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Vacuum Tube OTL power amp!!
Vacuum Tube OTL power amp!!
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Old 2nd January 2012, 01:40 PM   #701
Dimitris AR is offline Dimitris AR  Greece
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Hi Gregg ,very nice amp build , congratulations !! .
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Old 5th January 2012, 06:16 PM   #702
M Gregg is offline M Gregg  England
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Just for interest,

Mozeners fitted started burn in.... A couple of orange drop 716 in the 1st to second stage coupling just for a test..


Regards
M. Gregg
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Old 5th January 2012, 06:21 PM   #703
flatheadmurre is offline flatheadmurre  Sweden
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What voltage and current did you get ?

How even is it wthout the trimmers ?
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Old 5th January 2012, 06:30 PM   #704
M Gregg is offline M Gregg  England
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Quote:
Originally Posted by flatheadmurre View Post
What voltage and current did you get ?

How even is it wthout the trimmers ?
I haven't measured it yet just listening...I have only just completed the mod

So I will measure it as soon as I get a chance (work getting in the way)..

Regards
M. Gregg
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Old 5th January 2012, 06:46 PM   #705
flatheadmurre is offline flatheadmurre  Sweden
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How´s first impression ?
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Old 5th January 2012, 07:27 PM   #706
M Gregg is offline M Gregg  England
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Quote:
Originally Posted by flatheadmurre View Post
How´s first impression ?
It's very loud..

With two heaters on it's a bit much to stand in front of the speakers...I am also concerned about damage to the speakers the cones are being driven quite hard... at these volumes...YMMV

sound is clear and powerfull...its a bit early to tell yet it needs to burn in..

I'm only using the mozener as a clamp....so the heat will be less spread across the resistor and FET.. cap still in place at the moment...

I don't want to use the trim pot its another pain in the ....like fixed bias..
...it's almost cheating....so I might change a few resistors to get it close..LOL


Regards
M. Gregg
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Old 5th January 2012, 07:34 PM   #707
M Gregg is offline M Gregg  England
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Its interesting,

I think I prefer the sound of one heater ....wonder why ...sound is smoother and perhaps warmer..triode sound comes to mind...

Anyway I will do some tests when I get chance..

Regards
M. Gregg
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Old 5th January 2012, 07:39 PM   #708
M Gregg is offline M Gregg  England
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Thinking,

I have the zener voltage set so with one heater its not in conduction at idle..
With two heaters its in conduction at idle by a couple of volts..

Perhaps that is the difference..

Regards
M. Gregg
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Old 5th January 2012, 08:47 PM   #709
M Gregg is offline M Gregg  England
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The mozener,

Does clamp the cap voltage and prevents the increase of cap voltage when two heaters are switched in... << just an observation

The only thing I can think of is my speakers must drive well with just a few watts.. I have no other explanation...

Regards
M. Gregg

Last edited by M Gregg; 5th January 2012 at 08:53 PM.
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Old 5th January 2012, 09:04 PM   #710
flatheadmurre is offline flatheadmurre  Sweden
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You´re only benefitting from the constant voltage when running it hard.

At low OP it should perform the same as katodbias.
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