Fender Champ 12 (single ended 6L6) Buzzing Drive Channel

[smackoj]

I picked up this Fender Champ 12 a few months ago not really knowing what it is. I had never heard of this amp before. It has the red knobs that were common during the "Rivera Era" but I do not know if this is one of his designs? It is a great sounding amp and comes stock with a 12 inch Fender Blue label speaker which is my favorite speaker Fender ever used. The problem I am having is that the Normal Ch. is nice and quiet but the Drive Ch. is buzzing and very annoying. I loaned this amp to the guitar player on the church worship team and he likes to run it on the Drive Ch. but the buzz is killing his sound. Note: this is a big church with lots of music gear and high powered PA amps so I wonder if it is related to a ground loop problem? If anyone has a suggestion on where I should start to calm the noise, I would much appreciate the help.Thanks amigos,  Jack D

[dude]

Does the amp buzz at another place? Try the overdrive channel in your home.

[mresistor]

Where are the tube shields for the 9 pin tubes?  They are used to suppress rf and other electrical fields or noise.  I don't know if they will fix your problem but they should be used. think of them as a Faraday cage for the tube.

[smackoj]

Thanks for the replies gents. At home it only has a tiny bit of buzz. I will have to search but I know I have the preamp covers around here. That is a very good point and with all the wireless mics in the church could be the culprit.
I will report back after trying it with the shields on.

[jojokeo]

Hey OJ! What's up my friend? I just worked on one of these for a buddy in his studio last week. Very timely.

He had just bought it off Craig's list and had issues on the Drive channel. It was modded (don't know exactly what was done but was to increase OD) and I didn't have to take it apart to fix. His main issue was intermittent crap (aside from noise). Practically every nut on the pots under the knobs were loose interrupting the ground. Evidently they were dependent on the mechanical connection (always bad relying on that instead of a soldered wire!).

It may not help your issue but is something you always check. Also clean all of the jacks, pots, switches, and tube sockets and pins if/when you get a chance. If  you go inside check the wiring, many times these can be a rats nest of clusterf*&k. Re-routing the wiring is always good and usually helps. But first if everything else seems okay circuit-wise try popping in a different tube in V1 if not a lost noise type and check the others too while there.

Later amigo! jojo

[smackoj]

Commander JOJO!  Ola amigo. I have been inside and replaced the pwr filter caps. Do you think I should solder a ground wire across the pots? I will try all your suggestions. I like this amp although the reverb setup is below par. I am loaning it to a vg guitar player at a big church here in Denver but he likes the sound running on the OD channel. Because of the way they run everything through a big board and don't want amps on stage, we have to put the Champ in a closet and mic it. But the closet is full of wiring, phone junctions etc and I don't know if I can get rid of all of it, but I'm gonna try.
On a different subject: did you ever use that Jfet matching circuit? Does it work?
I am waiting for a RTSolder pcb to arrive for the Mad Professor Deep Blue Delay. There is a lot of buzz out there about how good it works. I am getting them from Aion Electronics. I have built several of his effects which are all clones of public domain effects circuits. Here is a link to the pcb if you want to have a look? I would like to hear your opinion on the Deep Blue.
https://aionelectronics.com/project/vector-deep-blue-delay-clone/

[jojokeo]

Sorry for the late reply OJ, I'm not a fan of soldering to the back of pots as it creates multiple ground returns aka loops. I run grounds directly to where they should go and/or to it's neg. power supply cap ground. The way works of course but people wonder why certain oscillations occur and other anomalies and it's a way of eliminating aspects out of the equation. Signal grounds are signal returns after all and are a way for signal influences and corruptions. There's other sources for trouble of course but always best to plan ahead and do what you can control.
I still have the jfet matcher but haven't had the need to put it to use yet since I haven't needed any extra phase pedals in a while (yes, I'm sure it works). I use a homemade jfet tester fairly regularly that tells me the pinch voltages and dissipation currents especially since my latest Steel String Special pedal has been completed. I'm getting a number of orders on this one already on the home front.
l think you'll like delay pedal, should be a good one to add to your rig.

[DummyLoad]

interesting reverb implementation: reverb is wrapped around the output stage. OT drives tank; JFET tank recovery amp to 1/2 12AX7 for mix amp. JFET bias power derived from 6L6 cathode bias also powers LDRs and OD LED indicator.


https://el34world.com/charts/Schematics/files/Fender/Fender_champ_12_schem.pdf


look for the usual suspects - leaking PS electrolytics: C101, C102, C103, C25, C19 


--pete