23-04-2018, 02:28 PM
Hi everyone. I have been busy with lots of things recently, but following my comment on Feathercurl's 'Static Electricity Detector' thread mentioning my electrometer valves I have finally got one in a circuit and I am learning.
I have Russian EM-6 dual tetrode electrometer tubes. Before I purchased, as I normally do, I obtained the relevant datasheet. It was not until somewhat later that I realised how little information there was around on using this type of tube (or maybe just how much there is on more mainstream devices and uses). After quite a bit of searching I did find some very basic information from many sources, but the only specific information often ends at valve voltmeters, which are similar but with less information / issues with input constraints. I did find enough, though, to put something together.
The basic circuit I got to is as shown. The dotted line on the circuit shows the original connection of g2b as in the skeleton circuit I found online. I thought I would try using this tube connection to balance things to zero. It is probably not recommended as the connection is also shown to screen as well and so ideally be grounded, but does appear to work in my “less stringent” application. G1 is connected to a positive potential as these appear to be basically space charge tubes. Originally I was heading a step too far, and using an op amp chip to amplify the output voltage, but ran into problems with it (this is why there is an un-connected pot in the case. I had removed the amplifier, and have now the pot). My original intention meant providing positive and negative supplies as well as 4.5V for the tube heater. I have left the power supply unchanged, but all the -5V does now is to supply the 'zero' pot. That is useful as I have found that I was able to centre the zero point on the pot by minor adjustment of the -5V. I arrived at the circuit component values by educated guesswork and trial and error to home in on the various values given in the data sheet. The material I obtained which gave the skeleton circuit also provided a small amount of information which helped. I have not shown decoupling capacitors, but the lines are decoupled.
To the present time I have only made a few observations rather than anything really specific. The photographs show a test setup with a multi-turn pot in a bridge circuit. This tested principles as I was easily able to balance the bridge and obtain what appeared to be accurate readings for known resistances. The valve itself appears very stable (particularly as compared with normal signal valves). Although the valve does seem to need a short time to stabilize after any major change, the zero setting does not vary much. Using a cheap meter (checked with my Fluke to the least digit on it), on leaving it switched on with a link across the input for three hours, zero initially set, it was at 1.3mV after an hour and flashing between 1.3 and 1.4mV after a further two hours. The valve itself, in circuit, has little or no gain, as would be expected, but it's very high input impedance appears to more than compensate for this. It may well be likely to have far more resistance to any input stresses, and moderate temperature changes seem to have little effect (less than perhaps with FET's). As it is designed for use with 5V it should well interface with semiconductor circuitry.
My intention is to keep this unit more for test of ideas. My main intention was for use in bridge circuits. I would like to use one of these for the use in the front end of a dedicated unit using perhaps an Arduino with it's analogue ports hence the ability to get data into a PC or other display. As the Arduino is limited to around a millivolt sensitivity at best then use of op-amps may be essential.
If anyone has any circuit information for application of the EM-6 I would find it very useful to see.
Thanks
Tracy
I have Russian EM-6 dual tetrode electrometer tubes. Before I purchased, as I normally do, I obtained the relevant datasheet. It was not until somewhat later that I realised how little information there was around on using this type of tube (or maybe just how much there is on more mainstream devices and uses). After quite a bit of searching I did find some very basic information from many sources, but the only specific information often ends at valve voltmeters, which are similar but with less information / issues with input constraints. I did find enough, though, to put something together.
The basic circuit I got to is as shown. The dotted line on the circuit shows the original connection of g2b as in the skeleton circuit I found online. I thought I would try using this tube connection to balance things to zero. It is probably not recommended as the connection is also shown to screen as well and so ideally be grounded, but does appear to work in my “less stringent” application. G1 is connected to a positive potential as these appear to be basically space charge tubes. Originally I was heading a step too far, and using an op amp chip to amplify the output voltage, but ran into problems with it (this is why there is an un-connected pot in the case. I had removed the amplifier, and have now the pot). My original intention meant providing positive and negative supplies as well as 4.5V for the tube heater. I have left the power supply unchanged, but all the -5V does now is to supply the 'zero' pot. That is useful as I have found that I was able to centre the zero point on the pot by minor adjustment of the -5V. I arrived at the circuit component values by educated guesswork and trial and error to home in on the various values given in the data sheet. The material I obtained which gave the skeleton circuit also provided a small amount of information which helped. I have not shown decoupling capacitors, but the lines are decoupled.
To the present time I have only made a few observations rather than anything really specific. The photographs show a test setup with a multi-turn pot in a bridge circuit. This tested principles as I was easily able to balance the bridge and obtain what appeared to be accurate readings for known resistances. The valve itself appears very stable (particularly as compared with normal signal valves). Although the valve does seem to need a short time to stabilize after any major change, the zero setting does not vary much. Using a cheap meter (checked with my Fluke to the least digit on it), on leaving it switched on with a link across the input for three hours, zero initially set, it was at 1.3mV after an hour and flashing between 1.3 and 1.4mV after a further two hours. The valve itself, in circuit, has little or no gain, as would be expected, but it's very high input impedance appears to more than compensate for this. It may well be likely to have far more resistance to any input stresses, and moderate temperature changes seem to have little effect (less than perhaps with FET's). As it is designed for use with 5V it should well interface with semiconductor circuitry.
My intention is to keep this unit more for test of ideas. My main intention was for use in bridge circuits. I would like to use one of these for the use in the front end of a dedicated unit using perhaps an Arduino with it's analogue ports hence the ability to get data into a PC or other display. As the Arduino is limited to around a millivolt sensitivity at best then use of op-amps may be essential.
If anyone has any circuit information for application of the EM-6 I would find it very useful to see.
Thanks
Tracy