Normal plate voltage, zero voltage on the cathode of a cathode biasedĪmp-almost anything. Pop, weakening or thinning of signal output, loss of tube heat, higher than Problems including complete loss of signal, red plating due to loss of bias Or dirty tube socket pins can cause all kinds of hard to diagnose intermittent Their plates and die quicker than preamp tubes. Rectifier tube-they can cause all kinds of problems including weird noises. Morghulis," "all tubes must die." Don't forget to try a new Power tubes usually wear out quicker than preamp tubes but as they say, "tubular Including everything from complete signal loss, hum, hiss, static to something A bad tube can cause lots of different symptoms Having a spare set of tubes to swap into the amp one at a time is a must for Suspect a bad tube as they are the most common failure point in a tubeĪmplifier. Power tube increase so this isn't a hard-and-fast rule. Does a volume, tone or master volume control affect the noise? WhenĪ control affects the noise it usually indicates the noise is entering the ampīefore that control but I have seen a volume control that caused noise in a bad You mustīefore doing any work inside an amplifier chassis. Use just one hand when working on a powered amp. Lethal shock can run between your arms through your heart. Never touch theĪmplifier chassis with one hand while probing with the other hand because a High voltage then have an amp technician service your amp. If you have not been trained to work with Tube amplifier chassis contains lethal high voltage even when unplugged-sometimes They are to troubleshoot, so keep learning. You know about how tube amps work the easier Following it will minimize damage due to a miswired amp. Many of these techniquesĪre turning on a new build amp or heavily repaired/modified amp for the first time I recommend you use a Being that I already replaced it it makes me thing that something in the transistor switching circuitry isn't working, and I guess it's POSSIBLE that THAT could be causing the noise as well.Technique for troubleshooting a tube guitar amplifier. I took a couple months off from this thing, came back to it last night fresh, and thought I'm gonna win this time, haha nopeĮDIT: I'm now realizing the noise is there on all 3 channels because regardless of the channel that's selected, the Ch 1 Gain pot still works. I also still get guitar signal out of the amp which I don't understand. I'm baffled that with all the tone caps disconnected that the crackle is still there. I've scoped around the tube but can't get any CLEAR display of where the source is (plate, grid, cathode) This is the only thing that got rid of it:ĭisconnected gain wiper and wired to external pot, no connection from tone caps, crackle GONE (crackle must be PRE-gain pot) Here's everything I've tried, to no effect:ĭisconnected all tone caps (still crackle ?)ĭisconnected DC filament supply from V1 and wired it to the AC filament supply I cleaned it all up, replaced the caps, and hard wired them to where they went. Refresher on the initial issues when the amp came in: The E+ supply caps had arced and burnt the pcb traces. The snaps, crackles and pops are in all 3 channels. Not seeing any DC on the pot itself on any lugs. I replaced the Gain pot, still crackle AND the gain pot is scratchy even being a new pot. Nothing from the Ch 1 tone stack is connected, the crackle is GONE. I removed the wiper wire and wired in another pot to the grid of stage two. OK, so, it's DEFINITELY before the Ch 1 gain pot. I removed RY5 (in Ch 1 tone stack) and replaced RY1. still crackle.Ĭannot clean the relays, they're enclosed. I've lifted the 20pf grid cap, the J175 jfet etc. If all is well before the Gain, which it is, and turning the Gain down, it also grounds the RY1b and 475k grid stopper. The source of the crackle has to be the relay or the supply. If I turn the Gain down, the crackle goes away, so I was convinced that it was a leaky coupling cap in the tone stack. I don't see the crackle on my scope for the first stage, however, Chnl 1 Gain functions on all channels, so it tells me that RY1b is not working. So I'm thinking the supply for it is causing this, but just a theory. Of note is that the RY1b is NOT switching, and I've replaced it. So, my question, anyone had a relay power supply or a relay itself cause crackle? I've checked and replaced just about every damn thing in that first stage. Gotta desolder a few things every time I need to access the solder side of the board.what a PITA. Now, the thing is crackling, and I've narrowed it down, after about 10hrs of troubleshooting. I then had a leaky coupling cap for Chnl 1 and replaced it. I cleaned all that up, rewired it, replaced both filters for that node. It came in with a short in the last filter supply, two traces had arced.
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