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| 影音天地主旨 ﹝請按主旨作出回應﹞ 下頁 尾頁 | 寄件者 | 傳送日期
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| [#1] 6F8G 噪聲 小弟剛在淘仔買了一對古董tung sol 6f8g來代原先的6sn7, 但發覺高頻噪聲大,30cm耳對著高音聽到si...si聲,為什麼呢？  |
kit271 正式會員183.xxx.xxx.78 |
2020-11-29 09:36 | |
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| [#2] 6F8G 噪聲 聲音無問題的,還彼滿意, 只是有噪音不爽 |
kit271 正式會員 183.xxx.xxx.78 |
2020-11-29 09:43 |
| [#3] 6F8G 噪聲 Microphonic or parasitic oscillation? |
mcc2018 會員 218.xxx.xxx.114 |
2020-11-29 10:01 |
| [#4] 6F8G 噪聲 Also need to take care of the maximum voltage between cathode and heater. |
mcc2018 會員 218.xxx.xxx.114 |
2020-11-29 10:28 |
| [#5] 6F8G 噪聲 Lastly, shielding may be required for the top cap grid. |
mcc2018 會員 218.xxx.xxx.114 |
2020-11-29 10:48 |
| [#6] 6F8G 噪聲 好的, 等我用示波器看看是什麼噪聲來 |
kit271 正式會員 183.xxx.xxx.78 |
2020-11-29 10:52 |
| [#7] 6F8G 噪聲 個轉插吸noise? |
BB1668 會員 45.xxx.xxx.19 |
2020-11-29 11:55 |
| [#8] 6F8G 噪聲 #4 支6F8G我是用在Cathode follower, 用來推kt88, 無錯他的k/f 電壓有250v之高,但我也把燈絲電壓也提升了200v, 即只差50v, 問題不大 最後修改時間: 2020-11-29 12:48:00 |
kit271 正式會員 183.xxx.xxx.78 |
2020-11-29 12:45 |
| [#9] 6F8G 噪聲 seem the high frequency rolls off characteristic has been changed 呢度咁多高手, 畫張線路圖出嚟應該有人幫到你嘅 haha as u said ..only 30cm.. lucky 最後修改時間: 2020-11-29 13:04:44 |
hahayanyan 正式會員 49.xxx.xxx.53 |
2020-11-29 13:03 |
| [#10] 6F8G 噪聲 #8 as cathode follower, the heater is better to be pulled to the dc voltage mid-point of the two cathodes. May need to check the KH spec. of 6F8G. 最後修改時間: 2020-11-29 14:00:02 |
mcc2018 會員 49.xxx.xxx.228 |
2020-11-29 13:55 |
| [#11] 6F8G 噪聲 if it is a schematic with component value of that section of your amp, then surely someone at here may able to help..haha it may help, if knowing what speaker you are using ..u heard sisi from the tweeter.. some tweeter kick in at not too high of the high frequency range too 最後修改時間: 2020-11-29 14:16:59 |
hahayanyan 正式會員 49.xxx.xxx.53 |
2020-11-29 14:14 |
| [#12] 6F8G 噪聲 線路,the replacement of 6SN7 is the Q3, the r12 and 13 I have modified to 47k, Vcc is around 450v  最後修改時間: 2020-11-29 14:33:38 |
kit271 正式會員 183.xxx.xxx.78 |
2020-11-29 14:17 |
| [#13] 6F8G 噪聲 may be some high hand..can help i guess we need to do something at "1" and "4" |
hahayanyan 正式會員 49.xxx.xxx.53 |
2020-11-29 14:26 |
| [#14] 6F8G 噪聲 Scope screen **The volume is short to ground already 個noise freq. 不太稳定, 由4k至10k上上落落, 有時突然有一兩秒會細左,之後又高番 轉番用其它JJ, EH膽完全無事  最後修改時間: 2020-11-29 14:32:10 |
kit271 正式會員 183.xxx.xxx.78 |
2020-11-29 14:29 |
| [#15] 6F8G 噪聲 Tough... 4 to 10k..., seem we cannot add filter at the output side And already 100k down to 47k at r13 May be the grid of that tube... Is too old haha However it is only 30cm... 最後修改時間: 2020-11-29 14:36:01 |
hahayanyan 正式會員 49.xxx.xxx.53 |
2020-11-29 14:33 |
| [#16] 6F8G 噪聲 Sorry, #14 is cased by 接觸不良,我再用8ohm dummy load, 見到了100khz左右起震  |
kit271 正式會員 183.xxx.xxx.78 |
2020-11-29 14:53 |
| [#17] 6F8G 噪聲 Then add some filter may be feasible around those 2 5k resistor if u care...but may not related to your issue why not if it is at that range .... and do something at 1 & 4 最後修改時間: 2020-11-29 15:03:51 |
hahayanyan 正式會員 49.xxx.xxx.53 |
2020-11-29 14:56 |
| [#18] 6F8G 噪聲 #14, it is typical parasitic oscillation， 6F8G 係一支不平衡既雙三極管, 佢用cap grid 那邊個 grid plate capacitance 係超低的，目的係在高頻應用時直接連接到大型的tune circuit, 在音頻應用時是需要加grid stopper resistor的, 但閣下的應用是balance splitter. 咁樣用一支雙管係有點麻煩，除非用兩支半份6F8G。 |
mcc2018 會員 49.xxx.xxx.228 |
2020-11-29 14:57 |
| [#19] 6F8G 噪聲 為今之計，先阻止寄生震盪，如下圖，加Rg=100K，先試cap grid那邊。  |
mcc2018 會員 49.xxx.xxx.228 |
2020-11-29 15:06 |
| [#20] 6F8G 噪聲 Grid stopper 我有落但只是1k, 之前我有經驗處理過這100khz起震,係同功率放大即kt88和output transformer有關連,非常難攪, 我試過將grid stopper升到去10k個震幅細左一半,但聲音變得很無生氣,到最後我要在每隻kt88的grid同陽極加粒470p mica先攪掂,應該係一種trade off 若mcc兄所講係6f8g有這種特性,我不會再為左佢又改機,我聽番一般新膽好了 |
kit271 正式會員 183.xxx.xxx.78 |
2020-11-29 15:17 |
