‘Tube Testers’ Category

Test Seeburg 2050 tube on Sencore Mighty Mite

The 2050 Gas Thyratron tube is a tube used in many Seeburg jukeboxes.  Even though a 2050 tube is not listed on the setup charts of Sencore Mighty Mite models TC162 and TC28, you can test them.

Settings are 6-A-5, socket #1.

The key to a proper test is that you MUST engage the LIFE TEST during emission testing to reveal a substandard tube that will not reliably handle the current levels needed.

Here is an example of testing a weak 2050 tube in a TC28.  Notice that the first picture, you may think that the tube is good because the emission is strong.  However, the 2nd photo shows that with LIFE TEST engaged, the emission drops to almost nothing.  This is the key to testing ANY tube in a Mighty Mite, but especially for any power tube, thyratron tube, or rectifier tube.

Testing 2050 without engaging LIFE TEST, fails to reveal a substandard tube

Testing 2050 and engaging LIFE TEST, finds the weak 2050 tube

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Sencore Mighty Mite chart data EAF801

Simon Flint from Australia contacted me today because he noticed that the Sencore Mighty Mite setup data for the diode section in tube EAF801 (which is an RF Pentode with Diode section) did not appear to be testing the diode section properly.  He wanted to know if I could investigate.

I examined the Telefunken datasheet for EAF801 and have determined that the Sencore setup data for this diode section of the tube is wrong.  It places far too much load on the diode, causing the meter to incorrectly read low emission.

The EAF801 diode section is only rated at 0.7ma according to the Telefunken datasheet, therefore the chart setting (D load) will draw far more current than the EAF801 diode can handle.  In fact, extended testing using this incorrect chart data will ruin this diode section.

My analysis suggested that Load G is the correct load for the EAF801 diode section.  Simon tested this load, and has verified that my analysis is correct.  Thanks to Simon for diligently testing the new load setting and verifying that it is now correct.

So for the diode section (only) for EAF801, the load should be G…not E.  Make a notation in your chart to reflect correct load (the 2nd line of the setup data for EAF801).  Purchases of my TubeSound Sencore mighty mite setup book will have this factory mistake corrected if purchased after March 12, 2021, and the correction will “look factory”.

CBS Hytron 12BH7 letter about Hickok test

Here is a letter from the Technical Service department of CBS Hytron tube company, dated June 1954, that discusses a common problem with tube testers.

In this letter [ PDF ], which I scanned and restored via Photoshop for better readability, a person from the Max Fischman Co of Pittsburgh wrote to CBS Hytron Co. asking them why so many CBS Hytron 12BH7 tubes were testing weak on their Hickok 533A tube tester.

CBS Hytron investigated the matter by testing 50 CBS Hytron 12BH7 that were known to be top quality and passed factory testing.  They also tested 12BH7 from other manufacturers.  Their analysis revealed that the test configuration — the operating point — for 12BH7 as provided by Hickok was incorrect to target the listed micromhos value of 2380 µmhos.

Learning points from this letter:

  1. Again, as I have tried to instruct in previous articles, there is no such thing as a “correct” (or single) mutual conductance score.  Mutual conductance is a result of the operating point of the tube (plate voltage, signal voltage, grid bias, etc.).
  2. Factory setup data OFTEN provides a substandard operating point for the tube in question.  This is sometimes because of mistake or carelessness in creating the setup data, and sometimes due to design limitations of the test circuit (one fixed signal voltage that is substandard for a particular tube, or a fixed plate/screen voltage that is substandard for that tube).
  3. Learning to KNOW YOUR TUBE TESTER is of utmost importance, not blindly relying on the results that you see on the meter.  A seasoned tech who worked with 12BH7 tubes on a regular basis would have discovered this issue and learned to work around this problem — either by creating a new Bias setting that more appropriately would target 2380 for a typical new 12BH7, or he would have noted what Gm score was more accurate at the bias point given in the setup chart.

 

NOTES: (1) the letter refers to mutual conductance readings as “Sm”, which I am not aware of that abbreviation.  I believe that “Gm” is the standard abbreviation.  (2) the secretary who typed the letter misspelled Hickok as “Hickock”.

