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 Post subject: Calibrating an old Tube Tester, Superior SICO TW11 TW-11
PostPosted: Nov Fri 05, 2021 3:22 pm 
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Location: Saint Augustine, Florida Area
I’m looking for some ideas on an easy way to calibrate my tube tester meter. The tester is a just-acquired old Superior (SICO) TW-11 Tube Tester. Thankfully, it's working as expected, given its age. Yes. But its meter readings appear to be about 10-20 percent lower than expected, something I’d like to try to correct. Since forum readers here have infinitely more experience with these cheap tube testers, hopefully there'll be an idea or two on how to approach this. It’s no big deal. And I want to keep this simple (KISS). Thanks a bunch. Some of this set's particulars are listed below.
// Thank you very much. Mark MM, in NE Florida.
.
~~ Condition: The TW-11 here is in surprisingly good shape, unusually clean, inside and out. No evidence of replaced parts/resistors. All six of the original resistors have been replaced with quality resistors of the same value.
~~ Line Voltage. Schematic shows a design line voltage of 117v. My line voltage is 122v, roughly five percent higher. This affects meter readings (see below re filament voltage). No variacs here. No line voltage adjustment on the TW-11.
~~ Filament Voltage: Given the above higher line voltage, the tube filament sockets have voltages that are roughly five percent higher than optimum. This excess results in meter readings higher than they should be. As an example, the optimum, required 12.6 volt filament voltage on the tube sockets are roughly 13.1 volts, with or without load (tube being tested).
~~ TW-11 Meter. The unit’s meter is over 60 years old. Given its age and dubious quality, it might be expected to read somewhat lower over extended use. The TW-11 has no meter calibration pot.
~~ Schematic. Reportedly, the schematic for this unit has remained unchanged over the TW-11 long production lifetime, even though there were production changes in resistor values. See below.
~~ Meter Resistor. Not shown on the schematic is an 1800-Ohm resistor soldered across the meter solder lugs. I am presuming this resistor was added during later factory runs. The schematic does not show this resistor. Rather, the schematic shows only one resistance for the whole meter, shown as 1200-Ohms. I have not tested or measured the meter’s actual resistance or determined its current rating.
// Thanks very much for your comments and all. // Mark MM, in NE Florida.


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 Post subject: Re: Calibrating an old Tube Tester, Superior SICO TW11 TW-11
PostPosted: Nov Fri 05, 2021 6:13 pm 
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Mark MM wrote:
But its meter readings appear to be about 10-20 percent lower than expected, something I’d like to try to correct.

Bear in mind that this is a relatively inexpensive piece of test equipment, not an instrument. Treat its readings as indications, not as verdicts.

How did you determine that its readings are lower than expected?[/quote]

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 Post subject: Re: Calibrating an old Tube Tester, Superior SICO TW11 TW-11
PostPosted: Nov Fri 05, 2021 9:13 pm 
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Location: Saint Augustine, Florida Area
Thanks, Dale, for that reminder. In answer to your question, The set was acquired by "one of our own" on this web site who made it clear that the meter was reading low. That was confirmed by testing multiple tubes on a buddy's separate tester (Hickok).
Second Published Schematic: Separate to all that, special thanks to contributor Walter Sch.. who forwarded via PM a copy of the manufacturer's later published schematic for the TW-11 unit. It was entitled by Superior Instruments (SICO) as, "Actual As Built Schematic". It has the same date as the original schematic, as 12.04.56. This second schematic shows changes to all of the resistors, plus, it adds resistance across the meter terminals (shown as "5.6k + 1k series"). It also reflects different wiring for the neon circuit which consists of NE-2 bulb, the resistor, and the capacitor. This schematic will be posted on this site's Test Instruments forum later this weekend.


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 Post subject: Re: Calibrating an old Tube Tester, Superior SICO TW11 TW-11
PostPosted: Nov Sat 06, 2021 12:02 am 
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It should be appreciated that most of the test equipment was made availing the same components as were used in radio, albeit in some, of vastly superior quality. That means that they fail the same way.

Over the years I have had simple analogue meters like AVO 7X and Peak 200H plus a few tube testers and and a couple of ignition coil testers where waxed paper caps leaking and a few other bits have failed. I would therefore suggest you touch nothing until you perhaps, get a schematic and have an appraisal of the parts that are likely assisting in throwing it off, as happened in my AVO; Which was a leaking cap.

Lets not rush into this. You will get a better response in Test Equipment.

I would suggest we close it & move it there.

Marcc


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 Post subject: Re: Calibrating an old Tube Tester, Superior SICO TW11 TW-11
PostPosted: Nov Sat 06, 2021 12:26 pm 
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Thanks for your reply and those interesting thoughts and tid bits, Marcc. Yes, indeed, the Test Equipment forum has been rife with shared experiences with this model. Some experienced users there have serviced several TW11 units, as you know. BTW, here's but one surprising example (photo below) of what I found hidden in mine, something that happened at the factory, seen here if you examine closely every solder connection on this tube socket.


