Just unboxed my Mojotone 5e3 kit. Advice for a first time kit assembler?

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102
Does lead free vs leaded solder make a difference? I’m about to start assembly today and was wondering if I should wait to solder until I get some old school lead core solder.
 

MasterEvan07

Where's that buzzing coming from...?
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Does lead free vs leaded solder make a difference? I’m about to start assembly today and was wondering if I should wait to solder until I get some old school lead core solder.
Only if you’re trying to be RoHS compliant. Non-leaded solder is more difficult to work with and doesn’t bond as readily. My Kester 63/37 rosin flux core is da bomb.
 

Barnzy

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All I’ve heard and read is that lead solder is easier to work with. I like success and that is what I am already used to so I won’t even bother to try lead free personally. But I don’t actually know for sure.

I just ended up deciding to buy a lifetime supply of Kester 60/40 knowing that I never want to deal with lead-free in case we don’t get along.
 

Barnzy

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I actually think this is the stuff I bought. One spool will probably do every guitar, amp and pedal I do with plenty left over.
 

profro

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67
Good luck and enjoy your build. I also did a Mojotone 5e3 and I absolutely loved the process and its an amazing amp. I will add this:

  1. They sound best turned up. You cannot get that sound at quiet levels.
  2. They sound amazing quiet too. Its almost 3D.
  3. They come with a padded input (lo or 2) and I would venture to say your guitar has a volume knob. Use them.
If you must get that cranked Tweed sound, but the Deluxe is too loud, I would suggest a Champ. Yes it can be loud too, but more often than not, I play my Champ. It will give up the Tweed goods at a lower volume. Yeah, its not a Deluxe but its in the same flavor.
 
Messages
102
So I’ve been slowly putting the components together and I am almost finished. I discovered a mistake though. I mistakenly soldered a 100ohm resistor instead of a 100k on the board. I removed the wrongly installed resistor from the board but it was destroyed in the process.

My question here is, can I replace the destroyed 100ohm with a random “100r” resistor that I bought in a large lot of resistors?
 

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jthomas666

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970
Yes... as long as it has the same (or greater)wattage specification. For example, don't replace a half-watt with a quarter watt. Note that some resistors will be quieter in the circuit than others. Carbon comp resistors can produce hiss.
 
Messages
102
Yes... as long as it has the same (or greater)wattage specification. For example, don't replace a half-watt with a quarter watt. Note that some resistors will be quieter in the circuit than others. Carbon comp resistors can produce hiss.
Thank you for that response. Forgive my ignorance but ohms are different that wattage, yes? If so am I able to determine wattage with my multimeter? I was able to verify that the two different resistors I have had similar ohms with the meter, but how would one determine the half watt vs quarter watt capabilities?
 

chromo

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Some things that haven't been mentioned that I think are important:

1) Learn how to safely discharge the filter capacitors. At some point you will need to troubleshoot, set or change the power tube bias, or otherwise stick your fingers into that amp. Make sure you know how to do it without taking hundreds of volts.

2) This was kind of mentioned, but make sure you have and follow a good start-up procedure. A light bulb limiter (google it) is probably the best and safest way, but you can do without so long as you're methodical and smart about it.

3) Get a physical copy of the layout and/or schematic and use a highlighter to "check off" components as they go into the amp. If you work this way you'll never get confused about what you've done and what is left to do, which is shockingly easy to do when building an amp. Take the pressure off and be methodical. Measuring every component before you put it (recommended by earlier poster) in so there are no surprises is part of this.

3) in particular speaks to the golden rule of amp building: do it right the first time, because the best approach to troubleshooting is not having to troubleshoot at all.



Does lead free vs leaded solder make a difference? I’m about to start assembly today and was wondering if I should wait to solder until I get some old school lead core solder.

Use leaded unless you can't because of regulations. It's much easier to work with. Lower melting point makes a big difference.

Good luck with your build!
 

mAx___

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1,005
My two cents. When soldering two or more components to the same turret/eyelet, make sure that you got good solid contact in all of them as sometimes things could look like they're soldered in place but they're not.
 

jthomas666

Member
Messages
970
Thank you for that response. Forgive my ignorance but ohms are different that wattage, yes? If so am I able to determine wattage with my multimeter? I was able to verify that the two different resistors I have had similar ohms with the meter, but how would one determine the half watt vs quarter watt capabilities?
Ohms are different from watts.

Ohms = the resistance provided by the resistor (attenuation)
Watts = the power handling capacity of the resistor

Ohms is measured by your multimeter.

The wattage that is needed for that resistor in that position should be provided by the company assembling the amp kit (probably 1/2 watt). Check the parts list or BOM.

