Anyone here familiar withe the Sencore Mighty Mite TC114?

ndes01njd

Member
Hoping someone in here wouldn't mind sharing some knowledge and advise on these questions and issues that I'm having.20180917_165454[1].jpg

I posted this in Vintage HiFi with no response yet:

Just got an old Sencore Mighty Mite TC114.

When setting up for individual tubes listed in the set up book there are several occasions where it lists 2 and sometimes 3 different settings for switch D which I think is only used for calibrating.

How do you know which setting to use for the most accurate test?

When reading the scale what unit of measure do the numbers represent? I guess a tube reading 95 is better than a tube reading 82 during an emission test but what does it mean?

When I zero the needle when off then calibrate for a tube the needle is no longer zero when turned back off. Am I screwing up some how or do I have a junk tester? I'm starting to think that the movement on the meters needle needs to be cleaned because after adjustments are made I can tap on the tester and get additional movement.
 
multiple settings, say for a 12ax7, means there are two (or three - like for compactrons)
sections (triodes usually) that need to tested separately - in fact, most 9-pin signal
tubes are dual triodes.

some folks sell tubes with numbers like 57/62 or 112/117 are usually from the "brand-name"
tube testers.

these are meaningless because: 1) tube manufacturers do NOT measure to these numbers
2) tubes have native characteristics like curves for given grid voltage at various plate loadings, etc
3) a number like 57/85 is only valid for the tube tester's test voltages and loads and is usually
not even close to what that tube sees in any tube circuit, 4) the test measurement of a tester
gives no correlation to design center values which you might follow when designing a tube circuit.

any tube tester is used to determine whether a tube is usable and that's it. emissions is like a
green light it will probably work - a red reading is like a red light in your car. it can also
test for shorts where something inside the tube shorts against something else. then
there's gas. and lastly, if the tube heaters don't light up then it won't test proper and
therefore will not work.

the needle may move due to circuit loading, and unlikely to be fixed with cleaning. maybe
something in the test circuit needs a recap or a resistor upgrade.

tube testing is all relative, you only need to pay attention when you test power tube quads
where the amp needs a matched quad due to cheaper design circuits where individual
tubes cannot be individually biased.

if you are into flipping tubes, I suggest you follow the leaders or develop a tester that
matches what you see in tube data sheets but in the meantime:

test, use, and enjoy the music
 
Thank you for the info!

Not knowing any better I bought the tester thinking it would not only identify weak tubes but also gauge their strength so I could somewhat match pairs and sets for different amps that I have. From what I understand in your response thats not so much the case.

means there are two (or three - like for compactrons)
sections (triodes usually) that need to tested separately

So when there are 2-3 listed settings the tube needs to be tested in (all) settings?

any tube tester is used to determine whether a tube is usable and that's it.

So there is no real way to gauge the difference between a strong and weak tube with what I have to work with?
 
While there are some new tester designs for the DIY crowd, perhaps putting the resources on hand to use is much easier than designing an ultimate tube tester.

An emission tester has some merits, especially one with perhaps the finest shorts and grid leakage tests available to the vintage analog tester crowd.

First, let us confirm the abilities of ur Sencore. Zeroing the meter should be done while the tester is on. After a tube to be tested is inserted and warming up, the Cal. pot setup can be tweaked.
Try a tube which you know draws some hefty current, like an opt tube. Switches set to 6 A 6...as opposed to 6 C 6... draw more current. Thus, a 6L6 will be forced in the Sencore series, to draw more current than a 6V6 or 7591. For emission testers, this variable current sesitivity and draw is not often found !
Congrats on having the 114 ! Does it have the nice mirror in the lid ? That was to see the TV picture after changing a tube. You pointed the mirror tiward the tv pic and hoped you didn't get a shock while you crouched behind the tv and swapped a tube. Today, the mirror functions nicely to get a two-sided picture of a tube under test....

The "Life test" is the treat with emission testers. In fact, lowering the filament voltage a step is one of the most revealing tests with any tube tester. So, that old, Tekefunken or Mullard ECC83, even drawing its' little current, will quickly indicate it's strength by checking it at the next lower fil setting. If the emission reading stays high, you have a winner. If it drops quickly and below the minimum ? point, you know that tube is tired. Some tubes drop a little. Some stay perfect (they will have a long life ahead) and some disappoint quickly.

Learning how to read and understand your tester will come quickly. There is a manual reprint on the bay, last I looked, for about $10. Check with the seller if the schematic and calibration procedures are included within the pages.

Your tester is more versatile than the scientific folks give it credit...Enjoy !
 
