Wiring Question (Answered)

[DH166]

Ok. Follow-up: Is it just the longer the wire that goes from V1 through to the board (the purple one in the layout) that needs to be shielded, or does that small wire that goes from the tip lug on the switch itself over to the insulated terminal (the blue one in the above pic) also need to be shielded wire?

[JMPGuitars]

Ok. Follow-up: Is it just the longer the wire that goes from V1 through to the board (the purple one in the layout) that needs to be shielded, or does that small wire that goes from the tip lug on the switch itself over to the insulated terminal (the blue one in the above pic) also need to be shielded wire?

There was no pic in your post, but if you're referring to the light blue wire connecting to the tip if the switch JACK, then yes, that's the wire we're saying to use shielded wire for.

The input jack to V1, V1 plates (p1 and p6), and the gain knob to V2 should all be shielded wires, in addition to the tremolo switch.

[DH166]

Thanks. Now, I may have been confused in the previous response. Prior to my last post, I was asking about the wire (purple in the layout) that goes from V1 p7 through the insulated terminal (at least it looks like it does) and onto the board to the 2.2M resistor. When I read the note about using shielded wire for the external switch, that's the wire I wondered about, but that one was not in the list of shielded wires in your last response. Is that wire shielded?

[JMPGuitars]

Thanks. Now, I may have been confused in the previous response. Prior to my last post, I was asking about the wire (purple in the layout) that goes from V1 p7 through the insulated terminal (at least it looks like it does) and onto the board to the 2.2M resistor. When I read the note about using shielded wire for the external switch, that's the wire I wondered about, but that one was not in the list of shielded wires in your last response. Is that wire shielded?

It shouldn't be necessary. That wire should be very short, as pictured.

The wire running to the jack is typically much longer than pictured, that's why it often needs shielding.

[DH166]

Ok. Next question: Have a look at the picture. As I'm now at the point of connecting the valves to the board, I've got a lot of parallel wires, such as the green pair and yellow pair coming off V4 and V5, and I'm concerned about that. Are these going to be far enough apart to avoid issues, or should those wires be twisted?

IMG-0685 (1).jpg

[JMPGuitars]

The length of those wires could be an issue, but don't twist anything.

You want to avoid running grids and plates in parallel.

You want the wires to be as short as possible, but still have enough extra to chopstick them if needed.

Some of those wires may need to be shielded, but follow the layout guide for now.

[DH166]

Lesson learned for next time. This was/is my first build and I wanted to do everything by hand. So, I fabricated the chassis from sheet aluminum and used measurements from a different source. So, I couldn't place things according to the layout. Now, I see why it's organized the way it is. So, as a guideline, does the necessity for shielding have more to do with what parts of the circuit are being connected or is it just to do with their length? Is there a rough guide to how many inches of distance a wire would be before you'd use shielded? Side question: What is 'chopsticking' that you referred to?

[JMPGuitars]

Lesson learned for next time. This was/is my first build and I wanted to do everything by hand. So, I fabricated the chassis from sheet aluminum and used measurements from a different source. So, I couldn't place things according to the layout. Now, I see why it's organized the way it is. So, as a guideline, does the necessity for shielding have more to do with what parts of the circuit are being connected or is it just to do with their length? Is there a rough guide to how many inches of distance a wire would be before you'd use shielded? Side question: What is 'chopsticking' that you referred to?

There's probably a book or two about amp building out there.

The purpose of shielding is to prevent the riffraff from using wires as antennas for unwanted noise. This is needed on V1 for the plate wires, as that spot is very sensitive. It might be useful on other grid wires as well. Building the amp will let you know when you...

Chopstick!

Chopsticking is taking a wooden chopstick, with one arm behind your back, so you can reposition wires using the chopstick and see how it affects any noise issues. Moving a wire half an inch away from another wire can often be the cure for a noise issue. Or slightly changing wire orientation so unfriendly neighbors aren't so parallel.

Thanks,
Josh

[DH166]

So, done wiring everything. Quadruple checked. Next up is testing voltages etc. I have the builder's guide from Trinity and various videos as my guide there. Side question: I have doubts about how I wired the selector switch for speaker impedance. I can see a metal tab inside the switch, but I'm not entirely sure of which pole it's selecting. Can I test it with the ohm meter some way before I power it up?

[JMPGuitars]

So, done wiring everything. Quadruple checked. Next up is testing voltages etc. I have the builder's guide from Trinity and various videos as my guide there. Side question: I have doubts about how I wired the selector switch for speaker impedance. I can see a metal tab inside the switch, but I'm not entirely sure of which pole it's selecting. Can I test it with the ohm meter some way before I power it up?

You can try, but unpowered, the OT readings aren't always so obvious. I would check the colors. Make sure the 4ohm is in the middle, and then see which color is selected in each position. You can check continuity (obviously with the amp disconnected from AC) with each wire to the output jack to see which is selected in which position.

