Choke specs for the Crack
- Thread starter JamieMcC
- Start date
With a Hammond 193C, you might be OK with just a CRC filter.
Hmm, I think I remember looking at simulations of replacing either resistor and concluding that it didn't make a whole lot of difference.
Paul Joppa
Moderator
There are two schools of thought:
On the one hand, the choke can pick up magnetic-field hum, typically from the nearby power transformer. So the choke should replace the FIRST resistor, allowing the later RC stage to attenuate any hum that gets into the choke.
On the other hand, the choke provides a higher impedance than a resistor, so if the last (third) capacitor is a high-audio-quality cap then you want it to isolate it as much as possible from the earlier, crappier capacitors in the power supply. So the choke should replace the LAST resistor, and be located and oriented to minimize pickup from any nearby magnetic component.
On the one hand, the choke can pick up magnetic-field hum, typically from the nearby power transformer. So the choke should replace the FIRST resistor, allowing the later RC stage to attenuate any hum that gets into the choke.
On the other hand, the choke provides a higher impedance than a resistor, so if the last (third) capacitor is a high-audio-quality cap then you want it to isolate it as much as possible from the earlier, crappier capacitors in the power supply. So the choke should replace the LAST resistor, and be located and oriented to minimize pickup from any nearby magnetic component.
JamieMcC
New member
Thanks wonderful info I feel like I'm getting a bit of education.
Does a choke get hot and need air to circulate round it to cool?
If I mount as in the pic below perhaps I can incorporate some form of shielding from the transformer with the materials used for the offset mounting some metal or composite channel section to create a base and partial sides or cover in copper foil shielding tape.
Does a choke get hot and need air to circulate round it to cool?
If I mount as in the pic below perhaps I can incorporate some form of shielding from the transformer with the materials used for the offset mounting some metal or composite channel section to create a base and partial sides or cover in copper foil shielding tape.
If you figure that the choke dissipates roughly the same heat as the 270 Ohm 5 Watt resistor, consider how much larger the choke is! Consequently, it will get warm, but not particularly hot.
I wouldn't shield the transformer or choke unless there is evidence that it is necessary. For example, if you laid your choke down so that it was oriented identically to the power transformer, you might need to expend that effort.
I wouldn't shield the transformer or choke unless there is evidence that it is necessary. For example, if you laid your choke down so that it was oriented identically to the power transformer, you might need to expend that effort.
captain widwiki
New member
Are there any problem if I put two chokes instead of the two 270ohm 5w resistors on the top of the chassis like the SEX ?
It's more of a space issue - you may find it difficult to fit them up there.
Grainger49
New member
If you opt for dual chokes don't mount them side by side. If they must be close mount them at 90 degrees to each other. But if you put them on opposite sides of the amp that should suffice for isolation.
captain widwiki
New member
OK thanks.
another question: What are differences between the Triad C7-X and the Hammond 193C ? Is there a better one ?
As I plan to put the two choke on the top of the chassis, the Hammond will look better...
another question: What are differences between the Triad C7-X and the Hammond 193C ? Is there a better one ?
As I plan to put the two choke on the top of the chassis, the Hammond will look better...
Paul Joppa
Moderator
Well they are both chokes LOL ... The 193 weighs more than three times as much, has twice the inductance and a similar current rating, has 2/3 the DC resistance, it's enclosed instead of open frame, and it's mounted vertically. Costs a lot more, too.captain widwiki said:
Incidentally, I believe the current-production C7-X is in fact made by Hammond, to the original Triad specs (more or less). The original was chosen back in the days of the original S.E.X. amp (we are fast approaching the 20th anniversary of that seminal product!) because it was available from Allied at significantly less cost than other chokes of similar specs. It's been a go-to workhorse for Bottlehead in several applications, mostly because it works and we know its foibles.
Fortunately, a power supply choke is not usually a critical component. For Crack, you want a current rating of 70mA or more, and probably a DC resistance of 200-350 ohms to keep the power supply voltage pretty close to original. I don't think either PB (the designer) or I have actually modeled a choke power supply for this application, so no comment on the best inductance. There have been discussions on how to model power supplies, and what behavior is best, at the Tube-DIY Asylum. But go there with your cynicism intact and post wiht your flame suit on - there is a LOT of misinformation surrounding the good stuff, and people get pretty excitable on the subject.
captain widwiki
New member
Thanks Paul I think I'll opt for the Triad C7-X and search for some transformer covers
JamieMcC
New member
Hi all, just wanted to say thanks to all those who helped hold my hand with the choke installation details and share a couple of pics of how its turned out. Keeping the fasteners out of sight behind the transformer worked well I intend to go back over the connection with some better insulation or shrink wrap to make the connections look a bit more tidy at a later date.
NightFlight
New member
Well, that cleared up all my questions. Thanks everyone.
modestmeowth
New member
mcandmar said:
What kind of circuit tweak is needed for the 193c?
