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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: 17 Nov 2010, 22:01 
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Joined: 16 Nov 2010, 22:19
Posts: 9
roggom wrote:
jaki54321 wrote:
Ok guys i am an idiot... I bought polarized caps for the 2.2 uF caps(C1) and I was wondering, when they come in the mail, can I still use them? I dont want to have to buy more and pay more shipping for 60 cents worth of caps =| Stupid shipping lol

No problem, just remember the (+) always faces the tube.

So as an input coupling cap the music signal comes into the (-) and out the (+)

Welcome to the board!


Thank you for the help and thank you for the kind welcome =)

I have another question. Should this circuit use direct or alternating current? I have a 120VAC to 12.6VAC power transformer and I was thinking about slapping a full wave bridge rectifier on it and a 7812 regulator for DC. But I did not know which type of current it should use. I think direct may be the best cuz when I build my valvecaster, it worked much better with direct... hmm... which should i use? :blush:


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PostPosted: 18 Nov 2010, 02:21 
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Joined: 03 Aug 2008, 20:22
Posts: 386
Location: Denver, Colorado
Jak, the amp runs on DC power. 120 to 12.6 is great, but you will need to build a filter system to remove the AC ripple. See the filter links I posted in the last 2 pages. The amp does not have any common mode rejection, or noise suppression of any kind. So any AC ripple in the DC power will be heard as 60 or 120 cycle noise, or buzzing.


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PostPosted: 18 Nov 2010, 12:28 
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Joined: 31 Dec 2008, 15:34
Posts: 441
jaki54321 wrote:
I have another question. Should this circuit use direct or alternating current? I have a 120VAC to 12.6VAC power transformer and I was thinking about slapping a full wave bridge rectifier on it and a 7812 regulator for DC. But I did not know which type of current it should use. I think direct may be the best cuz when I build my valvecaster, it worked much better with direct... hmm... which should i use? :blush:


Hi jaki54321

I guess Rogers already answered your questions, but to help you even more, it can be said that you're on the right track, if you're using the mentioned transformer. You'll get around 17,6 VDC out of it, after rectifiying ( 12,6 x 1,4 = 17,6 ) and this is an okay voltage, for the input of the 7812 voltageregulator, which can draw 1A output-current ( enough for both amplifier and filament ). Remember to mount a heatsink for the 7812 voltageregulator, it will get hot. :wizard:

To avoid hum, be sure to mount some good electrolytic caps, both in front ( + pin 1, common ground pin 2 ) and behind ( + pin 3, common ground pin 2 ) of the LM7812 voltageregulator. Ex. values between 2200 - 4700 uF, to ensure good filtering. It's also good to decoupling, the voltageregulator with ex. 100 - 470 nF bipolar caps, as near as possible, between pin 1-2 and pin 2-3, of the voltageregulator.

I hope info is understandable.


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PostPosted: 19 Nov 2010, 10:30 
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Joined: 16 Nov 2010, 22:19
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KrammeAcoustics wrote:
jaki54321 wrote:
I have another question. Should this circuit use direct or alternating current? I have a 120VAC to 12.6VAC power transformer and I was thinking about slapping a full wave bridge rectifier on it and a 7812 regulator for DC. But I did not know which type of current it should use. I think direct may be the best cuz when I build my valvecaster, it worked much better with direct... hmm... which should i use? :blush:


Hi jaki54321

I guess Rogers already answered your questions, but to help you even more, it can be said that you're on the right track, if you're using the mentioned transformer. You'll get around 17,6 VDC out of it, after rectifiying ( 12,6 x 1,4 = 17,6 ) and this is an okay voltage, for the input of the 7812 voltageregulator, which can draw 1A output-current ( enough for both amplifier and filament ). Remember to mount a heatsink for the 7812 voltageregulator, it will get hot. :wizard:

To avoid hum, be sure to mount some good electrolytic caps, both in front ( + pin 1, common ground pin 2 ) and behind ( + pin 3, common ground pin 2 ) of the LM7812 voltageregulator. Ex. values between 2200 - 4700 uF, to ensure good filtering. It's also good to decoupling, the voltageregulator with ex. 100 - 470 nF bipolar caps, as near as possible, between pin 1-2 and pin 2-3, of the voltageregulator.

I hope info is understandable.



this is starting to make more sense, I did the same thing with my valvecaster pedal. I got a 1000uF capacitor and I used it to filter out all the buzzing.

