19-05-2024, 01:32 PM
Ad hoc tests for Tetrodes, Pentodes, Hexodes and Beam Tetrodes.
The same gear as for triodes but with a second HT PSU, of some sort. Usually only low current needed.
You can somewhat test Heptodes, Octodes, Nonodes etc.
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) A screen grid supply. Can be fixed steps from 25V to 200V
5) Leakage tester. Can be made easily from the flash in a single use film camera! Should have 2M Ohm series resistance.
6) DMM to measure Anode voltage.
7) DMM to measure Anode current.
8) DMM to measure Screen Grid voltage
9) Optionally a DMM to measure Screen Grid current.
7) DMM to measure the control 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 each 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. Also the screen grid to control grid, cathode and other grids if they exist.
3) Check heater/cathode with leakage tester, if it's rated as isolated.
4) Set grid voltage to zero to check emission. Set screen grid to maximum in datasheet and all other grids if they exist either to cathode or screen grid according to data sheet or example circuit. The final suppressor grid, if not already connected to cathode should connect to cathode.
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 g1/control grid voltage slowly (less negative) and note grid voltage anode current starts to increase. This is the cut off voltage.
8) Set g1 / control grid to give anode current at half the maximum. Verify that g2 / screen grid voltage reduction reduces anode current.
9) Optionally set g2/screen volts to recommended. Reduce anode voltage towards zero. The Screen current should increase. The amount depends on kind of valve.
This testing applies to parts inside other valves, such as EBF, DAF, EBL, triode-hexodes (ECH), triode-pentodes (ECF) etc. Just leave the other electrodes open circuit, though leakage test to grid against other electrodes is worthwhile.
This doesn't fully test hexodes, heptodes, octodes, nonodes etc, but putting each grid to 0V or g2 volts as per data will at least test emission.
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 triodes but with a second HT PSU, of some sort. Usually only low current needed.
You can somewhat test Heptodes, Octodes, Nonodes etc.
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) A screen grid supply. Can be fixed steps from 25V to 200V
5) Leakage tester. Can be made easily from the flash in a single use film camera! Should have 2M Ohm series resistance.
6) DMM to measure Anode voltage.
7) DMM to measure Anode current.
8) DMM to measure Screen Grid voltage
9) Optionally a DMM to measure Screen Grid current.
7) DMM to measure the control 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 each 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. Also the screen grid to control grid, cathode and other grids if they exist.
3) Check heater/cathode with leakage tester, if it's rated as isolated.
4) Set grid voltage to zero to check emission. Set screen grid to maximum in datasheet and all other grids if they exist either to cathode or screen grid according to data sheet or example circuit. The final suppressor grid, if not already connected to cathode should connect to cathode.
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 g1/control grid voltage slowly (less negative) and note grid voltage anode current starts to increase. This is the cut off voltage.
8) Set g1 / control grid to give anode current at half the maximum. Verify that g2 / screen grid voltage reduction reduces anode current.
9) Optionally set g2/screen volts to recommended. Reduce anode voltage towards zero. The Screen current should increase. The amount depends on kind of valve.
This testing applies to parts inside other valves, such as EBF, DAF, EBL, triode-hexodes (ECH), triode-pentodes (ECF) etc. Just leave the other electrodes open circuit, though leakage test to grid against other electrodes is worthwhile.
This doesn't fully test hexodes, heptodes, octodes, nonodes etc, but putting each grid to 0V or g2 volts as per data will at least test emission.
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.·
