Precision 912 Tube Tester

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Precision 912 Tube Tester

Post by MEZLAW on Sat Nov 17, 2012 8:51 pm

I found one of these today at an antique show in Richmond Virginia;

http://www.swl-remotes.com/vintageradio/tubetesters.html

The dealer was asking $145 and by the time I left he was down to $110. I have no idea what they are worth. It was in great shape cosmetically.


Last edited by MEZLAW on Sat Nov 17, 2012 8:59 pm; edited 1 time in total (Reason for editing : spelling error)

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Re: Precision 912 Tube Tester

Post by willy3486 on Sat Nov 17, 2012 10:05 pm

I am not sure of the value but from what I have seen on Ebay being sold I say you probably got a deal. I have one of the Precision like the 10-12 on that page. If its not the 10-12 its close to it. I have had mine since the late 80s. It has been a exceptional test piece. I think you will be well pleased. I have a Hickcok as well. It works but needs a case and a new paper roller. I have the paper roll copied and in a book. I just bought a Sencore mighty mite from the 60s so I could test newer tubes. I don't think the roll charts I have has the test info on the precision and Hickok testers for some of the newer tubes. But for most of the tubes you run across I don't think you will be disapointed . The precision testers are really nice.

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Re: Precision 912 Tube Tester

Post by MEZLAW on Sat Nov 17, 2012 10:28 pm

I didn't purchase it yet, but I did get the dealers business card. I didn't make the purchase at the time because I didn't know the value and I do have a tube tester I bought new as a kid. It's a Lafayette TE-55, not much but it does OK for me.

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Re: Precision 912 Tube Tester

Post by Guest on Sun Nov 18, 2012 6:31 pm

That would be an attractive tester. I have a Knight 600 and lots of regret for not picking up one of the depot overhauled TV-7's that went on the market around 1993 for $20.

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Re: Precision 912 Tube Tester

Post by Dr. Radio on Tue Nov 20, 2012 8:42 am

Appears to be an emissions tester. It's beautiful, but I would not go crazy ($) on a simple emissions unit. Transconductance units cost more, but give you a better idea of the tubes performance. I'd like to find one as all my units are the emissions style Wink

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Re: Precision 912 Tube Tester

Post by MEZLAW on Tue Nov 20, 2012 9:31 am

Agreed, I think even $110 is too much to pay. It's not like he has many prospects looking for such a unique item! I'll let him sit awhile longer and maybe make an offer closer to Christmas.

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Re: Precision 912 Tube Tester

Post by 35Z5 on Sun Dec 30, 2012 5:46 pm

The Precision 6xx, 9xx & 10xx aren't mutual conductance but are a dynamic tester, more or less identical to the Jackson 648 series...

I have a pretty good collection of the early Precisions, including a 500 and a rather rare 900 which is the fore runner of 920(both have built in VOM) and models like 910, 912, etc that are std tube testers...

This is a 900A, the earliest versions(900) did not have the Loctkal socket, I have one of those as well... Best I can determine the 900 models were only built in 1938 & likely early 1939...



Note there is no roll chart in a 900, which is the only 9xx model that doesn't include one... The 900 also only has eight switchable circuits so tubes that have connections on all eight pins and a top cap can't be tested dynamically(must use emission), the 910 thru 954 have nine test circuits...

The 9xx series was introduced mid '39 and was discontinued in 1947... WW-II versions bought by Uncle Sam for the armed forces divisions are fairly common...


My early 912, still has it's orig Aug '39 roll chart...

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Re: Precision 912 Tube Tester

Post by Guest on Sun Dec 30, 2012 6:25 pm

That is a great looking set!

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Re: Precision 912 Tube Tester

Post by Bill Cahill on Sun Dec 30, 2012 8:00 pm

Precision tube testers are not great, at best. They are an emissions tester, and, work off the line. The power transformer is for filaments, only. The plate of the rectifier goes directly to the hot side of the line.
That is too much money for that tester. I wouldn't give more than about sixty dollars for it.
I have the model with the chart. They sure look impressive, though.
Bill Cahill

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Re: Precision 912 Tube Tester

Post by MEZLAW on Sun Dec 30, 2012 11:41 pm

I agree Bill and I'm not sure he will consider that low a price but I don't want it that bad either! I thought he was way out of line at $145

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Re: Precision 912 Tube Tester

Post by 35Z5 on Sun Dec 30, 2012 11:47 pm

Bill Cahill wrote:Precision tube testers are not great, at best. They are an emissions tester, and, work off the line. The power transformer is for filaments, only. The plate of the rectifier goes directly to the hot side of the line.
That is too much money for that tester. I wouldn't give more than about sixty dollars for it.
I have the model with the chart. They sure look impressive, though.
Bill Cahill

Guess you don't understand the difference in a dynamic and emissions tester eh Bill???

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Re: Precision 912 Tube Tester

Post by Bill Cahill on Mon Dec 31, 2012 12:29 am

I have a fairly good idea. And, emissions isn't that bad, but, dynamic is better. I used to use Eico tube testers which were dynamic. The problem with an emissions tester is they aren't as accurate as dynamic. Of course, no tube tester is always right.
Bill Cahill
My Hickock is both a dynamic, and, an emissions tube tester. But, as Hickock says, the true test of a tube for leakage, and, such is dynamic.

