Vox AC4 Question(s)

[dwinstonwood]

I'll get a faceplate made next. Maybe something like this.

[dwinstonwood]

Late last night when it was really quiet, I noticed that if I let a B flat on the sixth fret of the low E string ring out it would start to oscillate as it faded out.

Well, I woke up bothered by this. So, I moved the ground wire from the EF86 pin 2 straight to the input jack ground (it was connected to the board at the negative end of the cathode cap, and shared a ground wire from there), and I replaced the 1Meg resistor coming off of B+ to pin 1 of the EF86 with the 5.6Meg resistor shown on the Vox schematic. I also rearranged the red wire from pin 6 so that it is tucked down and does not cross other wires.

This almost completely eliminated the wavering B flat, and the low level hum is reduced, too. Quiet enough that it I have to stop playing and listen for it. I might also add some adhesive foil under the top of the cabinet since the chassis is open on top.

Finally, I ordered some better tubes. I had grabbed the cheapest ones originally, but after some research I found that there are some better EF86's than the Electro Harmonix, and better EZ81's than the JJ.

[dwinstonwood]

Grill cloth and custom faceplate installed. For a "first-time" amp build I'm happy with it.
I'd put my name on it.

[kagliostro]

Looks Nice

Franco

[tubeswell]

Very tidy

[dwinstonwood]

Thanks Franco!
Thanks tubeswell!

I still need to add the piping around the grill to cover up the small gaps.

I made some minor changes and the amp is now as good as I think I can get it.
I switched back to the 1Meg screen resistor from the 5.6Meg; I probably should have just left that alone. But, I have to tinker with stuff.
I did some research on filter capacitance and rectifier cathode coatings and I'm confident that I'm safe in these changes that I made. I was still getting some hum, so I bumped the first filter cap up from 30uf to 47uf, the second is the same at 30uf, and I replaced the third 8uf with a 10uf of the same brand as the others (F&T). I changed that one because I think I might have damaged it during soldering.
Now the amp is very quiet.
I replaced the JJ EZ81 and the Electro-Harmonix EF86 with a Tesla EZ81 and a Tung-Sol EF806 SG.
The amp now sounds better than ever, and it's very quiet. I like it a lot; it pairs with my Alnico II Tele pickups really well.

So, a genuine thank you to everyone who showed an interest, shared their knowledge and guided me through this. And, I didn't get zapped. (I did notice that warm tubes seem to drain the caps when the power is switched off, but I still connected my discharge tool to develop the habit.)

Wow, I'm ready to start my next build...
Sluckey, I'm thinking your Trem-O-Nator would be good with your AB763 Deluxe Lite.

[shooter]

Wow, I'm ready to start my next build...

call 1800gethelp if this becomes an addiction 

[DummyLoad]

Wow, I'm ready to start my next build...

call 1800gethelp if this becomes an addiction 

what's that again? guitar amps? <click> buzzzzzzzz (dial tone).


--pete

[dwinstonwood]

Yeah, I might be nearing the slippery slope. I've actually been thinking about what I can sell off on eBay from my "real money pit" hobby, radio control airplanes, to fund another amp project. There's some money invested there, after 30yrs of collecting airplane stuff.