review33 - 影音天地: 膽機細有細玩

#55 [johnnykmtang], 24-12-02 18:00
Hi Cody,

Ran the analysis of the 6SJ7 (triode mode) with choke load. The result is excellent.

B+ 185V, idle current : 8.8mA, output : +/- 40V.
THD : 0.25% (H2 0.25%, H3 : 0.02%)

The Hammond 156C plate choke (150H) is rated 8mA. Therefore, you may reduce the 6SJ7 current to 8mA by changing the cathode resistor to 680 ohm.

The amp should sound pretty good indeed.

JOhnny
#54 [CodyChan], 24-12-02 13:00
#53.
Hi Johnny,
FYI
#53 [johnnykmtang], 24-12-01 16:24
Hi CodyChan,

Wondering if you would share the schematic of your 71A amp. Love to learn the circuitry.

Johnny
#52 [CodyChan], 24-12-01 11:32
剛從日本回來, 上星期沒空回覆.
先祝各位細膽用家來年萬事勝意!
遲啲再更新我部製作中71A資料.
#51 [johnnykmtang], 24-11-27 00:50
Here is the schematic
#50 [johnnykmtang], 24-11-27 00:40
Helena 45 baby 改造後再次登埸

Changed the 6SJ7 plate 47K resistor to 27K for better linearity. Screen voltage : 120Vdc.
Fine tuned with FFT at oscilloscope for minimal distortion from 6SJ7.

The output transformer is Lundahl LL2766 50mA.

最後修改時間: 2024-11-27 00:43:46
#49 [BB1668], 24-11-24 17:44
我部机的輸出牛只有OPT-879

最後修改時間: 2024-11-24 17:44:25
#48 [johnnykmtang], 24-11-23 03:04
Hey Cody,

I don't think he LL9202 transformer will fit in your VT-25 amplifier. The size is way too big for it.
#47 [CodyChan], 24-11-22 14:32
其實依家部 VT-25 都好滿意, 不過轉吓新牛都好嘅.
#46 [johnnykmtang], 24-11-21 17:24
Hi Cody,

The VT-25 (10Y) tube plate resistance is approx 5K. The datasheet recommends using 10K load for 1.5 watts output.

Johnny
#45 [Welborne], 24-11-21 16:19
其實我手上仲有幾部超微型輸出機

Colin 5687s: 0.3w
Colin 5687 dc 5687: 0.9w
Colin 417a-dc-71a: 0.7w
日本 71a-Vt62 se: 4w
日本 6j5 - VT25: 1.5w
日本 Aa-Ca: 0.2w

以上機器主要是配合我手上最少效率95db-100db (50hz above)的揚聲器系統，有些可能要「打茅波」50hz加個subwoofer才能享受到這些蚊蠅輸出膽機帶來夢幻般的聲音，但如果不聽大棚音樂，其實不用開subwoofer，已經大聲到我諗一般屋企隔籬屋已經投訴，這不是一般玩法，但我絕對不介意。

還有一部 300B單端，輸出正路大概8W, 最近換了一對新嘅金音錸300B膽，聲音的確進步不少，尤其是細緻度，但跟以上的蚊蠅輸出機比較，味道還是相距甚遠，不過有8W應用範圍始終比較多一些，因為手上還有一些效率比較低的喇叭要服侍（91db對我來說已經是非常低效率)

最後修改時間: 2024-11-21 16:38:25
#44 [CodyChan], 24-11-21 14:11
LL-9202 price...
#43 [CodyChan], 24-11-21 13:55
#41.
Not yet!
Considering LL-9202 or LL-1620 for my lovely VT-25 SE.
#42 [gogo2010], 24-11-20 17:28
Thanks Welbrone 兄
#41 [johnnykmtang], 24-11-20 16:56
Hi Cody,

Have you bought the Lundahl OPT?

Johnny
#40 [CodyChan], 24-11-20 15:31
原來依家買Lundahl 牛有這東西送的!
#39 [Welborne], 24-11-19 15:18
Timbre of Sax才對
#38 [Welborne], 24-11-19 15:13
如果我冇記錯，應該係已經執咗嗰間本地錄音TIS 嘅其中一隻CD，好似叫做 Sound of Sax
#37 [gogo2010], 24-11-18 23:50
Re-#10
用耳筒聽好好聲，請問師兄唱片名稱，謝！
#36 [niceday009 ], 24-11-18 20:31
#34

我用Amorphous 及Hi B 材質分別做interstage, 非晶快速及細節好但厚度沒有Hi B厚，Barkhausen effect相信兩種芯都有，估計係coercivity force参數之大分別造成，Amorphous coercivity 低過Silicon Steel 10倍以上

依家用Nano Crystalline 但未試声而測試性能已經比兩款都更好，預期可到best of both worlds

但銀綫牛本人覺得只係賣卓頭，而且貴到冇譜

最後修改時間: 2024-11-18 20:40:30
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