- #4063 [niceday009], 24-05-15 22:26
- #4062 [niceday009], 24-05-15 22:20>>Even using parallel 6SL7 will provide sufficient drive voltage and extended high frequency bandwidth for the 300B.
Very true indeed, Cary only use single section 6SL7 to drive 300B, 6SL7 plate resistance is 40K
I once bought Cary CAD300B, push pull amp, 6SL7 single section drive 300B
最後修改時間: 2024-05-15 22:30:35 - #4061 [johnnykmtang], 24-05-15 21:28I have tried two types of LinLai 300B tubes for some time with shunt regulator at the cathode, i.e., fixed voltage at cathode. I biased it 70mA with 420V B+. The anode-cathode voltage is approx 350V.
Once the 300B tube got warmed up for about 30mins, the idle current start drifting higher. I had to reduce the idle current to 60mA which will be stable over long operating time.
The same happens to the EH and the Russian Gold Lion 300B tubes as well. I don't have the WE ones for testing. With use of RC cathode bias won't have such issue but we need to watch out when using fixed bias.
Johnny -
- #4060 [johnnykmtang], 24-05-15 21:15Should 300B tube to be driven with high power tubes like EL34, and 6V6 because of it's low grid capacitance???
I don't think so. Even using parallel 6SL7 will provide sufficient drive voltage and extended high frequency bandwidth for the 300B.
Johnny - #4059 [johnnykmtang], 24-05-15 18:27M7 schematic
- #4058 [johnnykmtang], 24-05-15 18:13Thanks for Wilson brought up the Miller Capacitance issue about the 12AX7 tube. This tube have been widely used in the high end audio amplifier for many decades.
I have a clone Marantz 7 phono + line preamp. I analyzed the phono circuit with the LTspice simulation. I had the NFB network cut out from the the circuit. The -3dB at the grid of the second 12AX7 is at 50kHz. If a cathode bypass capacitor is added to the 4.7K cathode resistor, the -3dB will be at 24kHz.
The original M7 phono circuit, the 2nd stage 12AX7 is having a 100uF capacitor.
The overall frequency response of the Marantz 7 preamp actually is real good >100KHz because it employs the NFB.
Johnny
最後修改時間: 2024-05-15 18:21:39 - #4057 [johnnykmtang], 24-05-14 07:09#4053, Hi Niceday,
I would say using the CCS-shunt voltage regulator makes the amplifier sounds more natural with very low background noises.
I like it.
Johnny - #4056 [niceday009], 24-05-14 00:11
- #4055 [niceday009], 24-05-13 23:46
中國制做,一貫風格,有型無.....
二次大戰日本人用嚟折磨囚犯
最後修改時間: 2024-05-13 23:49:04 - #4054 [niceday009], 24-05-13 23:12
Worth listening
300B single to drive the huge speakers
最後修改時間: 2024-05-13 23:13:37 - #4053 [niceday009], 24-05-13 22:18Johnny, How much difference when you add shunt regulator ?
- #4052 [niceday009], 24-05-13 22:15
- #4051 [johnnykmtang], 24-05-13 08:46This is the second pair of Mission 776 MC-Phono preamp with two 24Vdc CCS-Shunt regulator board.
The first pair phono preamp boards were given to my friend. He put them in a very nice chassis. He loves it a lot because it has very low noise, high gain, and most importantly very natural sound in comparison with this D3a LCR phono amp.
Johnny
最後修改時間: 2024-05-13 08:47:40 - #4050 [WilliamsonAudio], 24-05-10 01:12我都覺得Pathons會有足夠嘅頻寬。因為已經是一個產品。
我有時間再看清楚那一條公式。是否有一些特定條件。 - #4049 [niceday009], 24-05-09 22:04要drive 300B Miller Capacitance 一般推動胆內阻要20K内越少越好,12ax7 屏推300B唔得,用12ax7 接12au7 cathode follower, bandwidth 應該Pathos 考慮過屬於可接受範圍
- #4048 [WilliamsonAudio], 24-05-09 13:49
https://pearl-hifi.com/06_Lit_Archive/02_PEARL_Arch/Vol_08/Sec_31/2071_The_Miller_Effect.pdf
12AX7 -3dB =12.4kHz
但我用LTSPICE 去 Sim,
又沒有那麼低。 - #4047 [WilliamsonAudio], 24-05-09 08:10補上圖片
- #4046 [WilliamsonAudio], 24-05-09 08:10下面是臺灣張文俠的一段。
假設我們用一支p較高的真空管来推動300B,例如ECC83/12AX7,根擦真空管手冊得知ECC83/12AX7的屏
BErp在屏壓250V時篇62.5KS2。
-般三極的屏極負载電阻RL大多設定在屏内阻mp的3~7倍之間,我們取其中間值5倍爲屏極負載電阻,mp的
倍爲屏極負戴RL,即:
62.5K2x5=312.5K0
代入上式:
fc=159/RL{Cin+Cgp(1+A))
=159/0.3125{9415(1+3)]
=7.37KHz
----
如果屏阻用約100k, 頻應也有約20kHz - #4045 [WilliamsonAudio], 24-05-09 07:37#4043
我記得是12AX7 的頻應不高(沒有回輸),原因是內阻高和Miller effect.要用回輸來增加頻應。
所以後期的設計主流,就是用低內阻膽。當然沒有回輸設計也是主因之一。在無回輸情況之下,頻應也要足夠寬闊。在Low Tim 失真的石機設計。也是有這一條設計原則。
ARC, 開頭用12AX7.之后是6DJ8.現在是6H30
最後修改時間: 2024-05-09 07:42:59 - #4044 [johnnykmtang], 24-05-09 07:19In general, it is better to drive the Interstage transformer (IT) with low impedance. It is a lot easier to get better performance of the IT with lower inductance. Therefore, using the 6SL7 or 12AX7 isn't good with inductive load. The limitation is the IT.
Med/high gain triodes like D3a, C3g and 5842 which has low plate resistance would be nice to drive the IT or plate choke.
Johnny
最後修改時間: 2024-05-09 07:32:48 - 下一頁 (2 of 204)
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