Blues Jr III and self repair gone wrong.

[Veltek]

Good day! I am a first time poster here, and I am looking for some guidance. I have scoured the web and cannot find anything that is similar to the issue I am having. So, allow me to backtrace a bit, and give you guys and Idea of what is going on.

I had some crunchy knobs that needed to be cleaned out, and asked my brother (a mechanic by trade) if he had any Contact cleaner I could borrow. He lent me some and I sprayed it all up inside those pots. Got them nice and smooth... until they started to feel loose, and some very stiff too. Well turns out it was the wrong contact cleaner, and it was not safe for plastics, and I melted the shafts. So I ordered some snap-in pots online, looked up all of the resistances, and got everything desoldered, and resoldered. The first time I plugged in the amp, it came on fine, but the volume pot would not work. I still had sound though, a very clean, chimey, almost Deluxe reverb sound, that got overly loud overly quick on the master volume. So I figured I did a poor job soldering, and tried again. This time I got the Volume to work, but the master would cut in and out depending on if it was nudged the wrong way. And over all even the cleans sounded kinda muddy and bad. So I took the amp apart a third time, and worked on my soldered joints. The Master is good again, but the Volume will no longer work! I get very crisp clean tones, but 0 distortion or volume increase from the volume knob. I took it apart a fourth time, and ended with the same result as previously.

All my tubes glow as expected, there is no weird humming or buzzing. any distortion pedals sound like garbage in front of the amp now. I am thinking I either burned the board some where, I messed up one of the solder joints on the PCB mounted Valve socket, I messed up the R8 plate resistor between V1 and V2. or I plain have a bad Volume pot.

Any ideas or suggestions?

[tubeswell]

… I am thinking I either burned the board some where, I messed up one of the solder joints on the PCB mounted Valve socket,...
Any ideas or suggestions?

https://www.youtube.com/watch?v=f9RiXMf3z7A

[eleventeen]

The PC boards on those amps (I have heard from several sources) are of a very fragile type and are tough to desolder-resolder without pulling up some of the traces. Sounds like you have to recheck the connections to the pot pins of the offending pot and may have to solder wires to any or all those pins and duplicate (by parallelling) the trace in terms of where it goes at its other end with ordinary wire. Fender PC boards with traces only on one side can be VERY fragile and easy to pull the trace off the board or cause a crack in a pad where it connects to a component. Such cracks can be very tough to see. Point being, you can create a donut that never connects to the pot pin.


If your MV gets too loud too quick you may have bought & installed the wrong "taper". Most pots in an amp are tailored to increase or decrease NOT in a "linear" fashion (ten % of rotation produces 10% louder) but according to the response of the human ear. Trem speed is NOT such a pot...but in that case we are tuning the frequency of a low freq oscillator that drives the trem. Most of the others are "audio" taper. You may have installed an audio in place of a linear or vice versa. I believe most MV pots are linear, but consult your schematic to see if you have the right type.

[HotBluePlates]

... If your MV gets too loud too quick you may have bought & installed the wrong "taper". ...

Or he may have used too much solder and created a bridge from the pot input to wiper of the channel volume pot, right at the solder pads on the board. That would act like the volume is max all the time, making it seem like the Master volume is too sensitive.

These are the joys & pains of learning to work on amp electronics. Single-sided p.c. boards and non-plated-through-holes are a major pain.