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In Reply to: RE: Problem AN Kit One: Noise on Output Transformers posted by beto1 on May 21, 2015 at 10:22:46
A given amp has a limit to how many watts it can put out. Depending on the amp it may have the ability to briefly handle a larger "peak" wattage....or it may not.
SET amps often don't have much extra peak power and typically aren't well suited to low bass.
Certain types of music have limted dynamic range. This means much of the music places the same demand on the amp. Other types have much larger dynamic ranges. If you want to listen to this type of music you need a much more powerful amp.
For an amp to play music which reaches your ears at a certain degree of volume several things interact. Amplifier power, distance from speakers, how efficent the speakers are, etc.
So without us knowing amp power, music dynamic range, what hertz and dB gives the problem, how far you sit from speakers, how efficent the speakers are, the impedance plot of the speakers at the hertz where amp acts up, etc., etc., ETC.. Well then we simply can't help much.
From all that you have said it would be easy to "suggest" that you have the wrong amp/speaker combo for the type of music and volume you seek to reproduce. However that would be little more than an educated guess.
Perhaps an easy test might be to rent an active crossover and borrow a solid state amp. Have the 300B amp only play music above a 100-200 hertz and route the rest through solid state amp of at least a couple/few hundred watts. That would require speakers that allow bi-amping....or better yet add speakers just for low bass.
Frankly I was never happy until I had speakers (for the tube amp(s)) that were 100dB/watt or better (think horns) and routed lower bass through solid state amp(s) and then to a pair of 12" to 15" speakers per side. Basically you want to use pro-audio drivers for the speakers....drivers that are rated to handle 5...10...20 times the wattage you need to throw at them to get the volume you want.
And if you really want to do justice to stuff under 60-80 hertz range....and you like your music loud (105-110dB+)....don't be surprised to find you need 400 to 1,000 solid state watts. To think a 6 watt SET can do it with 91 dB speakers....well, that just isn't happening my friend (in fact you are likely doing your amp/tubes serious harm). IMHO 91dB speakers aren't suitable for most tube amps....let alone almost all SET amps.
Follow Ups:
Hi Russ57,thanks for your explanation. Your post appears as deleted, btw. I rescued it from my email.
"The transformer has stored a field that would like to oppose these changes. Under conditions of tube cuttoff/no current that field would like to produce an unlimited voltage to attempt to keep a current draw happening. This could cause a failure in the insulation of the transformers and ruin them. At maximum current draw you run the chance
of running your 300B's way above their current ratings and greatly reducing tube life."
This insulation failure happens with a huge increase on the trafo temperature while it is oversaturated? As far as I remember, always they are running at a low temperature.
My amp sounds very well, but your comment provoke me a little doubt about the health of the insulation on my pair of tx, how can I check if the insulation is still in perfect shape? or when this insulations fail, just kills the trafo and there is no more sound?
Also thanks for your advises about speakers.
I was researching on Lowthers and on 3 way systems, like the derivated from klipsch horns (Crites and others) or similars or maybe the 2 way duplex derivated from Altec 604 GPA, -. Drivers like you mention and a lot more like BMS,Beyma, etc, Volti horn,etc and several projects associated to them are under my sight now.
thanks again
"Under conditions of tube cuttoff/no current that field would like to produce an unlimited voltage to attempt to keep a current draw happening. This could cause a failure in the insulation of the transformers and ruin them."
The voltage of the collapsing field is controlled (limited) by energy transferred to the speaker. This is why tube amplifiers in general should only be operated with a load attached. I wouldn't be concerned about the above scenario unless you've violated this rule.
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Buy Chinese. Bury freedom.
Not at all, every time I have my amp on my work bench is connected to a pair of apeakers and a source. When is placed on the living room, of course the same thing.
thanks
The DCR across the primary of the output transformer will measure lower than it should if the insulation breaks down.
I agree, it wasn't until I put two 18" woofs in crossover over at 55 Hz and under that I really got everything I wanted out of the bottom end from my system with only 8 Watts per side.
Hey, thanks. I'm agree, of course.
My next project is a HEff horn speakers set, by the way. A long postponed project due to the cost and the time that take the research and design.
Harm to my amp? because of the over-saturation on the OP Tx?
I started this thread knowing that from the manufacturer point of view this is normal, but I guess not dangerous to my amp/tubes as they never warned me about . He talked to me about a few examples of amps with the same OP tx doing exactly the same rattle than mine. I'm only trying to expose this topic to a more exhaustive revision on this forum, engaging the community experiences.
Thanks for sharing yours.
Regards
p.s. I will ask locally to some folks on how to do some rigorous measurements, to the same thing with some numbers on the table.
.
Have Fun and Enjoy the Music
"Still Working the Problem"
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