左圖 : 表頭超多的TV-2
中圖 : 最通用的TV-7D/E
右圖 : 能測Gm的 I-77 (相片未照)
本文
很多人詢問測管機,還有貨嗎?
兩三年前國外進了一批測管機,其中TV-7約近30部,後來僅保留了品相最美的一部,最後,因為竹科的好友翁先生有需求,到頭來,連一台也沒留下,倒是,更為高價而罕見的TV-2看圖片,I-77都留下來,許多行家都和我一樣,這種測管機,多數成了非賣品,這些管機有何特點?
(1)TV-7 :
手頭上沒有TV-7的網頁說明,因此,套用國外網頁對於TV-10的說明:
the TV-10 is a mutual transconductance tester designed by Hickok.
 | Uses the mutual transconductance method of measuring tube quality. This is the most reliable method known for assessing tube quality. The TV-10 reads the mutual transconductance directly on the meter in micromhos while the TV-7 only reads a relative number on it's meter |
上述的原文翻譯如下:
TV-10用測量Gm的方式來決定真空管的品質,量測Gm為眾所皆知最可靠的真空管品質測量方法,TV-10直接由表頭上讀出Gm值,單位為umhos(微姆歐),而TV-7只能讀出其特殊表頭上的相對數值.
(2)TV-2 的特點如下 :
(1)底下為國外網站中對TV-2的描述,錶頭特多,在此借花獻佛:
The TV-2 was designed by Hickok for the US military. This an impressive looking tester with no less than 5 meters on the front panel. It takes a little longer to set up than most testers, but should give more accurate results than most testers. Of course, this tester uses the transconductance method for measuring tube quality. I don't recommend this tester for someone who is not technically savvy. It takes a bit to set it up correctly. This tester is well suited for the audiophile or antique radio enthusiast.
TV-2有6個表頭,看起來很過癮,而且使用量Gm的方式測管,非常精準,但是因為各種設定非常複雜,適合於對音響有非常狂熱之人來使用,這麼說來,我們豈不應該人手一台?
(3)I-77 的特點如下 :
This portable tube tester was designed by the Hickok for the U.S. Army. It is rugged and highly portable. Hickok tube testers have the reputation of being the best ones ever made. They are highly superior to the "emission" type tube testers; test results are much more reliable (ie. if the tester says the tube is bad, its bad. If the tester says the tube is good, its good.) Virtually all Hickok testers are of the mutual transconductance type, so you really can't go wrong with one.
Some of the key features of this tester are:
| Measures mutual transconductance which is the most reliable method of testing tubes known. |
| Tests most antique type tubes such as 45, 50, 2A3, 6B4G, 01A, 99, 6L6 etc. Also tests many Western Electric types such as 274A/B, 300A/B, 350A/B. (This tester is most well suited for testing older types. There is no data available for newer types such as 6CA7, 6550, 7027A, etc. If you need to test these types, don't buy this tester |
| Read transconductance directly or use "Good ? Bad" scale |
由原文翻譯,I-77幾乎是天下無敵的測管機,直接讀出Gm值,而且"(ie. if the tester says the tube is bad, its bad. If the tester says the tube is good, its good.) "如果I-77說這支管子是壞的,它就是壞的,說管子是好的,它就是好的",像不像測管機中的大師?
由上面這句話,顯然在暗示,"某些測管機",即使測量出管子故障了,還不見得是故障,難道他說的是TV-7嗎?
Gm量測DIY
由上所述,測量Gm的測管機,為最精準的測管機,而且,目前行家收集的,多是這種有Gm錶頭的測管機,可惜目前市面上這類的測管機真的很少,即使有,價格可能也不便宜,喝杯牛奶或許不需買頭牛,但是自己養的牛,應該比較容易控制牛奶的品質吧.
(1)先講最簡單的吧,如果你想測管,又沒有TV-7,建議你買個三用電表,就可以簡單配對,效果可能近似於TV-7吧,這種方式就是類似電晶體的直流分析,查個典型運用值,加個B+,加個陰極電阻,就可以測量,將柵級接地,量到的陰極電壓,除上陰極電阻,就是屏流,紀錄每顆管子的陰極電壓,就可以用來測管,夠簡單吧!
(2)要自己測量Gm會很難嗎?
不會,不過需要一些簡單的設備.
首先,Gm的定義為:dIp/dEg Ep=Constant.
因此,Gm類似於電晶體的小訊號分析(AC),首先,類似(1)的方法,可以將直流部分完成,其次,加個小訊號到柵極,再由屏級上的電阻量得屏流,Gm就等於ipac/egac.
實際測量,效果如何呢?
典型應用值:100V,0V,11.8mA,Gm=3100umhos
250V,-8.5V,10.5mA,Gm=2200
測量得 : 111.5V ,0V,Gm=2857 umhos
100V,0V,Gm=2912 umhos
(B)本站前級的6AB4: 看圖片
典型應用值:100V,-5V,3.7mA,Gm=4000
250V,-12V,10mA,Gm=3900
測量得 : 147.7V ,0V,Gm=3609 umhos
(C)試試地下室淹水的6AK5,不同廠牌,效果如何? 看圖片
Triode Connection : 典型應用值:180V,-6V,6.5mA,3500umhos,u=23.3,Rk=925
Rk用910,(A)Sylvania 6AK5 : 測得 Gm=3622umhos (直流控制 Ec=-4.6V)
(B)GE 6AK5: 測得 Gm=2988 umhos
因為偏壓調的不好,但可以清楚知道兩者Gm有顯著差異
(D)6N1P:典型應用值: 250V,Gm=3500-5500umhos,Rk=600,u=35+-8
第一次測試 : Gm=3923 umhos 看圖片
第二次測試 : Gm=3963 umhos
第三次測試 : Gm=3900 umhos
第四次測試 : Gm=3963 umhos
可見這四支管子有多好,Gm非常接近.
結論 : 剛開始量測時,工作點與典型應用值有頗大差異,但可以看出其關係,當條件設立較嚴謹時,幾乎可以完全與原廠數據完全相同.
當數量夠多時,Gm配對的群組就可以產生.
最好的測管方法,Gm讀值的測量,會難嗎?一點也不! (2005-01-03)