Can someone educate me on a few things?
My understanding is that the low -3db point is the frequency where the reactance of the choke is equal to the plate resistance. If this is the case it seems that a 50H unit should be fine. I don’t want to unnecessarily cut bass but this is going to be a small SE amp for FR speakers - not a sub woofer.
If the choke is rated at a DC current and I operate it at less current will its inductance effectively be higher in use? Is there a mathematical relationship?
Brian
My understanding is that the low -3db point is the frequency where the reactance of the choke is equal to the plate resistance. If this is the case it seems that a 50H unit should be fine. I don’t want to unnecessarily cut bass but this is going to be a small SE amp for FR speakers - not a sub woofer.
If the choke is rated at a DC current and I operate it at less current will its inductance effectively be higher in use? Is there a mathematical relationship?
Brian
You should check out the multi-tiered RF chokes for transmitters, all in series. Largest winding at the bottom, next smaller winding, next smaller winding . . .
Each one had decreasing inductance, and decreasing distributed capacitance as they got smaller and less turns.
The self resonant frequencies went up as you got to the smaller and smaller windings.
Check out a really old ARRL radio amateur's handbook (advertisements in the back).
Each one had decreasing inductance, and decreasing distributed capacitance as they got smaller and less turns.
The self resonant frequencies went up as you got to the smaller and smaller windings.
Check out a really old ARRL radio amateur's handbook (advertisements in the back).
BJosephs… its actually –6 dB, … and its for the frequency you designate as being “low enough”. For you, would that be 20 Hz? For most refined music listening, actually 30 Hz is just fine. But –6 dB is a bit restrictive.
Better — in the net-opinion of as many forums here as I care to remember — better is to design for 10 Hz, or 5 Hz. The "trick" is to stay away from the "wow and flutter" window of almost-every magnetic pickup victrola turntable. At 33⅓ RPM (just about ½ RPS or 0.5 Hz), there's a nice 10:1 ration between ½ Hz and 5 Hz.
That … in turn … gives quite a nice margin of exclusion for 5 or 10 Hz "neck" in the low frequency response design point.
Note this is only MY (GoatGuy) opinion!!! The rest of the posters are sometimes quite adamant about what lower-bound one should choose for designing the cut-off.
Just saying,
GoatGuy
Better — in the net-opinion of as many forums here as I care to remember — better is to design for 10 Hz, or 5 Hz. The "trick" is to stay away from the "wow and flutter" window of almost-every magnetic pickup victrola turntable. At 33⅓ RPM (just about ½ RPS or 0.5 Hz), there's a nice 10:1 ration between ½ Hz and 5 Hz.
That … in turn … gives quite a nice margin of exclusion for 5 or 10 Hz "neck" in the low frequency response design point.
Note this is only MY (GoatGuy) opinion!!! The rest of the posters are sometimes quite adamant about what lower-bound one should choose for designing the cut-off.
Just saying,
GoatGuy
You know … being an OLD (and I translate (transmit?) that as ancient), HAM, I actually remember those passages.
Thing is, you also really don't want to transmit thru the capacitance of the largest inductor that HF energy (I'm not talking RF here, but AF)
Just saying.
Tho not strictly ARRL, for AF, the Heavy-over-tiny rule works better.
Your mileage may vary.
Mine worked out well … in a "how does this really work?" experiment.
Just saying,
GoatGuy
GoatGuy,
True. RF and Audio frequencies are [generally] different orders of magnitude.
The old RF chokes were just an illustration of the concept of getting more bandwidth out of a choke.
I once used a 20 Henry 100mA choke as a current 'sink' for a pair of 6C45pi tubes in a "Long - Tailed" phase splitter. One expert thought the distributed capacitance would destroy the high frequencies of the splitter action. I told him I tested the impedance from 20Hz to 20kHz on the bench. It worked real well from 30 or 40Hz up to beyond 20kHz, in the amplifier, with good amplitude balance of the two phases.
As to frequency orders of magnitude, I once measured a 500GHz harmonic signal (yes, GHz). We are talking 0.6mm wavelength traversing down an extremely small waveguide.
The 100GHz signal could not squeeze down the small waveguide; brick wall high pass filter action. So the signal really was the 5th harmonic of the 100GHz source.
True. RF and Audio frequencies are [generally] different orders of magnitude.
The old RF chokes were just an illustration of the concept of getting more bandwidth out of a choke.
I once used a 20 Henry 100mA choke as a current 'sink' for a pair of 6C45pi tubes in a "Long - Tailed" phase splitter. One expert thought the distributed capacitance would destroy the high frequencies of the splitter action. I told him I tested the impedance from 20Hz to 20kHz on the bench. It worked real well from 30 or 40Hz up to beyond 20kHz, in the amplifier, with good amplitude balance of the two phases.
As to frequency orders of magnitude, I once measured a 500GHz harmonic signal (yes, GHz). We are talking 0.6mm wavelength traversing down an extremely small waveguide.
The 100GHz signal could not squeeze down the small waveguide; brick wall high pass filter action. So the signal really was the 5th harmonic of the 100GHz source.
... what can I say? !!!Hello GG, and thank you for sharing. I am very interested in trying this method for improving the driver tube for my SE amps. How does this scheme work, or will it be suitable as the anode supply in the driver tube of a SE amp?
Also, i am partial to octal tubes like 6sl7 and 6sn7, how would your circuit differ for accommodating those signal tubes? Thank you .808.
Yes, it works well in the "driver stage", for single-ended amplifiers. If you're going with a push-pull though, I highly recommend interstage transformers. They've gotten rather expensive, but are just marvelous at creating a pair of exactly complimentary outputs to drive the PP finals.
The only thing I'd do different would be to adjust the quiescent (zero-signal) current of either the SL or SN to run at about 6 mA. By adjusting the cathode resistor controlling the constant current FET source. And of course the pin changes on the socket. LOL.
GoatGuy
Just to circle back I did end up using a set of chokes purchased from Transcendar. Gery modified an existing design to get me to 100H with less than 1k DCR. Below is a link to the build thread.
A Loftin-White style SE with EL34
A Loftin-White style SE with EL34
If you decide to prefer the choke load and in time decide to try something different, I can recommend RC-160-15.. I have used them a few times and with very good results.
Not the cheapest, but configurable, shielded and with high resale value.
ISO TRANSFORMERS – 管球アンプ用トランス Audio Transformers for Tube Amplifiers
HK
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