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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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It is currently 03 Dec 2020, 06:36

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PostPosted: 02 Jun 2020, 16:02 
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Joined: 24 Feb 2017, 05:57
Posts: 2
hey everyone.. this is a great amp for headphones and the amount of effort that went into the build instructions is much appreciated and needed. i was able to play with mine for a few hours and when i set the bias for the last time i somehow arced or whatever happened that caused a spark from what looked like one of the exposed pins of the tube socket.. It no longer works. matter of fact the tube doesn't glow anymore and when i replaced the tube it still doesn't glow and the amp doesn't work. I am ok at following instructions but i don't know enough to know what went wrong and how to fix it... any ideas?


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PostPosted: 03 Jun 2020, 10:32 
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Joined: 11 Aug 2014, 06:54
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I'm no expert but here are a couple of things to try: with a multimeter, verify that each component is still within spec. If any resistors and capacitors are in parallel you'll need to disconnect one end before measuring. If everything is OK, then try replacing the MOSFETs and LM317s. They are sensitive to shorts.


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PostPosted: 04 Jun 2020, 00:42 
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Joined: 23 Feb 2017, 02:02
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For the tube to glow all you need is to feed 12v into the heaters, check you have 12v at the heaters.
Its unlikley the heaters do not glow unless you don't have a voltage feeding it or your tube socket is broken, then you can start troubble shoot other parts.

First by removing the LM317 and mosfet you can operate only the tube and check things are correct


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PostPosted: 11 Jun 2020, 05:46 
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Joined: 24 Feb 2017, 05:57
Posts: 2
Thanks guys. I decided to build it all over again which worked out great (with the first build there were a few areas that i could have done much better and so this build is a lot cleaner) I tested all my resirtors and caps and they all passed. I replaced the mosfet and power transistors and also used a much better tube socket... I sounds great. although it doesnt "amplify" the source signal that much it just makes so much more warmer and rich in the lows and the high are super clear without any harshness. I am impressed with how much the tube plays a part in this without much power at all (6.2 volts per channel) This is a great project for novice pedal hacks like me.. Is there a similar project for the 12ax7 used as a guitar pre amp that can be overdriven for that classic tube sound on guitar?


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PostPosted: 01 Jul 2020, 11:39 
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Joined: 01 Jul 2020, 11:33
Posts: 4
Hi, i just finished building this amp. I have a couple of questions,

1.) I currently have a hissing sound on all levels of volume. I have tried 4 different dc adaptors but they still give a hissing sound but the type of hissing varies from one adaptor to the other. Does the problem lie in the dc adaptors or do i have a bad capacitor?
2.) My left channel is louder than the right channel. Is there something i can do to fix this problem?

Thanks!


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PostPosted: 03 Jul 2020, 05:58 
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Joined: 23 Feb 2017, 02:02
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If one channel is louder you have the schematic connectied incrorrectly, or likeley to be using diffrent values on the two channels.
Very unlikley a tube is damaged causing huge mismatch in gain.

You need to use a LC filter to lower the switching noises, a very large capacitor on power supply does a similar thing.
The more inductance you can put in the better but watch out for core saturation limitng the filtering capaciblities when using high inductance cores.
Also low capacitance inductors in theory will help lower noise, but when you meausre it on scope it dosen't change a thing, I suppose only for very high frequency fliltering it matters.


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PostPosted: 05 Jul 2020, 08:28 
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Joined: 01 Jul 2020, 11:33
Posts: 4
Ok, i recently discovered the cause for my problems above and are currently looking for an upgrade.

1) What's the best capacitor for C3? I am looking to replace my current capacitor with Elna Silmic 2 or Nichicon KZ. The problem is that in my country i only can buy Silmic 2 at 470uf 16V. Looking at the reviews of the Elna Silmic 2, i think it is the best capacitor that suited my taste. However, i can buy the Nichicon KZ in 470uf 25V. I have read somewhere in this forum that 25V is more preferable than 16V on C3.
2) What's the best capacitor for C2?

I'm sorry that i have so many questions. Thanks!


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PostPosted: 07 Jul 2020, 07:29 
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Joined: 23 Feb 2017, 02:02
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Elna Silimic 2 will come relativly close to Nichicon KZ when used as the output capacitor to the headphones (C3)
Your not gaining much by upgrading to an Nichicon KZ.

C1 you can upgrade to an Erse Pulse X or an Elna, Nichicon KZ, Nichicon Muse BP,
Erese Pulse X will give you best sound over any polar capaictor.
You can use more expensive bipolar metalised polpropelene capacitors but those give you small gains while the cost is unresonable.
C2 you should use either KZ or Elna, both performs at a similar level in terms of overall sound quality.

If your driving 8ohm headphones you neeed to use an output capacitor of 4700uF
For 16Ohms you need to use an output capacitor of 22000uF
https://www.electronicproducts.com/RC_F ... ator.aspx#
Preferablly you want an cut off frequency arround 5hZ, the maximum tollerated is 10hZ, cut off at above 10hZ you start loosing base.


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PostPosted: 09 Jul 2020, 12:24 
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Joined: 01 Jul 2020, 11:33
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Will this circuit benefit from C1 bypassed by a capacitor such as the vishay MKP1837? I am looking to upgrade either the C1 with JFX/Solen PB or upgrading the C2 with Silmic 2 and bypassing my current C1 with the MKP1837 (C1 currently is an Epcos MKT)


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PostPosted: 10 Jul 2020, 10:28 
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Joined: 23 Feb 2017, 02:02
Posts: 677
Any metalised polypropelene capacitor from genine supplies like RS components, mouser digikey are an upgrade over SIlimic2 and nichiconKZ.
Anything from aliexpress is likley to be fake metalised polypropelene.

Do not use metalised polyester MKT is not for audio, poor sound quality.


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