Build Your Own Clone Message Board

no sooner do i get home from work where i was bragging about how sweet this things sounds, i plug the champ in, turn it on, leave the vol at 1 and let the thing warm up as i'm tuning my guitar.

about 10 seconds later, it starts buzzing, and it gets more intense for a few seconds until it tops out at a pretty loud level. what the heck??

i turned it off, unplugged, discharged the caps and checked for the obvious things... no loose wires, components are all soldered fine, intact fuse, etc.

powered it up again - same deal. very loud buzzing, gets worse when i plug the guitar in. i'm afraid i'm hurting my speakers - it's a harsh buzzing with some crackling going on.

thoughts? thanks in advance...

Post some pics please. And check all of your grounds.

grounds look good, i think... i'll post some pics in the morning - but i'm wondering what could possibly have gone wrong while i was at work that it would warm up and start buzzing??

Does the buzz get louder with the volume control? And do you know how to test for continuity with your DMM?

the buzz is weird... it is loud at 1-4 and gets really quiet at 5-6 and then loud again above that!

i've never tested for continuity before... in fact my electrical experience is limited to this amp and the two pedals i practiced soldering on to get confident enough to built the champ (both pedals work great).

How about voltages, have you tested voltage before?

i have tested voltages - but only to see if the caps were drained before checking out the wires, components and connections.

let me know if there's another angle of the amp i should take a picture of. i can link to a higher-res pic if needed.

I can't tell from the picture but what's that green wire in the middle, it doesn't look like it's connected to anything, maybe an optical illusion.

what you're seeing there are the heater wires i think - i forgot to twist them together so i used a bit of bare wire as a twisty to keep them from flopping around.

Not a good idea. I'd take that off and use a proper plastic wire tie. Bare wire inside a chassis with ~400 VDC present is just not good/safe practice.

It may have nothing to do with the buzzing, but I would definitely recommend getting all of that PT wiring and the green filament heater wires up away from the turret board. Those wires are all carrying AC, and can definitely induce noise/hum. See photo below:



Buzzing often comes from grounding problems, as Morgan mentioned, so I'd definitely be checking all your wiring and solder joints for ground connections.

will do. could buzzing like what i have going on be caused by something shorting?

curious that it gets worse when something is plugged into the inputs...

Need close ups of all the connection points: the jacks, the pot, and each tube socket. And sizing the pics to about 900 pixels wide works well for getting them large enough to see, but still fitting on the screen.

Yeah. Unplug the output tube so you don't need to have it connected to a speaker and take some voltage readings please.

Here is a schematic with reference voltages.

alright - i will do some work on it tonight, check grounds and voltages, and get back to you some closeups!

Here's a tutorial on taking continuity readings with your DMM: http://www.ladyada.net/learn/multimeter/continuity.html

Clip the black lead of your DMM to the amp chassis, and use the red lead to take continuity readings from every component lead that is supposed to be grounded: the top side of C1 and R4, R6, R8, C4, R9, C5, C6, C7, the grounded lug of the volume pot, the jack tips with no plug installed, the transformer grounding point, etc...they should all have good ground to the chassis.

Just an FYI--your DC voltage coming in from the rectifier will almost certainly be higher than shown on that Fender schematic. Not only did Fender tend to significantly understate voltage levels, but the Sovtek 5Y3 rectifier puts out about 30V higher than the 5Y3 tubes in production back in that day. Measuring the B+ voltage on my Champlifier gave a value of ~395VDC with the preamp and power tubes installed, not the 320V shown on that schemo. If you have those tubes pulled out, the voltage will be somewhat higher.

EDIT:

For comparison, I just ran a full set of voltage measurements on my Champlifier with the 3 stock tubes. All results shown in volts DC. Refer to above schematic for the A, B, and C points:

A (B+ rail) without 12AX7 & 6V6 installed: 453 V

A (B+ rail) with tubes installed: 399 V

B: 357 V

C: 310 V

6V6 pin 8 (cathode): 22.1 V

12AX7 pin 1 (plate): 196 V

12AX7 pin 3 (cathode): 1.51 V

That schematic is a little off too. That's a 5E1. You want the 5F1. The differences are minor and few, mostly that there's no choke and where the end of the OT primary connects. Here's the correct schematic.

http://buildyourownclone.com/champschematic.pdf

Thanks Keith, that's much better. I put up the 5E1 schematic because of the cathode bypass cap on the 1st tube; always forget about the choke on that one. Edited my post to avoid confusion.

A bad tube can also sound crackly too.

ok, i checked all the grounds, and everything looks good in that department. i was hoping to find the problem here...

took some voltages too (with the 6V6 removed):

Cap 1: 1.96
Cap 2 and 3: 228
Cap 5: 472
Cap 6: 441
Cap 7: 374

6V6 pin 3: 471
6V6 pin 4: 441

12AX7 pin 1: 228
12AX7 pin 3: 1.96
12AX7 pin 6: 228
12AX7 pin 8: 1.90

do those sound about right?

then i reinstalled the tube and turned the thing on and IT WORKS PERFECTLY! unbelievable. so i played for a good hour just now and no buzz. it has gone as quickly and mysteriously as it came. i'm not calling this issue solved though... for all i know it'll break tomorrow night! i'd like to get to the bottom of why it buzzed like it did so i can prevent it from coming back.

thanks again, all!

With the tube out you have pretty similar voltages to dvoodoo.

Sounds like a bad solder joint or the 6v6 was not installed properly and when you reinstalled it.... works great.

Unless there's a bad/loose pin socket in one of the tube sockets, it seems unlikely that one of the tubes wasn't properly seated. A more likely scenario would be a cold or cracked solder joint on one of the socket pins. That kind of defect could easily come & go with physical manipulation or just from the thermal cycling of warm up and cool down. I would think that the 6V6 or 5Y3 would be most prone to this because of how hot they run. You might try running the amp with the chassis open (CAREFUL!!) and poking around gently with a non-conducting object (wooden chopsticks are popular for this purpose) to see if you can make it buzz. If so, do some touch-up soldering on the problem joint(s).

Didn't you say you were using an NOS Jan 5Y3?

A NOS GE 5Y3GT, but not JAN. But I put the Sovtek 5Y3 back in for those measurements. Here are the voltages with the NOS rectifier:

A (B+ rail) without 12AX7 & 6V6 installed: 452 V

A (B+ rail) with tubes installed: 367 V

B: 329 V

C: 285 V

6V6 pin 8 (cathode): 20.4 V

12AX7 pin 1 (plate): 183 V

So it runs just about 30V lower on the B+ than the Sovtek tube.