Ok, im getting this now... Would this picture from this website work:

http://www.researchcell.com/wp-content/uploads/2010/01/Voltage-Regulator-Circuit-Diagram.gif


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PostPosted: 19 Nov 2010, 23:04 
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Joined: 28 Oct 2010, 00:11
Posts: 26
sknhd69 wrote:
hi, this is my first post [found the project via google] :mrgreen:
and this is also my first tube-based project :idea:

i've finished this project, it sounds great...but with some problem:
- too bright
- early clipping :(
- lack of bass :headphones:

i'm using Electro Harmonix 12AU7 and 4k7 resistor [instead 10k pot]
how to fix that problem? :up:

P.S: pic uploaded later :P
thanks :thumbsup:


I found that different tubes can require vastly different resistances to get
the bias correct and this is extremely important with respect your final
sound. I would suggest replacing the 4.7k resisitors with a 50k trimmer pot
and making sure that the bias is 1/2 of the input voltage.


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PostPosted: 20 Nov 2010, 08:48 
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jaki54321 wrote:
this is starting to make more sense, I did the same thing with my valvecaster pedal. I got a 1000uF capacitor and I used it to filter out all the buzzing.

Ok, im getting this now... Would this picture from this website work:

http://www.researchcell.com/wp-content/uploads/2010/01/Voltage-Regulator-Circuit-Diagram.gif


Hi jaki54321

Yes, it looks fine ....( but offcourse with a larger electrolytic cap, than the shown 220 uF ), try values between 2200 - 4700 uF. You could offcourse try 1000 uF, if there's hum, then try to enlarge the electrolytic cap, until hum is gone.


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PostPosted: 20 Nov 2010, 09:05 
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Posts: 441
skatefriday wrote:
I found that different tubes can require vastly different resistances to get the bias correct and this is extremely important with respect your final sound. I would suggest replacing the 4.7k resisitors with a 50k trimmer pot and making sure that the bias is 1/2 of the input voltage.


Hi skate

Agree, a larger value of trimpot can solve the bias for tubes, which got that problem ( at the same time a larger value would solve biasing for all thinkable tubes ).

Those who've got this problem, can use following illustration which uses a 47k trim pot for P1 (50k is fine too):

Image


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PostPosted: 20 Nov 2010, 12:05 
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Joined: 28 Oct 2010, 00:11
Posts: 26
After getting my breadboard circuit to work the next step, lacking
the ability to etch my own circuit board, was to transfer it to a
protoboard. I bought a small one from radio shack with bus bars
thinking this would be easier to solder than one with individual pads.

Got everything wired up and soldered in, applied power and R4
on one channel released it's prepackaged smoke. Replaced R4,
looking for any possible shorts and it released it's smoke again.

Note that when I have a tube in the socket my multimeter shows
connectivity between the power and ground rails. I initially thought
this was a short until I checked the tube itself and found only 10 ohms
of resistance between pins 4 and 5.

So the question is, any tips on diagnosing why R4 is smoking? I'm using
1/4 watt and I see the BOM suggests 1/2 watt, but the same resistor
did not smoke on the breadboard. I've stared at it for hours with no
insights coming to me as to how to diagnose this.

Any tips are appreciated.


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PostPosted: 20 Nov 2010, 14:44 
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Joined: 03 Aug 2008, 20:22
Posts: 386
Location: Denver, Colorado
Skate, the tube is fine, the low resistance of the filiments causes it to heat and boil off electrons (heater).

I have had the little 10 ohm resistor fry as you stated. It was on one of my first prototype boards, If I remember correctly there was an open run somewhere causing all of the current to be dropped accross the 10 ohm resistor. If possible take a pic for both sides of the board.

Using the busbar type of proto board can be tough sometimes, you have to jump runs here and there. If you have a dremmel tool, it will make life a bit easier, as you can cut runs when needed. You can also cut runs with a exacto knife.

The good thing is you have a good channel, do some readings with your ohmeter and compare channels (power off of course).

Also check pinouts, sometimes we wire the amp to look symetrical, so tube in the middle and resistors on each side and caps as well, but if you put regulators in the same fashion they are pinned Adjust Out In . So on one side the regulators face the front of the board the other they face the back.

I guess what I am saying is check your pinout.


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PostPosted: 20 Nov 2010, 18:05 
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Posts: 441
For some 12AU7 tubes, it's actually necessary to use 50K ( or 47K ) trimpots. I had tried a couple of tubes where even "in my case" 22Kohm trimpots weren't enough ( if i remembered it right, i measured 24 - 25Kohm after adjusting bias = to get half voltage ). Therefore i think 50K is a proper value, it should solve all kind of suitable tubes !

Info to those people who thinks 12AT7 and 12AX7 are suitable for this construction, i say DON'T. In an early stage i had tried several 12AT7 and 12AX7 for this construction and found out that, i had to use 100K trimpots, for bias ( measuring around 70Kohm ). When this is said, i won't recommend neither AT or AX tube for this build. :down: My experience were a distorted, blurred and/or thin sound, so i guess these tubes aren't suitable for this build !


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