My Very First Ever Build AA764 Vibro Champ. (Cab is here)

[tribi9]

I do not see the 330pf cap from pin 2 to pin 5 on the 6V6, it is shown on the schematic and layout. I had to down load your picture so I could blow it up to see better.

I am also concerned about under board wiring since we did not see any pictures of that. There is a lot going on in that layout most of which are just wires passing under the board but the other ones also indicated by dashes on the layout are connections.

Mark

Mark, I added the 330 pf cap but in the layout it looks like it should be on pins 5 to 8. On the schematic I believe it says it should go to heater and one of the grids (pin 5). Which one should it be?

I got it at 2 and 5.

Thanks

[tribi9]

And I just noticed something the humming stays at the same level with the volume off. (Loud but not extremely loud) but If I turn the volume knob up the hum gets louder as the pot gets turned.

I know I gotta be close.

I'm going to take voltages hum and everything and I'll post them.

Cheers

[tribi9]

And just to make it 4 in a row!

I got the amp to quiet down by turning the knob. If I keep it at zero I now get a loud whistle like sound. If I turn it up a bit it goes away. I f I kepp turning it comes back. I turned the tremolo speed knob and I could get the noise to have some tremolo/vibrato also I fiddled with the speed knob and the noise sped up.

[tribi9]

I JUST GOT SOUND!!!!!!!!!!!!

[tribi9]

So i'll explain...


I wired the input jacks the way shown in the schematic ( knew I had to have it right, the picture is pretty clear) and turned the amp on. and it was still humming pretty bad. I took a look inside and notice the can cap ground had come undone. I soldered it back up and turned it on. This time the amp was quiet. So I plugged in a guitar but nothing happened. I started taking voltages at all the spots shown on the schematic. For some reason I still had my guitar strapped and on my lap. The mutimeter on the table, the black lead clipped to the chassis, one hand inside the chassis only and the other one strumming. When I touched the bare wire I got with all the grounds, it crackled loud, followed by sound. I could not believe it. I strummed again and there it was. I poked the wire again and the sound went away, so I poked a third time and the sound came back.I couldn't really control the volume knob tho' If I turned it either up or down it would just feedback loud.


I played the amp for about 10 minutes. I used an 8 ohm spare speaker that I have to test it on the table. I'm only using that speaker to test it I won't be playing much through it.(I was previously moving it to a 4 ohm cab that I have but it was a hassle moving it and couldn't really do a lot of work there....)

Tomorrow or Sunday, Im going to rewire it (The pot side only) and follow some of the advice I've been getting from you guys on where to place the grounds.

Structo, Mark, Phil-S and everybody else that helped out,
Thanks so much, you guys have done an awesome good deed. You should have seen the smile on my face when I got sound. It felt so good!

I recorded some sounds, the camera mike sucks tho. (Sorry about that)

A little Hendrix rendition for testing purposes..


http://www.youtube.com/watch?v=h4DelRROVoA

[Structo]

if by touching that ground you got sound I would suspect a bad solder joint. How are your grounds connected to the chassis?

The 330pf cap goes between pins 5 and 8.


You say the wire to the negative terminal of the cap can came undone.

That leads me to believe your soldering isn't very good.

Go over every single solder joint in the amp and reflow them by heating them and touching a little new solder to the tip of the iron.

[Normster]

Sounds like an amp! Congrats!!! Keep in mind that the speaker will always sound like crap if it's not in a cab so don't judge the tone you're getting yet.

[tribi9]

if by touching that ground you got sound I would suspect a bad solder joint. How are your grounds connected to the chassis?

The 330pf cap goes between pins 5 and 8.


You say the wire to the negative terminal of the cap can came undone.

That leads me to believe your soldering isn't very good.

Ok, i'll move the cap and retouch the solder joints.

The wire for ground for the cap can wasn't soldered properly. the tip of rhe wire was inside the little hole on the ground tab but wasn't making contact with the tab.

My grounds are connected to chassis temporarily with a bare wire running to the one bolt/nut on the OT. I only did that to test it, Ill move the high current ones to close to the PT and the other grounds I'll move over to where the input jack is.

See pic for how it is now.

[IMG:800:600]http://i114.photobucket.com/albums/n271 ... c02027.jpg[/img]

[tribi9]

Sounds like an amp! Congrats!!! Keep in mind that the speaker will always sound like crap if it's not in a cab so don't judge the tone you're getting yet.

Thank you Normster. I'm stoked. My cab should be here next Tuesday or Wednesday.

I'll post some pics when it's all done up.

[Structo]

You might want to consider using a permanent ground buss for the preamp grounds.

Then ground only one end below the input jacks that the jacks also ground to.

You can either solder it directly to the back of the pots or float it above the pots with short ground wires to it from the lugs that need to be grounded.

Not sure with the angled front which is feasible but it is a common technique to use a ground buss wire for preamp grounds.

If you do, try to find something like solid 18 gauge bare tinned wire.
Or something similar.

Below I show how a D'Lite amp is grounded so disregard the other stuff there. I just wanted to show how it would be grounded there to the chassis.

[tribi9]

Thx Structo, I'm planning on doing something similar. Does the input jack need to be grounded tho? Isn't the sleeve grounded to chassis anyhow?

[Phil_S]

You da man Tribi9! Nice job. Amp seems to be quiet. I assume you fixed that loose wire by now. If you are satisfied with the noise floor, button it up. It's done. Dont' try to fix it 'til it's broken.

[tribi9]

THANK YOU Phil_S. Everything works except the Volume knob. When I turn it down all the way I still get sound. Not sure what's going on there.

[Phil_S]

Disconnect the pot. Put your ohm meter on the wiper and one outer leg. The do it with the other outer leg. You are looking for the ohms to be zero with the knob in the extreme postion, left or right, depending on which outer lug you are attached to. If it doesn't zero, replace it.

[tribi9]

I'll try that and report back.