Members Casey Posted January 19, 2011 Members Share Posted January 19, 2011 Amp is 100watt (60 watt option on a switch). runs on 4 6l6s. broke one of the inner 2 tubes. Can i pull it and another one and still be safe? Amp is an Acoustic Sound Corp Model 165 if that helps. here's a schematic. Halp! Trying to get to the place on time as it is rented and no interbutts on my phone.http://www.schematics-free.com/modules/PDdownloads/display_download.php?img=http://www.schematics-free.com/uploads/PDdownloads/acoustic_165.pdf&title=Acoustic%20model%20165%20Schematic%20Diagram Link to comment Share on other sites More sharing options...
Members eudaimonia02912 Posted January 19, 2011 Members Share Posted January 19, 2011 EDIT: Misread your post. You need to cut the impedance in half if you pull the other tube. I'd guess it would be safe for a show. Some amps can handle you doing this for years. Link to comment Share on other sites More sharing options...
Members Cougar Hunter Posted January 19, 2011 Members Share Posted January 19, 2011 If it has a phase inverter, then, yes, pull both inner tubes. you need to operate at a different impedance though. I forget if you cut it in half or what. Somebody else, chime in! Link to comment Share on other sites More sharing options...
Members Casey Posted January 19, 2011 Author Members Share Posted January 19, 2011 can you tell from looking at that schematic if it has a phase inverter? :[ Link to comment Share on other sites More sharing options...
Members Cougar Hunter Posted January 19, 2011 Members Share Posted January 19, 2011 turn the impedance selector to one setting lower. 16->8 or 8-->4 And, I'm pretty sure your 16 ohm cab would be correct at the 8 ohm setting. I could be wrong on that. Link to comment Share on other sites More sharing options...
Members Casey Posted January 19, 2011 Author Members Share Posted January 19, 2011 fml Link to comment Share on other sites More sharing options...
Members Cougar Hunter Posted January 19, 2011 Members Share Posted January 19, 2011 EDIT: I saw the schematic. You are fine to pull the two inner tubes. Link to comment Share on other sites More sharing options...
Members eudaimonia02912 Posted January 19, 2011 Members Share Posted January 19, 2011 turn the impedance selector to one setting lower. 16->8 or 8-->4And, I'm pretty sure your 16 ohm cab would be correct at the 8 ohm setting.I could be wrong on that. Seems right to me. Having too high of a load isn't such a big deal; it's having too low of load that's the problem, right? Link to comment Share on other sites More sharing options...
Members Cougar Hunter Posted January 19, 2011 Members Share Posted January 19, 2011 BTW, YES the 12AT7 is the phase inverter on that schematic. You're find to pull the inner two tubes, go down to the next lower impedance setting, and rock out. Link to comment Share on other sites More sharing options...
Members Cougar Hunter Posted January 19, 2011 Members Share Posted January 19, 2011 Seems right to me. Having too high of a load isn't such a big deal; it's having too low of load that's the problem, right? The logic is there, but that only applies to solid state amps. Link to comment Share on other sites More sharing options...
Members Casey Posted January 19, 2011 Author Members Share Posted January 19, 2011 It seemed to be fine tonight. the amp only has 8 and 4 ohm settings. It was on 4 ohms plugged into the single speaker in the first place therefore I couldn't go lower. Was that perhaps not right in the first place? It lasted for a 2.5 hour practice with no apparent problem... Someone get back to me on this, it's going to be a couple weeks before i can afford a new set of tubes and a trip to the amp tech to bias it. What can I get away with here? Link to comment Share on other sites More sharing options...
Members nakedzen Posted January 19, 2011 Members Share Posted January 19, 2011 Read here under impedance:http://www.drifteramps.com/safety.html Or here:http://www.londonpower.com/pwr-faq.htm The guys at London Power seem to be against the current way of thinking though: Q: In a magazine Q-A, a player wanted to pull tubes to reduce power, but the "expert" said this would cause a meltdown of the remaining tubes. Of course, it was suggested that the expert's attenuator product was the preferred way to go. Is any of this true?A: This is a person who should know better!Removing tubes from a multi-tube fixed-bias output stage is never a problem. You can remove any number of tubes, and yes, that means you can take one tube out of a two-tube amp; one, two, or three out of a four tube stage, et cetera. This sounds heretical to techs stuck in the mire of convention, but it is something that has been known since tubes were invented.The even-number tube extractions reduce power symmetrically. Neither the tubes nor the transformer will be damaged. Power will be reduced and so will frequency bandwidth - you will lose some bass and some treble. This is the point that switching the impedance selector to a less-than-load setting is supposed to correct, but it is completely subjective whether you should. The only 'should' of the matter, is do I like it this way, or do I like it that way?In the uneven tube extractions, asymmetric power reduction occurs. Conventional thought says "the one tube on one side of the circuit will be trying to match the output of the two tubes on the other circuit half". This is wrong. The single tube can only produce so much power, and that's all it does. It doesn't melt down. The transformer does not blow up.So, what's missing from conventional thought? The realization that tubes are "self-limiting power governors", which was stated in The Ultimate Tone (TUT), and explored in more detail in TUT2 and TUT3. TUT4 explores all of this in great detail. Our "expert" should get a copy.In the end, you can pull tubes to reduce power, unless the amp is cathode biased - then you have to split the bias resistor. In any case, you do not have to worry about the impedance selector either. Link to comment Share on other sites More sharing options...
Members cap'n'crunch Posted January 19, 2011 Members Share Posted January 19, 2011 There was a clip posted a few years ago of a 100 watt Marshall running on one (1) power tube. It actually sounded pretty good. Link to comment Share on other sites More sharing options...
Members Casey Posted January 19, 2011 Author Members Share Posted January 19, 2011 Read here under impedance:http://www.drifteramps.com/safety.htmlOr here:http://www.londonpower.com/pwr-faq.htmThe guys at London Power seem to be against the current way of thinking though: Very interesting. That makes me feel a lot better haha. any other thoughts on this? Slinger I owe you big time, thanks for saving my ass. Link to comment Share on other sites More sharing options...
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