Hey guys I'm new here!
I've been having trouble with my amp lately and I am trying to figure out whats wrong with it.
I have a Hughes and Kettner Switchblade 100W Head. I bought it used and for the first little while things were fine. The other night I turned it on and there was nothing but an extremely loud low pitched hum. When the amp is in standby the hum goes away, and when I turn up the volume the hum gets louder. If the amp is up loud enough, the guitar barely cuts through but is crackled and muffled. The hum is present whether there is anything in the input or not. I'm just wondering if anyone could tell me what the problem could be. This is my first tube amp and im still a noob
Thanks
Amp Problems... :'(
Moderators: pompeiisneaks, Colossal
Re: Amp Problems... :'(
Welcome to the fun!!
I did a quick search for a schematic but came up empty handed. Any chance that you have/can get one that can be posted up here? Even a couple of pics of the face and back plates and tube compliment would be helpful.
My general approach to amp troubleshooting is to start by evaluating/eliminating the simplest things first. Some of these very simple "tests" often quickly point to the problem source.
So...if you haven't already.....
Obtain good visual access to the tubes. Power it up in standby and verify the glow of the heater element in each tube. Take the amp out of standby and carefully inspect each tube for red plating. Once you calibrate your eyes to the heater element glow above, red plating will be obvious. As the name implies, the tube plates (large structure in the middle of the tube) will be glowing light orange to "fierce" red if this problem is occuring. It most commonly occurs in the power tubes due to biasing issues. However, I have seen it pre-amp tubes in instances where I have accidently shorted a cathode resistor. Oooops....!
Quickly shutdown the amp and let us know if you observe red plating. Continuing in this condition often causes more serious problems in more expensive areas of a tube amp!
One guitar, one cord directly into the input. Hopefully you have another amp to test them on to assure that they work as they should. Gently wiggle the cord/input jack while playing to see if the sound improves.
"Excercise" all control knobs/switches/foot switches/etc... (except power and standby) while playing to see if the sound improves.
Double check the connection(s) between the amp and the speaker. Wiggle them (cord, jacks, etc...) around while playing to see if the sound improves.
Hit a power chord and quickly lift one end of the amp ~1/4" off it's resting surface and let drop. See if the sound improves. I have quickly found many a loose connection in an amp after peforming the "drop test".
Give those a shot to start and see what happens. From here, I would start pulling/replacing tubes to attempt further isolation of the problem area. However, I hesitate recommending that now without seeing a schematic.
Any chance that you have access to a tube tester? Although not iron clad perfect in determining tube health, they can go a long way in helping along the trouble shooting process.
Hope that this helps!
Dave O.
I did a quick search for a schematic but came up empty handed. Any chance that you have/can get one that can be posted up here? Even a couple of pics of the face and back plates and tube compliment would be helpful.
My general approach to amp troubleshooting is to start by evaluating/eliminating the simplest things first. Some of these very simple "tests" often quickly point to the problem source.
So...if you haven't already.....
Obtain good visual access to the tubes. Power it up in standby and verify the glow of the heater element in each tube. Take the amp out of standby and carefully inspect each tube for red plating. Once you calibrate your eyes to the heater element glow above, red plating will be obvious. As the name implies, the tube plates (large structure in the middle of the tube) will be glowing light orange to "fierce" red if this problem is occuring. It most commonly occurs in the power tubes due to biasing issues. However, I have seen it pre-amp tubes in instances where I have accidently shorted a cathode resistor. Oooops....!
Quickly shutdown the amp and let us know if you observe red plating. Continuing in this condition often causes more serious problems in more expensive areas of a tube amp!
One guitar, one cord directly into the input. Hopefully you have another amp to test them on to assure that they work as they should. Gently wiggle the cord/input jack while playing to see if the sound improves.
"Excercise" all control knobs/switches/foot switches/etc... (except power and standby) while playing to see if the sound improves.
Double check the connection(s) between the amp and the speaker. Wiggle them (cord, jacks, etc...) around while playing to see if the sound improves.
Hit a power chord and quickly lift one end of the amp ~1/4" off it's resting surface and let drop. See if the sound improves. I have quickly found many a loose connection in an amp after peforming the "drop test".
Give those a shot to start and see what happens. From here, I would start pulling/replacing tubes to attempt further isolation of the problem area. However, I hesitate recommending that now without seeing a schematic.
Any chance that you have access to a tube tester? Although not iron clad perfect in determining tube health, they can go a long way in helping along the trouble shooting process.
Hope that this helps!
Dave O.
Re: Amp Problems... :'(
Man, that sucks. I remember when my first tube amp started going nuts (Crate VC 30). With any significant volume it'd start feeding back controllably. All my friends with their line 6s made fund of me because I had to get a stupid tube amp and look where it got me.
Sounds to me like something's loose. Do ampgeek's proscribed diagnostics double checking the input jacks. Before you start buying new tubes, and IF YOU FEEL COMFORTABLE doing this, pull the chassis out of the cab and turn it on with a speaker connected. Take a NON CONDUCTIVE probe (chopstick, etc, not a pencil) and lightly tap around on the components, wires and tubes. If something's loose, this should find it for you.
Have to warn you though, servicing PCB amps kinda sucks. If you don't have a bunch of hours behind a soldering iron, I might be tempted to take it in someplace to have it services. At the same time though, what fun is that? Nothing ventured, nothing gained. Do use your best judgement, though. Hope you're back on your feet soon.
Sounds to me like something's loose. Do ampgeek's proscribed diagnostics double checking the input jacks. Before you start buying new tubes, and IF YOU FEEL COMFORTABLE doing this, pull the chassis out of the cab and turn it on with a speaker connected. Take a NON CONDUCTIVE probe (chopstick, etc, not a pencil) and lightly tap around on the components, wires and tubes. If something's loose, this should find it for you.
Have to warn you though, servicing PCB amps kinda sucks. If you don't have a bunch of hours behind a soldering iron, I might be tempted to take it in someplace to have it services. At the same time though, what fun is that? Nothing ventured, nothing gained. Do use your best judgement, though. Hope you're back on your feet soon.
"In this world you will find hardship and trials; but take heart, for I have conqured the world."
John 16:33
John 16:33