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I am new to tube power amps. I understand that you always want to have speakers connected to provide a load to the tube amp output transformer.
I am actively biamping my Magnepan 1.6 speakers. (ie. the crossover function occurs prior to the power amp). So my power amps are directly connected to my tweeter and woofer elements of my speakers. The speaker drivers themselves present about a 4 ohm load (even without the crossover elements that would otherwise be there). This works fine with my SS amps today.
Moving to tube power amps, will the amps directly connected to the tweeter/woofer panels be ok and present the proper speaker load to protect the tubes and output transformer?
Currently I have a 63uF capacitor in line (on the + terminal) of the tweeter connection to my amp. The purpose of the capacitor is to protect the tweeter from DC/startup/shutdown thumps from my SS amps. Will having this capacitor which blocks DC cause any problems with proper operation once I switch to a tube amp?
Follow Ups:
Moving to tube power amps, will the amps directly connected to the tweeter/woofer panels be ok and present the proper speaker load to protect the tubes and output transformer?
in general, the question on whether a tube amp needs a load is one that is confusing. The simple answer is if the amp has a pentode output then yes and if it is a triode output then operating into an open load isn't a big deal.
The slightly more complicated explanation involves drawing a horizontal loadline on a set of triode and pentode curves and looking at the resultant full scale voltage swing. In both cases you get close to the full µ of the tube which is slightly more than the loaded µ in a triode and substantially more in a pentode. This is why guitar amps are set to short the outputs when the load (speaker) is unplugged. this gives essentially a vertical loadline making the output stage incapable of swinging any volts due to the µ of 0 whereas a 6L6 into an open load has a µ of close to 200. Taking a 10V drive into a purely inductively loaded stage with a gain of 200 has the possibility of generating very large voltage spikes which tends to be bad news for magnet wire insulation and output transformers in general.
dave
The cap will not be needed if you are using a tube amp since the output transformer will not pass frequencies that low, and will not pass DC.
but what if his amp has a problem and outputs a low frequency that could harm his tweeters?
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Yes, the cap is in place to protect the presumably more delicate tweeter from inadvertent misbehaving direct power amp outputs.
Yes, so that leads us back to your question.With the cap in place the output transformer is left unloaded at the lower frequencies but the tweeter is protected. Can that harm the output transformer?
I do not know for sure. If you were inadvertently playing low frequencies through it for any length of time it might. But one moment of a low frequency burst probably won't harm the transformer where as, one moment of low frequency burst through your tweeter would. Therefore, the cap.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Edits: 01/22/21
so the tweeter shouldn't see any low frequency input anyway, unless something goes wrong (which happens).
The DIYer in me says the cap is a good idea but the audiophile in me says it needs to be replaced with a REALLY expensive good quality one! :-)
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