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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: 29 Nov 2011, 21:00 
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Hi Ashkan, did you find the problem? It sounds like it could be a bad transistor or and improper bias setting on the side that is not drawing current.
Cheers

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PostPosted: 30 Nov 2011, 01:32 
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Joined: 02 Sep 2008, 23:22
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Hi Ashkan, if you have 1 ohm resistors in there then you need to see about 1-1.5V, across each for the required current. Be very careful increasing the current by slowly changing the value of the bias resistors, you can use a "dual gang pot" to get the value first and then measure it and re replace it with fixed resistors. take your time at this step as it is easy to apply to much current and blow the transistors.

-Dan

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PostPosted: 30 Nov 2011, 10:43 
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Joined: 13 Nov 2011, 09:37
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Location: Tehran, Iran
Hi Dan, Hi Gio
Thanks for the reply. Dan,I read the entire topic ''Hiraga 20W class-A amplifier'' in another forum. I saw pictures of setting the bias by you. I' m sorry that I am so much ignorant :( . but I don't know which resistors are the bias resistors.could you please inform me? and could you please tell me how to set the 500R trimmer. Is it for DC offset?
Ashkan


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PostPosted: 30 Nov 2011, 19:48 
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Hi there Ashkan, its ok have read here it will help you too.

http://www.tcaas.btinternet.co.uk/hiraga1.htm
http://www.tcaas.btinternet.co.uk/hiraga2.htm
http://www.tcaas.btinternet.co.uk/hiraga3.htm

The bias resistors are the 1.8k resistors
The 500R pot is for DC offset yes.

dont connect a speaker until you have got the bias correct and the amp has been on for 2 hours with bias.
then do the DC offset adjustment.
hope this helps

-Dan

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PostPosted: 02 Dec 2011, 09:02 
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Joined: 13 Nov 2011, 09:37
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Location: Tehran, Iran
Hi Dan , thanks a lot for the links .they helped so much. I will do it now.but could you tell me why the value that the schematic suggests for the bias resistors should not work at the first place ? is it because you have changed the out put transistors ? but you edited the schematic . why didn' t you put another value in there ? is the value unique for each built ?
you know when I was a teenager I could not understand why a C played by clarinet sounds B flat :D maybe something similar is going on here . thank you very much .
Ashkan


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PostPosted: 03 Dec 2011, 05:20 
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Hi Ashkan,

I think the original resistor values are to get you in the ball park with a safe level. then you adjust and tune to account for all the component differences once the amp is working ok.

And yes the transistor differences will have an effect on all this.

how is the amp going now ?

- Dan

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PostPosted: 04 Dec 2011, 11:02 
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Joined: 13 Nov 2011, 09:37
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Hi Dan, thanks for the reply. I am very busy right. I have to compose some music in a very short time ,then i will buy a potentiometer or two and then I will fix it hopefully.I will send a nice picture here if I could fix it. how is your amp? how old is it now? it must be a few months younger than your son.
Ashkan


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PostPosted: 24 Dec 2011, 03:36 
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Joined: 17 Aug 2011, 06:05
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Location: Australia
Hi

I've spent a bit of time with this cct and come up with this - first revision.

Image

Am very interesting to start some 'Class A' work and understanding more about solid state - while I learn at the same time about valves/tubes, and IC based amps :)

Going through the original schematic and the board layout, many of the components that are called out in the schematic, are, not laid out on the board, so I've done my best to integrate them accordingly. Note I've not used the standard 'transistors' in Eagle in the schematic but have set the B / E / C accordingly with wirepads.

I intend to revise the above PCB layout a bit prior to etching, happy to hear folks' thoughts.

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PostPosted: 19 Jan 2012, 14:27 
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Joined: 19 Jan 2012, 14:24
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I want to build the 30 watt version but I need a bit more power, how would I increase the wattage output? and is it safe?


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PostPosted: 05 Mar 2012, 06:05 
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Joined: 05 Mar 2012, 05:47
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hello all
I would like to know if Dan can change the schematic
from non-inverting to inverting
why use the difference of the feedback
Internally never sounds good


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