[DH166]

Cool. That makes sense. Next question: Since this build is solid-state rectified, how does that change the initial voltage testing? As I previously said, I'm using the builder's guide from Trinity (along with your impressively responsive and prompt assistance ), and below is from that guide.

Capture.JPG

Is that method just to account for the load the tube provides? Do I just go from one step to the next?

[JMPGuitars]

Leave the standby switch in the off position, then do your tests for that stage. Carefully.

Thanks,
Josh

[DH166]

Arrgh. I made it to step one. Amp plugged in, no tubes or speaker. Switched on power and immediate smoke. I took just a second to see vaguely where it was coming from, but I didn't want to leave it on obviously, so I didn't get a really close look before I switched it off. It came from near the 35v 2200uf cap and 180 ohm 5W resistor that go to the cathodes on the power tubes. What does this mean? Does this go back to the solid state rectifier? Should I have gone straight to testing voltages with the preamp tubes in?

Edit: I checked continuity in wires throughout the amp and found no shorts. I centered in on the area that smoked. Testing that 2200uf cap, my multimeter's capacitance reading only goes to 200u. So, I tested it on resistance and it doesn't go to infinity. On 20k ohms or lower, it settles at a number (.15 at 20k, .18 at 2k, 182.x at 200). Does that indicate a short? If so, did I just get a dud capacitor? Do I replace that cap and go again or did I do something wrong?

Further edit: Alright. Found this. I don't know how I missed it. I triple checked everything before testing, but there you go. A bend of resistor wire that got soldered to an adjoining turret. Is that enough to cause the smoke/possibly smoked cap?

IMG-0717.jpg

[Bieworm]

Looks like your PI circuit.. that would mean :

Or...your B+ is connected directly to ground at the turret where your 470k ground reference resistors should go to ground

Or...you didn't reference your ground reference resistors and connected them to the B+

Did you even ground the cathode resistor? You should run a ground wire from there to the star ground. The 470k ground ref resistors of the PI should be on that wire too

Question: why have you stuffed all that so tightly when you have lots of space left over on the turret board.

The soldering quality... you really need to study more about soldering techniques. Look for that in the signature links from Josh's posts.. I know you are a newb, and understand there's lots you still have to learn, so.. we'll support you on that.

[JMPGuitars]

Bieworm's first option is correct, your B+ is connected directly to ground. Cut that lead immediately, and also review the soldering technique thread and videos. There's a lot going on there.

You might want to correct your capacitors there, the foils should be pointing in the same direction. Either to the PI plates, or the least resistance to ground. In the schematic, they're pointed at the PI plates. But this isn't the most important thing in the world.

The resistance reading you were getting from your cathode capacitor is the cathode resistor in parallel with it.

Thanks,
Josh

[DH166]

Ok. Went back and cleaned up. Tested every connection on the turret board. Cleaned up solder joints. And... it works!!! It works really, really well! Probably in part due to my error in board layout that caused me to go back and use shielded wire for basically all of the hookups from the tube side of the board, the signal is super clean. You have to crank it way up to even hear a hum. It sounds really good. I also hand built the enclosure and speaker cab and I'm in the process of covering those in Tolex. When I finish that, I'll get a mic on it and post some sound. Thanks a million times to Josh for the continued free tech support. This was my first ever electronics build of any kind, and I couldn't have done it without your help.

[JMPGuitars]

Congrats!! Post some photos of the finished / updated build too. I'm sure people would love to see and hear it.

[DH166]

Here's a pic of the finished product. That's as close an angle as I'm giving, due to the seriously diy nature of the build . In addition to being my first amp build, it was my first cabinet or enclosure build, first upholstering in tolex, etc. You get the point. Let's just say I learned a lot of lessons for the next build. Anyhow, there she is. I built Josh's Tremolo TMB circuit, without the Paul Ruby mod (or any mods for that matter). I built a 2x12 cab to go with it that houses a G12M 25W and a G12H Anniversary 30W (essentially the Matchless mis-matched pair). I wasn't trying to build a Matchless cab. I just happened to find those two specific speakers on FB marketplace for $120 for the pair. Couldn't pass that up, as they were in great shape. I have a video, but I can't get it uploaded as an attachment due to file size. If you can tell me how to link that, I'll be glad to add it.

[JMPGuitars]

Nice job! For a first attempt, that's pretty awesome. For the front panel tolex that's coming up, the trick is to use spray glue on the tolex, and wrap it all the way around to the back of the wood panel. The front chassis panel will be pressed up against the tolex on the back of the wood panel.

Upload your video to youtube, and share the link here.

Thanks,
Josh

[DH166]

Alright. Here’s the link.

https://youtu.be/kzIo0SB2JPk