Epi Valve Jr Rebuild Help

[SeattleGreenhorn]

Hi guys. I recently finished a complete gut and rebuild of my version 3 valve jr using the Watts Tube Audio Voxy kit and a Watts Heyboer OT upgrade. Well, I fired her up and things didn't go like I hoped. I'm hearing a louder-than-normal buzzing sound coming from what I think is the PT and I'm smelling some burning plastic. (don't worry, I shut her down after it started smelling funny.)

This is my first build and obviously I screwed something up pretty bad. Maybe I shoulda listened when they told me not to try something like this with no experience.

Anyways, I'd like to try and salvage this thing, can anyone offer any ideas as to what's going on?

[galtjunk]

Re check everything twice.


If you don't try to do it, how will you ever gain experience?


Good luck.

[martin manning]

Yours should look just like this one (from http://acapella.harmony-central.com/sho ... -Audio-Kit ). Overheating of components and the odor that comes with it is probably the result of a wiring error or short somewhere.

[Jack Hester]

I'm hearing a louder-than-normal buzzing sound coming from what I think is the PT and I'm smelling some burning plastic. (don't worry, I shut her down after it started smelling funny.)

I put couple of his EVJr retrofits together, to see how good they were. The 'Fenderish' model was quiet (no hum) and sounded great. The 'Marshallish' model hummed badly and did not work. I went back over his layout, several times, and still couldn't figure what I did wrong. So, I contacted him. No reply. Sent several emails. No reply.

So, I reverse engineered it and made my own schematic. That's when I found a missing signal ground on the pre-amp end. The schematic made it very obvious. And, it became very obvious on his layout that it was needed. I added the ground, and the amp got real quiet and sounded just as good as the other one.

Also, because I fairly sure this won't be your last build. It's addictive. Take the time to fab up a lamp limiter. Prevents the smelly parts, and lets you troubleshoot at a reduced voltage/current.

Anyway, look for the not-so-obvious.

Jack

[martin manning]

...I reverse engineered it and made my own schematic. That's when I found a missing signal ground on the pre-amp end. The schematic made it very obvious. And, it became very obvious on his layout that it was needed. I added the ground, and the amp got real quiet and sounded just as good as the other one.

this is great, Jack! Can you post the schematic or at least the part with the missing ground?

[Zero4]

Also, because I fairly sure this won't be your last build. It's addictive.

I'll say!

[SeattleGreenhorn]

Okay, so I need to be looking for a bum ground then? That helps narrow it down, thanks!

No kidding about this being addictive. This basically turned into my second job.

I'm not an expert in electronics in any sense, I'm a musician that wants to be able to build my own tone out of what I have for not so much money. I'm sure I made some pretty silly mistakes this time around so here are a couple more question that might sound pretty stupid to some of you :

1.) The twin red and orange wires that come from the power transformer that go to the rectifier and the 4 & 5 pins of the power tube; does it matter which wire gets hooked up to which pin? In my mind, logically, if it mattered they wouldn't have made them the same color. But that's just me...

2.) I used shielded 20 gauge stranded wire to connect a couple spots where the guy that successfully built the same kit as mine a couple posts above used unshielded buss wire (I think, maybe it's just the leftover bits of a lead from a cap or resistor?). Would that cause problems?

Again, thanks a ton guys, I really appreciate the input!!!!

[Tubetronix]

On 1) no,it doesn't matter they are carrying AC. No problem on 2) either.

[Jack Hester]

Can you post the schematic or at least the part with the missing ground?

When I get home this evening, I'll find them and print to a pdf file. Not fancy schematics, but they help with troubleshooting.

As to the missing ground, I did not mark up the schematic to reflect which one it was. I just drew both of them from the layout drawings that he provided. Then, looked through the whole of each, and there it was. So, I added it to the affected drawing. Been too long for me to remember where 'there it was' is located. But, the schematics themselves may help in future troubleshooting. If he has schematics, he's not providing them. Just layouts as a download from his site.

Jack

[Jack Hester]

Okay, so I need to be looking for a bum ground then?

Not necessarily. Just one thing to look for. Mine happened to be a missing one. I put mine aside for several months, and worked on other projects. When I came back to it, and traced it again, from the layout, I knew that I had it built like the drawing. The schematic made it clear for me to see the loss in signal path. I've come to depend on schematics heavily for troubleshooting.

A year or so ago, I had an '54 GA-40 with issues. The schematic for that one is so poor, I CAD'ed my own, then had many other people to help me proof read it. When I had it correct, fixing the amp was a breeze. It had been miswired sometime in it's past. Did a cap job and corrected the wiring from the drawing, and it has been a fine player ever since.

Same with an Ampeg B-12-XY that I'm down to troubleshooting the Vibrato. The drawing on that one is poor, at best, though not as bad as the Gibson drawing that I started from. But, I'm CAD'ing that one right now. My amp does not match the factory drawing, for the two 6D10 tube assignments. I've marked up the factory drawing with the corrections and the component value differences. I'll relect those on my CAD schematic. I'm making a revision A to show the factory drawing. And a revision B to show my circuit.

Jack

[martin manning]

Here's the "Voxy" version... low-tech hand-drawn, cell phone pic. This set of Valve Jr. layouts on Watts' site is a good way to see one man's version of what makes Fender vs. Marshall vs. Vox tones in a simple circuit. There's a Supro version there too.

[SeattleGreenhorn]

Well, guys, I think I got to the bottom of it. It was pretty simple afterall. It turns out, apparently because I'm new at this, that I burned out most of the components getting them all soldered up. ...Oops.

So, for my next time through I plan to do some things a little differently. My first run through I stuffed the board and then connected all the wires I needed to connect. This time I think I'll do it the other way around so that the least amount of heat possible is being applied to the caps and resistors. Sound like a solid plan?

[ampgeek]

Just out of curiosity, what led you to that conclusion? I didn't catch any pictures of your work and I am interested in this topic.

I have built/worked on many dozens of amps and have never thought that I burned out a component. Well...except when I accidently contact a nearby item with the barrel of the iron.

I have re-soldered an individual item at least 10 times during the course of tweaking/testing/rebuilding on numerous occasions.

I use a heat sink on diodes and polystyrene caps only when I happen to think about it.

Sure...you want to avoid heating an item any more than you have to. But...the difference between once or twice creating an issue is hard for me to imagine. Even for a Greenhorn!!

I guess what I am saying is that you may not need to scrap it and start over.

Cheers,
Dave O.

[shoggoth]

Are you using a pencil soldering iron for electronics, or a big gun made for soldering pipes?

[SeattleGreenhorn]

Well, I used a multimeter to check continuity and, with the exception of the connecting wires, a couple resistors, and the rectifier, most everything was coming up dead. I was using one of those nice Fluke MMs too (I borrowed it from an electrician buddy at work) so I doubt that the MM was giving me bum readings.