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Old 17th October 2011, 10:52 AM   #101
lcoelho is offline lcoelho  Singapore
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Hi All tube guru's

Need some advice, I recently purchased the yaqin MC-10L

1. The amp is rated 52 watts, is this RMS or peak.
2. I notice when i crank up the volume after about midway there is not significant
increase in volume. any ida why or is my imagination.
3. Has any one used the 10L with a magnepan MMG 4 ohm, how is the sound and is
worth buying
4. I do plan to do the mod mentioned in these forum and elsewhere, I also want to
convert the bias to a SS one using the LM337 or a equivalent regulator, is this
wishfull thinking, can any advice the pros and cons.
Appreciate if some expert out there can help, please also let me know if my post is not in the right place( am new here)

lcoelho
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Old 17th October 2011, 10:09 PM   #102
Hi_Q is offline Hi_Q  England
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With tube amplifiers the output power is usually given in RMS Watts, or proper Watts as some will call it . None of your XXXX Watts Music Power here. Having said that, 52 Watts is I think a wee bit optimistic if you are expecting that per channel. Funnily enough it is one of the parameters I have not really bothered to check on my MC-10L, I expected at best 20 Watts per channel but did not measure the amp as it was loud enough for my dwelling space and when cranked up, normally for Pink Floyd, it certainly does not disappoint . I use a remote volume control, leaving the MC10's set at maximum but I could imagine your problem may be due to the source impedance of your signal being placed across the Yaqin's volume control. You may even find that if your input signal is on the low side then you may not be driving the amplifier enough to obtain maximum unclipped output. I have used numerous sources here ranging from Cassette and CD players, reel to reel tape decks, phono pre-amp and even a mini-disc player, all without problems as far as driving the amplifier is concerned. I am not so sure about the solid state bias though as I am led to believe that the present arrangement is self adjusting. For example, if your mains supply was to increase slightly then this would raise the B+ supply and cause the output tubes to conduct more. However, the bias voltage would also increase and to some extent would help to keep the original tube current in check. Exactly how good this is in practice would indeed make another little experiment worth while using my Variac (variable mains supply transformer) next time my amp is on the bench for its annual check over. If you regulate the bias then this counteracting effect will not happen and the tubes will be free to draw extra current.
That is what my belief is of the regulated bias argument, with auto bias this would occur naturally.
Hope this helps, sorry I have no practical experience of the speakers you mention, I am using dual concentric drivers with a sensitivity of 92dB and the sound stage is fantastic. Police sirens on the TV sound, when fed through the Yaqin, often fools me and has me going to the window... I have also had visitors reaching for their mobile phones when it was one on the TV that was ringing. Often we laugh here about such things, the sound is so natural and full of presence in the room. I never achieved anything like that with SS amplifiers though I suppose some will say you can but I think would cost much more than my humble (cost wise) system here. Having gone back to Tubes I think I will stay with them now until the grim reaper comes for me
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Old 18th October 2011, 02:04 AM   #103
lcoelho is offline lcoelho  Singapore
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Thank Hi-Q for the info, please post the results of your variac tests on the bias when you do it.
I have already purchased the Magnepan's MMG so am stuck with it, will see how it sounds
lcoelho
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Old 20th October 2011, 12:30 PM   #104
lcoelho is offline lcoelho  Singapore
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Has anyone tried the decware mod of putting a .01 uf polyester cap in place of the short between pin 1 and 8 in the el34 output tubes.
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Old 20th October 2011, 12:56 PM   #105
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Quote:
Originally Posted by lcoelho View Post
Has anyone tried the decware mod of putting a .01 uf polyester cap in place of the short between pin 1 and 8 in the el34 output tubes.
What is this supposed to do?
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Old 20th October 2011, 01:28 PM   #106
data is offline data  Australia
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I just googled it and they state that it improves the sound dramatically, more linear is what they suggest is happening

I wouldn't try it without consulting my designer friend first...

Though I'm interested what you think costis?
Part 1 DECWARE - The Hazen Mod
Part 2 http://www.decware.com/newsite/paper146.html

I assume this is the mod.
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Old 20th October 2011, 05:16 PM   #107
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Well, they have the word "guru" in the first line of their report. Can't be good. In general, it reads "We did this, we can't say how it works and it's the bestest mod ever!"

No thanks.
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Old 21st October 2011, 03:52 AM   #108
data is offline data  Australia
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Yeah, a bit risky without knowing more I think.

I'll ask my designer friend next time I'm on the phone with him.
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Old 21st October 2011, 04:24 PM   #109
Hi_Q is offline Hi_Q  England
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Mmmm...nobody seems to have an explanation and I am usually pretty hopeless at coming up with theories. However here are two for what it is worth, anybody else have one?
1) Is it possible that a very small amount of positive feedback is being applied, hence the apparent lift in certain areas of the audio spectrum?
Does this sound plausible or rubbish? A large signal is applied to the tubes grid causing a steep rise in tube current. More secondary electronics are reflected from the Plate to the suppressor but because it is no longer connected to cathode, attains a small negative charge. This negative charge is transferred by the capacitor to the cathode causing the grid to appear more positive - hence positive feedback. The levels concerned are not large enough to cause oscillation.
oh well!
Theory 2) Fitting a capacitor between suppressor and cathode effectively reduces the capacitance between plate and the earthy suppressor/cathode connection. Cannot really see this as any kind of argument at audio frequencies though.

Food for thought though...has this so called mod caused the Pentode to behave like a tetrode? i.e. has a kink (even small) returned in the tubes characteristic?

This does appear to be one of those mods that cannot be proven using instruments and only detectable using the lug hole. At $100 a throw I wish I could convince a lot of people about this!
Les
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Old 21st October 2011, 04:36 PM   #110
data is offline data  Australia
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Are their amps concerned Triode strapped?

For a DIY folk the cost is much less

I think I'll read those pages again

Last edited by data; 21st October 2011 at 04:41 PM.
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