testen van dubbele triodes op een AVO-buizentester (Techniek Radio/TV)

door Maurice , Dordrecht, 04.11.2008, 17:38 (5862 dagen geleden) @ hein

Was even zoeken waar ik het gelezen had, maar weer gevonden.

In zoverre even het wantrouwende uit het bericht tov testers algemeen even naast je neerleggen.
Kennelijk is de schrijven niet zo'n liefhebber.

Maar begrijp nu wel de contekst ivm de ECC's.
Misschien zou uitmaken dat de kathode en dus gloei omgeschakeld moet worden.
Bedoel bij de ECC83 werkelijk gloei zetten alleen op pen 5 en 9
of alleen op pen 4-9.
en niet op 4-5 en dan maar 1 deel testen.

Anders zou ik het niet snappen en zou dat het geval zijn bij alle gecombineerde buizen waarbij men steeds maar 1 deel test.

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FUNKE W19 etc., a overrated piece of junk?

quite possible and it´s fair to say because it does not make too much sense to check a tube's cathode capabilities under random conditions pre-determined by the tube tester maker - but that's exactly what these testers do! The Funke 16, 18, 19 do not provide any grid bias other than zero (grid & cathode strapped together) or -2V approx. to check for connection between grid & base prongs. To get the resulting plate current back within limits, Funke also reduces plate and / or screen voltages. This definitely is too far from real operation - and it does not allow measuring anything else like mutual conductance, hum, etc. In addition, the valves often do not become hot enough on these testers, so there often tubes appearing good on these testers while inserted in the circuit they should operate in, they develop inter-electrode shorts or show floating grid bias due to residual gas.

Mainly originates of the bad Funke design, the heater voltage is not stabilized and always too low or high, DC voltages are superimposed by AC because of too small charging and filter caps and so on. Also important reason of wrong measurements is Funke has changed the test cards again and again! This is why for the same type of tube tester and the same tube exist DIFFERENT test cards. Especially dual triodes like 12AX7, ECC83 that tests good on the „Funke“ in fact are often not good. On the Funke a good ECC83 starts at 1.9 mA, but in fact you can be sure that this tube is junk. In comparisons with other gm testers my view is I would´nt trust any ECC83 that is below 2,5 mA on the Funke = 65 to 70 % on a mutual conductance tester.

Generally I would not trust any tester that is an Emission-only tester. Emission alone does not tell the full story of a tube's condition. Each tester manufacturer established their own test criteria. To get a meaningful result about the "quality" of a tube it should be tested for Gm, (TRUE) mutual conductance, given in mmho, or dynamic mutual conductance in % (there is a difference and it can be a big one for some and not as critical for others, but this is another technical discussion)