Help : Anode load inductance
Hello everyone,
is it possible to estimate the sustainable mA load of an anodic load inductance where the available data are the inductance of 120H and its resistance of 1850 ohm?
Thanks to all who will answer me.
Hello everyone,
is it possible to estimate the sustainable mA load of an anodic load inductance where the available data are the inductance of 120H and its resistance of 1850 ohm?
Thanks to all who will answer me.
An equation with only 2 known variables, but that requires 3 known variables is not going to give the answer.
A properly set up measurement, with a known and variable DC current source to the choke, and a capacitively coupled AC signal source from a known impedance, and a scope or AC meter can give the answer.
Some experienced transformer and choke winders may be able to estimate the allowable quiescent current . . .
If you describe the dimensions of the laminations, and the material type of the laminations.
Sorry, I think there is no other way to know the answer.
Well, one more method, build an amplifier stage around it, and test if it has the low frequency bandwidth you want, and does not saturate at the low frequency signal voltage you want it to work at.
Note:
You also need to know the distributed capacitance of the windings. That controls the high frequency roll off of the choke, in an actual circuit.
I am estimating that with 120H and 1850 Ohm DCR, high frequencies may be as much a problem as the low frequencies.
What tube type are you going to drive the choke with?
plate current?
plate impedance, rp?
A properly set up measurement, with a known and variable DC current source to the choke, and a capacitively coupled AC signal source from a known impedance, and a scope or AC meter can give the answer.
Some experienced transformer and choke winders may be able to estimate the allowable quiescent current . . .
If you describe the dimensions of the laminations, and the material type of the laminations.
Sorry, I think there is no other way to know the answer.
Well, one more method, build an amplifier stage around it, and test if it has the low frequency bandwidth you want, and does not saturate at the low frequency signal voltage you want it to work at.
Note:
You also need to know the distributed capacitance of the windings. That controls the high frequency roll off of the choke, in an actual circuit.
I am estimating that with 120H and 1850 Ohm DCR, high frequencies may be as much a problem as the low frequencies.
What tube type are you going to drive the choke with?
plate current?
plate impedance, rp?
The inductances in question (there are 2) are resin-coated in a copper metal container measuring 7x7x9 cm. Impossible to understand the material used.Some experienced transformer and choke winders may be able to estimate the allowable quiescent current . . .
If you describe the dimensions of the laminations, and the material type of the laminations.
I have no idea how to use them if I can't even roughly estimate their mA capacity.
I would like to use these chokes to load the anode of the driver instead of the resistor. No use on power stages. Whoever sold them to me told me they should hold about 30mA. But there is no technical documentation as it is unbranded.Probably max 10mA , for a driver tube , absolutly not for the power output stage
Build a triode circuit.
Start with 20mA or 25mA quiescent current through the choke to the plate.
Put a 20Hz signal to the grid, see how large you can get the signal, before the sine wave has an obvious distorted shape.
Reduce the DC current to 10mA or 15mA. Test at 20Hz again.
Decide what is important, 20Hz, 30Hz, 40Hz.
Test again at those frequencies, and currents, Etc.
Pay attention to your triodes plate impedance, rp is differnent at the different plate currents (it varies versus quiescent current).
100H @ 20 Hz; the inductive reactance is 2 x pi x F x L = 12.566k Ohms, that is in series with the DCR of 1850 Ohms.
If it saturates, the impedance will be far less than that.
Start with 20mA or 25mA quiescent current through the choke to the plate.
Put a 20Hz signal to the grid, see how large you can get the signal, before the sine wave has an obvious distorted shape.
Reduce the DC current to 10mA or 15mA. Test at 20Hz again.
Decide what is important, 20Hz, 30Hz, 40Hz.
Test again at those frequencies, and currents, Etc.
Pay attention to your triodes plate impedance, rp is differnent at the different plate currents (it varies versus quiescent current).
100H @ 20 Hz; the inductive reactance is 2 x pi x F x L = 12.566k Ohms, that is in series with the DCR of 1850 Ohms.
If it saturates, the impedance will be far less than that.
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I don't have sophisticated measurement equipment such as an oscilloscope and so on.Put a 20Hz signal to the grid, see how large you can get the signal, before the sine wave has an obvious distorted shape.
