Archibald Capacitor Question

[EBK]

I have another Archibald question. The build doc says:

Before powering up for the first time, set the T1 trimmer to 50%. After powering up, use your DMM to measure the voltage at the test point. Adjust T1 until you read about 6.3v for the heater voltage. With the trimmer in the middle, it will already be very close to that.

I have only had to bias a pedal couple of times so I want to be clear on how to do this. With my DMM put the black lead on a ground point on the pedal and the red lead on the pad that is labeled "63.v TEST"? Because of the higher voltage in this pedal (my first tube one) do I need to be careful of touching anything while doing this??? And do you have to re-do this bias if you move form 9v to 12v and back?

No special precautions are needed here, other than being careful around that LM317 voltage regulator.  It gets mighty hot.  And once you get the heater voltage adjusted, it will work for 9V or 12V without needing further adjustment.

Yes, black lead to ground and red to the test point.  Set your DMM to DC voltage measurement mode.

[joelorigo]

Thank you! Getting close to that point in this build.

[joelorigo]

Should it be 6.3 exactly? the trimmer I used is very sensitive and it's easy to barely touch it and go over and under. Closest I have gotten is 6.28.

[jimilee]

Should it be 6.3 exactly? the trimmer I used is very sensitive and it's easy to barely touch it and go over and under. Closest I have gotten is 6.28.

Nah, 6.28 is fine.


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[joelorigo]

Great, thanks!

[joelorigo]

Ok, hopefully my last questions on the Archibald before I make post my first build report on this forum!

I finished it and it seems to work. All the knobs and switches do what they are supposed to. And it does sound really good. There is a certain characteristic about the overdrive that is spongy like an amp but also like a drive pedal. It seems to have it's own thing. Thanks for all the advice on this project already.

But, is it normal, that when I have it in Hi-Lo mode, with the Gain at about 9 o'clock, the Hi & Lo knobs at about noon, Bias full CCW, that even with the Level all the way up it is just under unity volume? This has just been at 9v. Have not tried 12v yet.

[EBK]

But, is it normal, that when I have it in Hi-Lo mode, with the Gain at about 9 o'clock, the Hi & Lo knobs at about noon, Bias full CCW, that even with the Level all the way up it is just under unity volume? This has just been at 9v. Have not tried 12v yet.

I just tested mine at those settings.  I am at unity with Level just a hair past noon, and it definitely gets louder as I move the Level up from there.

[joelorigo]

Hmmmm. Let me try it again. It's possible I had the gain all the way down and was getting that result.  Also, I will try it at 12v.

[joelorigo]

Yea, I misspoke in my Feb 10 post.

What I have is - with Gain full CCW, the Hi & Lo knobs at about noon, Bias full CCW, with the Level all the way up, it is just under unity volume? This is at 9v.

I did try it with 12v and it just over unity with those settings. The only reason I asked is because I even line the sound of the pedal with the Gain full CCW. Just want to see if that is normal.

[joelorigo]

For anyone following this now or in the future, I switched 12AX7s and the output was significantly greater. One of the tubes I am trying was causing noise in an amp a couple of years ago but instead of isolating which one it was I just replaced both v1 & v2 in the amp. So I had 2 sitting around and I'm assuming I put the problem one in the Archibald first. Unless a bad tube would cause more output.

[jwin615]

Well, that sucks but glad it was sorted.