19-05-2024, 01:11 PM
(This post was last modified: 19-05-2024, 01:12 PM by Mike Watterson.)
Ad hoc tests for Triodes
The same gear as for diodes but with a high voltage PSU
Gear
1) PSU for heater/filament. AC or DC
2) Anode power supply. 10 to 300V DC. Less than 20mA.
3) Grid power supply. Either a 100K pot on 3 x 9V batteries in series or a 0 to 30V LV PSU and you earth the + out!
4) Leakage tester. Can be made easily from the flash in a single use film camera! Should have 2M Ohm series resistance.
5) DMM to measure Anode voltage.
6) DMM to measure Anode current.
7) DMM to measure the Grid voltage.
Procedure:
1) Check filament. Resistance is about 1/2 when cold. Power up slowly. Stop if it seems too bright and recheck valve type and spec.
2) Check grid to anode leakage when heater/filament powered with the leakage tester. Anode volts should be higher than rating in data as that's a minimum.
3) Check heater/cathode with leakage tester, if it's rated as isolated.
4) Set grid voltage to zero to check emission.
Check Anode forward volts/current using PSU. Do not exceed current rating. Might be 0.5mA to 10mA. We only care about the current, i.e. emission.
5) set grid to -1V and verify anode volts can be increased.
6) Set grid to -30V. Should be no anode current. Increase anode volts to max on data. (100, 200 etc). Verify anode current is still near zero.
7) Keeping anode volts in (6), reduce grid voltage slowly (less negative) and note grid voltage anode current starts to increase. This is the cut off voltage.
The triode testing applies to triodes inside other valves, such as EABC, DAC, ECC, triode-hexodes (ECH), triode-pentodes (ECF) etc. Just leave the other electrodes open circuit, though leakage test to grid against other electrodes is worthwhile.
You can do 4 to 7 with a 2N3819 / J310 or any depletion mode N JFET and a Low voltage PSU. Zero gate is quiescent current without bias. Enhancement mode FETs need a positive gate and bipolar transistors are easier to deal with using a variable resistor in series with 1.4V battery or a constant current source, though technically a 0V to 1V voltage source is better.
Make sure the heater/filament is within +/- 2.5% of rated 0.65/0.7, 1.15/1.2, 1.35/1.4, 1.8/2.1, 6.3, 12.6, etc voltage or that if a series valve that it's within +/- 2.5% of the 100, 150, 200 or 300mA series rating. Actual use is ideally at +/- 10% but you want it more accurate for tests.
Battery valves may be better tested at the lower number and octode/heptode mixer/osc should be also tested at 1.1 for 1.4V types and 1.8 for 2V types.·
The same gear as for diodes but with a high voltage PSU
Gear
1) PSU for heater/filament. AC or DC
2) Anode power supply. 10 to 300V DC. Less than 20mA.
3) Grid power supply. Either a 100K pot on 3 x 9V batteries in series or a 0 to 30V LV PSU and you earth the + out!
4) Leakage tester. Can be made easily from the flash in a single use film camera! Should have 2M Ohm series resistance.
5) DMM to measure Anode voltage.
6) DMM to measure Anode current.
7) DMM to measure the Grid voltage.
Procedure:
1) Check filament. Resistance is about 1/2 when cold. Power up slowly. Stop if it seems too bright and recheck valve type and spec.
2) Check grid to anode leakage when heater/filament powered with the leakage tester. Anode volts should be higher than rating in data as that's a minimum.
3) Check heater/cathode with leakage tester, if it's rated as isolated.
4) Set grid voltage to zero to check emission.
Check Anode forward volts/current using PSU. Do not exceed current rating. Might be 0.5mA to 10mA. We only care about the current, i.e. emission.
5) set grid to -1V and verify anode volts can be increased.
6) Set grid to -30V. Should be no anode current. Increase anode volts to max on data. (100, 200 etc). Verify anode current is still near zero.
7) Keeping anode volts in (6), reduce grid voltage slowly (less negative) and note grid voltage anode current starts to increase. This is the cut off voltage.
The triode testing applies to triodes inside other valves, such as EABC, DAC, ECC, triode-hexodes (ECH), triode-pentodes (ECF) etc. Just leave the other electrodes open circuit, though leakage test to grid against other electrodes is worthwhile.
You can do 4 to 7 with a 2N3819 / J310 or any depletion mode N JFET and a Low voltage PSU. Zero gate is quiescent current without bias. Enhancement mode FETs need a positive gate and bipolar transistors are easier to deal with using a variable resistor in series with 1.4V battery or a constant current source, though technically a 0V to 1V voltage source is better.
Make sure the heater/filament is within +/- 2.5% of rated 0.65/0.7, 1.15/1.2, 1.35/1.4, 1.8/2.1, 6.3, 12.6, etc voltage or that if a series valve that it's within +/- 2.5% of the 100, 150, 200 or 300mA series rating. Actual use is ideally at +/- 10% but you want it more accurate for tests.
Battery valves may be better tested at the lower number and octode/heptode mixer/osc should be also tested at 1.1 for 1.4V types and 1.8 for 2V types.·
