Wiring Question (Answered)

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Wiring Question (Answered)

Post by DH166 »

So, I PM'd this one to JMP, who suggested such questions would benefit other newbie builders if it was public. So, here's my original question about heater wiring, with answer. Also, submitted for any helpful suggestions or general mockery, is a pic of what I've got done so far. I realized after I got my parts in from amplified parts that I'd gotten the wrong gauge wire for the heaters and the only solid core 20 ga I had was cloth push-wire. So, that's what I went with.
DH166 wrote: ↑Sun 08/22/21 2:09 pm
I'm building your Modern Classic and I'm starting to do the heater wiring. Note that this is my first scratch build. I'm good through the EL84's, as that's pretty straightforward. For the preamp tubes, however, I'm confused about the wire (light green in your layout diagram) that goes just to pin 4 in the power tubes and then goes to pins 4 and 5 in the preamps. What's the order there? Do I go into 5, then to 4, then to 5 on the next socket? Also, it looks like the two pins' connections touch, but I'm not sure. Do I strip enough wire to feed it through 5 and then bend it back around through 4? Thanks for your help

John
Hi, you're talking about the heater wiring. You'll notice that preamp tubes and power amp tubes are not wired the same, and their heater arrangements are different. I suggest looking at the datasheets. Google "12ax7 datasheet" and "el84 datasheet." Take a look at the labels for the pins- note the heaters, cathodes, grids, and anodes. The power tubes (pentodes) also have "screens" which are noted as grid 2 (or g2). The preamp tubes are dual triodes, meaning 2 triodes in 1 tube.

Pins 4 and 5 on the power tubes are two separate heater connections. On the preamp tubes, pins 4and 5 are ONE wire connection, the other connection being pin 9. Be consistent in your wiring, and note that the two color green wires in the heater wiring always go to the same pin numbers.

Like you said above, I strip enough wire for one wire to go through both pins 4 and 5 on the 12AX7 tubes.
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Re: Wiring Question (Answered)

Post by JMPGuitars »

Hi again,

I highly recommend you read the threads and watch the videos linked in my signature. There's a few issues that stand out already, but most important are the solder technique, and the spots where the cloth was burnt. It's okay to use the cloth wire, but you need to take extra care not to rip or burn sections of it. 22AWG is also fine for the 18W heater wiring.

Thanks,
Josh
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Re: Wiring Question (Answered)

Post by DH166 »

Thanks for the feedback. I'll take a look. Just fyi, the cloth isn't burnt. I tried twisting it with a low-speed drill, and that clearly works better with pvc than cloth. I did inspect it, and none of the rubs are through the second layer of cloth. So, no exposed wire. Also, I checked my work with the multimeter, and I have continuity through all connections so far. That said, I'm always willing to learn. I'll check out the links.

That said, you said other things stood out. What are they?
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Re: Wiring Question (Answered)

Post by JMPGuitars »

DH166 wrote:
Sun 08/22/21 5:04 pm
Thanks for the feedback. I'll take a look. Just fyi, the cloth isn't burnt. I tried twisting it with a low-speed drill, and that clearly works better with pvc than cloth. I did inspect it, and none of the rubs are through the second layer of cloth. So, no exposed wire. Also, I checked my work with the multimeter, and I have continuity through all connections so far. That said, I'm always willing to learn. I'll check out the links.

That said, you said other things stood out. What are they?
Sure, I could see how that would happen. But damage is damage, and you don't want the wire insulation damaged. When it gets that way, you should at least use heat shrink tubing to protect the wire.

So lead dress is everything, especially with the heaters. That means it should look perty. Nice even tight wraps, good symmetry, no gaps, etc...

Here's an example of an amp I recently completed (obviously just the heater wiring here):
jmpguitars-heater-wiring.png

Look closely and you'll see the important details. Clean mechanical and solder connections. Tight even wraps, no gaps, etc... That's 20AWG PTFE coated wire...and heat shrink, because I loooove heat shrink. ;)

Thanks,
Josh
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Re: Wiring Question (Answered)

Post by DH166 »

Hmm. That does look pretty darn good. I don't think I can get that thick cloth wire twisted that neatly. As much as I'd rather get kicked in the nuts by a dwarf than redo that tedious job, I just might have to. I have yards and yards of 22 AWG solid core. Is 22 thick enough? Alternatively, I can find 20 AWG stranded at all the major sites. Which would be better?
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Re: Wiring Question (Answered)