Reduce the DC current to 10mA or 15mA. Test at 20Hz again.
I think I will use chokes with triodes working in the region of 10-20 mA maximum, evaluating the performance solely from the point of view of sound quality.
How do you evaluate proper loading based on sound quality? It seems you want to do highly experimental tests w/o the proper equipment to do it. It's kinda ridiculous. You need to know what optimal low distortion sounds like before you go play into higher distortion regime and see if that's better. You may never get there and you'd never know. You can try with a couple of cell phones with audio apps on them generate the signal on one and detect it with an FFT app on the other. I don't know.
Other alternatives if you do not have any test equipment . . .
Design an amplifier to use a fully specified plate load choke.
Or,
Design an amplifier to use a plate load resistor
Or
Design an amplifier to use a CCS, Constant Current Source plate load.
Designing around parts that are not fully specified is a little like asking a blindfolded Archer to hit the Bulls Eye.
Design an amplifier to use a fully specified plate load choke.
Or,
Design an amplifier to use a plate load resistor
Or
Design an amplifier to use a CCS, Constant Current Source plate load.
Designing around parts that are not fully specified is a little like asking a blindfolded Archer to hit the Bulls Eye.
Xl = 6.28fL, where L is inductance and f is frequency, So let us take 30hz as our lowest f, Xl then becomes 22.6kohms, this is in parallel with your rp. you can calculate gain....no point worrying about reactance at 20khz, it will be very high....Help : Anode load inductance
Hello everyone,
is it possible to estimate the sustainable mA load of an anodic load inductance where the available data are the inductance of 120H and its resistance of 1850 ohm?
Thanks to all who will answer me.
compared to its dc resistance of 1.85khms, 22.6k is very large so you can just ignore and move to estimate gain..
This issue is typical of any unknown choke that someone comes across and wants to use in a valve amp.
Perhaps I can suggest the first parameter to assess is power dissipation as a way to design a reasonably safe idle anode current. Chokes on a common E-I core can be compared to other commercial chokes of similar size and shape that have a dc current rating and a known DCR - where dissipation is current squared by resistance. Is your choke similar to any commercial choke you have seen? If not then power dissipation can be estimated based on surface area, as that dictates how many watts can be dissipated to ambient by convection. There are more elaborate ways to assess things like internal temperature rise,but they require more effort.
The other parameter is incremental inductance at a nominal idle dc current (as estimated by assessment of dissipation). I can suggest using the measurement method I use, as it combines AC and DC measurements in the same manner as a normal choke is used, and is perhaps as simple as it comes assuming you have a reasonable meter or two.
https://dalmura.com.au/static/Choke measurement.pdf
Perhaps I can suggest the first parameter to assess is power dissipation as a way to design a reasonably safe idle anode current. Chokes on a common E-I core can be compared to other commercial chokes of similar size and shape that have a dc current rating and a known DCR - where dissipation is current squared by resistance. Is your choke similar to any commercial choke you have seen? If not then power dissipation can be estimated based on surface area, as that dictates how many watts can be dissipated to ambient by convection. There are more elaborate ways to assess things like internal temperature rise,but they require more effort.
The other parameter is incremental inductance at a nominal idle dc current (as estimated by assessment of dissipation). I can suggest using the measurement method I use, as it combines AC and DC measurements in the same manner as a normal choke is used, and is perhaps as simple as it comes assuming you have a reasonable meter or two.
https://dalmura.com.au/static/Choke measurement.pdf
Try to use Arta software and Limp to check the stuffI don't have sophisticated measurement equipment such as an oscilloscope and so on.
I think I will use chokes with triodes working in the region of 10-20 mA maximum, evaluating the performance solely from the point of view of
With a good sound card you can see the specs
This is the first step to learn something and start with a minimal test set
The test is without dc current but gives you an initial idea
Then always with Arta or REW you can check live the Freq answer and Thd vs Frequency
At 20 kHz the parasitic can became important
Take care
In every case which is the gain you need?
Also you have to select a proper tube as Rp, not more of 3-4 kohm I think
Walter
Normally even the commercial anode inductors of some brands almost never offer more rating data than the value in H, the sustainable mA and the resistance in ohm. From experience it is not difficult to understand that any inductance (even PSU power inductors) can handle more mA of current the lower its resistance in ohms.In every case which is the gain you need?