Attachments:
Tube Tester SICO TW-11 No Solder.20211029_193402~2.jpg
Tube Tester SICO TW-11 No Solder.20211029_193402~2.jpg [ 823.16 KiB | Viewed 696 times ]
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 Post subject: Re: Calibrating an old Tube Tester, Superior SICO TW11 TW-11
PostPosted: Nov Sat 06, 2021 12:54 pm 
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One often wonders as to what went on with quality assurance and some who Monkey with equipment & demonstrate a massive lack of skills, or any semblance of organisation. I was asked to write a little article for a radio magazine here in this very subject. Personally I have seen some real oddball things that never should have happened in a factory.

There are lessons to be learnt. Recently I had a 6D6 separate from its base as the solder had never taken on all pins (posted) same radio a fibril sticking out of a primary tap (photographed for article) a socket like that where pin7 6V6 had not been soldered, yet the radio had the evidence of more than one repair. I like a couple of manufacturer's did make a point of putting marker pen on every node as I check it so I know I have not missed it.

You will be pleased that you found it and it gives provenance to my point that the first thing to do with an apparatus unknown to you is check it. The chassis that came with the 6D6 also came with two caps with an end in mid air & one was a wrong cap. Both were duds.

If there are people who have serviced them, then surely there has to be schematic.

Marcc


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 Post subject: Re: Calibrating an old Tube Tester, Superior SICO TW11 TW-11
PostPosted: Nov Sat 06, 2021 3:57 pm 
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I would wonder if the undocumented 1800 ohm resistor is dragging down the readings.


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 Post subject: Re: Calibrating an old Tube Tester, Superior SICO TW11 TW-11
PostPosted: Nov Sat 06, 2021 5:08 pm 
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Mark MM wrote:
That was confirmed by testing multiple tubes on a buddy's separate tester (Hickok).

That is comparing apples and oranges. You would need to compare your TW-11 to other examples of the same model.

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 Post subject: Re: Calibrating an old Tube Tester, Superior SICO TW11 TW-11
PostPosted: Nov Sat 06, 2021 5:10 pm 
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AuroraOldRadios wrote:
I would wonder if the undocumented 1800 ohm resistor is dragging down the readings.

Possibly - Mark would need to measure the meter resistance with the 1800 Ohm shunt in place to see if it measures 1200 Ohms.

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 Post subject: Re: Calibrating an old Tube Tester, Superior SICO TW11 TW-11
PostPosted: Nov Sat 06, 2021 7:10 pm 
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the 1800 ohm resistor may have been selected at the factory for calibration, or it may have been considered as part of the meter when it was built. Or someone subbed in a replacement meter movement somewhere along the way and needed that value to get the thing in calibration.

I'd resist assuming it's not supposed to be there just yet. Best way to know is find someone that has one of these and see what its got in it.

Ditto, btw, with other resistors. Some may have been selected during calibration at the factory, and may or may not agree with the schematic and parts list.

And, a big +12 to the concept that one cannot compare the readings of one tube tester to those of another. That goes triple for different models and different manufacturers. Neither tubes, nor tube testers, were ever intended to be precision devices.

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 Post subject: Re: Calibrating an old Tube Tester, Superior SICO TW11 TW-11
PostPosted: Nov Sat 06, 2021 8:36 pm 
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You might try reducing your line voltage to 117 vac by using a variac . But as mentioned earlier it is not a precision device. Also you should make a couple calibration/ reference tubes for your own piece of mind. Use say a 6L6 and a 12au7 and record the readings you get on these tubes and then set them aside. Then later if you suspect something has changed check your reference tubes.
Henry


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 Post subject: Re: Calibrating an old Tube Tester, Superior SICO TW11 TW-11
PostPosted: Nov Sun 07, 2021 12:06 am 
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Perhaps it would be pertinent to post a link to a circuit showing where the mystery bit was found: I have never found it unusual to find bits with no ownership. Found a 0.4mfd dud cap swinging in mid air in a set lately & it's not listed. Even slipped chasses only to have a cap/ caps fall out onto the bench?

Marcc


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 Post subject: Re: Calibrating an old Tube Tester, Superior SICO TW11 TW-11
PostPosted: Nov Sun 07, 2021 1:37 am 
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Higher line voltage results in higher heater and plate voltages which should produce higher meter readings. But your readings are lower than expected. Therefore I would not expect that line voltage has much to do with what's going on here.

Since all of the resistors have been replaced with new ones believed to be correct, one very possible issue is that the meter has lost some sensitivity due to aging of its permanent field magnet. Problem is, none of the TW-11 schematics that have come to light so far reveal what the nominal sensitivity of the meter is, only its resistance. You'd either need to know the voltage or current for full scale deflection to determine if the meter has normal deflection or if it is reading low due to a weak magnet. Probably the only way to find out at this point would be to compare your meter to one from a TW-11 that reads normally.

