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Choke and resistor as an anode load, in series, would it make a difference which were first? Does the choke still exhibit it's impedance if located before a resistor of equal dcr going to the plate?
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I Have done this in an amp that runs both EML 20b Tubes and RS241 . I used the fancy yamamoto sockets that have ux4 and b4 pin holes in one socket and then there is a voltage dropping resistor to the pins for both the anode and filaments for the rs241 . I could not really convince myself I could hear the difference between resistor followed by choke or choke followed by resistor while it was on the breadboard .
Hi. Depends on the inductance of that choke, and the resistance of the resistor. The R may have been intended to get the desired voltage.
...a phono preamp or related circuit where he's making the plate load part of the filter. An intentional filter is the only reason to use a choke in series with a resistor that I can think of. That would cut highs and boost lows, so it well could be part of an RIAA circuit. Could even be a good idea; fewest parts, etc. You would have to make sure that the circuit is pretty insensitive to variations in tubes, or use a low impedance tube like a 6CG7.
Crap, now I'm thinking about working on one, like I don't have enough to do.
Another possibility is a choke loaded SRPP. The DCR of the inductor alone is usually insufficient to match the cathode resistor of the "bottom" triode. So, some resistance in series is installed. It really doesn't matter how the R and L are stacked.
Eli D.
To first order, circuit is same. Shunt capacitance, from choke winding to core will have a reduced effect if the choke is in the ground end of the series circuit, giving a more gradual high frequency roll-off (resistor likely has negligible capacitance to ground). Possibly not a measurable effect within the audio frequency range.
I agree. The shunt capacitance of the choke winding to a grounded core (and possible shield) may have a measurable effect at high frequency. Assuming that this is an anode load to Vbb, the "grounded" side is actually the side connected to the plate supply voltage Vbb.
.would it make a difference which were first. no as far as the math is concerned but some might say it sounds different
Does the choke still exhibit it's impedance if located before a resistor, yes
however R and XL are not in phase so they don't just add up, see link
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Edits: 05/22/12
I learned something. But do you think that the equation given holds up for a physically separate resistor and an inductor? It definitely applies to the resistive and reactive components of what an inductor per se does, but I wonder whether the effect of the discrete R would just be additive to the quantity calculated using the equation shown.
I found I liked the choke at the anode and the resistor to B+ but try it both ways and see.
dave
Why would you want to do that?
Invalid entry, that did not answer my question
Detail as to why you do things or want to do things are important in order for someone to answer your question.
Personally I think it's a silly idea and there are better ways to do it. Does that answer your question?
I assume hennfarm is talking about an anode choke load. Probably common cathode bias...B+ rail is the same for driver and output tube.
I have the same issue....
Choke for AC impedance, but the DCR of the choke is too low so cathode/anode current must be limited.
Can't be done by the cathode resistor, that has to set the bias.
If it is not done with a resistor in series with the choke, then how better to do it?
robert
Kellymon, that is exactly what I am up against. Thank you everyone for your replies, and Stephen, my apology my caffinated am mania.
It could also be in the cathode of a diff pair and a resistor is needed to bias the pair properly. Dave Slagle's post gave the options for the anode scenario.
I would prefer to use the resistor in the B+to drop the voltage to the choke loaded stage followed by a cap and then a normal choke loaded stage. Unless the 2 stages are DC coupled and then the option may be to have the resistor in series with the choke.
cheers,
Stephen
Interesting suggestion Stephan...basically you would add another pi filter stage?
For example, if the existing filter was already LCLC you would add another stage for the driver only? So the B+ to the driver would look like Rectifier> cLCLCRCL Driver Anode?
What would you suggest to hennfarm to use as a -3db rolloff point so he can determine a cap value?
robert
If there was room, funds or the parts lying about, I would use a separate supply for the driver but otherwise yes to your conclusion. But for some other people and other circuits, who knows, the series R and L might be fine. We all have prejudices and without trying out everyone's ideas, how can anyone say the have "the answer" and then only for that circuit or that person.I ended up with this exact situation in one of my phono stages but the choke loaded stage was the output. I've since rejigged it and the high value dropper is now a long tail in a DC coupled diff pair output.
Every circuit is different and without all the details of whole circuit, recommendations would be pointless which brings us all the way back to my original question ;) I tend not to calculate stuff but use LTSPICE as it can give a better overall picture.
cheers,
Stephen
Edits: 05/24/12
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