Hello everyone,
I had the "opportunity" to get 24 Telefunken tubes, model E88CC. I'm pretty confident they are genuine, for reasons I won't mention here. I have a uTracer and tested all the tubes. I made two tests :
From what I read, is that I should get the typical Ia around 15mA at its minimum, mostly between 100 and 110%. However, most tubes are in the range 70-85% for Ia.
Below an example for one E88CC, and I would like you to comment it. The question is, are all these tubes good for the waste recycling ? Or do I oversee something and I'm sitting on a "small fortune" ?
I had the "opportunity" to get 24 Telefunken tubes, model E88CC. I'm pretty confident they are genuine, for reasons I won't mention here. I have a uTracer and tested all the tubes. I made two tests :
- quick check, where I set heater at 6.3V, Ua = 90V, Ug = -1.3V, and verified the Ia, which should be a typical 15mA.
- the curve tracing, where I'm able to measure the current in the two triodes at the same time, in function of Va and Vg. In fact the same as above but for multiple points.
From what I read, is that I should get the typical Ia around 15mA at its minimum, mostly between 100 and 110%. However, most tubes are in the range 70-85% for Ia.
Below an example for one E88CC, and I would like you to comment it. The question is, are all these tubes good for the waste recycling ? Or do I oversee something and I'm sitting on a "small fortune" ?
Code:
Telefunken E88CC
SECTION 1
Test conditions:
Va : 90 (V) Swing +/- 9 V (10%)
Vg : -1.3 (V) Swing +/- 0.13 V (10%)
Test results:
Ia : 11.41 (mA) 76 % of nominal 15 (mA)
Ra : 3.05 (kohm) 117 % of nominal 2.6 (kohm) Ra = dVa/dIa
Gm : 9.92 (mA/V) 79 % of nominal 12.5 (mA) Gm = dIa/dVg
mu : 30 (-) 92 % of nominal 33 (-) mu = Gm*Ra
SECTION 2
Test conditions:
Va : 90 (V) Swing +/- 9 V (10%)
Vg : -1.3 (V) Swing +/- 0.13 V (10%)
Test results:
Ia : 11.19 (mA) 75 % of nominal 15 (mA)
Ra : 3.15 (kohm) 121 % of nominal 2.6 (kohm) Ra = dVa/dIa
Gm : 10.5 (mA/V) 84 % of nominal 12.5 (mA/V) Gm = dIa/dVg
mu : 33 (-) 100 % of nominal 33 (-) mu = Gm*RaAttachments
The datasheets specify the test condition as Va=90, Vg=-1.2V but lowering Vg by 0.1V hardly makes a difference. According to the datasheet Ia should then be above 13.5mA so these are at end-of-life.
If you feel the slightest hesitation in using them, I can take care of them and I can promise that they will have a good home. 😉😉😉😉😉😉
What will not happen is giving them away as used to see them for sale as NOS on the bay for hundreds of € a few days later. I have built headphone amplifiers using 6DJ8 and they work well in that one.
By the way some datasheet mention -1.3V and some -1.2V as typical Vg test value but bohrok2610 is right, the difference is negligible.
By the way some datasheet mention -1.3V and some -1.2V as typical Vg test value but bohrok2610 is right, the difference is negligible.
Don,t know about "end of life " but gm in my Mullard book gives 12.5 (mA/V) ,so yes they have been used but IMO using an AVO VCM MK4 they still have life left in them and again --IMO- I would not give them away.
Unless your tracer has been calibrated exactly with that brand of tube and is running according to specs there is not much to deduct from those results.
Different brands will give different results for the same model number. When checking manufacturers' recommended operating points you might find total different values - e.g. the Mazad ECC83 has a total different optimal operating point from e.g. a Mullard or Philips.
So I would not worry too much, best place to check these in in circuit and if they work there then just enjoy.
Edit: I just checked and Philips states 12mA for 90V, not 15mA (that is for 100 V), the genuine (old) Telefunken datasheet says > 9mA at 90V. Always check the original datasheets, different manufacturers are not the same.... (which is why tube rolling is noticeable at times). According to my intepretation these fully meet Telefunken's spec's and are not below spec.
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PS 2
I regard tube testers more as a "works" or "does not work" test and highly overrated pieces of equipment especially for drivers.
Unfortunately some mu tracers work only with short pulses and they do not give the proper results - a tube needs to be tested with the full anode current, not a pulsed current, the anode needs to have ben brought up to temperature.
Also be aware that if a tube has been sitting on the shelf for a long time (20, 30, 50 or more years) the vacuum may have deteriorated and hence measuring results are more than likely not spot on.
There is an article from Morgan Jones Baking Valves" ( "baking_valves-pix-pdf" or Baking Tubes Procedure - Help... ) which is worthwhile reading. It shows improvement after the tube has been heated up for a while activating the getter (either in circuit or by baking them).
I would have no hesistation using them.
I regard tube testers more as a "works" or "does not work" test and highly overrated pieces of equipment especially for drivers.
Unfortunately some mu tracers work only with short pulses and they do not give the proper results - a tube needs to be tested with the full anode current, not a pulsed current, the anode needs to have ben brought up to temperature.
Also be aware that if a tube has been sitting on the shelf for a long time (20, 30, 50 or more years) the vacuum may have deteriorated and hence measuring results are more than likely not spot on.
There is an article from Morgan Jones Baking Valves" ( "baking_valves-pix-pdf" or Baking Tubes Procedure - Help... ) which is worthwhile reading. It shows improvement after the tube has been heated up for a while activating the getter (either in circuit or by baking them).
