I love the 5e3. Just not mine! Please help.

[g1]

The mojotone schematic (http://music-electronics-forum.com/a...-schematic.pdf) shows an option for independant volumes, is it wired that way?
Otherwise compare yours to the one that works and see if there is a wiring difference at the input area.

[JohnRose81]

Oh btw, here's how it sounds.

[JohnRose81]

If I'm plugged into the bright channel, the bright volume works fine, if I'm plugged into the normal channel the normal channel volume works fine, and the tone pot works fine for the bright channel (on 5e3's the tone pot doesn't affect the normal channel). The only thing is that the volumes don't interact. So I don't see how it could be a failed pot. And no matter what channel I'm in, they don't interact.

[Chuck H]

Could be a failed pot from excess soldering and heat. If one pot is acting as a variable resistor that might explain it. What happens when you plug into the mic channel and adjust the normal channel?

[JohnRose81]

Hey all. 2 updates. Well 3. One is that I love you guys for helping me out. Secondly, my dad, unknowing to me, bought a 5e3 kit and brought it over and said build it. Knocked it out in 4 hours while he was at the mall and it worked perfectly as soon as I switched it on. Must say, it looks better inside than mine does. Bought new, stiffer wire and that really helped. Also bought really really skinny solder so it heats quicker and is easier to get into small spaces.

THIRDLY and lastly, my two volume knobs on my 5e3 aren't interacting. They both work perfectly if I'm plugged into their respective channels, but if I'm in the normal channel and turn it up to like 4 it's nice and warm and cleanish and then I try to crank up the bright channel volume to like 12, nothing happens just gets more hissy. If I don't turn up the bright channel, it's nice and no noise. So what's going on and why aren't the volumes interacting? I checked wiring and everything, nada wrong.

[Chuck H]

My point is that if he had built the amp that wire wouldn't have been missing because he would have know it had to be there for the circuit to work. When you're just copying you don't notice these things.

[JohnRose81]

Rote? What I really really need is to teach myself how to read these things.

http://www.recproaudio.com/diy_pro_a..._5e3_schem.gif

The amp tech looked at my amp and couldn't figure it out. Said it looked fine, touched up some solders, but it didn't work. So he read that schematic and found the problem in about 2 minutes, soldered on a wire and away I went. Made me a little upset that I didn't catch it. When I get home, I'm gonna make sure it was that wire.

[Chuck H]

It get's better as you start understanding the circuits more. You won't miss things like that as much because you'll no longer be building entirely rote.

[JohnRose81]

Okay, figured it out. I didn't have a wire on the back. Oddly enough, on both fiber boards that I built, I didn't have this wire. I can't believe I missed it twice. Sounds great. One thing is that when I crank it and hit the low E string, it sounds like the amp is going to blow up. HA! I'll deal with it. The amp totally sounds like Blue Jean Blues by ZZ Top.

[loudthud]

How would I measure from pin 9-4? Am I measuring AC or DC?

Set your meter to AC volts. Measure from pin 9 to pin 4 of the 12AX7. Make sure you are touching the probe to the socket pin, not the wire soldered to it.

Connect one probe to pin 9 and the other probe to pin 4. You can do this when the amp is in standby mode, it will be safer because the high voltage will be off. You still need to be careful, don't let the probes slip and short things out. Don't touch any part of the amp, hold the probes a safe distance from the tip. If you have any kind of clip that allows you to attach one of the probe wires to the circuit, use it as long as there is no possibility it will short to the chassis.

How would I measure the resistance across the speaker terminals?

The amp should be turned off for this test, or just about any time you are measuring ohms. Connecting voltage to the meter when it is set to measure ohms may damage the meter or give an inaccurate reading.

Set the meter to measure Ohms. If the meter has more than one range, use the lowest range, usually 2K. As a test, touch the probes together to verify you get a low reading below 1 ohm. The way your meter works, the resistance of the probes and interconnecting wires are added to any reading you take. The speaker has two terminals. Touch one probe to one of the terminals and the other probe to the other terminal.

[g1]

Try it. Meter set to ohms, one probe at each end of the cap. (the cap that goes to pin3 of the 12AX7)

Put the speaker in. Now it reads 155.

So you got a reading of 155 ohms across the cap? It should be 1500 or 1.5K ohms. Recheck it and recheck ohms from 12AX7 pin 3 to chassis ground.

[JohnRose81]

How would I measure from pin 9-4? Am I measuring AC or DC? How would I measure the resistance across the speaker terminals?

I will do this as soon as I get home.

[loudthud]

Go over the voltages one more time. If pin 1 of the 12AX7 is higher than F3, that means current is flowing the wrong way (or there is a measurement or wiring error). Set your meter to AC volts. Measure from pin 9 to pin 4 of the 12AX7. Make sure you are touching the probe to the socket pin, not the wire soldered to it. Remove the tube from the socket and inspect the socket. Do the contacts look bent or discolored?

You should be able to see two glowing filaments inside the 12AX7. Do they look equal in brightness?

The voltages on both power tubes should be the same. Check again, no typos.

Unplug the speaker. Measure the resistance across the speaker terminals. It should be about 6 ohms. Now plug the speaker in. The resistance across the speaker should now measure very low, one ohm or so depending on you meter. Now unsolder one of the wires from the speaker jack that go to the output transformer. The resistance measured across the terminals of the speaker should go back up to 6 ohms. Now measure the resistance from the unsoldered output transformer wire to the terminal where you undoldered the wire, it should be 6 ohms. This checks that there is no short at the speaker jacks.

[Chuck H]

You can still learn if you take it to a tech. They will usually talk shop with you about what happened and what they fixed. I sure would. Especially with an enthusiastic builder. You're bound to learn. This sort of thing can be very hard to troubleshoot as a novice, or in our case from a remote perspective, but a tech with the amp on a bench should be able to do it pretty easily. It'll cost a little but the learning experience will be invaluable. It's not at all uncommon for a novice to build an amp and then require a tech to troubleshoot it. It happens all the time. It does suck out a little of the savings, but that's not the point. The overall experience will get you closer to being able to build, tweak and maintain/repair your own amps. PERSONAL CONTROL OVER YOUR TONE!!! Nothing like it. If you're actually interested in becoming THAT guy it won't seem like wasted money. More like a first person lesson. I did it with Dan Torres when he was still working out of his home!!! He gets a little rough press here and there but he was one of the first players in the game and VERY enthusiastic. Combined with his experience that counts for a lot. It was a good place to start. I hope you can find a tech that actually knows vintage guitar amp circuits and wants to share. It'll be great.

[JohnRose81]

Well that's it for me. I'm freakin stumped. Clean build. Good solders. Can't find anything wrong visually. Still pretty much no volume and it's slightly distorted. Checked grounding points. They're good. Speaker maybe? It should be good. Tested it and know what the positive and negative leads are on it. So it's hooked up right. Jack inputs look good for the speaker also. Guitar inputs and pots are nice. All wires are to their correct post. All caps are correct. All pos and neg sides of caps in the right direction. Back of board is wired right. Fuse wires seem right. Same for on/off and light. Tubes light up. All voltage readings are ok except pin 3 on the 12ax7 or whatever was on the readings.

About to take this to a tech but damn! That will piss me off. I wanted to build this and really learn.