Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Lectroid on June 28, 2022, 04:55:32 pm
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I'm installing a choke for the first time in my new build. I've always assumed that the two wires coming out of a choke, connected between B+1 and B+2, could be connected either way. Now that I'm there, I realize I don't really know. :dontknow:
Throwing my ignorance on the mercy of the court, with schematic attached. One wire is blue, the other red. Does it matter which way the two wires are connected?
Thanks!
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Yeah, it is that easy, just connect one of the choke wires to the A HT node (rectifier output & reservoir cap) and the other to the B node (screen grid supply & dropper to the phase splitter C node).
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An HT choke is just a coil of wire wrapped around a chunk of metal laminations. It doesn't matter which end of the coil is connected to the reservoir cap - the self-inductance works the same either way around
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Nevertheless chokes have inner and outer winding. Maybe there is improvement for noise reduction? I wouldn't know what makes more sense, since a choke puts out EM. I think the question is interesting.
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You must connect the red lead to the 32µF cap and connect the blue lead to the other 32µF cap. See how easy that is. :laugh:
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Does this choke diagram help?
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Nevertheless chokes have inner and outer winding. Maybe there is improvement for noise reduction? I wouldn't know what makes more sense, since a choke puts out EM. I think the question is interesting.
The ‘noise reduction’ (i.e., elimination of ripple current) is the result of self inductance within the coil. The coil turns are so close that the flux density field is forced to join up around the whole coil. The strength of the electromotive force within this field (which produces the self-inductance within the coil) is a function of the number of turns/wire length, the permeability of the mass within the field, and voltage and change in current. The ‘inner’ part of the flux density field is the gap in the center of the coil (where the laminations are). It is not in the turns that are closer to the center of the coil, because the magnetising current within the flux density has been forced to join up (because the turns are so close together).
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You must connect the red lead to the 32µF cap and connect the blue lead to the other 32µF cap. See how easy that is. :laugh:
you guys get red and blue wires? mine always come with two black wires which makes it super easy: one black wire to plate node and other black wire to screen node
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The choke coil terminals have AC voltage on them. The input terminal has the higher level of AC voltage (especially the situation for a choke input filter), which is why it can be a benefit to make it the connection to the 'inner' end of the coil, as that then better shields the higher Vac end of the coil from capacitive coupling to nearby circuitry. This hum/noise concern is not such a worry for CLC filters, but it may depend on layout.
Similar to placement of the PT, magnetic coupling from the choke may also benefit from checking its orientation within an amp.
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Thanks for everyone's contributions, lots of good information delivered with the usual humor. :icon_biggrin:
Sorry, trobbins, this is an OEM choke from Hammond organ, so no AC ratings. Interesting info, though.
One more question? The choke I have is rated 14H while the AB763 schematic shows 4H.
a) Is 14H better in the circuit, i.e., will it reduce ripple even more?
b). Or is it a case of: 4H is enough, any more is just overkill but won't hurt anything?
Thanks again all!
EDIT: A similar recent thread with good discussion:
https://el34world.com/Forum/index.php?topic=29099.0 (https://el34world.com/Forum/index.php?topic=29099.0)
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That sounds like the little choke from an AO-43. 14H is OK but if your amp uses anything bigger than 6V6s the current capacity will likely be too small.
BTW, I have several old AO-?? amps that have red and blue leads on the chokes. Ampeg must have liked that color scheme. :icon_biggrin:
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@sluckey,
That sounds like the little choke from an AO-43. 14H is OK but if your amp uses anything bigger than 6V6s the current capacity will likely be too small.
Yes, it's from an AO-43. I've asked a few questions here about this build already.
In an earlier thread about my hoping to build a Pro Reverb-ish amp, someone suggested that the Hoffman AB763 1-channel circuit might support 6L6s if my p/s voltage was high enough.
https://el34world.com/Forum/index.php?topic=28897.msg318182#msg318182 (https://el34world.com/Forum/index.php?topic=28897.msg318182#msg318182)
So-- Tube Depot sells a ~4.5H / 75mA choke for the Fender 6V6 amps and a 3.5H / 100mA choke for 6L6 amps. Apparently the higher number of turns for more Henries comes at the price of a higher DCR, and lowered current. So my free 14H choke will siphon off a lot of current. Have I got that right?
My AO-43 PT puts out a measured 328-0-328VAC from 120VAC wall current. With a SS rectifier I’m hoping to get ~450 volts unloaded. Which might put me into 6L6 territory if I can get 430-440VDC to the 6L6 plates.
But you’re saying that I might not make that if I have a 14H choke eating up a lot of current. Is that right or have I totally misunderstood?
Bottom line: Should I spring for the smaller 4H choke to get the max current flow? Would the 3.5H choke put me in range of driving those 6L6s?
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my free 14H choke will siphon off a lot of current.
it will block a lot of fast changing current, it will siphon off a small portion as heat.
the job of an inductor is to "resist the change in current".
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shooter,
Thanks, that straightened me out. I was confusing the current drop from DCR with the inductor's hum cancelling effect. I think I get it now.
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Write down the Henries and the Ohms and the Pounds. Get into Hammond Mfg's site, chokes, and find a comparable. The rated current of theirs will be similar to yours. (There has been little change in this field of technology since the 1940s.)
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I used that A0-43, PT and 14H choke with 6V6’s, 6L6s and EL-34. with GZ34 and SS on all of these tubes: B+ with GZ-34 was about 400/405 (all tubes), SS about 15v more, all tubes
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...Get into Hammond Mfg's site, chokes, and find a comparable...
Yep, Hammond has a big range of chokes of various H's and DC current ratings:
https://www.hammfg.com/electronics/transformers/choke/153-159?referer=968
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Just getting back to this after domestic commitments. My wife loves a big lawn; she doesn't have to mow it.
... Get into Hammond Mfg's site, chokes, and find a comparable. The rated current of theirs will be similar to yours. (There has been little change in this field of technology since the 1940s.)
That's a great tip.
So - Hammond has a choke with 14H, similar resistance (429 ohms vs. 468 ohms on mine,) but twice as heavy, rated at 75mA. Could we assume the AO-43 choke is somewhere around 35-40mA?
I used that A0-43, PT and 14H choke with 6V6’s, 6L6s and EL-34. with GZ34 and SS on all of these tubes: B+ with GZ-34 was about 400/405 (all tubes), SS about 15v more, all tubes
Sounds like I can build it to use either 6V6s or 6L6s after all, assuming that the current draw of the screens and preamp tubes won't exceed 25 mA. It won't have the 440V plate voltage of the Pro Reverb, but it probably won't overpower the choke, either.
Make sense?
Thanks again.