Post by JMPGuitars »

DH166 wrote:
Sun 08/22/21 7:19 pm
Hmm. That does look pretty darn good. I don't think I can get that thick cloth wire twisted that neatly. As much as I'd rather get kicked in the nuts by a dwarf than redo that tedious job, I just might have to. I have yards and yards of 22 AWG solid core. Is 22 thick enough? Alternatively, I can find 20 AWG stranded at all the major sites. Which would be better?
Some people like solid core, I prefer stranded. 22AWG or 20AWG are both good for the heaters (usually anyway, but you need to check the specs on the wire). Marshall uses 22AWG for heater wiring.

If you get new wire, get either high heat PVC or PTFE.

It may be a tedious job, but it's a job that practice makes perfect, and you'll thank yourself later when you look at the improved amp...and then thank yourself again when you play it.

Thanks,
Josh
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Re: Wiring Question (Answered)

Post by DH166 »

Alright. Redid the wiring. Better?
98E1351E-53B0-41CD-B02E-B4ED3CBBCDE3.jpeg
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Re: Wiring Question (Answered)

Post by JMPGuitars »

DH166 wrote:
Sat 08/28/21 5:50 pm
Alright. Redid the wiring. Better?
Much better! ...couple things tho. ;)

Be careful not to over tighten the wires. They're probably, fine, but you don't want to break the wire or the insulation.

Why is there electrical tape there? Did something get burnt?

I also would suggest adding more insulation to where you spliced the new wires to the green wires. That spot scares me a little. For future reference, normal practice is to run the green wires to the first power tube, then place new wires after that point. If splicing high current wires, I might double the heat shrink tubing covering the connection, and go a minimum of half an inch past the connection on each end.

Side note: this is why I like the GDS/Heyboer or Mercury Magnetics power transformers that use solder lugs instead of wire leads. Much easier to redo something if needed.

Thanks,
Josh
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Re: Wiring Question (Answered)

Post by Doxie man »

DH166 wrote:
Sat 08/28/21 5:50 pm
Alright. Redid the wiring. Better?98E1351E-53B0-41CD-B02E-B4ED3CBBCDE3.jpeg
You could have just used a stand-off/terminal strip where you made the wire splice and then you’d also have an ideal location to build an artificial filament CT using (2) 100R resistors and reference your filament ground (through those resistors) to the power tube’s cathode. It’s much better than using the PT’s CT. 👍
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Re: Wiring Question (Answered)

Post by DH166 »

JMPGuitars wrote:
Sat 08/28/21 6:09 pm
DH166 wrote:
Sat 08/28/21 5:50 pm
Alright. Redid the wiring. Better?
Much better! ...couple things tho. ;)

Be careful not to over tighten the wires. They're probably, fine, but you don't want to break the wire or the insulation.

Why is there electrical tape there? Did something get burnt?

I also would suggest adding more insulation to where you spliced the new wires to the green wires. That spot scares me a little. For future reference, normal practice is to run the green wires to the first power tube, then place new wires after that point. If splicing high current wires, I might double the heat shrink tubing covering the connection, and go a minimum of half an inch past the connection on each end.

Side note: this is why I like the GDS/Heyboer or Mercury Magnetics power transformers that use solder lugs instead of wire leads. Much easier to redo something if needed.

Thanks,
Josh
Thanks for the feedback. I see what you mean about the transformer. I bought from Classic Tone and that's what I got. The splice was to allow for right angles. The existing green wires from the PT weren't long enough to make a right angle where they came out and also where they turned toward the 1st EL84. So, I spliced it. Next two questions (which are probably painfully obvious to the non-newb), view the picture below. In reading about wiring the power switch, I've read that you should read 0 ohms in the 'on' position. I get 0 ohms when the switch is down, in its current orientation. Is there a way to switch that, or do I have to physically turn the switch over and just deal with the lugs being less accessible? Also, is there a difference between the lugs on the power switch? If so, how do I know which one is which, and which goes to the IEC and which goes to the PT? Finally, on the lamp, one lug is labeled '+' and the other is unmarked. Does the positive wire up to the 6.3V lug on the PT and the other to the 0?

