Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Gary_S on June 08, 2013, 07:54:09 pm
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How do you determine the phasing of the windings of the secondaries? Do you measure from one HT winding of the secondary to ground and then do the same with the other HT winding?
This is because i've been reading Merlin Blencowe's Power Supplies book and he talking about testing PT's if you're not sure of voltages etc.
He says to connect two secondary windings in series and then measure them. How do you connect them in series? if that's not a dumb question. I mean i know how to connect components in series and parallel but not a PT's windings!
So for instance on my Marshall 50w if i wanted to determine secondary phasing how would i do it with the PT obviously connected in the amp? Would it be a case of testing, like i say in the first paragraph above from each HT winding to ground and reading the phase off the MM? Merlin's talking in most cases of testing a PT on it's own.
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How do you determine the phasing of the windings of the secondaries?
This only matters if you need to connect 2 or more different windings in parallel or series. If each is being used on its own (as is typical in most guitar amps), then phasing of windings is irrelevant.
... He says to connect two secondary windings in series and then measure them. How do you connect them in series? ...
Pick a winding. Call one lead "#1" and the other "#2". Do the same for another winding. Apply power to the primary and measure the voltage present on each winding by itself. Take one winding's #2 lead and connect it to another winding's "1 lead. Apply power to the primary and measure voltage between the two remaining leads not connected to anything. If the voltage is the sum of the individual winding voltages, then lead #1 of each winding will be the same phase; if the voltage is the difference of the two windings, then lead #1 of one winding is in-phase with lead #2 of the other winding.
What I described was placing the windings in series, and you'll see it's just like any other component type being placed in series.
So for instance on my Marshall 50w if i wanted to determine secondary phasing how would i do it with the PT obviously connected in the amp? ...
This doesn't apply to your 50w Marshall because you're not attaching any 2 windings to the same point/component. Phasing only matters when you connect one winding directly to another, either in series or parallel.
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Thanks HBP, why would you need to connect any of those windings in series or parallel in the first place? When he talks about applying mains power to these trannies how can you do that if the PT is not in an amp? Do you have to have some special kind of power supply or something for applying the power. When i emailed him and asked him a question about this he said that most of these tests are all done on a PT on it's own before it's built into any equipment so you'd need to have some special kind of power supply for testing it?
Not that i'm gonna be doing this but it's just, on reading that section of the book, i want to understand what he means.
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why would you need to connect any of those windings in series or parallel in the first place?
Maybe you have a transformer with two 6.3VAC/2A secondary windings. Connect them in parallel (properly phased) and you now have the equivalent of a single 6.3VAC/4A secondary. Or, connect the two secondaries in series (properly phased) and you will end up with a 12.6VAC/2A winding with a center tap. Thinking of the secondaries as batteries may make it easier to understand.
When he talks about applying mains power to these trannies how can you do that if the PT is not in an amp?
Simply connect the line and neutral conductors of a power cord to the two primary leads and plug into a wall outlet.
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Thanks Sluckey, so just to be clear i would take the wires from a mains cable, here in the UK our live wire is brown and our neutral is blue and actually connect them to the primary wires? then plug the mains cable in at the mains to power the PT?
As i say i'm not doing it, the only transformers i have are in my amps!, but i want to understand exactly what he's meaning in the book.
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yes and yes.
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Thanks Sluckey, appreciate the knowledge :smiley: