Tube-tester settings and results

Tester settings for AVO mk4 Characteristic Meter, values (except for pin settings) can be used on other testers as well

tube pin settings Uh Ug Ua Ia gm
45 264300000 2.5 -50 250 34 2.1
45A 264300000 2.5 -68 325 43 2.3
2C45 364200000 7.0 -40 250 29 ?
VT45 264300000 2.5 -50 250 34 2.1
VT52 264300000 6.3 -61 300 44 2.2
CV596 264300000 2.5 -50 250 34 2.1

 

General results for gm are stated to be 2370µA/V at the settings above, but I have not found any tubes that reach this value. Out of the 10 tubes I have tested (9 of them were n.o.s.) the average gm was exactly 2200µA/V. I think you should take this figure as a reference for "good" tubes. The limit I set for a "good" tube was at 70% of this, which is 1540µA/V. This is the absolute bottom limit for a "good" tube but this means it will already be wearing down at this point. New tubes are anywhere from 2000-2400µA/V.

Raising the heater voltage from 6.3V to 7.5V (my tester does not have 7.0V) only increases emission by a little resulting in only 3 to 5mA change in anode current depending on the anode voltage. All the tubes I have tested were 6.3V types. I don't have any tester experience with the 7.0V types but am trying to get a hold on some of these tubes just to compare them.

NOTE: All results described below are taken from an AVO mk4 Characteristic Meter...

To get a clear picture on the specs of these different tubes I set two reference points for the operating parameters. The first is a fixed bias voltage of -61V, the second a fixed anode current of 44mA. The transconductance (gm) was measured at 44mA through the anode. Most tubes have a deviation from the given bias, these values are always average tube characteristics. Because of this a certain bias value may give a higher current on one tube than on another. Because of this the gm test was done on a fixed current.

 

tube brand Ia @ -61V Ug @ 44mA gm filament remarks
445 DeForest Audion VV
201A Boonton (45ST) VV
45A Super Silvertone 28.5 -59 1400 VV note 1, used (60%)
VT52 Tung-Sol 28 -54.7 2400 VV ST14
VT52 Hytron 18.5 -49 2200 VV
VT52 Hytron 30 -55 2200 VV
38142 Hytron 26 -53 2200 VV slim ST glass
VT52 Sylvania - - - VV ceramic supports
VT52 Sylvania 19.5 -49.2 2150 VV
VT52 Sylvania 36 -56.6 2150 VV
VT52 Western Electric - - - VVV
VT52 National Union 26 -53.3 2000 VVV used (90%)
VT52 Senco 20 -51 2200 VVV
VT52 Senco 34 -57 2200 VVV
VT52 Senco 36 -58.5 2100 VVV
VT52 Philco 22 -52 2400 VVV
VT52 Raytheon - - - VV

* I still have to test these types. 

note 1: bias for the 45A was set at the following Ia @ -68V, Ug @ 43mA, gm @ 43mA

© Jim de Kort