my first build. It works beautifully, here are pics! C&C

[Dr d]

Nice build!!! Curious about the PI voltages. Were these voltages intentional? I am struggling to get anywhere near a 10v difference with a balanced tube on my #124.
Cheers.

[David Root]

DC balance is not what you need. You need to find the AC balance point (signal generator) then vary the trimpot until you get maximum harmonics from your guitar.

Generally the AC and DC balance points are not too far apart, so with a DC balanced PI tube you're likely pretty close to begin with.

[David Root]

Double post.

[Joost]

Nice build!!! Curious about the PI voltages. Were these voltages intentional? I am struggling to get anywhere near a 10v difference with a balanced tube on my #124.
Cheers.

The only thing I did during the build was cherry pick all my components to the values that were closest to the ones in the schematic (I ordered way more than I needed to be able to do this). It seems to have worked everywhere except the PI. All other values were right on the money

[Dr d]

DC balance is not what you need. You need to find the AC balance point (signal generator) then vary the trimpot until you get maximum harmonics from your guitar.

Generally the AC and DC balance points are not too far apart, so with a DC balanced PI tube you're likely pretty close to begin with.

Hi David, I am confused....are we to assume that the #124 schematic PI voltages reflect an unbalanced tube? With my balanced PI tube am I looking for near equal DC voltages? If so, why is this amp different from the high plates which seem happiest with @ 5v difference.

[Joost]

DC balance is not what you need. You need to find the AC balance point (signal generator) then vary the trimpot until you get maximum harmonics from your guitar.

Generally the AC and DC balance points are not too far apart, so with a DC balanced PI tube you're likely pretty close to begin with.

Hi David, I am confused....are we to assume that the #124 schematic PI voltages reflect an unbalanced tube? With my balanced PI tube am I looking for near equal DC voltages? If so, why is this amp different from the high plates which seem happiest with @ 5v difference.

And do I need to do something to make the 10v DC difference happen like it says in the schematic?

[erwin_ve]

Hi Joost,

Looking good, be proud of your first built!

On the PI tube; DC voltages can be close but often are not.
Every balanced tube has a different transconductance and mu on the triodes. They should be close, but 5-10v dc balance is normal when getting 0-2 v on a AC balance.

[martin manning]

What you are shooting for is to get the gain of the inverting and non-inverting sides of the PI to be approximately equal under AC conditions.

If the two triodes and all of the components around them were identical (including symmetrical plate load resistors), the gains would not match because the circuit itself isn't electrically symmetrical in operation. To remedy that, the plate loads are miss-matched. The difference in DC voltage on the plates at idle conditions is there because of the different plate loads, and it is just an artifact of setting the circuit up for AC balance.

Starting with a balanced tube is good because you have a better shot at getting the electrical balance you are after, and getting it within the adjustment range of the trimmer.

[Joost]

Hi Joost,

Looking good, be proud of your first built!

On the PI tube; DC voltages can be close but often are not.
Every balanced tube has a different transconductance and mu on the triodes. They should be close, but 5-10v dc balance is normal when getting 0-2 v on a AC balance.

Thanks! Well no matter where I put the PI trimmer, I never get more than 1 DC volt mismatch on the PI.

[talbany]

WOW!! .... A copy of a copy..Accept that looks better than an original copy..

This is a First...

Tony

[Joost]

WOW!! .... A copy of a copy..Accept that looks better than an original copy..

This is a First...

Tony

*hahaha* I think there was a compliment in there as well so that's how I'll take it but that's why I thought the name was kinda funny.
Anyway, most is just copied from the original.

Btw, on a different subject, moving the gain trimmer to the front is highly recommended! Now you have gain, drive and ratio to voice your overdrive!

[dcribbs1412]

Congrats on a great looking build
shes a beauty
looking forward to pics the loop implementation
Thanks for sharing


Darin

[boldaslove6789]

The built looks great! Should be very a very versatile amp, much more so than Two Rock's half a D-lator and even Dumble's passive loop. I hate caryying around tons of gear (rack case etc.) to get everything to work right.

[M Fowler]

Great looking build.

Now I am to embarassed to post my builds.

Mark

[hans-jörg]

Thanks! Well no matter where I put the PI trimmer, I never get more than 1 DC volt mismatch on the PI.

This I cant understand. Maybe you dont wait enough. After every setting you have to give it time to set. After 5-10 second you should see effect. But more than 1 VDC.
I have there a matched e83cc. and 120/110k on plates. So you (me) are in any case mismached. I have there a trimmer with a spiral so you need 20-30 turns from one side to the other. I started in the mid pos. (5k/5k) and turned in direktion of feedback side. So the feedback side will get more volts than the other (as schematic wants). I´m noe at around 7VDC different and it started that every tone wants to feed back. Here I stoped.
This story is to be continued .
But what I wanted say is: with the 10k trim you should see a lot more than 1 vDC different.

Best

Hans-Jörg

BTW for first build ... wow.
Not my last will look like yours.