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Thread: Music Man HD150 output

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    Music Man HD150 output

    Whatís the clean output of a Music Man Hd150 supposed to be? Iíve put it on a scope and have read about 85 clean watts before compression. Is this about right?

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    Sounds weak. Are your supply voltages good? What about the idle current?

    http://www.pacair.com/mmamps/Misc__I...del_chart.html

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    G1 are Music Man amps truly what the stated RMS wattage is? It'd be the first amp company I know of where this is the case. IE a 100W Twin Reverb does not put out 100W of clean signal with no compression or distortion.

    But yes I agree check the supply voltages and bias current.

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    G1 are Music Man amps truly what the stated RMS wattage is? It'd be the first amp company I know of where this is the case. IE a 100W Twin Reverb does not put out 100W of clean signal with no compression or distortion.
    But 85W would not be 15% below 150W.

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    clean signal with no compression or distortion.
    Remember, these are guitar amps, not hifis. It is about how much power can be shoved into a speaker, not what can be made pure and pristine. Some amps do not run clean at all, but we would not then rate them as zero watt amps.

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    Quote Originally Posted by lowell View Post
    G1 are Music Man amps truly what the stated RMS wattage is? It'd be the first amp company I know of where this is the case.
    Like Helmholtz said, 85W is just too low. If he'd said 130W, I wouldn't be so quick to say it's a fault.
    I know these rely on very cold bias to make such big power, that's why I asked about idle current. But supply rails must also be up to par.
    And for what it's worth, I don't think modern Fender uses 50W or 100W spec. for their tube amps? We just call them that based on 2 or 4 power tubes.

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    Fender schematic were titled things like 100 or 135 watt models. I was just looking at some Dual Showman Reverb drawings.

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    Yeah, but that was when they had better tubes that could maybe deliver that power?
    Spec. for the modern 65 Twin re-issue is 85W at 5% THD in the schem. and they use 85W in the marketing literature.

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    Thanks guys... Hem I didn't say anything about 15% below so not sure where you got that figure from.

    Customer says amp isn't as loud as it was before. Typical haha... so we are trying to measure the output in the hopes to have some real data to present to them and explain that it is working fine. The amp is LOUD, and plenty loud and clean IMO. They drove 3 hrs to bring the amp to us, then picked it up, brought it home, then complained about the volume and are now frustrated. They didn't want to trust the amp sound when picking it up, cause they wanted to use THEIR guitar which they apparently didn't bring with them. So... yeah it's one of THOSE scenarios.

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    I didn't say anything about 15% below so not sure where you got that figure from.
    I mentioned 15% down because this about what I would consider acceptable, like 85W instead of 100W in the Fender Twin example. More than 40% below rated can't be normal. With that high plate voltage and 4 decent 6L6s this amp must be able to deliver well in excess of 100 clean watts.

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    Okay gotcha, thanks

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    Bias is at 25.5ma, +/-16v rails are good, 22v rail is good, screens are at 377v and plates are 759v

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    That is very hot bias for Music Man. Most of their amps run the tubes around 6mA. That's a big part of how they make the kind of power they are rated for.
    Also, can you tell us the chassis model number?
    Attached Files Attached Files

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    And of you look at the VERRRRY similar power amps in Peavey VTX models, they also recommend 6-8ma, by reading drop across the cathode drive emitter resistor and calculating.

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    I forgot, in this case, that 25mV across 3.9 ohm is for 2 power tubes, so only 3mA per tube.

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    2275 150
    http://www.pacair.com/discus/messages/6/35.html
    I was going off the section 1 instructions for 25ma per emitter resistor.

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    Sorry, Iíve meant mV this whole time, not mA

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    As voltages and idle currents look ok, did you try new tubes?

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    Also check the screen resistors going to pin4 of each of the output tube sockets.

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