Home |
Search |
Today's Posts |
#1
Posted to rec.audio.tubes
|
|||
|
|||
Help in choosing a PT
I'd like to make a PP guitar amp of around 30W using a pair of EL34s.
The range of current is estimated to be from 175 to 225 mA. The rectifier will be silicon. I have two candidates from Hammond: 1) 263CX 116VA 180-0-180 250 mA using a full wave bridge rectifier. 2) 273BX 182VA 350-0-350 175 mA using two half wave rectifiers. The 263CX seems like a good choice. However, it does not have a 6.3 vac heater winding. The 273BX has a 6.3 vac heater winding but would have to run above its 175 mA rating. But it has the higher VA rating. And when it is putting out 175 mA, the average current on each side is 175/2 and running cool, right? So, could the PT be safely pushed higher? If so, how high? Could it output a total of 175sqrt(2) = 248 mA? Would it saturate? In this case the current peaks on each side would exceed the PT's rating, but the I^2R rating would not be exceeded. TIA, Joe |
#2
Posted to rec.audio.tubes
|
|||
|
|||
Help in choosing a PT
In article . com,
"Joseph Meditz" wrote: I'd like to make a PP guitar amp of around 30W using a pair of EL34s. The range of current is estimated to be from 175 to 225 mA. The rectifier will be silicon. I have two candidates from Hammond: 1) 263CX 116VA 180-0-180 250 mA using a full wave bridge rectifier. 2) 273BX 182VA 350-0-350 175 mA using two half wave rectifiers. The 263CX seems like a good choice. However, it does not have a 6.3 vac heater winding. The 273BX has a 6.3 vac heater winding but would have to run above its 175 mA rating. But it has the higher VA rating. And when it is putting out 175 mA, the average current on each side is 175/2 and running cool, right? So, could the PT be safely pushed higher? If so, how high? Could it output a total of 175sqrt(2) = 248 mA? Would it saturate? In this case the current peaks on each side would exceed the PT's rating, but the I^2R rating would not be exceeded. My understanding is that transformers like these, those that are designed for use with center tapped full wave rectifiers using two diodes, are rated so that when the entire secondary winding is used with with a full wave bridge rectifier, the current rating must be reduced so that a 250 mA winding becomes something more like 177 mA when using a full wave bridge rectifier. Also the current rating is generally higher if a choke input filter is used. Also it is my understanding that transformer saturation is controlled by the primary voltage, not the secondary load current. However I'm not a transformer guy so you should probably wait for one to confirm all this. Regards, John Byrns |
#3
Posted to rec.audio.tubes
|
|||
|
|||
Help in choosing a PT
John Byrns wrote: My understanding is that transformers like these, those that are designed for use with center tapped full wave rectifiers using two diodes, are rated so that when the entire secondary winding is used with with a full wave bridge rectifier, the current rating must be reduced so that a 250 mA winding becomes something more like 177 mA when using a full wave bridge rectifier. Actually, a full wave bridge uses the transformer more efficiently. Also the current rating is generally higher if a choke input filter is used. Yes, slightly, by extending the conduction angle ( period ) which reduces the rms value of the load current. Also it is my understanding that transformer saturation is controlled by the primary voltage, not the secondary load current. It is indeed. Entirely so in fact. Graham |
#4
Posted to rec.audio.tubes
|
|||
|
|||
Help in choosing a PT
John Byrns wrote
...Also it is my understanding that transformer saturation is controlled by the primary voltage, not the secondary load current. Not directly. It is useful to consider the primary winding as its inductance in series with its winding resistance. In parallel with that inductance is the reflected secondary load resistance in series with the secondary winding resistance. Saturation occurs when the *current* through the primary inductance exceeds a certain value. It is true that for most transformers we should be using, the peak current depends to a good approximation upon the voltage across the primary, and the frequency. However, as current is drawn from the secondary, it causes a voltage drop across the primary inductance. For a given frequency, this results in a drop in peak current. Consequently, as more current is drawn from the secondary, saturation becomes *less* likely. cheers, Ian |
#5
Posted to rec.audio.tubes
|
|||
|
|||
Help in choosing a PT
Eeyore wrote
Also it is my understanding that transformer saturation is controlled by the primary voltage, not the secondary load current. It is indeed. Entirely so in fact. Rubbish Ian |
#6
Posted to rec.audio.tubes
|
|||
|
|||
Help in choosing a PT
Ian Iveson wrote: Eeyore wrote Also it is my understanding that transformer saturation is controlled by the primary voltage, not the secondary load current. It is indeed. Entirely so in fact. Rubbish For all practical purposes its purely the volt-seconds that count. Graham |
#7
Posted to rec.audio.tubes
|
|||
|
|||
