First D-style (102) build opinions solicited & build thread:

[Raoul Duke]

Everything is reading as it should be now - 12v at the coils, 12 at pins 1 and 5 on the chassis plug regardless of manual switch settings, 12 on pins 2 and 4 when chassis switches set to pedal, when set to manual - 2 and 4 drop down to 0.

[martin manning]

What happened?

Is your DMM ok? Batteries fresh?

[Raoul Duke]

In pedal mode, when I measure voltage at pin 2 on either switch when lit, it’s 0. When switch not lit, I get 12 at pin 2.

Just changed the batteries, but it was my mistake. I have the type that you have to switch to the correct setting for what you’re measuring. I was in AC 600v setting trying to measure DC.

Again, I apologize. Really dumb mistake.

[martin manning]

Ok, sounds much better. So you have a working footswitch now?

[Raoul Duke]

Do the voltage readings make sense for correct pedal operation?

[martin manning]

Yes, I believe so. I was suggesting earlier that you can measure continuity at the relay contacts to verify that they are switching.

[Raoul Duke]

Yes, thanks again Martin!

I got so frazzled by my mistake that I went back and tried to measure everything correctly just to be as thorough as possible and not a total waste of your time, lol.

Learned some more today…

[Raoul Duke]

Martin,
Did some searching for signal generator apps and there are quite a few as well as a bunch of online sites that seem to do the same thing. Also - being a solid early Gen-X’er and slow to upgrade stuff that works perfectly fine for my needs - I happen to have an I-pad with a headphone out jack.

I’m thinking this might work out for what I think I need for the testing - I just need to know what to look for in the signal generator app.

I understand the pluses and minuses and practicality of “which” tests and “when” and see Ian’s point of view for sure. I also see the other side and am really enjoying the learning process that goes with the testing part. Knowing that the PI exercise may just be a “ball park” - I’m still game to follow the steps and learn some more. We’re on the home stretch with this amp and although I’m anxious to see how it turns out, I’m not in a big hurry. Your lessons and advice are a great help and have really increased my understanding (despite some of the goofy s**t I’ve done recently).

I appreciate ALL the help I’ve gotten from everyone here; both actively (folks in chiming in with excellent advice and guidance) and passively (all the great info on TAG when you take the time to search and learn).

Very Gratefully,
“The guy who figured out the amp but can’t figure out the footswitch”

[martin manning]

...I happen to have an I-pad with a headphone out jack.
I’m thinking this might work out for what I think I need for the testing - I just need to know what to look for in the signal generator app.

What you need is a sine wave at a couple of volts RMS. Find a free app or web site that can produce a 400Hz - 1kHz sine and measure the output voltage you can get. I'm guessing your headphone out will be lower than that, maybe 1V RMS, but it's worth a try.

I understand the pluses and minuses and practicality of “which” tests and “when” and see Ian’s point of view for sure. I also see the other side and am really enjoying the learning process that goes with the testing part. Knowing that the PI exercise may just be a “ball park” - I’m still game to follow the steps and learn some more.

Sure, learn how it's done and make some measurements. Your PI tube's sections may not be well matched, and you can discover that now. The best way to set the PI balance is by feeding a sine into the Power Amp In, and your power amp is complete. The B+ is going to be very close to where it will end up with the preamp and FET pulling another ~6mA.

[Raoul Duke]

I'll keep researching the generator input then.

Found a perfectly balanced 12AX7 GE long plate in my tube hoard. Thinking it might be a good PI candidate.

[martin manning]

Nice! How did you determine that the sections are matched?

[Raoul Duke]

Bought it from an old radio guy who claimed it was balanced, then had a retired avionics tech/HAM radio enthusiast friend with a well-maintained Hickok tube tester verify that, then carefully put it away.

There was a time I was looking for one but then saw how anything you but nowadays would need major servicing, so I stopped looking.

[martin manning]

Probably close enough then. Some modern tubes are so far off that the 10k trimmer isn't enough to balance them out.

[Raoul Duke]

I’ve heard horror stories about finding decent PI tubes, so whenever I think I have a balanced one - I put it aside.

Is it safe to assume that a Bluetooth receiver with a 5v power supply will give me enough juice to do the PI test? Been trying to figure this out for a couple hours and I can’t find anything definitive. I know this isn’t the “Bluetooth Receiver Garage”, just figured I’d ask.

Searching Craigslist for used test equipment locally as well. Maybe I’ll get lucky and find something cheap that does everything…

[martin manning]

I think most will be at or below consumer line level output, 1V RMS. Unfortunately that's not going to get the output up to half power. You could still run signal through it, listen to it and get some measurements.