Champ help needed please

[skydog]

I have a '73 SF Champ. I have installed the Torrez mod, upgraded to a Weber Sig 8 and replaced the 2 prong cord with a grounded 3 prong. Otherwise, it's stock and I believe original parts. The problem is at almost every volume level (worse at higher volume) there is a noticeable staticy breakup similar to a radio getting bad reception. Very much more noticable on a sustaining chord than single notes. Any suggestions on what to look for? Thanks.

p.s. I had it in recently for this and it came back with a new rectifier tube (which I don't think needed replaced) and they de-ox'd the pots. Needless to say none of this fixed the problem, and I won't be going back to that tech! All tubes are new also.

[skylabfilmpop]

I don't know the Torres mod per se aside from the kits having a fairly bad rap but if R1 and R2 in the champ were reduced from 68k or removed, put them back. YOu probably can reduce them to say 47k. One of the points of these resistors is to help reject RF . The Tech also may not be at fault as sometimes the RF getting into your amp is geographically specific, that is it may hapen at your house and not at the shop. Seems likely that if the amp is gairy you might have raised the cathode resistor values too high and the preamp tubes are running a little wildly, without seeing the kit though I could not tell for sure.

[Fretts]

Maybe this could be a cold solder joint. Did they clean and tighten up the tube sockets too? Have you tried it into a different speaker? How sure are you about the speaker?

[donnyjaguar]

I had a tube with leakage between the filament and cathode cause this problem. It was very annoying to troubleshoot the whole amplifier only to find out that I could've fixed it without taking the chassis out. :)

[RupertB]

I suggest checking the bias. My Vibro Champ and the Champ clone I built both passed too much current with the stock value cathode resistor. The overdrive was shrill and buzzy. Both benefited from having their cathode resistor increased from 470 (stock) to 820 ohms. I also changed the cathode bypass cap to one rated for 50v (instead of the stock 25v).

Now they have a little more head room and the overdrive is much sweeter and smoother.

[HKGuns]

Check all your grounds for positive contact and grounding.

[skydog]

Thanks to everyone for the help, especially Fretts as a bad solder joint proved to be the problem. I went through every joint and reheated it quickly and added a small amount of solder. Plugged it in and I got reminded why I like this amp so much in the first place!