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mfaughn 27th February 2012 08:23 PM

Output Transformer Power Rating Question
 
What does the power rating of an output transformer mean?

I've read about people extracting more power from output transformers than their erstwhile ratings would indicate.

Is this safe?

What are the results on sonics?

How much is too much?

Supposing I have some output transformers that are being used in an amplifier that is capable of more power than the transformers are rated for BUT I never turn up the gain so high as to actually produce more output power than the transformers are rated for. What then?

Do the answers vary depending on whether the amplifier is class A or A/B?

trobbins 27th February 2012 10:25 PM

Depends entirely if you're a guitarist - using 60W OT's for 100W overdrive is often a real pleasure.

DF96 27th February 2012 10:36 PM

Issues include heating, DC core saturation (for SE), primary inductance, insulation quality. As trobbins says, it also depends on whether you are making an instrument or a reproducer.

mfaughn 27th February 2012 10:45 PM

Well, I'm interested in both but my immediate interest is in reproducers.

HollowState 28th February 2012 12:09 AM

Quote:

Originally Posted by mfaughn (Post 2925417)
What does the power rating of an output transformer mean?

It refers the maximum power output level it can pass over it's entire frequency range without overload distortion. The lowest octave is the main limiting factor.

Quote:

I've read about people extracting more power from output transformers than their erstwhile ratings would indicate.
This is true, but there are restrictions and/or consequences. If you do not need the lowest octave (30-60Hz), then you can pass more wattage then it's rating. As an example, I use 60 watt OPTs with PP 6550's and because I crossover at 60Hz before the amplifier, I can easily push 100 watts through it. And that's a nice clean sine wave, not simply music. The lower frequencies would overload and distort at that level.

Quote:

Is this safe?
Within the constraints noted above it is safe for normal program material. I would not consider steady state high power waveforms (sine waves) to be safe for the transformer's useful life.

Quote:

What are the results on sonics?
For a quality transformer, not much provided you stay within the limited frequency range.

Quote:

How much is too much?
This is dependent on the individual transformer. But I would speculate no more then 50% above maximum above 60Hz.

Quote:

Supposing I have some output transformers that are being used in an amplifier that is capable of more power than the transformers are rated for BUT I never turn up the gain so high as to actually produce more output power than the transformers are rated for. What then?
No sweat, provided you keep the power level below maximum rating. You'll hear the distortion when it goes above.

Quote:

Do the answers vary depending on whether the amplifier is class A or A/B?
Generally no. Power is power regardess of the class of operation.

mfaughn 28th February 2012 12:15 AM

Thanks HollowState. That was just what I was looking for :spin:

AJT 28th February 2012 09:12 AM

frequency response and power levels are inter-related:

http://i5.photobucket.com/albums/y15...3/dynaco_4.jpg


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