I've only just seen this thread and I've got some serious listening to do right now, but I wouldn't have expected a change in distortion in an ECC88 from placing it in a magnetic field. I'd be most interested to see a measurement of a pentode/beam tetrode using aligned grids - I think almost all of the later small european TV pentodes (PCL82 etc) were really beam tetrode. If anything is going to be sensitive to a magnetic field, these should be.
straw.. oops .. magnetic fields forever ......
The beam deflection tube data sheets say right on them they are sensitive to magnetic fields and should be shielded, and one would expect them to be. The path of the sheet beam determines which side by side plate gets hit.
No doubt aligned grid beamers or pentodes will show an effect if the magn. field direction is right. Screen current will go up.
For normal tubes, the literature says they are not very sensitive to magn. fields. Slight curvature of the electrons just causes them to hit another part of the plate, so no big effect.
Where I HAVE seen a large effect in normal tubes is when operating at very low plate voltages with a strong magnet. For my vacuum tube current mirrors I use thermionic diodes as the input correctors. And they operate with just the bias voltage of the subsequent pentode across them. I have seen a threefold variation in perveance in the diode when a ferrite speaker donut magnet was placed over the diode with the field aligned along the cathode axis. This makes the low velocity electrons spiral around the cathode on their way to the plate. (radius of curvature = mv/eB with relativistic factor necessary for 1000 Volt or above) The plate's electric field no longer acts along the electron path effectively that way. An extreme case of this effect would be the microwave magnetron tube where a cathode aligned magn. field nearly causes cutoff of conduction.
Obviously, normal tube operation doesn't reach these extremes, but one can certainly get hum problems in preamp tubes placed too near to xfmrs.
Don
The beam deflection tube data sheets say right on them they are sensitive to magnetic fields and should be shielded, and one would expect them to be. The path of the sheet beam determines which side by side plate gets hit.
No doubt aligned grid beamers or pentodes will show an effect if the magn. field direction is right. Screen current will go up.
For normal tubes, the literature says they are not very sensitive to magn. fields. Slight curvature of the electrons just causes them to hit another part of the plate, so no big effect.
Where I HAVE seen a large effect in normal tubes is when operating at very low plate voltages with a strong magnet. For my vacuum tube current mirrors I use thermionic diodes as the input correctors. And they operate with just the bias voltage of the subsequent pentode across them. I have seen a threefold variation in perveance in the diode when a ferrite speaker donut magnet was placed over the diode with the field aligned along the cathode axis. This makes the low velocity electrons spiral around the cathode on their way to the plate. (radius of curvature = mv/eB with relativistic factor necessary for 1000 Volt or above) The plate's electric field no longer acts along the electron path effectively that way. An extreme case of this effect would be the microwave magnetron tube where a cathode aligned magn. field nearly causes cutoff of conduction.
Obviously, normal tube operation doesn't reach these extremes, but one can certainly get hum problems in preamp tubes placed too near to xfmrs.
Don
Hum is a different matter- the pickup of AC fields is well-understood and not surprising.
What has surprised me is the popularity of devices which are alleged to reduce magnetism in tubes and other components, supposedly improving the sound. And there have been anecdotes about the positive effects of degaussing on tube amps, and my guess is that these amps use pretty conventional tubes.
The ECC88 is a frame-grid triode, so I thought that it might be a good candidate to show these effects.
What has surprised me is the popularity of devices which are alleged to reduce magnetism in tubes and other components, supposedly improving the sound. And there have been anecdotes about the positive effects of degaussing on tube amps, and my guess is that these amps use pretty conventional tubes.
The ECC88 is a frame-grid triode, so I thought that it might be a good candidate to show these effects.
Re: Re: Quite fast...
Right.
I once mused philosophically that tubes were not as "natural" as transistors in that it's not in the nature of an electron to leap from is parent conductor, hurl itself through a vacuum and slam at high velocity into another conductor.
Since then I've been "getting into" tubes (though I'm still a big pussy and am using them at relatively low voltages) and one of the things that interested me was the effect of the electrons slamming into the plate.
I did some experimenting, looking at the noise due to this effect and noticed that while the noise at first glance looked random, it really wasn't.
Having millions of electrons all bombarding the plate at roughly the same time made it impossible to separate the non-random elements from the random elements. Fortunately I've a friend who works at a high energy physics lab who was kind enough to cobble together a device that would allow just one electron to go from the cathode to the plate.
Using a 6GHz DSO, we captured the waveform of a single electron hitting the plate. And while this was able to prove that the resultant noise was not random in nature, it didn't seem to reveal much else.
Then I got thinking of the film Hunt For Red October, where the sonar operator took a recording of the so-called "seismic anomaly" and slowed it way down, which then revealed that the "seismic anomaly" was really man-made.
So I took the 'scope data and converted it to a linear PCM wav file and played it back through my sound card at 44.1k, orders of magnitude slower than the original sampling rate.
