#1
Hey was just playing about with my alchemist and after switching channel and then switching back i have lost a lot of distortion???
Could it be a preamp tube has blown? they are all lighting up and look the same and so are the power tubes.

any suggestions?
#2
did you lose gain or volume? if you lost Gain could be a component in the tone stack or somewhere got fried if all tubes are lighting up. but I would check the tubes to make sure you see all of them lighting up and it's not just light from a nearby tube.
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#3
just changed every tube, one at a time and place all the old ones back and it seems to be ok now???

Should it be something to worry about? i.e something wrong with its electronics?

Matt
#4
Quote by amatas83
did you lose gain or volume? if you lost Gain could be a component in the tone stack or somewhere got fried if all tubes are lighting up. but I would check the tubes to make sure you see all of them lighting up and it's not just light from a nearby tube.


It's happened again
what happened is when I am playing on the mercury channel it starts out with high gain and just dims down after a few mins. As it would if I turned the gain down.


Open cathode bypass capacitors in preamp - if they go open, the stage they're in loses gain, but does not otherwise fail. If they short, it dramatically shifts the bias point, and may cause distortion as well as low volume. http://www.geofex.com/ampdbug/lowpower.htm
this sounds like what is going on with.
Anyone know what this is and how to fix it?
Last edited by Mattinho at Jul 7, 2010,
#5
Anyone have any clues what it could be and how i can fix it??? Its not the tubes as they are all working fine.
#6
The cathode bypass capacitors are a possibility. You could always replace them if you have any ability to solder and use the internet to learn what to do and what not to do when inside an amp. Or you could just take it to a tech. The thing is, I'm not sure why it would vary between full bypass and partial to no bypass. What's custom about it?
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#7
Quote by mmolteratx
The cathode bypass capacitors are a possibility. You could always replace them if you have any ability to solder and use the internet to learn what to do and what not to do when inside an amp. Or you could just take it to a tech. The thing is, I'm not sure why it would vary between full bypass and partial to no bypass. What's custom about it?


Would the capacitor need changing or just re-fitting. I'm pretty sure it is this as the description matches my problem.

The custom is just the way it looks

Where would the capacitor be? I can solder but not sure what i'm looking for??
also what does it mean to be 'open'?
Last edited by Mattinho at Jul 7, 2010,
#8
It means that either one of the leads isn't making the connection or that the component failed. To me, it sounds more like a lead on one of the bypass caps is moving around and making an intermittent connection. I'm not familiar with the Alchemist board so I can't tell you where it is but if you can't identify it, you might not want to try it yourself, especially if you don't know how to drain the power supply caps.
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#9
Quote by mmolteratx
It means that either one of the leads isn't making the connection or that the component failed. To me, it sounds more like a lead on one of the bypass caps is moving around and making an intermittent connection. I'm not familiar with the Alchemist board so I can't tell you where it is but if you can't identify it, you might not want to try it yourself, especially if you don't know how to drain the power supply caps.


How easy is it to drain them, do you need any special equipment?

If its a wire moving is it the vibrations of the amp doing it as i haven't moved it for a while and it just happened out of the blue

Thanks for your help
#10
http://www.youtube.com/watch?v=Rg3-dZC5Fww

That's a decent tutorial. But be aware that the voltages can definitely kill you if you're not careful/don't know what you're doing.

And yes, it's likely that there was a cold joint on one end of a bypass capacitor that broke and is now vibrating around when you play the amp.
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#11
Somehow I doubt it's a cap, it sounds more like a bad gain stage preamp tube. Preamp tubes will still light up and work even if they are going bad, and fading gain sounds like what tubes tend to do sometimes, as they heat up, the filaments move and make less of a connection.

If your clean channel has no problems, then it has to be the gain stage tube. But I assume your amp is a multi channel amp, so does it have more than one gain stage tube?

Also, typically, when caps go, they don't just start to go, they freaken die on the spot, most of the time, a loose connection is possible, but it would not make sense why the gain would come back after waiting a while.

Always start with the easiest solution first, replace all the tubes, weather you think they are bad or not. If the problem is still there, then move onto the next easiest solution, don't just go straight for what you think is the problem, cause if your wrong, and it turned out to be that easy solution you skipped, you'll be pissed.
#12
have you checked if the valve sockets' solder pads are still good? sometimes, the pad lifts or cracks and you lose connection.
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#13
i'll dig out the stock tubes for the amp and give them a try, hopefully it is a tube because i don't fancy playing with the boards yet.

Thanks for all the help guys
#14
Quote by Mattinho
i'll dig out the stock tubes for the amp and give them a try, hopefully it is a tube because i don't fancy playing with the boards yet.

Thanks for all the help guys



No problem, just remember, and this applies to life as well, always try the easy solutions first, I don't know how many holes in walls and nice long peal outs I've left on the road from being pissed off by not figuring out to do the easy thing first.

Hope if works out for you.