As for getting it into calibration, meter magnets can be recharged if you can find a shop that still does analog meter repair, but they are going to run into the same problem. Without a spec to shoot for they won't know how much to recharge it to bring it into calibration. I would be tempted to replace the 5.6-k resistor with something else--perhaps a 10-k pot connected as a rheostat--to see if it will bring the meter reading up to a more suitable place. Making the shunt resistor higher in value will force more current through the meter and increase its deflection.

One thing to note is any numerical or relative percentage scales are to be taken with a full salt shaker. Companies like SICO did not obtain bogey samples of every tube under the sun and adjust their tube charts to read 100% for each tube type. They probably did test a few then they extrapolated the load settings for the rest to put the meter pointer somewhere into the green for any tube that had about 65% of factory new performance.

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 Post subject: Re: Calibrating an old Tube Tester, Superior SICO TW11 TW-11
PostPosted: Nov Sun 07, 2021 6:04 am 
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Looking at the circuit of that I would not actually class that so much as a having a transformer as such, but a tapped ballast, or auto transformer giving you a hot chassis situation.

It would appear that the internal resistance of the meter is 1200 Ohms and it calibrates using the 10K. With the information available And all discrete components in spec.one should be able to get some sort of clue, perhaps a Variac to set the input one should be able to get a clue as to the meters fsd current.

It may be that the resistor was used to try & get a loaded reading? Some of those similar units were Zeroed (fine tuned) on "Line" with a tube in it drawing heater / filament current?

Marcc


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 Post subject: Re: Calibrating an old Tube Tester, Superior SICO TW11 TW-11
PostPosted: Nov Mon 08, 2021 3:21 pm 
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Thanks again, to Chris, Marcc, Henry, Barry, Dale, Aurora, and Thomas Edison.

Yes, in later TW-11 productions, like the unit here, a resistor was added across the meter along with changes in other resistor values along with a wiring change for three components of the neon NE-2 circuit. That later production schematic is shown below, just fyi. Thanks for all the advice and comments here, guys. I now have a short list of checks and changes to make. 73. //Mark MM


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TW-11 Updated Amended Schematic Tube Tester..jpg
TW-11 Updated Amended Schematic Tube Tester..jpg [ 308.8 KiB | Viewed 522 times ]
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 Post subject: Re: Calibrating an old Tube Tester, Superior SICO TW11 TW-11
PostPosted: Nov Mon 08, 2021 6:02 pm 
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That schematic is actually the original schematic that someone has modified.

DM


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 Post subject: Re: Calibrating an old Tube Tester, Superior SICO TW11 TW-11
PostPosted: Nov Tue 09, 2021 1:24 am 
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That circuit also appears on Radio Museum. It would be a courtesy, one would think, to do as I have done to reverse engineered circuits like a recent STC chassis 59 where a circuit could not be found; As one example, of one sent to two sites to help others. The Schematic was clearly marked as to its origins, as it was not original, what mods were made, why and what set/s it was referenced back to. That set had been hacked.

I would be interested to know if "fsd" is actually marked on the meter. It is more common to have something like 2mA, 1mA on the face for the purpose of calculating shunts & series resistances. That sort of thing can also be useful for disconnecting & testing a meter to see if its got issues. The only other way is note if its correct on ohms at various points, which would then indicate voltage & resistance issues in the tube testing section rather than the meter movement.

Marcc


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 Post subject: Re: Calibrating an old Tube Tester, Superior SICO TW11 TW-11
PostPosted: Nov Tue 09, 2021 1:13 pm 
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The meter movement needs to be verified for both current and resistance. An easy way is to place a known resistor in series with it and connect to a variable dc supply. The resistance can be determined by the ratio of the voltages across the resistor and the meter movement. Ohms law will give the current.

example: for 1K resistor and 1200 ohms, movement voltage should be 1.2 times resistor voltage. Current = V resistor / 1K

RRM


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 Post subject: Re: Calibrating an old Tube Tester, Superior SICO TW11 TW-11
PostPosted: Nov Tue 09, 2021 2:38 pm 
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I am thinking along different lines. E.g. The AVO 7x has a 2mA movement. Therefore irrespective of its internal resistance we need 2mA to drive it to full scale. At what safe supply voltage is irrelevant, as long as the resistances give 2mA through the meter and it goes to full scale. Variance indicating an issue.

Marcc


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 Post subject: Re: Calibrating an old Tube Tester, Superior SICO TW11 TW-11
PostPosted: Nov Tue 09, 2021 5:09 pm 
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Here's a safe way to verify the specs of your panel meter, confirms what others have mentioned and gives you a step by step. Precision and accuracy is as good as your DVM

https://www.bbtvtestequipment.com/testing-a-panel-meter

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