter originally. It looks like an electrolytic to me. It looks original. The meter is still 'bouncy' even with the new cap. I wonder if this is correct or if there should be something else in there? It doesn't show this on the schematic.
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I attempted calibration last night. It was out quite a bit, but not quite as much as I expected. Some of the pots were a little scratchy, but a few quick rocks with the adjuster cleaned them up. All went pretty well, according to the instructions - UNTIL I got to the point to calibrate the Em current. NOTHING! Double checked my settings, verified with another set of instructions, still nothing. Tried a different meter, - same, nothing. It is the step where you set the 6L6 for Em test, then put milliamp meter between the plate and grid jack on the front of the tester, then use the bias control to set for 20 ma, then set P11 for 3 on the 10v bias scale. Soooo - could be the reason why this tester was never used?? Going to check resistors and controls around the Gm Em switch, shunt etc, voltages on the plate and screen switch, and see what is there - or not.
I made some tests and so far haven't found any open resistors. Checked plate and screen voltages, compared between this one and a known good 111 and found the voltages almost identical, so it looks like things are starting to get interesting.
Added:
I just discovered that I can test rectifier tubes, which are Em tested, on this tester. I tried several different types. But, I still cannot Em test any amplifier tube. I tried several different types also, different socket and pin arrangements. None will test Em, but all will test Gm. This is starting to sound like a wiring error. Looks like I am going to have to go through the build steps and hope to find something.
I just spent more than an entire day going through the construction manual checking all the wiring - step by step. Result? Big fat 0!
Nothing I could see wrong. Well, I did find a couple of oddities, such as a calibration control wired backwards and a grid connection to the loktal tube socket center that I am not sure about. So, I am troubleshooting. So far, screen and plate voltages are present. I did find that when I switch the screen only to a different voltage, it checks (meter registers). Seems it only does not measure on the B setting, yet it shows the correct screen voltage on the tube. Plate setting makes no difference, nor does rocking the switches. So - this is where I am right now. Got the old 111 apart and am comparing.
Problem solved!
Defect in power transformer. I was studying that 50v ac feed for the G2 (position B), since all the others worked and discovered it is derived from the filament transformer 50V tap. Remember, the 111 uses separate power and filament transformers. The plate is fed AC 160v on the EM test from the power transformer, and the grid is fed 50-55v ac also. See where I am going with this yet? It didn't make sense that the voltages were all present, yet it still wouldn't work. ONLY the 50v ac was giving trouble. All others were working, so that meant the rest of the circuit had to be ok. Then I got to thinking about 'tube theory'. Could the transformers be out of phase? Double checked the wiring - connected correctly. I reversed the primary of the power transformer only. Bingo! Setting B" come to life and things calibrated right in! The G2 source was actually shoving the tube into cutoff via the screen grid. There was a positive half cycle on the plate while a negative half cycle was on the screen grid. The tube was doing exactally what it was designed to do, so no meter reading on that setting.
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In a nutshell, the primary of the power transformer was reversed internally. So I switched terminal 1 & 2. A factory defect, which explains why this was never used. A bear to figure out, simple to fix. A fringe benefit of all this is that I got to know this tester, basically have a NOS instrument.
I still am chasing a minor problem in that is the meter jumps some when doing a test, esp the Gm test on the more sensitive settings. Cleaned switches, checked solder connections. Not sure what to make of this. Isn't much, maybe 200-500 umhos. Don't notice it on the Em much or the higher plate shunt settings. Don't notice it on the old 111, same tubes. It was doing this before the big resto, so it isn't anything new. May be chasing a ghost.