Also you have to select a proper tube as Rp, not more of 3-4 kohm I think
In my case the resistance of 1850 ohm indicates that the sustainable current will certainly be quite low. Comparing this figure with commercial products, it seems reasonable - also considering the size of the object - to estimate that 15-30 mA is a range in which to move without problems. Some manufacturers also indicate the max current beyond which the inductance goes into saturation, and this evaluation is often a margin of about 30% more than the rated value. Therefore I don't think it is wrong to try to use it with driver tubes that work well around 20mA.
I generally prefer to use triodes or pentodes triode-mode with an internal impedance of no more than 3000 ohms, and here the choice is quite large.
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"In my case the resistance of 1850 ohm indicates that the sustainable current will certainly be quite low."
Better to indicate physical size, or a photo. For example I have two choke windings on the same core, where each choke is 400H 80mAdc rated but measures 280H at 80mAdc at 50Vac 100Hz with a DC resistance of 1340 ohm, or alternatively two sections of the two chokes in series were measured at 380H at 80mAdc at 50Vac 100Hz with a DCR of 1250 ohm.
By measuring incremental inductance at say 50% of anticipated idle, and at 150% of anticipated idle, then compare the droop (if any) of inductance (keeping the Vac the same).
If you use a soundcard/software option, which certainly works (see example in the link I posted in #12) then note that the calculated inductance value (eg. by REW) will be relative to the excitation voltage applied to the choke and the frequency point. That test will show the first self-resonant frequency (perhaps likely around 3-10kHz), but I doubt trying to determine THD would be too relevant or relateable to other chokes per se.
Were you aiming to use the choke in a parafeed type circuit with feedback, as there are then other low frequency resonances to work through.
Ciao, Tim
Better to indicate physical size, or a photo. For example I have two choke windings on the same core, where each choke is 400H 80mAdc rated but measures 280H at 80mAdc at 50Vac 100Hz with a DC resistance of 1340 ohm, or alternatively two sections of the two chokes in series were measured at 380H at 80mAdc at 50Vac 100Hz with a DCR of 1250 ohm.
By measuring incremental inductance at say 50% of anticipated idle, and at 150% of anticipated idle, then compare the droop (if any) of inductance (keeping the Vac the same).
If you use a soundcard/software option, which certainly works (see example in the link I posted in #12) then note that the calculated inductance value (eg. by REW) will be relative to the excitation voltage applied to the choke and the frequency point. That test will show the first self-resonant frequency (perhaps likely around 3-10kHz), but I doubt trying to determine THD would be too relevant or relateable to other chokes per se.
Were you aiming to use the choke in a parafeed type circuit with feedback, as there are then other low frequency resonances to work through.
Ciao, Tim
I think I will use chokes with triodes working in the region of 10-20 mA maximum, evaluating the performance solely from the point of view of sound quality.
Well, why not? You've got the parts, and some idea in mind, so give it a try. You don't need anybody else's validation, and nobody can measure it anyway. Nothing is perfect; we swim in uncharted waters, much more with iron cored inductors than in any other audio realm. Build an amplifier with them and see how it runs. Paraphrasing Paul Klipsch, if you listen to an amplifier that you've built, it will sound great. That's how we got OG stuff.
Break a leg,
Chris
No circuit parafeed.Were you aiming to use the choke in a parafeed type circuit with feedback, as there are then other low frequency resonances to work through.
Something simple.
Like this circuit here:
Attachments
The diagram published is only indicative, as are the values of the components shown. These will be decided after the choice of the driver tube.Is there another load than the 100k? 2mF is a substantial capacitance, and e-caps may add some complexity if output dc offset is a concern.
No circuit parafeed.
Something simple.
Like this circuit here:
If you use a simply attenuator, like 20 and 40 dB, you can check with Arta o REW the performance of the real circuit taking the output signal.
MAinly at low and high frequency
With a 24bit/192 kHz sound card ( tha have a not an great headroon in input) you can have a bw of 96 kHz that is enough to understand the way.
The response and the Thd vs freq are the basics tests
If you use a simply variable negative bias you can see also the results at low frequency changing the bias current of the tube.
Walter
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