OR120 build issue

[orangekick]

Hi, this is my first post here. I just completed a build using the attached layout. When I fire it up, everything looks fine. The circuit tests for continuity and appears to be fine. Plugging in a guitar presents a different issue. There's no volume until the master is cranked. When there is sound, it's very gated. I can try to take some pics and attach those. Does anyone have any idea what might be causing this issue from looking at the layout?

Thanks!

[soundguruman]

very gated...
The bias on your output tubes may just be too far negative.
Try reducing that bias voltage.

[orangekick]

Okay, I tried that. It's still doing the same thing, only a hair louder. Also, the master volume does nothing until the last 15% of the knob. It needs to be almost wide open for any sound.

[soundguruman]

If it's a hair louder, than maybe you have bias overkill.

What is the bias voltage on the output grids anyway?
Can you measure it?

[potatofarmer]

From looking at the layout drawing? No. A list of the voltages at every tube pin is a good place to start.

[soundguruman]

No. What is the ACTUAL voltage? ON your output tube grids NOW?
NOT from the drawing.

What is the voltage to ground on pin 5 of each output tube?

[orangekick]

I'm seeing -25.4 on pin 5 of each power tube. There are EH EL34s in the amp.

[soundguruman]

With the amp plugged into a speaker, and turned on,
are the output tubes getting HOT?

I am making an educated guess, that the tubes are almost dead cold.
If they are remaining COLD, (or only slightly warm), when amp is ON, the bias is way off.

The output tubes should get PLENTY HOT. When the amp is ON.
And pretty quickly after the power is on....they should become pretty hot hot hot.

I am thinking your bias voltage should be no more than about -17 volts. I will check that shortly...lemme see here...
No, should be -37 says on schematic.

But check to see if those output tubes get plenty HOT within about 3 minutes, or less, of power ON.

ARE the output tubes staying cold or slightly warm?
OR are they heating up really good?
(hot enough to burn your finger?)

The amp will never work if the output tubes are staying cold....

[orangekick]

Okay, I left it on for a few minutes and the tubes are definitely hot.

[potatofarmer]

Yes, we can do a 1st vs 2nd degree burn test. And then when that tells us nothing, we can measure the voltage and idle dissipation of the output tubes to figure out if they're biased correctly.

Buuut since the resulting sound with the master dimed isn't described as "distorted to all hell" it's more likely that signal is getting dumped somewhere before the output tubes. So either a tube is wired incorrectly or there's a wiring issue between tubes, volume, tone, master, whatever. Making a chart of the voltages read at each tube will narrow the hunt down significantly.

[soundguruman]

It's a rudimentary test...
confirms that high voltage is working...confirms that bias is not too cold...

Well it says -37 on the schematic, and the tubes are hot...
So it could be a problem in the audio path.
so maybe it's not the bias if the tubes are hot.

So now, go thru and write down the voltages on all your tube pins, and maybe you can spot the bug...

[orangekick]

Okay, thanks. I'll go through and write down all of those and post them.

[orangekick]

The sound IS distorted to all hell. I thought that I put that in the first post, but I see that I did not. It sounds like a super, ultra fuzz pedal not unlike something made by Devi Ever.

[soundguruman]

"And then when that tells us nothing, we can measure..."

It tells me a lot of things.
It may tell you nothing...

Depends on how tuned in you are.

Sure, I have a butt load of test equipment...

but I am using several other methods, besides test equipment.

My "tests" do not end with test equipment.
I am a technician...and a musician...who combines both disciplines.

AND I am speaking in terms that a musician would understand, without becoming overly-technical.

Are the tubes hot hot hot?
It tells me that the bias is not too cold---in a way that a non-tech would understand.

Measuring- yes.
Listening - it's the other half of the job.
Testing with guitar, instead of sine wave - this is the part that "techs" don't understand. It's the important missing piece.

[orangekick]

Yes, they are hot. They are too hot to touch.

As for your comments, I tend to trust my ears more than most things. I realize that equipment can tell us what things are supposed to be doing, but our ears might tell us otherwise. It seems like this should all be about finding a balance between the two worlds.

Just a little disclaimer here, this is only my third build and each build has been a different circuit. Perhaps this was a bit much to attempt this early, but I wanted to do it, so here I am. I'm still learning the terms and might call something by something that it's not, but I welcome constructive criticism and want to learn.

I was measuring and got to the power tubes to find that I was missing a connection. It's a rookie mistake, but I did find it. I'm draining the caps now. I'll make that connection and report back.