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 NEW  Matt presents bias and operation data for the 6V6 tube in SE operation - 6V6 Single-Ended (SE) Ultra Linear (UL) Bias Optimization.

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PostPosted: 03 Feb 2011, 04:03 
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Joined: 06 Apr 2010, 05:48
Posts: 17
Thankyou very much my man, thought you'd gone on to pastures new! I'll make the changes soon and let you know. Again, my thanks. I'm sure there's a thread here for these changes, whilst it was of course meant to be a cheap/1st time project, i think the changes could be implemented with no real costs other than extra batt or upping the p.s. The limit i'd presume to be the fets voltage limit (can't remember it) but, the tube would like as much as poss eh. It would give people a few options and, stop the 'next' build because they wouldn't have to, your circuit having all the options. Think of it as a GTI version. It's, at the end of the day, all there after all. Just a thought. Cheers


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PostPosted: 08 Feb 2011, 14:25 
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Joined: 08 Feb 2011, 12:53
Posts: 2
Location: UK
Hey,
I have a quick question, I'm not a noob to electronics by all means, but i am a noob to valves (hence this project)

I noticed some early clipping occasionally and as a little test I hooked the output of my amp to a scope, run a 200Hz sine wave through it and found that when my amp clips it only clips on the positive side not the negative? Is this due to the nature of the circuit/valve?

Thanks for any insight.


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PostPosted: 14 Feb 2011, 09:16 
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Joined: 13 Dec 2010, 07:11
Posts: 11
Location: Lancashire, England, UK
Hi everyone,

I've just finished building this amp (my first tube project) and i have to say i'm impressed with it already. I made the PCB using the iron transfer method which give me less than perfect results with the tracks not very well defined in places but it does work. It was the first PCB i'd ever eched myself so i was happy, lol. Think i'll use a proper transfer sheet next time.

As other people have noted, i had problems bringing the bias down to half of the supply voltage, i'm using 50k multi-turn presets which doesn't seem to be high enough for my JJ ECC82 tube. However!! (isn't there always an however??) after leaving the amp to run in for a while (i'm up to around 10 hours now) the bias voltage has gradually dropped down by itself and i'm now able to bias the amp correctly. Not sure why this is.

Unlike others i've not had a problem with hum at all, maybe i'm lucky. I've used both a 12V 5A SMPS and a variable 30A linear PSU and both are dead quiet.

I've connected this amp directly to my Marantz CD player and i've found it incrediblly quiet and open. This thing really does show up bad CD's, some of them leaving me wondering what had happened to the treble. "War of the Worlds" sounds fantastic though, you can even hear the tape hiss before it gets cut off by the noise gate they used during the remastering :D

All i need now is to box the thing :)


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PostPosted: 14 Feb 2011, 13:01 
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Joined: 13 Dec 2010, 07:11
Posts: 11
Location: Lancashire, England, UK
Deathcore wrote:
I noticed some early clipping occasionally and as a little test I hooked the output of my amp to a scope, run a 200Hz sine wave through it and found that when my amp clips it only clips on the positive side not the negative? Is this due to the nature of the circuit/valve?

Hi Deathcore,

Is your bias set to half of the supply voltage? Many people including myself have had trouble getting the bias down to 6V (assuming a 12V supply). My bias gradually came down over the course of 10 hours use and is now fine. If it doesn't come down you could try either replacing the bias pots for 100k's or placing a resistor in series with the 50k pots. You might have to play with the value of that resistor but a 47k might be a good start.

Hope you get it sorted.
Brian.


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PostPosted: 14 Feb 2011, 14:25 
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Joined: 08 Feb 2011, 12:53
Posts: 2
Location: UK
Yeah,
Ive just checked again since i reset and scoped the output and they've only drifted about 0.02v, the bias is set to half the supply voltage, I used 50k pots initally so i didn't have much trouble with it.

It's as though it may be saturating rather then clipping, I'll have to get some pics of the scope,
I honestly can't think of why it does it, but I'm sure it's something stupid that I'm overlooking.

Nice to hear you're happy with it, I'm ecstatic with mine besides the above problem, which only becomes apparent when i have a low input to the amp.

Thanks for the reply.


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PostPosted: 15 Feb 2011, 11:13 
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Joined: 13 Dec 2010, 07:11
Posts: 11
Location: Lancashire, England, UK
It is clipping only when the input is low? Sounds odd as you wouldn't expect that unless the bias was WAY off. Might be an idea to double check component values, orientation and placement. I'm no expert with valve amps so hopefully someone with more experience will be along soon to help.


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PostPosted: 18 Feb 2011, 00:16 
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Joined: 07 Aug 2010, 06:24
Posts: 44
Location: India
Seems the bias is wrong, clipping only in one side most probably means a problem with the bias. Check with no input at first if the bias is drifting again and again then you might need to take a deeper look

_________________
"Problems cannot be solved by the same level of thinking that created them" -Albert Einstein


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PostPosted: 18 Feb 2011, 10:27 
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Joined: 18 Sep 2010, 12:48
Posts: 81
If I want to connect speakers to this amp...

what are the modifications to be made to the circuit?

change C3 and R5?
or make the R4 higher?

thanks!


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PostPosted: 26 Feb 2011, 15:34 
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Joined: 26 Feb 2011, 15:02
Posts: 30
Hello,

here the schematics and PCB for another NP-100v12. Definitively battery powered. SLA are sheap, MEAN WELL charger also. All parts supplied from Farnell, Bürklin (100µ/EPCOS/MKT), or Mundorf (6,8µF MCAP and Di/Dt MCAP ZN 0,1µF).
Attachment:
HYBRID-AMP-SCH.pdf

Attachment:
HYBRID-AMP-PCB.pdf


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PostPosted: 01 Mar 2011, 07:01 
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Joined: 31 Jan 2011, 12:06
Posts: 3
I have just build a prototype,works well, but I want to try it at 30 volts. I have 15 volts AC to feed into a voltage doubler, then filter it using about 4mf caps and feed in into the amp. I will use another power regulator for the heater. Do I have to make any adjustments to the amp beside put heatsinks on? The datasheets say that the irf510 and lm317 could take 30 volts.


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