The wattage of the resistors that you have should be provided by whoever sold the resistors to you. You might look over the packaging or at your email inbox if you bought them online. Generally, bigger resistors are used when a higher wattage resistor is needed. I sometimes have difficulty discriminating 1/4 watt and 1/2 watt resistors by eye alone as some 1/2 watt resistors are relatively smaller these days.
 

galibier_un

Silver Supporting Member
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2,390
Just be very careful when you power up the amp. You can handle the parts while building the amp but once it's powered up, there are lethal voltages that you won't encounter when tinkering with a powered up 9v pedal.

Also, in electronics school, they taught us to wrap & crimp a wire or component when connecting it to a terminal. Solder should be used to stabilize a connection and not actually make the connection. So many times I see people shove a wire in a terminal's hole, solder the connection, and have intermittent troubles down the road with heat/cool cycles.

Hope it works first time but learning how to safely resolve any issues is another skill set.
I want to put a fine point on @VaughnC's advice, in light of the OP not knowing the difference between ohms and watts ...

Please take some time out and learn some basic electronics - ohms law and such - BEFORE you power up for the first time.

This, to keep from frying parts, and in addition to not shocking yourself or worse.

You'll want to verify things like power dissipation and such.

One of many good places to start is Rob Robinette's site.

... Thom
 
Messages
102
So I’ve gotten everything all wired up, soldered in, the mistake I found has been remedied…
I built a light bulb limiter based on the Rob rob website. I tested the light bulb limiter with my Marshall dsl last night and it functions correctly.

So I plug in the 5e3 and the pilot light on the chassis lights up, but the limiter does not. No smoke, no burning smell, no noise, no arcing… what do you make of this? I assume something isn’t right.
 

Ampegged

Silver Supporting Member
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1,628
So I’ve gotten everything all wired up, soldered in, the mistake I found has been remedied…
I built a light bulb limiter based on the Rob rob website. I tested the light bulb limiter with my Marshall dsl last night and it functions correctly.

So I plug in the 5e3 and the pilot light on the chassis lights up, but the limiter does not. No smoke, no burning smell, no noise, no arcing… what do you make of this? I assume something isn’t right.
Sounds like all is well if the limiter is not lighting up...if it does light up (bright), that means you have something wrong in the amp.
 

galibier_un

Silver Supporting Member
Messages
2,390
So I’ve gotten everything all wired up, soldered in, the mistake I found has been remedied…
I built a light bulb limiter based on the Rob rob website. I tested the light bulb limiter with my Marshall dsl last night and it functions correctly.

So I plug in the 5e3 and the pilot light on the chassis lights up, but the limiter does not. No smoke, no burning smell, no noise, no arcing… what do you make of this? I assume something isn’t right.
So, the limiter functioning correctly on your Marshall means the bulb is moderately bright for a second or three, and then it dims.

If it's not lighting up at all on your new build, the first thing I'd check is the filament voltages. We know your PT is feeding the lamp, so if you've wired the filaments correctly, you should be drawing enough current to light the limiter's bulb. Plug in the preamp tubes first.

I'd then plug in the rectifier and take readings on it, as well as taking voltage readings on the preamp tubes.

...Thom
 
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Messages
102
So I’ve tried a few things and was hoping to get a little more input from you guys.

With the tubes in, my light bulb limiter glows bright, dims for a second or two then gets a little brighter again. It isn’t glowing very brightly like I’ve seen in YouTube videos with a bulb that gets very bright.

My continuity check from the inputs to the outputs seem to be ok.

My filament voltages seem to be half of what they should be.

I’m getting not much DC readings from my board.

The rectifier tube in v5 gets pretty hot, pretty quickly. I haven’t noticed that it glows. The rest of the tubes do not heat up at all.

There is no sound when I plug a cable to any of the inputs. Yes I have the speaker plugged in.
 

pdf64

Member
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8,929
The wattage of the bulb used, and how that balances with the load that the amp presents to it, plays a big part in all this.
 

galibier_un

Silver Supporting Member
Messages
2,390
My continuity check from the inputs to the outputs seem to be ok.

My filament voltages seem to be half of what they should be.

I’m getting not much DC readings from my board.
You need to be more precise with your language, with actual voltage readings - AC filament, DC for everything else.

I'd expect RobRob to have a basic troubleshooting writeup. Look there for more details and report back with numbers instead of qualitative words like "not much".

[edit]I suspect you've been on this page: https://robrobinette.com/Tube_Guitar_Amp_Troubleshooting.htm

... Thom
 
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