 

TV-7 micromhos conversion calculator

TV-7 tube tester micromhos calculator
Meter: µmhos

DIRECTIONS:

  1. Enter your meter reading (0 – 120) into the “Meter” box.
  2. Choose your Range Switch position in the drop-down box.
  3. Press the “Calculate Gm” button and read your micromhos score.
  4. Press “Reset” button to clear your entries or to start another calculation.
  5. Invalid entry ( meter > 120 ) will automatically reset the calculator.

NOTES:

  • calculator works for all TV-7 models: TV-7/U, TV-7A/U, TV-7B/U, and TV-7D/U
  • calculator requires javascript
  • Range A on TV-7 is only used for emission testing of diodes and rectifiers — no mutual conductance reading exists. Therefore, I have omitted Range A from the calculator. The Range A meter reading is an arbitrary emission score that is evaluated in relation to the “Minimum Value” notation in the setup book.
  • Range B signal voltage is 5.0v ac with bias 0 to -40 vdc
  • Range C signal voltage is 5.0v ac with bias 0 to -40 vdc
  • Range D signal voltage is 1.0v ac with bias 0 to -40 vdc
  • Range E signal voltage is 0.5v ac (500 mV) with bias 0 to -40 vdc
  • Range F signal voltage is 0.5v ac (500 mV) with bias 0 to -4 vdc.  Range F is 0 to 30,000 micromhos, not 60,000 as reported elsewhere.  Click to “Read the rest of this entry” below for details.
  • ©2014 TubeSound

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TubeSound TTM-1 Tube Tester & Matcher

Meet the TubeSound TTM-1:

  • Testing of almost all amplifying tubes (triode, tetrode, pentode, beam power) from antique 4-pin (such as a #10, #45, or #50) through 9-pin novar (such as a 7868).   Socket configuration — 4-pin, 5-pin, 6-pin, 7-pin medium (aka 1625), 7-pin miniature, octal, loctal, 9-pin-miniature, and 9-pin novar.
  • All tests use exact tube operating parameters found in any “Receiving Tube Manual”
  • 5 digital meters (each better than 1% accuracy, as verified with two Fluke DMM’s) continuously monitor the tube operating parameters.  1 meter for each plate voltage, screen voltage, grid voltage.  1 meter for plate current, 1 meter for heater voltage.
  • VR (voltage regulator) tube testing throughout its entire operating range.  VR tube voltage drop continuously monitored, and starting voltage is easily observed
  • Mutual Conductance testing via grid-shift method
  • testing of tube Amplification Factor
  • Plate current matching at any single operating point, or you could plot a set of curves.

Design specifications:

  • regulated plate voltage, variable 0 to 500 VDC (0 to 410 continuous)
  • regulated screen voltage, variable 0 to 500 VDC (0 to 410 continuous)
  • regulated grid/bias voltage, variable 0 to -100 VDC
  • plate current up to 200 ma
  • heater voltage accurate within 0.1v.

My intention was not to replace any vintage tube tester, but instead, to supplement functionality that does not exist in traditional tube testers.  For example, transconductance testing is certainly much easier using the dynamic test of a B&K or Hickok.  Likewise, grid leakage sensitivity is best tested in a Mighty Mite or similar machine.  But none of those machines recreate the static operating parameters that a tube will see in an amplifier, therefore they do not meet the needs of some tube buyers who want their output tubes matched for idle plate current at the operating parameters of a real amp.  Moreover, no standard tube tester will properly test a VR tube and allow you to monitor its performance over its entire operating range.

Photos below show testing of a new Sovtek 5881/6L6WGC using two different receiving tube manual examples from 6L6GC “Typical Operating Conditions, Class A1 Amplifier – Pentode”.  The third photo demonstrates testing a new 0A2 regulator tube.




I have a few cosmetic issues to finish, but otherwise the first model is complete (for now). I have ideas for other features that I may add in the future. The TubeSound TTM-1, in combination with our classic tube testers, covers a wide range of tube analysis that will meet the needs of sophisticated customers.


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