Tweedle Dee Build

[Ledzepp007]

Decided to build a 5E3, but figured I might as well have at a dumble versiion of the circuit.

I also happened to have a ClassicTone PT (18016) that I have had for a really long time (been through two moves) that should provide the proper voltages. I started adding the hardware to the chassis today and notice that one of the bolts on the PT had been bent (probably from moving). I attempted to bend it straight, but in doing so stripped the bolt. I was able to get the nut off the bolt and knock the bolt out with a hammer. Then, due to my OCD, I knocked the rest of the bolts out and replaced them with some 6-32 x3/4" bolts that I had in the toolbox and mounted it to the chassis with #8 keps nuts.

As I was cleaning up, I pulled up the info sheet for the transformer off of the ClassicTone website which, to my dismay says explicitly to not remove their bolt or nuts and to mount to the chassis with their nuts on the exterior of the chassis and keps nuts on the interior.

Did I screw up the transformer? Why would they want you to mount it that way?

[sluckey]

I knocked the rest of the bolts out and replaced them with some 6-32 x3/4" bolts that I had in the toolbox and mounted it to the chassis with #8 keps nuts.

I'm surprised that 3/4" long bolts were long enough. I'm really suprised that you put #8 nuts on #6 bolts.   

to my dismay says explicitly to not remove their bolt or nuts and to mount to the chassis with their nuts on the exterior of the chassis and keps nuts on the interior.

That's how I mount all transformers of that style.

[Ledzepp007]

Sorry, was really tired and typing on my phone. 8-32 x3" bolts.

Do you think it will be okay if I just put some 8 nuts in place of the original nuts and mount as suggested? Is there anything special about the bolts that the manufacturer uses?
 

[sluckey]

I knew there was a logical explanation. 

You'll be fine replacing the bolts and nuts. You should reuse the bushings and any insulating tubes that were on the PT. 4 nuts are used to keep everything together then another 4 nuts to mount the PT.

[Ledzepp007]

Thanks. Extremely helpful.

[eleventeen]

The critical part is the insulating tubes. Do NOT leave those out. If the originals have become damaged, I would urge you to go get some small diameter soda straws of the right diameter and see if you can wrap the bolts with the plastic straws and then use the damaged cardboard/fiber sleeves which would then become spacers. If you can't find small diam straws, maybe you can slit too-big ones and still wrap the bolts.


All my reading about transformers says the laminations are supposed to be insulated from each other. If you run the new bolts through the corner holes with no spacers, the sawing action of the threads could easily wear away the lacquer coating on the inside of the holes. With no spacer nor insulator in there you could short out laminations with the naked bolt. I can't tell you what the exact effects might be but they are almost certainly not good. 


And by the way, when it comes time to cinch down the mounting nuts and then the ground lug(s) on those tranny bolts, be aware that ordinary generic hardware-store bolts, especially long ones like you have, are made with soft, crappy steel to make rolling out so many threads easier. That means you can and will shear off those bolts should you overtighten them rather easier than with the originals. That would suck, to use the technical term. 


Just trying to keep you out of the soup. 

[Ledzepp007]

Thanks for the help.

Another random question: 10K trimmer resistors (for PI balancing I think) are somewhat difficult to find. I actually had one, but it is only rated for 150mW. I'm guessing I need one rated for higher power? I have looked and I'm only seeing one rated for 1/4W.

[Ledzepp007]

For reference,  here's the layout.

[Ledzepp007]

Any guesses? Am I going to have to hunt down a bigger one?

You can see how small the pot I have is in the picture

[sluckey]

Use the one you have. If it burns up, scrape out the ashes and get a bigger one.

[Ledzepp007]

Finished the amp up this weekend. Worked first power up. Sounds good. Very Bassy through a 2x12. Very musical amp. Dig it.

Now the problems: it has the exact same hum as the Voxy amp I built a few weeks back. Almost sounds like a transformer hum. I'm going to change my grounding scheme a little bit, but I'm starting to wonder if the wall power isn't clean at my house. Is that possible?

Also, could having the chassis outside of a shielded cab cause it to pick up some noise?

[Ledzepp007]

Further investigation:

Removing V1 removes the noise. Tested the tube in another amp. Not the tube. Good. Problem is somewhere before the pots. Tapping around, I get (not surprisingly) the most noise from where the inputs go into V1 (p2 and p7). Moving the heater wires around does nothing to the 60 hz hum.

I then attempted to bridge the channels at which point the amp must've shorted somewhere because it immediately got super hot. I'm guessing this means that I likely wired the inputs incorrectly? They each work individually. Alternatively, perhaps I should use shielded wire for the inputs?

[sluckey]

I then attempted to bridge the channels at which point the amp must've shorted somewhere because it immediately got super hot. I'm guessing this means that I likely wired the inputs incorrectly? They each work individually.

I don't suspect jumping the channels caused the amp to get super hot, especially since the inputs work individually. I rather think that's just a coincidence.

[Ledzepp007]

Didn't make sense to me either. But as soon as I unplugged it the overheating stopped. My sense is some shielded wire may do the trick.

Any other ideas? Could something weird with the input jack wiring cause this?

[sluckey]

Shielded wire ain't gonna fix that. If the inputs are wired according to that layout there's no way the inputs are causing the amp to overheat.

Which component(s) is/are overheating?

[Tweeds]

Nice variant of the 5E3 indeed, never heard of it though?  Did you make the board,?

Thanks for posting it...

[drew]

^ It's a Tweed Deluxe that Dumble modified for Kenny Wayne Shepherd.  There is a thread about it on ampgarage.com which you can read if you're not scared off by the "Reported Attack Site" warnings.

[Tweeds]

Thanks much...yeah I've seen those messages, what happened there is it safe now, or??

[drew]

Unclear what got the site flagged.  Owner has sporadically claimed it's going to be resolved, but a year has gone by.  I don't think any of the guys who continue to use the site have reported any problems from doing so, but act at your own risk

[galtjunk]

I visit Ampgarage every day.
I get the warning messages and continue on to the site.
I have not had any problems with my computer after visiting the site.

I built the Tweedle Dee with a VVR controlling both the preamp and the output.