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Old 30th July 2010, 12:58 PM   #1
cbj591 is offline cbj591  United States
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Default At Last....First Build Complete...6V6/6SL7

Good morning,


Finally....I have finished my first build.

I never thought I would get to this stage due to the nagging hum issues I was having.

I want to thank everyone for their help and advice through out the build and troubleshooting process.

The sound is great but a little compressed or stuffy. The bass response is good and the highs smooth. I guess I will experiment with some different tubes to see if I can tweak the sound a little more.

Next project - ECC82 or C3G/C3M preamp.


Cheers
Brian
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Old 30th July 2010, 01:09 PM   #2
OneyedK is offline OneyedK  Belgium
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Nice, can we see a schematic?
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Old 30th July 2010, 06:27 PM   #3
cbj591 is offline cbj591  United States
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Schematic attached
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Old 30th July 2010, 06:44 PM   #4
Arnulf is offline Arnulf  Europe
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Looks very nice ! Unlike those ugly cables sticking out the front Have you considered putting the volume and bias adjust potentiometers there and moving those sockets to the back side of the enclosure ?
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Old 30th July 2010, 07:00 PM   #5
cbj591 is offline cbj591  United States
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There is no volume control and it is fixed bias. The volume is controled through the pre amp I am using.

I dont really care for the inputs being up front either, but since this was my first amp, I wanted to keep the signal input as short as possible to minimize problems.

Cheers
Brian
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Old 30th July 2010, 11:49 PM   #6
Ian444 is offline Ian444  Australia
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Quote:
Originally Posted by cbj591 View Post
The sound is great but a little compressed or stuffy. The bass response is good and the highs smooth. I guess I will experiment with some different tubes to see if I can tweak the sound a little more.
Hi Brian, the amp looks great, that is a stone or marble chassis isn't it? The missus says its granite.

Regarding the sound, you could try simply disconnecting the 47uF cathode caps on the 6V6's, or try much larger caps, like 470uF.
I had a similar circuit in an amp recently and found that seperate cathode loads (the 1K/1000uF) on the input tube (6SL7) gave a cleaner sound, despite comments that the circuit as it is may have better inherent balance. Anyway, there's a couple of things you can try before going tube rolling, if you get the urge...

Regarding "fixed bias", your amp is known as self-bias or auto-bias. The "fixed bias" amps have the output tube cathodes going to ground and a negative voltage is supplied to the grids of the output tubes, usually via trimpots to set the bias. Yep, the terminology seems all back to front.

Ian.
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Old 31st July 2010, 12:00 AM   #7
cbj591 is offline cbj591  United States
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Thanks Ian for the tip. I will give that a try.

As far as the chassis. It is Corian. It is a solid surface countertop material. It works great and machines well.


Also thanks for the clarification on the atuo-bias/fixed-bias termanology.


Cheers
Brian
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Old 31st July 2010, 12:44 AM   #8
cbj591 is offline cbj591  United States
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Quote:
Originally Posted by Ian444 View Post

I had a similar circuit in an amp recently and found that seperate cathode loads (the 1K/1000uF) on the input tube (6SL7) gave a cleaner sound, despite comments that the circuit as it is may have better inherent balance.
I'm not sure what you mean by separate cahtode loads (1k/1000uF). The capacitor on the input is 100uF.

Do I need to try disconnecting one or the other, or do something different?

Thanks for the advice

Brian
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Old 31st July 2010, 01:36 AM   #9
Ian444 is offline Ian444  Australia
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Sorry, I meant 100uF. You could try 470uF or 1000uF in that position also. You will find that different size caps can/will affect the sound.
See attached schem, picture is better than words. Not sure if you are going to want to undo some of that tidy circuitry though...
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Old 31st July 2010, 01:51 AM   #10
cbj591 is offline cbj591  United States
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Making changes is no problem...

I have higher quality components (Takman and Mills resistors, Black Gates and Audiocaps) waiting to be used once I can get the sound to a point I am happy with.

I know the components will make a difference also, but I know there is room for improvement before I get to that stage.

Thanks
B
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