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Re: Precision 912 Tube Tester

Post by Resistance is Futile on Mon Dec 31, 2012 12:43 am

From Wikipedia, the free encyclopedia


A tube tester is an electronic instrument designed to test certain characteristics of vacuum tubes (thermionic valves). Tube testers evolved along with the vacuum tube to satisfy the demands of the time, and this evolution faded with the tube era, yet with the High-End advent, they became a pricey piece of equipment. The first tube testers were simple units designed for specific tubes to be used in the battle fields of World War I by radio operators, so they could easily test the tubes of their communication equipment.
Contents
1 Types of tube testers
1.1 Filament continuity tester
1.2 Tube checker
1.3 Emission tester
1.4 Short circuit test
1.5 Parametrical tester, DC Type
1.6 Parametrical tester, AC Type
1.7 Mutual conductance tester
1.8 Dynamic conductance tester
1.9 Oscilloscope tube curve tracer plug-in

Types of tube testers

Filament continuity tester

The simplest one is the filament continuity tester, usually with a neon lamp connected in series with the filament and a current limiting resistance fed directly by the mains.

Tube checker

The simplest of all tube testers. Tubes are used as low power rectifier, at a fraction of its normal emission. By mistake referred to as Emission Tester sometimes.

Emission tester

Next in complexities is the emission tester, which basically treats any tube as a diode by carefully connecting the cathode to ground, all the grids and plate to B+ voltage, feeding the filament with the correct voltage, and an ammeter in series with either the plate or the cathode. This effectively measures emission, the current which the cathode is capable of emitting, for the given plate voltage, which can usually be controlled by a variable load resistor.

Older testers may call themselves Plate Conductance if the ammeter is in series with the plate, or Cathode Conductance if the meter is in series with the cathode.

The problems of emission testers are:
they do not measure key characteristics of tubes, like transconductance
they do not perform the tests at real load, voltages and currents
they test the tube under static conditions, which are not even near the dynamic conditions the tube would work with in a real electronic device
tubes with grids, might not even show the real emission because of hot spots in the cathode, hidden by the grids under normal conditions

The advantage of an Emission Tester is, from all types of tube testers available, it gives the most reliable warning for tube wear out. If Emission is at 70%, transconductance can be at 90% still, and gain at 100%. Best and most popular Version used by the German army, is the Funke W19.

The disadvantage of an Emission Tester is, it can test a good tube as bad, and a bad tube as good, because other qualities of the tube are ignored by this type of Tube Tester. In America, Drug Store Tube Testers were very popular, and were intended to make money for their proprietors. Many Tubes were sold that were not needed based on the criteria of Low Emission. A Tube with Low Emission will work perfectly fine in most circuits, and should not be replaced by that indication alone, unless it measures much lower than specified or if it indicates a short.

Short circuit test

Usually, emission testers and better testers have a short circuit test which is just a variation of the continuity tester with a neon lamp, and which allows to identify if there is any shortcut between the different electrodes.

Parametrical tester, DC Type

This tester Applies DC voltage to the Tube under Test, and datasheet values are verified under real conditions. Good examples are Funke W20 and Neuberger RPG375.

Parametrical tester, AC Type

This tester Applies AC voltage to the Tube under Test, and datasheet values are verified under conditions which simulate DC operation. Most popular are the AVO testers.

Mutual conductance tester

The mutual conductance tester tests the tube dynamically by applying bias and an AC voltage to the control grid, and measuring the current obtained on the plate, while maintaining the correct DC voltages on the plate and screen grid. This setup measures the transconductance of the tube, indicated in micromhos.

Dynamic conductance tester

The dynamic conductance tester is just a variation of the emission tester with its implications, where a proportional AC voltage is applied to each electrode. This tester exists thanks to Jackson mainly to avoid infringing the patents of the mutual conductance tester held by Hickok, but obviously do not provide the same measurements.

Oscilloscope tube curve tracer plug-in

A full set of characteristic curves for vacuum tubes, and later for semiconductor devices, could be displayed on an oscilloscope screen by use of a plug-in adaptor, or on a dedicated curve tracer. An example is the Tektronix 570;[3] this instrument as of 2011 is rare but still sought after, and sells for thousands of US dollars.

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Re: Precision 912 Tube Tester

Post by 35Z5 on Tue Jan 01, 2013 7:05 pm

Well you guys can refer to the dynamic testers as just a emissions tester but if you know how to use one, the dynamic testers provide more info than a run of the mill emissions tester...

In a std emissions tester, generally all elements other than cathode are tied together, not so in a Precision 9xx series... There are separate voltage supplies for all elements(B-J buttons on 912 pictured), so if say a grid or plate connection is open inside the tube it's going to test bad, not so on a tester that ties all the pins together... On those you can toss the grid/plate cap out the window and most of the time there is little difference in the reading, again not on a 9xx series, loose the top cap and you get nothing... Also there is a variable voltage supplied to the control grid(s) through control C, that will provide proof the tube will conduct or not... Vary that setting and you'll change the meter reading(no it's not a load control, that's D)... The pentagrid types have setups for both the amp & osc to be tested, let's see your std emissions tester do same...

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Re: Precision 912 Tube Tester

Post by jerryhawthorne on Wed Jan 02, 2013 5:43 pm

I have a 912 and for it's limited use, I love it. Yes, just a low end emission tester but it will test any tube you can find! I also have a book put together for the tubes that are not on the roll. It will tell me if the tube is dead or shorts. I find that most tubes tested weak on it are just fine. Overall, I like it for its ability to test most any tube for emission. I don't rely on it to tell me if to tell me if a tube will work well, let's face it even the most expensive of tube testers won't really tell you if an oscillator will work properly. I just use it as a guide. I'm working on a Philco 38-116 now and most all tubes read in the weak area. Well, the radio runs strong! Love my 912, it looks cool and takes little space.
Jerry

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