經過了一百多日子的等待 我的AMP老弟終於從日不落國開船過鹹水到美麗的福爾摩沙 在接到他已經到台灣的通知書後，趕緊在星期六一早，搬家嫁娶入厝皆宜的大好日子裡，選好良辰吉時到大安郵局接機。花了吃奶力氣把這個22公斤卻有點不良於行的AMP老弟請到我停在百公尺外的車裡 再以迅雷不及掩耳之勢，興沖沖的跑到光華商場買個升壓器，把110V升到240V服侍這個AMP老弟。 終於，我和我的拜把兄弟，PRS，兩人互望後鼓起勇氣把他PLUG IN，刷了第一個CORD，隨便跑一點音階，頓時我的嘴角終於微微上揚，也不管汗水已經從我的額頭流到了褲頭，我用我微紅的的眼眶，和PRS巴底兩兩相望，"就是這個聲音！就是這個聲音！我兩不需言語， 卻由彼此心中發出會心的一笑" 隨後我倆又陪著AMP老弟渡過了一些快樂時光，只是心中都默默的想"啊怎麼那個GAIN和LEVEL旋鈕好像沒啥作用，怎麼轉都沒變化"，卸下背板，看到前級的兩根12AX7老弟露出隱晦的橘光，不似後級那兩根6 L6老哥和另一根12AX7同鄉那麼意氣飛揚的綻放微亮卻充滿自信的光芒，我雙手俯著12AX7兄弟（後來發現他們不是雙胞胎，一隻叫Fender，另一隻叫Edicron），辛苦你們了，好好休息吧。 終於經過了一個夜晚的煎熬，今天就像接到急急如律令，快馬加兩鞭的到西寧市場找尋他們的宗親們，前衛音響，沒開。隔壁那間，也沒開。也罷，信步踏入西寧市場二樓，最後終於在一家店中找到來自偉 大中國的12AX7，快馬加三鞭的回家換上新兄弟。 我和我的PRS又重新對AMP老弟臨幸，也不管今天溫度已經到達三十七度七，隔壁鄰居已經在拍窗抗議，我倆就自顧自的海皮。終於我發現我需要冷靜，便和AMP老弟說，等我一罐啤酒的時間我就再來看你， 台啤的清涼讓我如久旱逢甘霖，再拿起我的PRS巴底準備繼續HAPPY，可是這次刷下去好像有點問題，那個聲音好像被鎖在厚厚的保險箱裡。告訴自己別心急，趕快按照SOP Check One Two Three。結果看到6L6老哥和那支12AX7小同鄉不再綻放光明。 故事說到這裡，以下是我的問題，希望十方大德前輩兄弟可幫我解疑。 現在後級三根真空管都不會亮了（6L6*2，12AX7*1），在後級電路版上那三個保險絲也沒燒壞的痕跡，在那段奪命的台啤時間中，我沒聽到任何的聲音，以及沒聞到任何東西燒掉的味道，那還有什麼可能的 地方嗎，請不吝指點一二，謝謝
Zakky, </font><blockquote>引言:</font><hr /> ,,前級的兩根12AX7老弟露出隱晦的橘光，不似後級那兩根6 L6老哥和另一根12AX7同鄉那麼意氣飛揚的綻放微亮卻充滿自信的光芒 </font>[/QUOTE]這算正常吧....後級一般會比較亮啊!!,,,, </font><blockquote>引言:</font><hr />,,,,找到來自偉 大中國的12AX7，快馬加三鞭的回家換上新兄弟,,, </font>[/QUOTE]所以你是換了前級管嗎???... Did you checked the biasing?? As the bias is set lower the amplifier will operate closer to Class-B. The tone would be a little "thinner" or less full since the amplifier would not be hitting it's output tubes saturation point quite as easily. If the amplifier is biased very low, higher volumes will encounter crossover distortion. Properly biased in a lower range, the overall clean headroom of the amplifier will be greater. As the bias is adjusted higher, toward Class-A operation, the tone will be "thicker", "fatter" or more full. The overall headroom of the amp will be less, since the signal level at the grid, added to the bias voltage will be closer to the tubes saturation point. The amplifer will distort easier (musical distortion, not that nasty crossover distortion stuff) If you amp set it too low, then no harm can be done. If the bias is set too high, then there is the possibility that the output tubes will not be able to dissipate the extra heat, the plates will start to glow. The tubes will do a major meltdown. There is a possibility of power transformer and or output transformer failure if the failing tubes short. .... Edited from "The Tube Amp Book" 4th edition by Groove Tubes. The proper method of biasing a tube amplifier requires a signal generator, an oscilloscope, a volt meter and preferably a dummy load resistor. First, remove the power tubes and measure the bias voltage at the grid (usually pin 5). Adjust the bias voltage to the most negative voltage (-50 is more negative than -40) then install the power tubes. The tubes are now over-biased and are running cool with lots of cross-over distortion. Now, connect the proper impedance load to the output of the amp and apply a 2000 Hz sine wave to the input. Turn the volume of the amp up to 70% output, or just prior to clipping. View the output waveform on the scope. Notice the notch indicating cross-over distortion in the signal. Adjust the bias control gradually until this notch just disappears. The amp is now properly biased. Obviously the specifics will vary from amp to amp and somewhat from tube to tube. This is certainly not the all inclusive tutorial on biasing tube amps, but the basic information is correct and can be applied to most any tube amp.