Thanks
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Re: Wiring Question (Answered)

Post by JMPGuitars »

DH166 wrote:
Sun 08/29/21 11:16 am
Thanks for the feedback. I see what you mean about the transformer. I bought from Classic Tone and that's what I got. The splice was to allow for right angles. The existing green wires from the PT weren't long enough to make a right angle where they came out and also where they turned toward the 1st EL84. So, I spliced it. Next two questions (which are probably painfully obvious to the non-newb), view the picture below. In reading about wiring the power switch, I've read that you should read 0 ohms in the 'on' position. I get 0 ohms when the switch is down, in its current orientation. Is there a way to switch that, or do I have to physically turn the switch over and just deal with the lugs being less accessible? Also, is there a difference between the lugs on the power switch? If so, how do I know which one is which, and which goes to the IEC and which goes to the PT? Finally, on the lamp, one lug is labeled '+' and the other is unmarked. Does the positive wire up to the 6.3V lug on the PT and the other to the 0?

Thanks
IMG-0069.jpg

As Doxie mentioned above, a small terminal strip would be a good idea in place of the splices. Then the wires aren't just floating, and you don't have to worry about insulation issues at that point. Though I don't know why he would suggest not using the PT CT. Adding the resistors he mentioned is forming an artificial CT (Center Tap) and I have no idea why you would want an artificial CT when a real one exists. Stick with the PT's CT.

That switch is a SPST (Single Pole / Single Throw). It makes no difference which side is wired to what. What I typically do is wire the switch first, then mount it. The direction of the toggle depends (usually) on if there's writing on your faceplate determining which way is up. You will get 0 ohms / continuity when the switch is on. There's no changing that. You should get no reading, or very high impedance, and no continuity when the switch is off.

For the pilot lamp, yes, the + goes to the voltage source. However, you should double check that you're using the correct voltage lamp prior to wiring it. Could be a 6V or 120V or 220V etc...

Thanks,
Josh
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Re: Wiring Question (Answered)

Post by DH166 »

Thanks. So here's the PT wired to the lamp, power switch, and IEC, as well as the OT wired to the selector. Looking at pics of people's builds, it didn't seem that lead dress was as important on these (I'm guessing because they don't carry signal to/through the gain stages?). So far, I've tested everything for continuity across any of my connections. I don't know how to do that for the leads coming directly from the transformers though, since they aren't yet under power. I could prick through the jacket of the wire upstream of the solder and then wrap it back up with tape, I guess, but I really don't want to risk breaking the wire. How do I test those connections?
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Re: Wiring Question (Answered)

Post by JMPGuitars »

DH166 wrote:
Sun 08/29/21 2:31 pm
Thanks. So here's the PT wired to the lamp, power switch, and IEC, as well as the OT wired to the selector. Looking at pics of people's builds, it didn't seem that lead dress was as important on these (I'm guessing because they don't carry signal to/through the gain stages?). So far, I've tested everything for continuity across any of my connections. I don't know how to do that for the leads coming directly from the transformers though, since they aren't yet under power. I could prick through the jacket of the wire upstream of the solder and then wrap it back up with tape, I guess, but I really don't want to risk breaking the wire. How do I test those connections?
You need to twist all those wires. ;)

Those are all AC signal, and you want them twisted nicely, similar to the heater wiring. As it is now, you're likely to have a lot of transformer hum and other noise issues.

You don't need to test your PT connections, especially not for continuity. Never test continuity like that on a live amp either, test resistance. The way you test your PT connections is to VERY CAREFULLY test your voltages when you get to that stage.

One question: You said you're building the "Modern Classic" - are you building that with a solid state rectifier, or tube rectifier?
If you're using a tube rectifier, then you need to take that rectifier wiring you connected to the pilot lamp, and connect it to the tube rectifier instead. IF the rectifier heater wiring is sufficient to supply both the lamp and the rectifier heater current load, then you can use another small terminal strip to wire both pieces from that connection. If it's not sufficient for both, you would actually need to connect the pilot lamp to the other heaters...and still want to convert that to a terminal strip.
If you're using a solid state rectifier, then carry on. ;)

Terminal strip:
terminal strip.jpg
Obviously be careful not to connect anything to the ground lug in the middle if it doesn't belong there.

Thanks,
Josh
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Re: Wiring Question (Answered)

Post by JMPGuitars »

Here's that same amp I showed the heater wiring above, but complete:
_JMP1936.jpg

Lead dress and soldering technique are basically the most important parts of any build. Take your time and enjoy the process.

