Question:
I have decided that if this hum issue is really heat related I would like to use a 250w computer power supply hooked up to a temperature monitoring system and four cooling fans to cool off the Mesa/Boogie Subway Blues amp I'm working on. The fans will put out a little less than 20db and the whole system will run about $65US. Do you think it will be quiet enough and still get the job done? Does it need to be anymore quiet? I also need some insight on what I need to be cooling exactly. Should I be focusing on just the vacuum tubes or the whole head of the amp? Any info is appreciated since I would like to contact the owner tomorrow and get the ball rolling on the repair/modification. I know you have an opinion or insight Major Tom. I sure hope you read this.
Answer:
If it were me, I would just use one 110 volt muffin fan wired in and running all the time, and forego the temperature monitoring stuff, The power supply itself will add to the heat... Gotta get back to work, lemme get back to you - send me a PM if I forget. Meanwhile, if you can, take a pic or two of the back of your amp, and post it
Tom
Answer:
My recommendation would be to fix the hum problem, as opposed to constructing a workaround - that's not normal, so its the "right" thing to do, which usually works out better in the long run, and secondly heat up problems tend to escalate into a solid problems eventually.
If you want to test the fan thing, if you have a small fan in the house, you could just set it a couple feet in back of the amp, blowing on it. Otherwise, a computer power supply seems like overkill - if you're looking at 12 volt fans, you could just use a 12 volt DC wall wart power supply, or you could get a small 110 volt fan.
As far as the hum problem, a couple questions:
Are you using the amp at high gain settings? If so, does it hum at clean to moderate OD settings?
Does is hum without anything plugged in to the input jack? If not, its probably not the amp per se, but a ground loop.
What are you using in between the guitar and the amp? If its just a cord, have you tried another one?
Tom
Answer:
1st part- I totally agree on fixing the problem. I'd always rather fix it than just go the easy way out.
2nd part- I'll try a fan tomorrow and see how it goes. I'll also get some pictures.
3rd part- it seems to occur all the time. The amp doesn't have a gain so the only way I can OD it is using the guitar and a pedal if that's what your talking about.
4th part- not sure I'll check that out tomorrow.
5th part- I have used it with and without a pedal and different cords.
Answer:
I would try a regular room-type (box, circle, whatever) fan blowing onto the amp for a couple of use cycles. If the problem goes away, your situation is most likely that you have overheating components. If the problem remains, it could easily be something else. My Boogie Studio .22 starts doing weird stuff (including, but not limited to, hum) when the phase inverter tube (in the v3 position for my amp) is giving up its ghost.
If it ends up looking like you have overheating components, it would be good to try to get to the bottom of why they're overheating and try to fix that before it turns more serious.
Nate
Answer:
I used to have two marshall JCM 800's that I wuold tour with. I always had them cranked to 9. This was pushing the tubes extremely hard and most shows were at least 2 hours. I started using just a standard house fan behind each amp to cool it off and that worked fine.
Answer:
Is there a way I can look at the tubes to see if they are working normally? They've been changed multiple times and it keeps coming up but maybe they can tell me something if I know what to look for.
Tom- you mentioned a "muffin fan." Could you explain a little more?
Answer:
Muffin Fan is/was a term used for small cooling fans for electronic gear, same as computer case fans, usually 3" or 4", although many would be too noisy and powerful for a computer. Here's a 120 volt version at Radio Shack, although its a bit pricey...
Muffin Fan
There's no real way of looking at a tube to tell if its working right that I know of, except: if it doesn't light up (dead) or if it is lit up brighter than it should be, indicating its drawing too much current (soon to be dead) . Best thing to do is have spare tubes for swapping out. I always save any that are still functional when I replace them, put them in a box, and designate them as UBG's. Used But Good. Still good for testing the amp, or as an emergency replacement at a gig.
Answer:
Alrighy. I'll have some time to use a fan tomorrow to see if it helps it out. I'll also take some time to look at the tubes and make sure they are all glowing about the same.
If I was to wire a fan into the amp, how would I go about doing that? I'm sure I can do it. Just wondering what the correct way would be.
Answer:
I tested the amp with a fan behind it. I still had the same issue. This is not sounding good.