When I heard the result, I felt rather like the astrophyscists in the film Contact when they finally decoded the data in the signal they'd received and discovered that it contained the blueprints for some sort of machine.
And just like Contact, what I heard will have profound consequences for both the scientific community as well as the religious community. I'm still feeling quite well, "weird" about the whole thing. Not to mention feeling very apprehensive at my becoming known to the whole world virtually overnight.
There's a press conference scheduled for tomorrow morning at 7:00 AM Eastern Time. Since that's less than 12 hours from now, I figure it would be ok to share the .wav file with the folks here.
So without further adieu, here is the "sound" of a single electron slamming into the plate at high velocity:
oneelectron.wav
se
audiousername said:
Right.
I once mused philosophically that tubes were not as "natural" as transistors in that it's not in the nature of an electron to leap from is parent conductor, hurl itself through a vacuum and slam at high velocity into another conductor.
Since then I've been "getting into" tubes (though I'm still a big pussy and am using them at relatively low voltages) and one of the things that interested me was the effect of the electrons slamming into the plate.
I did some experimenting, looking at the noise due to this effect and noticed that while the noise at first glance looked random, it really wasn't.
Having millions of electrons all bombarding the plate at roughly the same time made it impossible to separate the non-random elements from the random elements. Fortunately I've a friend who works at a high energy physics lab who was kind enough to cobble together a device that would allow just one electron to go from the cathode to the plate.
Using a 6GHz DSO, we captured the waveform of a single electron hitting the plate. And while this was able to prove that the resultant noise was not random in nature, it didn't seem to reveal much else.
Then I got thinking of the film Hunt For Red October, where the sonar operator took a recording of the so-called "seismic anomaly" and slowed it way down, which then revealed that the "seismic anomaly" was really man-made.
So I took the 'scope data and converted it to a linear PCM wav file and played it back through my sound card at 44.1k, orders of magnitude slower than the original sampling rate.
When I heard the result, I felt rather like the astrophyscists in the film Contact when they finally decoded the data in the signal they'd received and discovered that it contained the blueprints for some sort of machine.
And just like Contact, what I heard will have profound consequences for both the scientific community as well as the religious community. I'm still feeling quite well, "weird" about the whole thing. Not to mention feeling very apprehensive at my becoming known to the whole world virtually overnight.
There's a press conference scheduled for tomorrow morning at 7:00 AM Eastern Time. Since that's less than 12 hours from now, I figure it would be ok to share the .wav file with the folks here.
So without further adieu, here is the "sound" of a single electron slamming into the plate at high velocity:
oneelectron.wav
se
SY said:Make that "on the order of magnitude of 0.01c," then!
I'm searching though my tube collection for a small-signal beam tetrode...
I note with somewhat more than casual interest, that you didn't remove the word "relativistic" from post #1, as it doesn't apply to the paltry speeds below about 90%..
Tisk, tisk..
Cheers, John
SY said:
I know, that's why I busted your chops...
SY said:
Relatively speaking, maybe, maybe not..
Just havin fun...
Hi Sy.
It was interesting, the fridge magnet. If you put one on the other, and slide them, you should see that north and south alternate in stripes. That causes the overall field to drop down as you leave the surface..figure it goes away at about two to three stripes widths from the surface.
Cheers, John
Silly games
I've just been listening to a test amplifier that has a slightly gassy 6AS7G with a rather fetching blue glow near the surface of the glass. Taking one of those "magnet on an aerial" tools for retrieving dropped bits from the insides of engines, I waved it nearby. Seconds of fun can be had moving the glow around!
I've just been listening to a test amplifier that has a slightly gassy 6AS7G with a rather fetching blue glow near the surface of the glass. Taking one of those "magnet on an aerial" tools for retrieving dropped bits from the insides of engines, I waved it nearby. Seconds of fun can be had moving the glow around!
Try a really strong rare earth magnet on the face of your ex-wife's TV. Hours of recrimination...
FWIW, I did a few of my runs with the D28 magnet at various orientations, to no avail. I'm still searching my garage for a beam tetrode to try your suggestion; lots of power tubes archived, but all my small signal pentodes appear to be pentodes.
FWIW, I did a few of my runs with the D28 magnet at various orientations, to no avail. I'm still searching my garage for a beam tetrode to try your suggestion; lots of power tubes archived, but all my small signal pentodes appear to be pentodes.
SY said:
Well, GPS satellites have to be calibrated for relativity, not for their own orbital velocity and gravitational strength, but for tracking aircraft and whatnot. But that's a side effect of predicting their path down to indivual meters after travelling millions to get there.
For generally less precise concerns, 0.1c is where non-relativistic relations come into view (for instance, using a syncrotron for MeV levels instead of a cyclotron, to accelerate subatomic particles).
Tim
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