If I don't have that particular one, I have one that is very close...in the top cover there should be a manual with all the settings for all the tubes it can test. Not sure how accurate
or how definitive it is, but at least as good as the old hardware/drug store machines ;)

Just don't bet the bank on it, as who knows last time it was calibrated (as same for mine). That said, tubeactive may have better info...
 
Zeroing the meter should be done while the tester is on. After a tube to be tested is inserted and warming up, the Cal. pot setup can be tweaked

It has 2 seperate adjusters for calibration. From what I understand one I believe is for the needle at rest when off just like an old amprobe tester would have. The second is identified as "CAL" which should be used when on and loaded.
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The "Life test" is the treat with emission testers. In fact, lowering the filament voltage a step is one of the most revealing tests with any tube tester. So, that old, Tekefunken or Mullard ECC83, even drawing its' little current, will quickly indicate it's strength by checking it at the next lower fil setting. If the emission reading stays high, you have a winner. If it drops quickly and below the minimum ? point, you know that tube is tired

in the top cover there should be a manual with all the settings for all the tubes it can test


I have a copy of the original set up book on a disc which came with the tester and although it doesn't give instruction to the questions I have listed, it advises this same voltage drop test. Seems to me that basic ohms law would say that if you drop the voltage on a restive circuit that the current would drop also, so I'm not understanding why a good tube wouldn't drop, but thats not my main question. I just want to be able to identify a strong vs weak tube. Not just good vs bad.
 
to the last questions from the OP:

if there two or more test settings, then try all, if for no other reason than to see if the sections
match if they are all the same configuration (triode for example) - this ensures they are not
defective, and in some fashion, compatible with each other if they test similar.

comparing tubes using a tester is not a 100% test - some tubes that fail one or more of the
tester's tests may work perfectly fine in an amp, tubes that do match (in some fashion by
comparing the results of the tester) may not necessarily work well in many tube circuits
that may require closer matching for all the parameters and at the operating environment.

here's a typical example - shared power output cathode biasing vs, individual output biasing
versus computerized biasing (to allow different tubes in the output stage and being able
to maintain biases for different tubes) which translates to perfectly matched pairs,
somewhat matched pairs, and a mix of el34 and 6550.
 
I have a Sencore TC114 Might Mite II. Have had it for about 15 years, after a friend of mine found one in his attic and gave it to me. Still have the original tube manual and the mirror is intact. I'm sure it could use some restoration but have never gotten around to it. Have used it many times to check all kinds of tubes.
 
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Multiple test settings mean that you're testing the individual sections of a multi-section tube. Think multiple tubes in one envelope. So, test accordingly. For example, a dual triode tube, like a 12ax/au/at7, you're looking to see if both sides are comparable. Some tubes have multiple sections totally different from each other, like the aforementioned compactrons. Some circuits use only one section, therefore a tube with a bit of run-time in this position will show it as a strong side /weaker side.
An emissions test just shows how much potential "grunt" it can do, bias load & such not so much. However, with it you can cull the obvious duds quick. Best test of a tube is to try it in a piece of gear. I've had old radio tubes that fail miserably in my hickok 533a mutual conductance tester that work reasonably well in a radio, so ymmv.
 
ndes01njd, You are thinking too technically about an averaging testing, non-precision device. Any emission tester mimics a milliammeter, but not with the precision of a transconductance tube tester's meter. Please realize you cannot match tubes or read accurate current measurements with an emission tester.

When we lower the filament V a bit, a newer tube, a non-abused tube will "stay strong" (while testing) longer than a tube which has less life left. This will be easily verified over time and testing more than a few tubes. When I use a transconductance tester, some of my "new testing" ECC83s read the same or drop only a tiny bit at 10VAC filament, instead of 12.6VAC filament. With the transconductance, "micro-mho" reading devices, adding a current meter can make matching tubes much more certain.

For now, enjoy and use what you have. Cull the weak tubes. Organize and set up a safe zone for the hopefuls. "Dispose" the shorted tubes. With the lowered filament Life test, you will quickly recognize which opt tubes stay strong. If your technical insights get the better of you, insert a miliiammeter into the circuit. You will still not be able to current match the tubes with an emission tester.

Just realize that the emission test is not "like an amplifying tube circuit" while most transconductance tube testers do, indeed mimic amplifying circuitry. An emission tester is usually thought of as a tester which makes all tubes into a diode. They either conduct and pass the tester's design and rated current well; or not. Most importantly, as you will surmise over time, the Grid Leakage and Shorts tests on the Sencores rivals some very expensive testing devices...I have had numerous tubes check ok on my Hickoks, then fail the leakage test on the Sencore. That leakage on an opt tube indicates a probable red-plate catastrophe over a short time of usage...

