Dear forum
I hope you can help me with the following:
As a guitarist enthousiastic and electronic designer, I built myself a tubetester for the usual suspects: ECC83, EL84, EL34. The schematic and explanation of the circuit can be found at: http://www.checkout-systems.com/tubetester/
As you may notice I have a gas test button in my setup. The grid voltage is either connected direct or via a 1Meg resistor. Now if I test an ECC83 tube at 230VDC for gas, the anode current will slightly increase. A good tube shows little increase (<1%). However if I then measure the same tube at 115VDC and hit the gas test button it will always decreases the anode current ánd with a relatively large amount of 15-20%. This is the case for good tubes and lesser tubes.
Apparently there is more then one phenomenon at work here. Could it be that at 115VDC (anode voltage) the tube already goes into low-voltage mode? Space charge? Are there any specs about grid leakage to Anode voltage?
2nd question:
I have a number of ECC83´s that show an increase in current of some 15% when I hit the gastest button. It alarms me but I may draw the wrong conclusion. I also read that turning a ´gassy´ tube on for a few hours could cure its gas?
Hope to hear from you.
I hope you can help me with the following:
As a guitarist enthousiastic and electronic designer, I built myself a tubetester for the usual suspects: ECC83, EL84, EL34. The schematic and explanation of the circuit can be found at: http://www.checkout-systems.com/tubetester/
As you may notice I have a gas test button in my setup. The grid voltage is either connected direct or via a 1Meg resistor. Now if I test an ECC83 tube at 230VDC for gas, the anode current will slightly increase. A good tube shows little increase (<1%). However if I then measure the same tube at 115VDC and hit the gas test button it will always decreases the anode current ánd with a relatively large amount of 15-20%. This is the case for good tubes and lesser tubes.
Apparently there is more then one phenomenon at work here. Could it be that at 115VDC (anode voltage) the tube already goes into low-voltage mode? Space charge? Are there any specs about grid leakage to Anode voltage?
2nd question:
I have a number of ECC83´s that show an increase in current of some 15% when I hit the gastest button. It alarms me but I may draw the wrong conclusion. I also read that turning a ´gassy´ tube on for a few hours could cure its gas?
Hope to hear from you.
There is a good explanation of the various grid currents in Radiotron Designer's Handbook 4th.
You have the ideal platform for testing the idea that leaving a tube hot tends to clean-up the vacuum. Leave a tube on test overnight.
Small triodes are at near ZERO risk of damage due to grid currents, because of the large plate resistors normally used. A 15% shift in a no-resistor test is <7% shift in real use, which is less than tube-to-tube variation.
You have the ideal platform for testing the idea that leaving a tube hot tends to clean-up the vacuum. Leave a tube on test overnight.
Small triodes are at near ZERO risk of damage due to grid currents, because of the large plate resistors normally used. A 15% shift in a no-resistor test is <7% shift in real use, which is less than tube-to-tube variation.
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