Hi
Does anyone know the value of choke L100 in the output stage of the 303.
I am going to replace all the components on the driver boards. Is it possible to make from scratch this particular inductor ? I know DADA do a range 2uH upwards. prefer to wind my own as long as its in spec. The driver board I have is the one with the transistor / 2 diode arrangement for the biasing. Thanks
Does anyone know the value of choke L100 in the output stage of the 303.
I am going to replace all the components on the driver boards. Is it possible to make from scratch this particular inductor ? I know DADA do a range 2uH upwards. prefer to wind my own as long as its in spec. The driver board I have is the one with the transistor / 2 diode arrangement for the biasing. Thanks
Thanks for that, I'm gonna see if I can research how to make one from scratch, I have loads of electronic bits about the place, just need a calculator of some sort to determine the number of turns and what " core " to use . ?
From pictures I have seen of 303 boards, I believe they used a ferrite core. Most of us would recommend using an air cored inductor, for lower distortion, but it will be physically larger than the original. The problem with a core is that you need to know its effective permeability. For an open ended core it is probably in the region of 10-20, but I'd use an air core. There are calculators out there for this. Perhaps 303 owners could comment whether there would be room to mount an air cored coil "in the air" on the board or elsewhere in the chassis. It does not have to be on the board but could be on the loudspeaker connector live socket.
Generally those inductors can be done wiring 12/15 turns of enamel wire over a 10ohm@1W resistor and soldering it in parallel to said resistor.
Thanks for the replies, an air core inductor will fit and there is room, but I want to keep it as original as possible
I remember as a kid making an inductor with a 10 ohm , { 1 watt minimum } resistor { think it would be carbon film } then winding the enamel copper wire around it to end up with the choke. If I get chance, I might remove the already fitted choke and see if it can be reversed engineered, ?
looks laquered though.
I remember as a kid making an inductor with a 10 ohm , { 1 watt minimum } resistor { think it would be carbon film } then winding the enamel copper wire around it to end up with the choke. If I get chance, I might remove the already fitted choke and see if it can be reversed engineered, ?
looks laquered though.
Be careful winding chokes round resistors as so many are magnetic these days; even the leads are often steel
Brian
Brian
That’s interesting re resistor leads being steel ?
I think I’ll look into air cored , also a toroidal ferrite
I think I’ll look into air cored , also a toroidal ferrite
yes, now you mention it, when I was making some circuits on pcb's, I was forever pulling off the cut offs from resistors / capacitors etc from off of the side cutters, { maybe its in the manufacturing process ? }
The tendency I've noticed is that as components have become smaller, the lead wires are often copper to help remove the heat. But, I've also got some examples of a 5W resistor which the body was magnetic. Carbon film type resistors inthe 2W range are more like the size of older 1W devices now, so it may be better not to use a resistor body any longer anyway. Though if you do, it is worthwhile checking for steel construction/ leads. Although, even if the leads were steel they are so small in diameter compared to the resistor (or should be) that the magnetic coupling will be low.
Lower distortion? It may be better to use an inductor without a hysteresis effect, but at low levels of magnetisation I'm not sure if it would be significant.
D
Deleted member 537430
What about amperage rating? I’ve heard 6 but can you go less? And how far can you deviate from the 6.8 uH value?
From what I recall of the image, the wire on the choke does not look as though it is 6A rated.
The current limiting circuitry is going to prevent currents more than about 4A, so I suggest 2A rated wire would be more than sufficient. The resistance in the winding is low, so the power is not going to be high and it is the power which is the real concern.
As to the value, I recall that the Quad was designed to be stable particularly with an electrostatic speaker which Quad sold, so that was said to be about 2uF load equivalent.
If you do not plan to use ELS's then you could probably reduce the inductance but if you are still using hometaxial 2N3055's (the originals) I would keep with 6.8uH as they have trouble maintaining high frequencies.
I used 3.3uH but with faster devices although I've never had ELS speakers to be unduly concerned about the loading.
The current limiting circuitry is going to prevent currents more than about 4A, so I suggest 2A rated wire would be more than sufficient. The resistance in the winding is low, so the power is not going to be high and it is the power which is the real concern.
As to the value, I recall that the Quad was designed to be stable particularly with an electrostatic speaker which Quad sold, so that was said to be about 2uF load equivalent.
If you do not plan to use ELS's then you could probably reduce the inductance but if you are still using hometaxial 2N3055's (the originals) I would keep with 6.8uH as they have trouble maintaining high frequencies.
I used 3.3uH but with faster devices although I've never had ELS speakers to be unduly concerned about the loading.
D
Deleted member 537430
Hi John, thanks for your answer. Yes, I’ll be using the amp exclusively for the ESL-57. I’ll also be using the original RCA38494’s (2N3055) which I salvaged from an older amp. They’re in really good shape. (I’m trying to keep the amp as original as possible.)
The company I’m using for parts has 6uH and 8uH chokes rated at 3A. I think the original was actually 6.8uH. Anyhow, I’m thinking either one would work. Hoping for consensus.
The company I’m using for parts has 6uH and 8uH chokes rated at 3A. I think the original was actually 6.8uH. Anyhow, I’m thinking either one would work. Hoping for consensus.
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They aren't made with enough accuracy for you to worry about he difference. For safety I would use 8, but there isn't much in it.