为胆疯狂 在 2003-9-13 3:29:26 发表的内容
单端电路跟本就不全在A1和A2累电路形色，A1和A2只能在推挽中，如果在单端有就已经好大失真了
间单来说单端就系用一只管来工作正负两个波，在电路上还要看工作电压才能定它的静态电流，才能做好达到好声 |
怎么会没有 A2 ! 查清楚再说吧. 像 805 管就一定工作於A2. 845 可设计於 A1 或 A2. 不错 A2 失真是比较失真大，所以我说何必为几W 放弃 A1 音质. 你测一下它在满功率时屏流跟静态比较一下便知. 以下二个 Link 就是在讨论 A2 - 会英文的话请看看 :
http://db.audioasylum.com/cgi/m.pl?forum=set&n=10850&highlight=A2&r=&session=
http://db.audioasylum.com/cgi/m.pl?forum=set&n=567&highlight=A2&r=&session=
The basic operating principle of controlling current flow in a tube (hence controlling voltage) depends upon the grid of the tube having a negative voltage potential with respect to the cathode. The grid is placed between the cathode and anode. Electrons are boiled off the cathode and are highly attracted to the positively charged anode. The more negative charge on the grid there is, the less current flow there is between the anode and cathode as the negative charge "repels" (poor term) the electrons that are trying to get from the cathode to the anode. The more positive charge there is on the grid, the less resistance there is to the moving electrons and the more current flow.
Driving a tube into A2 means that you are applying a positive voltage on the grid with respect to the cathode for part of the audio signal cycle. What this does is create current in the grid structure of the tube by attracting some of the electrons from the cathode emission. The anode is still significantly charged more positive so it still draws the majority of the current flow. Some of the beefy transmitting tubes like the 811 and 572 are designed with sturdy grid structures to handle the current that A2 operation induces (this was done with RF transmitting in mind, fortunately, they can handle class A2 for audio frequencies as well). A tube like the 2A3 does not have as sturdy of a grid structure. If you drive it into A2 regularly, you will cause increased wear on the fragile grid structure. Eventually, the grid burns up/blacks out and can no longer control the current flow. FWIW, when there is no signal on the grid, the tube is running at the maximum amount of plate power dissipation that the cathode bias allows. When you apply a signal on the grid, it swings more negative for part of the cycle thereby reducing current flow. So, on average, the tube runs cooler when it is providing power into a load. Practically speaking, the tube will last longer driving a load than it would sitting at idle. Although, that means doodley squat if you frying the grid structure driving into class A2 continuously.
4 watts rms roughly equals 8 watts peak power. RMS is the effective continuous power. An 8 watt RMS 300B amp will have 16 watts of peak power. Peak power is a relatively worthless number and if you are judging by specs, it should be ignored.
Tom §.
