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Is it normal for a tube amp to draw less power at full volume?

tifune

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I have recently been trying out tube amps I see what the fuss is about. First was the Monoprice Pure Stereo - on sale at target.com, of all places. probably the best looking amp I've ever seen for <$400, but typical Monoprice quality issues. When using BT, right channel didn't work unless volume knob was at 101%. 101% = turn volume to 100%, then twist one more time until R channel starts working.

Next up is Nobsound 6P1 6.8W stereo amp. Not a good fit for my use case, driving 5x pairs of old Paradigm Titans via Niles channel selector, but the Monoprice's 10W did the job so I thought how much difference can -3.2W make? (A: way more than I expected).

Also very pretty, though. I can see how tube ethusiasts are inspired to write 6moons essays once you're at the end of your day sitting in a darkened room watching those tubes dance, but personally I'm going to need some AP data (for lack of a better term) to believe in things like tube rolling, etc.

Weird thing with the Nobsound - I have a watt meter connected to the outlet and, using my TempoTec HD/Hidisz S8, the 6P1 draws ~95W with volume from about 15-85%. After that, the power draw drops to about 80W. This does not happen with no load, only when playing music. Sound quality drops quite a bit suggesting I'm overpowering the amp, but why would it sort of give up?

Is this normal behavior for a tube amp? The Monoprice didn't do that, but I have nothing else to compare. Any ideas why this is happening? I realize the Niles complicates things, but this happens with only 1 set of speakers active so the Niles should just be acting as a passthrough in that situation
 
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Blumlein 88

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I don't know if this happens often or not (I suspect not). Not knowing the power supply of the Nobsound it is hard to say. Some SET's use coils in the power supply. Maybe at higher current thru the transformer the ps inductor is saturating which lowers effective inductance. Also could be PS caps are too small and they can't fully recharge so voltage of the PS sags.
 

fordiebianco

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peng

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I have recently been trying out tube amps I see what the fuss is about. First was the Monoprice Pure Stereo - on sale at target.com, of all places. probably the best looking amp I've ever seen for <$400, but typical Monoprice quality issues. When using BT, right channel didn't work unless volume knob was at 101%. 101% = turn volume to 100%, then twist one more time until R channel starts working.

Next up is Nobsound 6P1 6.8W stereo amp. Not a good fit for my use case, driving 5x pairs of old Paradigm Titans via Niles channel selector, but the Monoprice's 10W did the job so I thought how much difference can -3.2W make? (A: way more than I expected).

Also very pretty, though. I can see how tube ethusiasts are inspired to write 6moons essays once you're at the end of your day sitting in a darkened room watching those tubes dance, but personally I'm going to need some AP data (for lack of a better term) to believe in things like tube rolling, etc.

Weird thing with the Nobsound - I have a watt meter connected to the outlet and, using my TempoTec HD/Hidisz S8, the 6P1 draws ~95W with volume from about 15-85%. After that, the power draw drops to about 80W. This does not happen with no load, only when playing music. Sound quality drops quite a bit suggesting I'm overpowering the amp, but why would it sort of give up?

Is this normal behavior for a tube amp? The Monoprice didn't do that, but I have nothing else to compare. Any ideas why this is happening? I realize the Niles complicates things, but this happens with only 1 set of speakers active so the Niles should just be acting as a passthrough in that situation

Efficiency vs output level is not going to be constant, and the two different amp's voltage and current limits will most likely be different and that might also help explain the different behavior.
 
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