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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: 06 Nov 2017, 16:36 
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Joined: 23 Feb 2017, 02:02
Posts: 132
I would try a larger input cap maybe 3.3uF, or even a 4.7uF-10uF polar cap on input, sometimes the grid/input of the valve is not negative enough with respwect to cathode and input impedance becomes high.


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PostPosted: 07 Nov 2017, 01:29 
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Joined: 18 Oct 2011, 03:15
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Morning KochiyaYamato, thanks for the tips, i thought there was nothing i coukd do, as it was already below audible range etc. Will pick some for caps and give it a try


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PostPosted: 12 Nov 2017, 17:30 
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Joined: 18 Oct 2011, 03:15
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Changed to a battery, what a difference!!! Ultra quiet!,, didnt hook up the posh cans but no hum at all. Still getting nasty hum with the wallwart, but it is ok when the 50k pot is at 0, so if i use source to adjust vol. its ok. Middle of the pot is worse for hum. Tried a 1000uF cap acroos power supply but dont think it did anything. Also tried additional caps across input to earth and tha just screwed things up, sounded really wierd, lost all treble, from some instructables post.
Building another one now, got some more tubes on order, will use for pre amp into an MF DrT i have. Have one for work, iphone into a pair noise cancelling bose qc15, make them sound almost decent. I have crappy plastic boxes, trying to find a nice wooden job. Going to order a book on valve amps, but i think i should get to know this simple circuit first!,,, i am hooked for sure :-) big shout out and thanks to Rogers Gomez. Would love to do some more low voltage builds, not ready for all that high voltage stuff!,,


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PostPosted: 03 Dec 2017, 05:33 
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Joined: 02 Oct 2017, 15:01
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Hi there
I am looking to use this amp as a preamp in my hifi system, this will go before my power amp of course. Will I still need the MOSTFET and lM317 as a for the current gain and constant current source if they are not directly driving the headphones?
Anything else I should look out for when using in a hifi system?
Thanks in advance! Great circuit cant wait to build! Thank you so much for all the time and effort put in!


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PostPosted: 11 Dec 2017, 17:03 
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Joined: 11 Dec 2017, 16:28
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I built this circuit using 2200uf output caps instead of 470uf and IRL530s instead of IRF510s
What is the difference between the IRL and IRF versions of these parts?
I had before this a Bravo Audio V2 which came with IRF 610s and an upgrade guide recommended IRL 510 or IRL 530s, they didn't say 'IRF', so I was wondering what the difference was.

I seem to get decent sound, I guess. About 2x amplification factor, voltage-wise.

BTW, here are project photos.


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PostPosted: 12 Dec 2017, 06:08 
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Joined: 23 Feb 2017, 02:02
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Matt911 wrote:
Hi there
I am looking to use this amp as a preamp in my hifi system, this will go before my power amp of course. Will I still need the MOSTFET and lM317 as a for the current gain and constant current source if they are not directly driving the headphones?
Anything else I should look out for when using in a hifi system?
Thanks in advance! Great circuit cant wait to build! Thank you so much for all the time and effort put in!

As a pre amp, you do not need the mosfet and lm317.
You directly connect a hifi cap at where r3 4k7 joins 12au7, at the output of the cap, you put a 100k to ground instead of the 1k.
You measure output voltage dc to be zero at your pre amp before you connect to power amp.


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PostPosted: 13 Dec 2017, 00:49 
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Joined: 10 Dec 2017, 21:55
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Does anyone have the schematics and pictures or layouts of the amp version that koogar (Rupert Hirst) made that had a power supply and a power on delay built in? I have tried pulling all his links with internet archive but the ones with the plans werent archived. His plans sound like they were the most improved. Or does anyone have a way of contacting him? Thanks


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PostPosted: 13 Dec 2017, 04:29 
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Joined: 11 Dec 2017, 16:28
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I found that when I tried to use electro-harmonix or Gold Lion tube I needed a resistance much higher than 4.7 K. I'm doing alright with a 56k resistor, as I presently lack any 50 or 100 K potentiometers. The voltage isn't 6 volts at 56k, it's more like 5.8 or 5.9 volts


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PostPosted: 25 Jan 2018, 18:43 
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Joined: 23 Feb 2017, 02:02
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LSOJ wrote:
I found that when I tried to use electro-harmonix or Gold Lion tube I needed a resistance much higher than 4.7 K. I'm doing alright with a 56k resistor, as I presently lack any 50 or 100 K potentiometers. The voltage isn't 6 volts at 56k, it's more like 5.8 or 5.9 volts

This is normal, all valves have slightly diffrent specs and varyting operating point should be exprected and normal.
When the votlage isn't at 6v that means the maximum output voltage is reduced.


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PostPosted: 07 Mar 2018, 05:42 
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Joined: 22 Dec 2017, 22:44
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I made a version of this but increased the plate voltage to 24V and added a USB DAC/AMP:
https://thenack.com/2018/03/the-mongrel/

Sounds nice!


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