Extra AVO mk4 test settings


 

tube pin settings Uh (V) Ug (V) Ua (V) Ia (mA) gm (mA/V)
6B4G Sovtek single-plate 026 040 300 6.3 -36 250 60 5200
300B Sovtek ** 264 300 000 5.0 -70 350 67 3200
300B Sovtek ** 264 300 000 5.0 -70 350 52 3700
AVVT300B-SL 264 300 000 5.0 -76 400 70 3000
M7 642 300 000 4.0 -2 400 3 1600
RS241 642 300 000 4.0 -10 400 30 3500
S6 642 300 000 4.0 -4 400 34 4400
6H30P 741 326 410 6.3 -10 200 20 - - - -
6H6P 741 326 410 6.3 -7 200 20 - - - -
6S45P 141 321 641 6.3 -2.2 200 25 - - - -
6S19P 646 326 461 6.3 -46.5 175 50 3700
6S41P 301 640 200 6.3 -74 250 90 4200
1626 036 040 210 12.6 -31 250 20 2300

 

note:  The values for bias current at a given bias voltage is not always the same. Each tube has it's own characteristic and will vary slightly at the same bias voltage. To test the tubes you should always bias the tube at the given bias current (!), not the bias voltage. When the tube is nearing the end of it's life the current will decrease to levels well below the nominal values for new types.

**  I tested two "matched" tubes but got results that were spread too wide to give an accurate reading for this tube. The tubes were also very unstable in their setting, resulting in a currently jumpy current through the anode. This too affects reliability of the results. In short: not a fun tube to measure. Trying the Sovtek on the standard 400V setting also caused my AVO to go into protection at around 70-80mA. I've tested other tubes at 400V / 100mA so the tester is not the problem, alas... These tubes might sound good, but don't try to run them at the edge of their specs, things might go wrong.

 

If anyone has other AVO data which they wish to share, I will be glad to place it here....


Uh Heater voltage (given)
The specified values are not always the actual working parameters. The AVO has only a limited amount of heater voltages and some tubes will be a little over or a little under the nominal given value for a tube. Example: the RS241 is tested at 4V while the heater should be 3.8V.
Ua Anode voltage (given)
The voltage applied to the anode for testing purposes.
Ug Grid voltage (setting)
The voltage applied to the grid in order to produce a current through the anode of the tube. This is also know as the bias setting.
Ia Anode current (result)
The current that flows through the anode caused by applying a bias to the grid.
gm Transconductance (result)
The relation between input voltage and output current of a tube. The values given are nominal values. NOS tubes are mostly higher than this value, but I have seen many that are just below it as well. The gm is the fastest way to see how far a tube is used, or if it is really still new. The gm gradually decreases as it nears the end of it's life. Values below 70% of the nominal gm are taken to be "bad" tubes for audio use although they still may be functional for a long time to come.