| Fire Hazard? [message #7848] |
Mon, 06 November 2006 16:05  |
KustomKyle
Messages: 14
Registered: February 2006
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Junior Member |
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A unique situation I thought I'd get the pro's opinions on. I bought a Frankenstein head and am running in through a 4-ohm cabinet. I had the cracked fuse housings replaced and a 3-prong power cord installed. Top-notch job on both. However, when he closed up the amp again, he didn't notice that the price tag (still hanging off of one of the knobs) was in between the face of the amp and the bottom-front part of the frame (where the face meets the naugahyde in the front). I cut off the protruding part of the tag - so you can't see it by looking at it. BUT - is this any sort of fire hazard? The amp runs a little hot because it's driving a 4-ohm cabinet. But it doesn't seem to get hot around that area, and it doesn't seem to get hot enough to burn anything. But you guys are the experts. Thanks.
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| Re: Fire Hazard? [message #7850 is a reply to message #7848] |
Mon, 06 November 2006 20:53  |
C4ster
Messages: 686
Registered: June 2001
Location: Mukwonago, WI (Milwaukee...
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Senior Member |
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No, there are no heat generating components that close to the front. But all it takes is a couple of screws, slide the amp chassis out and remove the offending tag. Besides, while it's out, just check out the top quality components that went into that amp of yours. Don't be afraid to inspect the very essence of the amp. Whoops, a little to sensual there. These are great amps made to higher standards than ANYTHING made today. It's true the franks were designed for 8 ohms, most guys here will admit to driving theirs into 4 ohms, thereby abusing the very nature of the beast. Again, a little to dramatic. If you hear the amp distorting with a funky kind of distortion, increase the load to 8 ohms and don't allow the amp to overheat. These amps had more insulation than ventilation and need to dissipate it somewhere. A fan has been suggested. Good luck. I think I have had a few too many picso sours here in Peru. I can't wait to get back home.
Conrad
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| Re: Fire Hazard? [message #7855 is a reply to message #7853] |
Tue, 07 November 2006 21:08 |
C4ster
Messages: 686
Registered: June 2001
Location: Mukwonago, WI (Milwaukee...
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Senior Member |
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OK here is the straight poop. Heat is the big enemy of transistors. That heat is developed by the current flowing out of your transistors and into your speaker. This sounds like Sesame Street. I forgot a huge plus for the Frank models. The transistors are mounted on the chassis behind the screen on the back. It would be much easier to cool that amp than a Plexi front model. Their transistors are hiding underneath in a dead air space. When you place a lower ohmic load on an amplifier, the current through the transistors could double. The power dissipation would go up quite a bit. Then you need more cooling to keep the transistors cool. Now cool is a relative term. If you can't place a finger on the transistor and hold it there for a short period of time, like touching a soldering iron, it's too hot. But again, short bursts of power, as music is, allow the transistors to cool between bursts. Under these conditions, a very loud burst could drive more current than the transistors can handle. Causing them to short out. By the way, transistors never open up, they always short. But with all that info, it is still better to run the amp with the proper load. The perceived sound level may very well be more speakers rather than more power. You are moving more air. You didn't say what the cabinet configuration you have. I am presuming a 4x12 cabinet. I don't know why. And when you are pushing more bass you need more power to achieve that level, so more distortion. One more thing, transistors do not heal. So every time you overheat the transistors, they can and do degrade slightly. Eventually they will fail, so keep that heat in check. Whew!!
Conrad
Steve, I don't have a distortion meter so I can't make that comparison. I just use basic testbench equipment, Fluke meter, Oscilliscope and resistive loads. I just increase power unitl I see clipping and call that max power.
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| Re: Fire Hazard? [message #7861 is a reply to message #7860] |
Wed, 08 November 2006 17:17 |
C4ster
Messages: 686
Registered: June 2001
Location: Mukwonago, WI (Milwaukee...
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Senior Member |
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When any solid state device fails it only has 2 options. I suppose that they could go out of spec but for the most part, electronic circuits are designed to ignore differences in components. When they fail however, either they completely blow off the board, an open circuit or they short and become a piece of wire. And in the process, all 3 leads of the transistor become 1. The reason for this is that the 3 leads are the Emitter, Base and Collector. The area between the Emitter and the Collector, the Base, is very thin. Atomic thin. When the Base is destroyed, the Emitter and Collector fuse together. AKA, a short, taking the base with it. Then you start blowing fuses, hearing loud hum from the speakers and distortion if there is any sound other than hum. At this point. if the fuses don't blow, the speakers will. On this post, we have heard all the different variations of failure. Now, if you say you can keep your hand on the transistors, the large metal ones on the back, don't change a thing. just remember all amps have a limit. It's just that a Fender will sound one way when they are over driven and a Kustom will sound different. One last point, you might eant to replace your filter caps. That will give you more headroom before distorting by keeping the power supply voltages higher and more stable.
Conrad
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