Help in choosing a PT
In article ,
Eeyore wrote: John Byrns wrote: My understanding is that transformers like these, those that are designed for use with center tapped full wave rectifiers using two diodes, are rated so that when the entire secondary winding is used with with a full wave bridge rectifier, the current rating must be reduced so that a 250 mA winding becomes something more like 177 mA when using a full wave bridge rectifier. Actually, a full wave bridge uses the transformer more efficiently. Exactly, however that does not contradict what I said, the maximum current rating is still reduced. The total power output capability of the winding increases however because the output voltage approximately doubles, while the current rating is reduced by less than a factor of two. Regards, John Byrns |
#8
Posted to rec.audio.tubes
|
|||
|
|||
Help in choosing a PT
Eeyore wrote
Also it is my understanding that transformer saturation is controlled by the primary voltage, not the secondary load current. It is indeed. Entirely so in fact. Rubbish For all practical purposes its purely the volt-seconds that count. "For all practical purposes" and "Entirely" are rather different. Further, "for all practical purposes" is still wrong. Some mains transformers saturate with no load. Further, mains frequency varies from country to country. This is an international group. You may argue that your introduction of the "volt-second" covers this second point. You are squirming and confusing the issue. What you originally said was wrong and silly. Own up. Ian |
#9
Posted to rec.audio.tubes
|
|||
|
|||
Help in choosing a PT
Ian Iveson wrote: Eeyore wrote Also it is my understanding that transformer saturation is controlled by the primary voltage, not the secondary load current. It is indeed. Entirely so in fact. Rubbish For all practical purposes its purely the volt-seconds that count. "For all practical purposes" and "Entirely" are rather different. Further, "for all practical purposes" is still wrong. Some mains transformers saturate with no load. Such as ? Further, mains frequency varies from country to country. This is an international group. You may argue that your introduction of the "volt-second" covers this second point. You are squirming and confusing the issue. What you originally said was wrong and silly. Own up. For all practical purposes it's right. There's no *need* to introduce a more complex explanation and I doubt he wanted one. I would hope that the OP is smart enough not to buy a 60Hz transformer for use on 50Hz, this is covered by the volt-seconds issue btw. Graham |
#10
Posted to rec.audio.tubes
|
|||
|
|||
Help in choosing a PT
You are not worth educating.
Your original statement: Also it is my understanding that transformer saturation is controlled by the primary voltage, not the secondary load current. *** It is indeed. Entirely so in fact.*** Is nonsense, as I pointed out. It is not true that it is entirely controlled by primary voltage. It is not true that it is entirely not controlled by the load current. Anyone who believed you could make serious mistakes in circuit design or transformer specification. Now shut up and go away. Ian "Eeyore" wrote in message ... Ian Iveson wrote: Eeyore wrote Rubbish For all practical purposes its purely the volt-seconds that count. "For all practical purposes" and "Entirely" are rather different. Further, "for all practical purposes" is still wrong. Some mains transformers saturate with no load. Such as ? Further, mains frequency varies from country to country. This is an international group. You may argue that your introduction of the "volt-second" covers this second point. You are squirming and confusing the issue. What you originally said was wrong and silly. Own up. For all practical purposes it's right. There's no *need* to introduce a more complex explanation and I doubt he wanted one. I would hope that the OP is smart enough not to buy a 60Hz transformer for use on 50Hz, this is covered by the volt-seconds issue btw. Graham |
#11
Posted to rec.audio.tubes
|
|||
|
|||
Help in choosing a PT
Ian Iveson wrote: You are not worth educating. Your original statement: Also it is my understanding that transformer saturation is controlled by the primary voltage, not the secondary load current. *** It is indeed. Entirely so in fact.*** Is nonsense, as I pointed out. It is not true that it is entirely controlled by primary voltage. It is not true that it is entirely not controlled by the load current. Anyone who believed you could make serious mistakes in circuit design or transformer specification. Utter nonsense. It was a simplification but a valid one for the purposes of the discussion i.e. secondary current is *not* the issue wrt saturation. Graham |
Reply |
Thread Tools | |
Display Modes | |
|
|
Similar Threads | ||||
Thread | Forum | |||
Need Help Choosing an Amp | High End Audio | |||
Choosing between the KISS amplifiers | Vacuum Tubes | |||
Desperately need help on choosing a mic for live vocal performance!!! | Pro Audio | |||
Choosing a Microphone for live recording | Pro Audio | |||
ICE Topic: Choosing a Headunit. | Car Audio |