I would have no hesistation using them.
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Unfortunately you are misreading the datasheets. Both Philips and Telefunken state the same. What you probably are missing is that while Uab is 100V, Ugb is 9V which means that grid is 9 volts positive. So measured at 0V at grid, plate is 90V. And both datasheets state that at that operating point less than 13,5mA Ia is end-of-life.
I'm not saying that these tubes are unusable. However these are long-life tubes (10000 hours expected) which would indicate that these have seen quite long time in operation to have reached end-of-life condition.
Attachments
I have both AVO VCM163 and uTracer. AVO tests tubes at full anode current but I have rarely seen any difference compared to uTracer results. I have found both tube testers to be truly valuable pieces of equipment for all types of tubes.
DO-NOT-OVERTHINK-IT
I suggest my own 12AX7 tester, with cathode and plate resistor values matching what ECC88 needs, typically suggested in the datasheet or worst case "borrowed" from a commercial amp schematic which uses them.
Just a small box with a Noval socket, a couple components as needed, in my case I used Guitar jacks because I make Guitar amps but you use what you prefer.
You can quickly and easily test, UNDER REAL CONDITIONS:
* that plate voltages under autobias conditions are roughly what expected or not.
* gain
* hum/noise
* even (uncalibrated but useful, specially if comparing many) microphonism, by plugging output into an amp+speaker and lightly tapping them with a metal rod or something.
* as shown circuit allows cascading both stages, simulating a high gain guitar preamp.
* you do not need to build a dedicated supply for it, 4 crocodile clips allow you to "borrow" Ground, Filaments and +B from any other amplifier you have on or near your bench.
* lots of these have been built by fellow Guitar Amp Techs, who love its simplicity and straightforwardness.
^^^^^^^^^^^^^^^^^^ THAT +1000
I suggest my own 12AX7 tester, with cathode and plate resistor values matching what ECC88 needs, typically suggested in the datasheet or worst case "borrowed" from a commercial amp schematic which uses them.
Just a small box with a Noval socket, a couple components as needed, in my case I used Guitar jacks because I make Guitar amps but you use what you prefer.
You can quickly and easily test, UNDER REAL CONDITIONS:
* that plate voltages under autobias conditions are roughly what expected or not.
* gain
* hum/noise
* even (uncalibrated but useful, specially if comparing many) microphonism, by plugging output into an amp+speaker and lightly tapping them with a metal rod or something.
* as shown circuit allows cascading both stages, simulating a high gain guitar preamp.
* you do not need to build a dedicated supply for it, 4 crocodile clips allow you to "borrow" Ground, Filaments and +B from any other amplifier you have on or near your bench.
* lots of these have been built by fellow Guitar Amp Techs, who love its simplicity and straightforwardness.
Attachments
Best wishes for 2021, Juan Manuel! The idea of using crocodile clips for 300V DC is a habit better not made popular 🙂
OP has uTracer. You are not seriously suggesting that your tester would be more appropriate?
Amadeus Mozart says-
Post # 7-
I regard tube testers more as "works not works " .
Yes in most tube testers but not in mine where graphs can be calculated and much more than an " emission tester " that's why it was used by many UK government departments -Ministry of Defense - Weather stations etc mine was bought as ex government privately with all the paperwork pertaining to a certain Southern England weather station.
Please check up the difference between an "emission tester " and a tube/valve characteristic tester , many European countries produced high class testers just look at the price difference between cheap testers and professional testers .
Mine is totally analogue -no rolling tube types on a display .-
C:\Documents and Settings\Guido\Documenti\Guido\Stesura manuale AVO MK4-OPERATOR\AAA_03.prn.pdf - manual_5ed__multipage.pdf
Scroll down to -
The ability to plot complete sets of mutual characteristics -
Ia/Vg1-Ia/Va-Is/Vg1-Is/Vs
Testing of rectifiers under reservoir conditions with a full range of DC loading .
Testing of signal diodes under suitable DC load.
The indication of grid current and valve softness --directly on the meter scale.,the non-operative
Testing of separate sections of multiple valves , the non-operative section of the valve being maintained at reasonable working electrode voltages .
I have complete refurbished it --took several months including upgrading a certain vital high current sensing resistor from 0.3 % precision to 0.1 % precision.
Post # 7-
I regard tube testers more as "works not works " .
Yes in most tube testers but not in mine where graphs can be calculated and much more than an " emission tester " that's why it was used by many UK government departments -Ministry of Defense - Weather stations etc mine was bought as ex government privately with all the paperwork pertaining to a certain Southern England weather station.
Please check up the difference between an "emission tester " and a tube/valve characteristic tester , many European countries produced high class testers just look at the price difference between cheap testers and professional testers .
Mine is totally analogue -no rolling tube types on a display .-
C:\Documents and Settings\Guido\Documenti\Guido\Stesura manuale AVO MK4-OPERATOR\AAA_03.prn.pdf - manual_5ed__multipage.pdf
Scroll down to -
The ability to plot complete sets of mutual characteristics -
Ia/Vg1-Ia/Va-Is/Vg1-Is/Vs
Testing of rectifiers under reservoir conditions with a full range of DC loading .
Testing of signal diodes under suitable DC load.
The indication of grid current and valve softness --directly on the meter scale.,the non-operative
Testing of separate sections of multiple valves , the non-operative section of the valve being maintained at reasonable working electrode voltages .
I have complete refurbished it --took several months including upgrading a certain vital high current sensing resistor from 0.3 % precision to 0.1 % precision.
Sometimes it helps to keep them with heater power applied, a couple of hours, something to do with the getter.