NOSValves Posted March 2, 2014 Share Posted March 2, 2014 Brad, Be careful with having a music signal pumping into a tube amplifier with no load present it can send them into oscillation especially if the volume is up. Craig Quote Link to comment Share on other sites More sharing options...
bracurrie Posted March 2, 2014 Author Share Posted March 2, 2014 Brad, Be careful with having a music signal pumping into a tube amplifier with no load present it can send them into oscillation especially if the volume is up. Craig Thanks Craig. Yes I do have the ability to turn the incoming signal off when there is no load. But to understand further, what happens when a tube amp goes into oscillation? Quote Link to comment Share on other sites More sharing options...
babadono Posted March 3, 2014 Share Posted March 3, 2014 Brad, Be careful with having a music signal pumping into a tube amplifier with no load present it can send them into oscillation especially if the volume is up. Craig Thanks Craig. Yes I do have the ability to turn the incoming signal off when there is no load. But to understand further, what happens when a tube amp goes into oscillation? To quote Bruce Smith, All Pro defensive end for the Buffalo Bills "Bad things, Man. Bad things." Your "amp selector" box should put a dummy load on any tube amp output when it is not going to the speakers. Solid State gear is generally more tolerant of no load conditions but to be ultra safe it should have dummy loads also. Quote Link to comment Share on other sites More sharing options...
bracurrie Posted March 3, 2014 Author Share Posted March 3, 2014 Brad, Be careful with having a music signal pumping into a tube amplifier with no load present it can send them into oscillation especially if the volume is up. Craig Thanks Craig. Yes I do have the ability to turn the incoming signal off when there is no load. But to understand further, what happens when a tube amp goes into oscillation? To quote Bruce Smith, All Pro defensive end for the Buffalo Bills "Bad things, Man. Bad things." Your "amp selector" box should put a dummy load on any tube amp output when it is not going to the speakers. Solid State gear is generally more tolerant of no load conditions but to be ultra safe it should have dummy loads also. i think I have found a miles switch that will sense music and make the switch. When I change which amp is getting input music it will be connected to the speakers. Quote Link to comment Share on other sites More sharing options...
NOSValves Posted March 3, 2014 Share Posted March 3, 2014 Brad, Be careful with having a music signal pumping into a tube amplifier with no load present it can send them into oscillation especially if the volume is up. Craig Thanks Craig. Yes I do have the ability to turn the incoming signal off when there is no load. But to understand further, what happens when a tube amp goes into oscillation? Oscillation is the output section becoming unstable which if allowed to go on will result in a spectacular spark show from the output tubes and in extreme conditions a loss of output transformer. Some tubes amps can handle no load situation other cannot the safe bet is don't do it! Quote Link to comment Share on other sites More sharing options...
mustang guy Posted March 3, 2014 Share Posted March 3, 2014 Craig, Would a resistor be an appropriate dummy load? If so, what wattage and ohms? Also, is this important on a pre-amp output? It seems like it would be the same thing just a smaller amount. In that case, what would be an appropriate load method for a preamp. The specific reason I ask is I have a source switch I am working on, and almost using. I am not worried about amp load, as I am using a Niles switch and 12v relay. My switch, however, has an off position where the pre-amp and amps are all disconnected. Should I install a resistor across the GND and power on the off terminals? If so, what ohms's? Quote Link to comment Share on other sites More sharing options...
babadono Posted March 3, 2014 Share Posted March 3, 2014 Oscillation is the output section becoming unstable which if allowed to go on will result in a spectacular spark show from the output tubes and in extreme conditions a loss of output transformer. Some tubes amps can handle no load situation other cannot the safe bet is don't do it! Like Bruce said "Bad things, Man. Bad things." Quote Link to comment Share on other sites More sharing options...
babadono Posted March 3, 2014 Share Posted March 3, 2014 (edited) Yes, resistor = dummy load. I would think you would want to match what ever output impedance tap your using on your tube amp. So if your using the 8 ohm tap you use an 8 ohm dummy load resistor. If you can assure there will be no signal drive when the tube amp is switched out you could easily get by with say a 10 watt resistor. But if signal will still be present or possibly present you need to match the output wattage of your amp. 60 watt amp = 60 watt load resistor or greater. As far as loading a tube preamp I will defer to people with more expertise. Edited March 4, 2014 by babadono Quote Link to comment Share on other sites More sharing options...
captmobley Posted March 3, 2014 Share Posted March 3, 2014 Niles DPS-1 I use a pair to switch my corner horns from 2channel to fronts for my HT. The only bad feature is the connections are very small and close together. Quote Link to comment Share on other sites More sharing options...
Don Richard Posted March 3, 2014 Share Posted March 3, 2014 As far as loading a tube preamp I will defer to people with more expertise. There is no problem running a preamp, whether tubed or not, without a load because they are designed to operate into a high impedance. The output loading issue is confined to tube power amps. Quote Link to comment Share on other sites More sharing options...
Taz Posted March 4, 2014 Share Posted March 4, 2014 I had a thought that a speaker selector switch could be used in reverse. Crazy? I have a few that I plan to use in reverse. But I will check under the hood to make sure I only have switches hooked up and don't get no surprise such as speaker protection. Nobody switches my stereos but me. I can not afford to have tube amps damaged at this time. john Quote Link to comment Share on other sites More sharing options...
NOSValves Posted March 4, 2014 Share Posted March 4, 2014 Craig, Would a resistor be an appropriate dummy load? If so, what wattage and ohms? Also, is this important on a pre-amp output? It seems like it would be the same thing just a smaller amount. In that case, what would be an appropriate load method for a preamp. The specific reason I ask is I have a source switch I am working on, and almost using. I am not worried about amp load, as I am using a Niles switch and 12v relay. My switch, however, has an off position where the pre-amp and amps are all disconnected. Should I install a resistor across the GND and power on the off terminals? If so, what ohms's? Hard to say all of that would be amplifier dependent. Higher power the amplifier the higher the wattage required. Usually no need with a preamp... Quote Link to comment Share on other sites More sharing options...
bracurrie Posted March 4, 2014 Author Share Posted March 4, 2014 I have a few that I plan to use in reverse. But I will check under the hood to make sure I only have switches hooked up and don't get no surprise such as speaker protection.I have been told that the switch has to make and break both the positive and ground, which makes sense. Quote Link to comment Share on other sites More sharing options...
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