We have modified Sunaudio SV-6L6SX to adapt the use of the small but famous 45 tube on the output stage. The reason is that 45 tubes, especially  the old globe style tube are said to produce the most spacious and gorgeous sound in the direct heat triode family tube. We have make audition on several 45 output tube amplifier (Yamamoto A-08s and other as well) and confirm the true fact.

我們把一部SV-6L6SX改装,輸出管换用名氣相當高的45三極灯胆。理由很簡單,45這類極品,尤以舊庒波型胆為例,是三極管系列中最能發掘出絕妙色音及浩瀚音場的妙胆。這個傳說在監聽其他名器如YAMAMOTO A-08S 等鉊機得到証實。

We inspect the circuit construction on Sunaudio products and proceed our plan. The end result is very encouraging and probably exceed out expectation as well. The 45 tube gives a smooth and fresh feeling throughout the audio spectrum. The tonal balance is exceptionally well it effortlessly extends beyond on both the low end and high range. The sound stage is huge with every instrument or performer in its exact location. We can hear more details and something that is not noticeable before from our familiar test CDs. The audition is very exciting and enjoyable, and it make us conclude that 45 tubes are one wonderful audio tube that deserve much better attention and praises.

在深入研究Sunaudio列系的線路後改裝落實了,結果令我等十分鼓舞,喜出望外。這個45灯胆在全頻音域中都有圆滑流暢,生動鮮活的表現,音準平衡度異常出色而高低頻兩邊伸展亦似乎是毫不費力,音場巨大,樂器與演奏者定位明確。從熟悉的CD中可以聽到更多細節及以前聴不到的弱音。這次監聽可以說是極為精彩及令人回味,亦從而令我們得出一個結論~這個45妙灯值得各位密切留意及推崇。

 45及80波月旦

  schematic diagram of SV-6L6SX

  schematic diagram of SV-2A3

把SV-6L6SX改裝用45腔十分容易(你懂的話)。兩個線路以較下可以發現它們是大同小異的,差別只在不同的輸出牛及在SV-6L6SX中的回輸電阻,SV-2A3有交流噪音調校器及不同數值的陰極電阻,兩款機種都共用同一款電源牛,不過功率管燈絲電壓接法稍有不同而已。

將SV-2A3線路作為藍圖,我們將SOT-525換為SOT850,把棕色線(5kohm)接到輸出管的屏極,次級如常接到喇叭座(黑線接黑色插座,黃色線接紅色插座),那2支綠色大電阻要換成1.5K25W的品種。要確定所有其他的接線及零件都銲妥及正確無誤,再三確實後就可以完工了。把新的45管插入管座開機,暖機後調校交流調控器把噪音至最小,最後坐下來欣賞辛勞的回報。

Modification of the SV-6L6SX to use 45 tubes is not so difficult (if you know how of course). Compare the two schematics you can find the construction is nearly  the same, with only difference in the choice of output transformers, some additional feedback resistors on the 6L6SX,  the use of hum pots on the SV-2A3,and also the values on the cathode resistors. The same power transformer is used for both amplifiers with only the difference in the connection for the filament of the power tubes.

Using the SV-2A3 schematic as blue print we simply replace the SOT-525 with the SOT-850 with 5 kohm (brown wire) connected to the plate of the output tube. The secondary of the SOT-850 is connected to the output in the same way, black wire to ground (black terminal) and yellow wire to the red terminal. The two cathode resistors(big green monster) for 2A3 tube (750 ohm 50W) are replaced with the same type but two 1.5Kohm 50W instead. Make sure the connection of all the wirings co-response to that of the SV-2A3. Double checked and then mission accomplished. Just plug in new 45 tubes to replace 2A3 tubes and adjust the hum pots to get minimum hum. Sit back and enjoy.

兩款機種使用的電阻是不同的,SV-2A3用AB電阻,而SV-6L6SX用KAWAI,音色不一樣,其實你可以依自已喜好換用不同牌子的零件。

最簡單直接的升級方法是換用舊裝的波晅,我們常備各種牌子予你選購。

(Resistor used on the original Sunaudio SV-6L6SX is different from that of the SV-2A3 where AB carbon resistors are used. You can actually try to use different type of components to suit your personal preference.)

 

 

我們經常被問及有關45與2A3可否互用的可能性,答案是可以及不可以-視乎機種的設計及電源牛大小問題。我們並不鼓勵用家嘗試把2A3放在古董45放大器上,但用在近代機種如SUNAUDIO45是可行的。原因這件機種的火牛是可以提供2A3管燈絲所需2.5A的電流量,而45管子只需約1.2A而已,而陰極電阻較高的數阻(1.5K歐姆)亦會把屏流限制至一樣甚至更少。由此可見,若把2A3管子放在古董45機種上電源牛很快便會過熱,因為現在燈絲電流加倍了。

We sometimes come across the question of whether it is possible to put 2A3 tubes on the amplifiers that are using 45 tubes and vice-versa. The answer is yes and no depending on the construction of these amplifiers. We do not encourage you trying 2A3 tubes on vintage unit that are using 45 tubes , but it is quite alright to use on some modern amps such as our Sunaudio 45 tube amplifier. You can see that the power transformer is designed to use for the 2A3 tube which has a filament current of 2.5 amps whereas it is only 1.2 amps on the 45 tube. The higher value of the cathode resistor (1.5 kohm) automatically reduces the plate current to a lower value which is the same, or even less when the 2A3 is inserted to replace the 45 tube. If you put 2A3 tubes on vintage 45 tube amps the power transformer heats up quickly due to the excessive drawn by the filament since now the current is now double.

You must examine the circuit of your amplifier carefully and understand what you are trying to do before you swap the tubes. It is best to make more study and research, and ask for help from some competent person before you do the experiment.