Be resourceful...use what you have available...strive for better in good time...

If there are any antique radio clubs in your area, or other audio folk nearby, possibly hooking up with an owner/user of a better tester will give more insights and "food for thought."
 
When I zero the needle when off then calibrate for a tube the needle is no longer zero when turned back off.

It seems you do have some dirt, corrosion, or stiction inside the meter itself. This is not uncommon for equipment that old that has sat for a long time, especially if it sat in less than optimal storage conditions.

I have a very rare 1950's radiation meter (not one of the common yellow ones) that has a very bad case of this. It's fortunate that a radiation meter does not have to be used frequently, but sad that the instrument is basically ruined because of this.

With the unit off, zero the meter by making small adjustments to the adjustment on the meter itself (plastic screwhead). Then gently tap the meter to move the needle, and see if it comes back to the same place (zero).

You can also make the needle move by (reasonably) rotating (yawing) the whole unit, or by turn it on momentarily.

It may get better over several tries. (a little OCD really helps. What could possibly be more fun that doing this for several hours?)

It's a good tester. Reasonable size, and yes, it will be very good for matching pairs or quads of tubes, as others have mentioned above.

Don't worry too much about the exact numbers. It is kind of like "S" units on (most, older) receiver signal strength meters. 2 CB's (for example) sitting right next to each other, and fed from the same antenna will probably report different "S" unit readings for a given received signal, but 2 different signals, that read the same on a particular CB (and antenna system), are, in fact, about the same signal strength at the antenna.

Wikipedia: "Most S meters on traditional analog receivers are not calibrated and in practice can only provide a relative measure of signal strength based on the receiver's AGC voltage."


These posts about tube testers make me miss mine. I remember it being large, fairly modern for the time, and when opened, it had sockets on both sides in a "landscape" orientation. From looking at pictures now, it must have been a B&K "Dyna Quick" 650. I had to sell it because of moving around, as people do at that age, but I wish I had it back now.
 
Thank you everyone for all the great information and advice. Now my basic understanding of things has broadened a bit. Only had it for a short time but have already made noticeable improvements on my Maggie, not having to play games guessing and wasting time. Was able to immediately Identify some good and bad tubes as well as several that were doing just fine but failed the voltage drop test miserably.
 
Good afternoon all. I know this thread is a bit old, but I'm hoping someone can answer a quick question about the MM II TC-114.... I'm restoring mine and trying to determine the appropriate values for R9 and R10. The schematic in the manual (and parts list) show R9 as 120k ohm, and the schematic shows R10 as 100k ohm. HOWEVER, my tester clearly has a 150k ohm R9 and an 83k ohm R10, based on the color bands. See pics.
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The difference between the spec &what's in yours isn't great. Probably not critical. As nothing looks toasted in there, probably ok to leave as-is. How do you mean "restoring", is there physical damage to it, & is it now functional?
 
it was full of gummy junk and the electrolytic caps were visibly leaking. About half the resistors were more than 10% out of spec, especially the sand covered tri tap resistor. There is some rust on the case, but the internals look liek they were spared any direct water contact.

I've replaced everything that was out of spec (except these two resistors) and put a new, known-good tube in it, cleaned the sockets, switches, etc.

I've actually noticed, upon further inspection, that the physical circuit involving these two resistors, and the associated short indicator bulb, doesn't match the manual, either! It appears that R10 and the bulb have been swapped, in addition to the difference in values. For this reason, I haven't powered it up, though when I first snagged it, I brought it up on my variac to check and make sure the transformer was good and the meter worked. Both pieces worked, so I shut it off to begin the overhaul.

See attached, labeled photo
 

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The 2 resistors in question only deal with the neon bulb. As there's next to no load on them when bulb is firing, & none when it's not, nothing to gain by replacing those. Your tester may have a slightly different neon bulb with a different trigger voltage than what's on paper, hence the slightly different resistors.
 
Many thanks, Cat! I sort of figured it wasn't relevant to the function outside of the shorts test, so I brought the tc114 up to 115VAC, did the cal/zero adjust, then checked the internal voltages. Everything seems to be working reasonably well. I'm below on the voltages listed in the specs, but when I bump the line up to 120VAC, things come pretty much in line, except pin 8, which stays around 4.8V DC and spec says 6V.
Also need to tighten up some of the pin sockets, but otherwise, this is a great little tester!
 
Cool beans! Check your line voltage, it's likely close to 120. Factor that in on your voltage readings. If you're within 10% of everything, call it good. Tube testers aren't precision lab-grade items. You want to be able to cull the obviously bad ones, these devices will do that reliably.
 
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