Thanks,
Josh
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Re: Wiring Question (Answered)

Post by DH166 »

For the love of Pete, you're startin' to wear me out! :x Alright, I'll go back over it. And I'm using a solid state rectifier. I'm going off your schematic and the layout dated 10/2020. I misinterpreted that layout, which shows those wires stranded separately (I guess for clarity of color distinction). So my plight now is that all those wires are trimmed for length. I can de-solder and start over, but I'll have to splice to make them long enough. So is it sufficient to splice, solder, and tape those wires, or do I need to install three more terminal strips?

Pardon my obvious frustration. I am genuinely grateful for the help and the prompt replies.

Hopefully, at least, some other first time builder will stumble across this and benefit from my errors. Sheesh.
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Re: Wiring Question (Answered)

Post by JMPGuitars »

DH166 wrote:
Sun 08/29/21 4:57 pm
For the love of Pete, you're startin' to wear me out! :x Alright, I'll go back over it. And I'm using a solid state rectifier. I'm going off your schematic and the layout dated 10/2020. I misinterpreted that layout, which shows those wires stranded separately (I guess for clarity of color distinction). So my plight now is that all those wires are trimmed for length. I can de-solder and start over, but I'll have to splice to make them long enough. So is it sufficient to splice, solder, and tape those wires, or do I need to install three more terminal strips?

Pardon my obvious frustration. I am genuinely grateful for the help and the prompt replies.

Hopefully, at least, some other first time builder will stumble across this and benefit from my errors. Sheesh.
No worries, you're not the first person frustrated by some of this stuff. We've all been there at some point!

Whether or not you use a terminal strip, or splice wires is up to you. If you do splice them, do a really good job. Make sure there's extra insulation, and maybe double the heat shrink if you can.

There's also lots of options for terminal strips. For example:
6-lug-terminal.jpg

The best bet is to plan ahead, ask questions in advance, and then move forward. There's lots of galleries here (under Gallery and Archive on the left navigation menu) with tons of build photos to give you ideas.

If I knew how to neatly twist wires in Visio, I would, but I never bothered to learn. Sorry. ;) ;)

I think the easiest way to answer the question of "should I redo this part?" is to think if you saw the photos of the amp built that way, would you buy it? That's not to sway you in one direction or the other, only to consider the quality of the work done once the choice is made.

BTW- lots of other users on here could show you the progress they made from their 1st to 3rd or later builds. Experience makes a world of difference, as does feedback on here.

Thanks,
Josh
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Re: Wiring Question (Answered)

Post by DH166 »

Josh,

Alright. Re-did wiring from the PT to mains and switches and from the OT to selector, twisting and adding right angles. As a side note, since with your build I have the layout and schematic but not a manual, I have been using the Trinity 18W builders manual as a rough guide for the order in which to build (wince. competitor. I know). Of course, at each step, I'm making sure that everything I'm doing (to the best of my knowledge) correspond to the components, values, etc inside my actual chassis. Which leads to my next question. This design uses a solid state rectifier. The manual I'm using (again, just referencing for build step order. I know, components and values vary), indicates testing the power supply at this stage of the build by measuring voltages across the iec terminals, the terminals on the switch, the socket of the rectifier (which socket I obviously don't have), and the sockets of the power tubes. So, couple questions:
1. Do you agree that testing these voltages is the correct step for this point? (again, VERY carefully. I know. Lethal voltages)
2. How do you measure the voltages on the solid state rectifier? Since the two sets of diodes run parallel into the 100ohm resistor, and each row has its own lead from one of the 290V taps on the PT, do you measure each separately upstream of the resistor? Do you measure after the resistor?

Thanks as always
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Re: Wiring Question (Answered)

Post by Bieworm »

You can perfectly follow the Trinity guide. Stephen knows his stuff very well!
I also test the power supply when wired. Don't forget to add the DC from the rectifier to the filter cap.. or you can not test the B+. Be aware these are "unloaded" voltages, thus higher than the eventually wired up amp.
The rectifier measuring points are the 2 HV AC wires going in and the B+ at the
conjunction of the outcoming DC voltage.
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Re: Wiring Question (Answered)

Post by JMPGuitars »

What Bieworm said. And it's all good, we like Trinity around here. They're certainly one of the better sources/resources out there.

Thanks,
Josh
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Re: Wiring Question (Answered)

Post by geoff 1965 »

I agree,that Trinity build guide is very thorough,also you get great feedback from them if you ask about any of their amps.
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