10k for 170V and IN-18 does sound very high. 2mA instead of 6mA? To quote a thread on tubeclockdb.com <http://www.tubeclockdb.com/forum/4-builders-forum/6481-in-18-cathode-poisoning-problem?limit=6&start=0> (about cathode poisoning with IN-18s), someone was measuring 3.1mA with those specs, so the maintenance voltage would be more like 140V. Also, I thought more recent kits recommended 8k2 resistors? Presumably this would give a current of around 3.6mA. It did not affect his experience with cathode poisoning.
Apart from the power supply issue, I think one reason people run IN-18 with a low current is to avoid the 'infamous blue dot'. This happens more as you crank up the current. As Greg has pointed out (and the thread on tubeclockdb.com corroborates), running tubes at too low a current will lead to premature cathode poisoning. On Tuesday, May 19, 2020 at 6:48:49 AM UTC-4, Richard Scales wrote: > > Very sorry for asking such a fundamental question. > > I thought I had this all sorted but I'm having a problem in correlating my > understanding with what I see others doing. > > When checking specifications for IN-18's over at Tube-tester.com - he > suggests: > > Ignition Voltage 170V > Voltage drop 150V > Nominal current 6mA > > So I deduce, with a 170V HV supply, the series resistor should be (for > nominal current) (170-150)/0.006 = 3K3 > > Similarly for something like ZM1040, supply volts 170V, maintaining volts > 140V, nominal current 4.5mA, series resistor (170-140)/0.0045 = 6K6 > > I note that in kits such as PV Spectrum and others - for this kind of tube > they specify 10K series resistors. > > Am I mis-interpreting the specifications, in particular those for the > IN-18 as the voltage references are worded slightly differently? > > Are the tubes in question being driven at a lower current on purpose? > > I'm ready to learn! > > Richard > > > > > > > -- You received this message because you are subscribed to the Google Groups "neonixie-l" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To view this discussion on the web, visit https://groups.google.com/d/msgid/neonixie-l/67df8bf3-8c7e-4ce8-b8ca-cc08cc2a283c%40googlegroups.com.
