Antique Sound Lab Mg-Head Otl Mark 111 Tube Question?
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milesbeyondjazz

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I just bought the Antique Sound Lab MG-Head OTL Mark 111 headphone amp.While I am overall very pleased with the sound,I have a question about the tubes.The 2 end tubes get very warm and bright,but the middle tube is just barely lit up and is just slighly warm to the touch.Is this normal or is their something wrong with the tube?And how expensive are tubes to replace?
 
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milesbeyondjazz

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Since I am very new to tubes and headphone amps in general any help would be greatly appreciated.
 
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adhoc

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from the ASL website - these are the tubes that the OTL mk3 uses: 6BQ5 x 2, 12AX7 x 1. while i personally do not have any experience with these tubes, i do know the following:

1. the 12AX7 is a preamp tube.

2. the 6BQ5 (EL84 equivalent iirc) is a power tube.

it is perfectly normal that a power tube should run much hotter than a preamp tube as the dissipation values for the former are usually much higher. in this case the maximum plate dissipation for the 6BQ5 is 12W while the 12AX7 has a max plate dissipation of just 1W.


the amp manufacturer might also have chosen to run the preamp tube far below its max specs. this might also be a reason for it's relative 'cool-ness'. you may want to ask ASL about this.

hope that helps!
 
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milesbeyondjazz

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Yes it helps quite a bit,thanks.And I have to say I really love this amp so far.It matches up well with both of my main phones(Grado 325i and my Beyer DT770s).I never knew what I was missing when I was just using the headphone jack from my Sony receiver.The only bad thing is now Im wondering if I should try some Senn 650s.Headphones are addictive.
 
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adhoc

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Quote:

Originally Posted by milesbeyondjazz
Yes it helps quite a bit,thanks.And I have to say I really love this amp so far.It matches up well with both of my main phones(Grado 325i and my Beyer DT770s).I never knew what I was missing when I was just using the headphone jack from my Sony receiver.The only bad thing is now Im wondering if I should try some Senn 650s.Headphones are addictive.



you're most welcome!


i'm curious - does your grado distort at high(er) listening levels using the OTL output choice?

and... 'headphones are addictive'? my friend, you havent taken up tuberolling yet...
 
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milesbeyondjazz

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I would'nt say the 325's distort using the otl mode.Its more like they become very bright(which isn't all bad.)I find that by turning the sound down on my budget Sony Cd player it reduces some of the brightness.I hav'nt spent alot of time with the DT770s yet.Thats on my agenda the next time I get a day off from work.And I'm still thinking about some 650s.
 
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