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Discussion in 'Shock Brother's DIY Amps' started by Phrygian77, Oct 22, 2020.
@tubegeek they leave out of lot of info in that. It's kind of just a general guide.
Of course - but there's a lot of handy info in one place, everybody should know it exists.
Just like everybody should have at least one ARRL yearbook from the pre-transistor era with its bitchen power supply section. You want to know how to work safely? Follow their advice for deadly kilovolt transmitter power supplies, and you'll be just fine.
And the RDH4 and Morgan Jones and Horowitz & Hill and...
But those are too big to attach to a forum post so - "it seemed like a good idea at the time."
Anyway not all things to all people, just some things to some people. Best I can do.
From what I understand mounting it to a metal chassis is fine. There are rubber pads to protect it from the chassis and top mounting plate. The bolt goes through the center. The key is that it can't form a loop from top to the bottom. This seems to confuse some people about what the bolt can come in contact with. The bolt can be grounded to the chassis on the bottom side, but the top mounting plate and bolt should not make contact with the chassis.
As I understand it, the rubber pads are there to prevent the wire layers from being pinched and possibly abraded, not as any kind of insulation. The tape wrapped around the outside would take care of that.
The other way to mount them is vertically on a U-shaped bracket. In this style, it is essential that the mounting bolt through the middle is completely insulated from the U.
I suppose a plastic U would be just fine, too, but I haven't seen that done.
In the hifi audio world the one "knock" on toroidal power transformers is, they have wider bandwidth than conventional transformers, and this means they will couple more garbage from the power line if your wall power is dirty.
I think it's a minor knock honestly, and they have many good features that go in the "plus" column.
Perhaps I am misunderstanding. Physics tells me energy does not just appear or disappear.
So where does the heat go? I have read up a little since tubegeek posted the Hammond guide. I have not found anything substantive to explain the info posted in the guide.
From what I have read the PT winding is considered to be equal impedance and non-consequential. The smoothing cap and load may make the difference. One size does not fit both configurations? I will have to wrap my head around that. I can appreciate the heat loss when discussing a choke vs cap/load but that is not what is being discussed.
Perhaps you, tubegeek, or a shock brother can steer me in the right direction.
I'd like to learn.
The issue with the available current when you are considering DC rectified from AC and a cap-input filter - as I understand it - is that the circuit is only drawing current in brief "jolts" rather than continuously. The caps store charge, they charge up to the peak value of the AC wave, and they only drain and dip in voltage slightly before the next charging peak comes along. The diodes conduct for a small portion of the cycle so there are some inefficiencies in the process.
I'm looking for a better reference - that explanation seems to explain the 62% of the full wave bridge but not the 100% of the full wave center tapped configuration, at least to my mind. I'll see what I can dig up.
My thought lies with the filter requirements of the *Two-phase Rectifier* vs the bridge rectifier. I am thinking the bridge rec might need less filtering to get to the same quiescent dB. That could explain the difference. The Hammond guide and the other references I looked at gives no indication the filtering is any different between the two rec methods.
(The Valve Wizard described a *Two-phase Rectifier* the same as Hammond's *Full Wave Capacitor Input load*.)
And, I think I even misunderstood this somewhat.
Yeah. It doesn't jive too well with the Hammond guide.
Makes me think of a movie quote. "Hang the code, and hang the rules. They're more like guidelines anyway."
Hammond lets itself off the hook with this.*A transformer's A.C. current rating needs to be recalculated from the D.C. load current.*
I think I'll have to review the elprocus "transformer utilization factor" claims further.
@Lowerleftcoast there's was some glossing over going on in that article also.
Here's some more interesting info.
ESP - *GREAT* site. Will read after the ballgsme
The resistance of the windings causes a greater loss in series, more resistance, than it does in parallel, less resistance.
Another interesting bit... this was in reference to a center tap full wave rectifier.
"The capacitor ripple current is unaffected in principle, except that it will be slightly lower for a given VA rating since it is directly related to transformer winding resistance."
Horowitz & Hill go straight at it, seems pretty relevant.
Well, mounting this thing to the Princeton Reverb chassis isn't really going to be practical. It's just too big. I've got a 17x8x2 Trainwreck style chassis I can use, although I was thinking about using that for a B-15 build.
This whole conversation about full wave CT vs bridge made me realize that these 100VA toroidals is capable of way more than I realized. So, what to do with transformer?
Stared thinking some more and...
It would be tight, but it could go inside...
Yeah, when considering this toroidal wiring options, the Horowitz & Hill article makes more sense than the Hammond and elprocus offerings. I find it interesting the Hammond guide doesn't refer to losses.
The sound-au article gives some compelling info with flux density but as it discusses an output transformer it claims "The magnetic field created by one half of the winding is cancelled by that from the second half, leaving a net steady state magnetic flux of zero." I would think the exact same thing is happening with the PT CT configuration "leaving a net steady state magnetic flux of zero." In that case any loss must be from wiring size because, if I read it right, the articles disregard inductance.
So, I am convinced there is some heat generated within the PT when it is wired with a CT vs parallel. They are not same-same. I am not convinced there is much difference though unless the comparison is made between two transformers that use different awg wire with different wiring ratio and configuration. Toroid PT vs PT CT. (Apples vs oranges.)
I need to do some more research to buy it hook, line, and sinker.
Can you do the stand-up mounting?
That's a Super Lead chassis in my last post. Quad 6V6s, fixed bias, probably do three gain stages plus cathode follower, and a pre-PI master.