CENTRAD 751 (Techniek Radio/TV)
door Koen 
, GENT, 09.08.2010, 16:03 (5220 dagen geleden)
Hallo,
weet iemand of en hoe je een gelijkrichterbuis kunt meten op de centrad 751? Ik heb de handleiding nog eens nagelezen, maar kom er niet helemaal uit.
Mvg. Koen
CENTRAD 751
door Thierry Magis 
, east Belgium, 09.08.2010, 17:14 (5220 dagen geleden) @ Koen
Hello,
What kind of rectifier tube do you want to test ?
For this tubes you have generally two anodes and you have to make two measures!
Example with one EZ81, first test is with the keys (SELECTEURS) combination AACBDDCCCC ; second test with the combination ACCBDDCACC.
Key combination is easy to understand.
A = Anode
B = cathode
C = unused pin
D = heater (of course 2 pins have to be D, except cold cathode tubes)
Key 1 = pin 1 and so on.
So after adjusting heater voltage and plug the tube on, place the keys on the 1st position (given for the tube in the manual) and turn on the instrument. The FONCTION rotating selector will be now used for the different steps.
1st step : "ESSAI FIL" will test the heater. If bad, the neon light on. If it's like that, you can throw the tube...
2nd step : "ESSAI ELECTRODES" (4 positions), will check if no internal short-cut between the tube elements. Note : at this moment, the tube will be heated to test with hot elements. Better to give time to reach normal temperature.
3rd step : "MES" will check if the cathode still gives enough current. The meter has 3 zones : BONNE (tube ok) DOUTEUSE (tube poor) MAUVAISE (dead or very low emission)
4th step : "ISOL CATH" will measure the insulation between cathode and heater. Don't do this test on direct-heating tubes (like 80), it will of course indicate a short-cut ...
You have to do this 2 times, for each key combination ! Turn OFF the instrument when changing key combinations!!
Is this helpful for you ? This is a very quick translation of the manual.
Regards
Thierry
CENTRAD 751 - supplement
door Thierry Magis , east Belgium, 09.08.2010, 17:25 (5220 dagen geleden) @ Thierry Magis
To be complete :
the SELECTEUR (key) number 0 is the type of tube in test :
A : rectifiers and ordinary tubes
B : battery tubes (low emission)
C : small diodes
D : magic eyes
To adjust exactly the instrument on supply voltage (mains) : when making the first test of "ESSAIS ELECTRODES", adjust the potmeter "AJUSTAGE DU SECTEUR" to make the meter needle reaching the good position (indicated on the scale).
This instrument is very simple, just having basic functions, but works well.
When having tubes with grids (other than rectifiers), all must be connected to anode, corresponding key in position A.
Understanding the keys positions, you are able to imagine the combinations for tubes missing in the manual. It's very easy.
Regards
Thierry
CENTRAD 751 - supplement
door Koen , GENT, 10.08.2010, 17:03 (5219 dagen geleden) @ Thierry Magis
Thierry,
thanks for your explanation. Perhaps I didn't put my question clear: at the centrad 752, there is a "redresseuse"-knob, which I don't find on the centrad 751, so I wondered if I could test the UY41 tube on the 751. The problem is that I did test the UY41 on the centrad 752, and it had no emission, so I would like to doublecheck the tube on the 751, but there is no "redresseuse"-knob.
Kindly regards, Koen
CENTRAD 751 - supplement
door Thierry Magis , east Belgium, 10.08.2010, 17:35 (5219 dagen geleden) @ Koen
Hello
on the 751, just place the "selecteur" number 0 on position "A" , and of course the good combination on others selecteurs for your tube!
You should have an indication on the meter during emission test, if no the tube is dead ! With some kind of tubes you have to wait a moment until it reaches the temperature.
The 752 is more reliable (and recent) tester, with more functions, than the 751. I owned this two models but just kept the 752.
If you have problems to use the 752, feel free to ask me. I know this appliance very well and tested several hundreds of tubes with. I never seen translations of the french manuals.
Tip with the 752 : one of the critical points to check in this tubetester is the heater voltage selector and pin selectors. There is often bad contacts in this selectors, and the heating voltage drops when there is a tube on test ! Obviously, when it's like that the measure result is bad because the tube doesn't receive the correct voltage (or any voltage at all) !
regards
Thierry
CENTRAD 751- Pin-selector mistake
door Maurice , Dordrecht, 09.08.2010, 19:01 (5220 dagen geleden) @ Thierry Magis
Thierry
Remark that ONLY for B9 and B7 the selectors are numbert correctly.
Key 1 = pin 1 and so on.
See this picture I made for the 751
Ex is selector starting at E0
Where E0 selector is the funtion you want to test
Centrad had in mind to select E1 and E2 as filiament for all tube bases.
At B7 and B9 they give it up apperantly....
![[image]](images/uploaded/201008092255324c606b44d764a.jpg)