hi tube friends
i have built few of those nice green tube indicators
all work, but some have even without any signal small green strip on top and bottom
I wonder if the vr2, please see the schematics, is there to adjust something
my circuits do not have vr2, just the input signal sensitivity
thanks
i have built few of those nice green tube indicators
all work, but some have even without any signal small green strip on top and bottom
I wonder if the vr2, please see the schematics, is there to adjust something
my circuits do not have vr2, just the input signal sensitivity
thanks
Attachments
As they are/were for tape recorders , I knew them as EM87 previous versions were used in tube radios .
Yes you can build a circuit to adjust them as that was the original purpose of them as signal strength indicators.
Nowhere near as nice as the early radio ones .
Here is a side-contact (SC) type ( used in the UK & Germany -circa 1930,s ) I have several like that, the emission dropped after a number of years compared to the other tubes in the radios .-
Cathode-Ray Tuning Indicator
Yes you can build a circuit to adjust them as that was the original purpose of them as signal strength indicators.
Nowhere near as nice as the early radio ones .
Here is a side-contact (SC) type ( used in the UK & Germany -circa 1930,s ) I have several like that, the emission dropped after a number of years compared to the other tubes in the radios .-
Cathode-Ray Tuning Indicator
Normally in an old tube radio the grid controlled the signal coming from the radios AVC which varied in strength depending on the signal this controlled the cathode rays appearing on the top of the tube ( or side as in newer tape recorder versions)--the anode ( plate ) voltages had one anode ( plate ) direct and the other through a resistor which set the target voltage which could be varied for a range of grid voltage change .
Obviously the above modern circuit does not conform to normal practice but is implemented to allow a set voltage value to conform with the operation ( in a set manner ) of the "Magic Eye " cathode -ray indicator .
In other words helps with the sensitivity /level of the display giving a fixed indication which is not what they were made for as they were designed for variable indication relative to the signal input.
Target currents were usually fixed so a certain current level was required depending on the design of the tube.
This will vary depending on the tube design so voltage is increased to cause the CRT to "strike " at the correct designed voltage/current.
Obviously he don't have any CRT specification books but adjusted it to a level he liked.
Obviously the above modern circuit does not conform to normal practice but is implemented to allow a set voltage value to conform with the operation ( in a set manner ) of the "Magic Eye " cathode -ray indicator .
In other words helps with the sensitivity /level of the display giving a fixed indication which is not what they were made for as they were designed for variable indication relative to the signal input.
Target currents were usually fixed so a certain current level was required depending on the design of the tube.
This will vary depending on the tube design so voltage is increased to cause the CRT to "strike " at the correct designed voltage/current.
Obviously he don't have any CRT specification books but adjusted it to a level he liked.
yes..... appears to me as it varies the plate load, thus serves as adjustment for signal sensitivity.
here is the schematics I got from ebay kit, this is what I cloned few more times
as you can see, the pins 9 and 7 go to high voltage supply through 220k
schematics in first post have 100k and trimmer there
I have about eight of these 6E2 tubes, and built three pairs of indicators so far
two tubes are weak in green light, I will discard those
I matched six remaining into three pairs, to sort of move the same way
There is big variability between these, they are cheap chinese copies, I guess
One thing that bothers me, with no signal, there is little of the green bar always left, but its never equal between the two, so its sort of weird
If I can adjust this to be equal between the left and right tube, that's all I need
So I will add that trimmer and see what happens...
as you can see, the pins 9 and 7 go to high voltage supply through 220k
schematics in first post have 100k and trimmer there
I have about eight of these 6E2 tubes, and built three pairs of indicators so far
two tubes are weak in green light, I will discard those
I matched six remaining into three pairs, to sort of move the same way
There is big variability between these, they are cheap chinese copies, I guess
One thing that bothers me, with no signal, there is little of the green bar always left, but its never equal between the two, so its sort of weird
If I can adjust this to be equal between the left and right tube, that's all I need
So I will add that trimmer and see what happens...
Attachments
ok, I had some time to experiment with 6E2 indicator.
I replaced 220k resistor with 100k and 100k trimmer. It got worse. I mean by lowering the resistance, the green bar with no signal got bigger.
So I had to go other way around. I put 220k back, and added 100k trimmer in series. In one tube I was able to dial in the green bar almost to the beginning. Perfect. For other tube I had to add additional 100k. Now the starting point with no signal is almost at the outer edges of the tubes, and more importantly, I can adjust both the same way. This works for me, and eliminates differences in the tubes. Good.
Now the time to put it in some foam board box.
Cheers!
I replaced 220k resistor with 100k and 100k trimmer. It got worse. I mean by lowering the resistance, the green bar with no signal got bigger.
So I had to go other way around. I put 220k back, and added 100k trimmer in series. In one tube I was able to dial in the green bar almost to the beginning. Perfect. For other tube I had to add additional 100k. Now the starting point with no signal is almost at the outer edges of the tubes, and more importantly, I can adjust both the same way. This works for me, and eliminates differences in the tubes. Good.
Now the time to put it in some foam board box.
Cheers!
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It was so cheap I bought it (GHXAMP Low Voltage 6E2 Cat's Eye Drive) assembled, but I did some measurements. of the 6E2 tube including driver. It has a input volume potmeter, so mV is out of my amps speaker terminal- I use it as a VU meter for my headphone amp. The amp is a KT88triode couled with an APPJ Headphone adapter added
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Not sure where to post, but AppJ Headphone adapter mod followed the 6E2 investigations
Modified the series resistance of 3 parallel 12 ohm resistors by adding 1000ohm in series with 2 of them . Lowering output and making Tubeamp work at 2.3volt output instead of 0.07V. Reducing noise by 30db . 6550 tube is working at very flat operating line due to 168ohm load at speaker terminal, but still tube operate below 500V max triode voltage .
Sounds very nice now at 0.3% 2H , the slight bass boost (o.5db) the 12 ohm output resistance AppJ terminal 2 gives is actually nice.
I apologise for the sloppy work , out of training.
Modified the series resistance of 3 parallel 12 ohm resistors by adding 1000ohm in series with 2 of them . Lowering output and making Tubeamp work at 2.3volt output instead of 0.07V. Reducing noise by 30db . 6550 tube is working at very flat operating line due to 168ohm load at speaker terminal, but still tube operate below 500V max triode voltage .
Sounds very nice now at 0.3% 2H , the slight bass boost (o.5db) the 12 ohm output resistance AppJ terminal 2 gives is actually nice.
I apologise for the sloppy work , out of training.
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