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| [#5003] 單端胆機同好會 #4995 Hi Bambino 師兄。 DHT 燈絲也是信號的一部份。所以燈絲供電的質量和方法，都會直接反映在音質上面。而你分享實驗的經驗絕對係寶貴。 最後修改時間: 2025-04-03 08:22:39 |
WilliamsonAudio 正式會員182.xxx.xxx.249 |
2025-04-03 08:20 | |
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| [#5004] 單端胆機同好會 在作品上加入手動偏壓調節或自動偏壓調節，是更能穩定保持膽的音色及狀態。 |
新老手 會員 59.xxx.xxx.92 |
2025-04-03 09:00 |
| [#5005] 單端胆機同好會 #5001, 呢幅soft start regulator, 是否出自Morgan Jones 本膽機天書？ |
Baker.Steven 正式會員 203.xxx.xxx.3 |
2025-04-03 10:55 |
| [#5006] 單端胆機同好會 #5005 這個電路我第一次見係在Elektor 1987 年SRPP 前級。 這個圖就是從這個文章找出來的。 LM317 網上相信也有好多類似的設計。但需要作出一些改動。所以應用圖上的線路就更加直接。因為已經設計驗證。 可能Morgan Jones 書上面也有。但我也不能確定。 最後修改時間: 2025-04-03 13:08:10 |
WilliamsonAudio 正式會員 182.xxx.xxx.249 |
2025-04-03 13:06 |
| [#5007] 單端胆機同好會 各位師兄好奇一問，發熱線加咗time delay咁電子管屏極係咪都需要有相關設備。如果係，雙方嘅延遲時間係咪要一致定係要一先一後。 |
DY2036 正式會員 182.xxx.xxx.64 |
2025-04-03 13:57 |
| [#5008] 單端胆機同好會 大家講的是soft start = 軟啟動 = 電壓緩慢上升。不是delay startup = 延遲啟動。它們是兩件不同的事。 |
羅密歐 正式會員 203.xxx.xxx.160 |
2025-04-03 14:56 |
| [#5009] 單端胆機同好會 唔好意思講錯咗應該係軟啟動先至真。 |
DY2036 正式會員 182.xxx.xxx.139 |
2025-04-03 14:59 |
| [#5010] 單端胆機同好會 #5002 非常同意voltage regulator沒有軟啟動的功能. 我只係話可以限制開機時產生的浪湧電流. 舉例, 300B燈絲電壓5V. 1)使用VR時開機一瞬間立即提供5V (on cold filament, ie low resistance), 電流會短暫大過1.2A (有current spike出現) 2)沒有VR時開機,因剛開機loading還很底,輸出電壓會短暫太過5V (on cold filament again), current spike比1)更大. 所以VR只可限制浪湧電流,不能完全消除. 可能我喺#5000寫得吾夠清楚. 我覺得slow-start是有效的方法. 只是沒有slow-start機制時,使用適當的PSU regulation或smoothing都會有幫助減少對DHT的傷害. 註: case 2沒有使用VR需要從新調整輸出電壓至5V (at equilibrium) 最後修改時間: 2025-04-03 15:31:55 |
bambino 正式會員 210.xxx.xxx.231 |
2025-04-03 15:30 |
| [#5011] 單端胆機同好會 #5007 燈絲供電用slow-start目的是保護和延長燈絲使用期限. 但真空管係燈絲未夠熱時提供屏壓容易出現cathode stripping. 所以燈絲供電用slow-start,但立刻提供B+吾係好事. ".....發熱線加咗time delay咁電子管屏極係咪都需要有相關設備。...." 回到你的問題. 我覺得吾一定屏極都需要有相關設備. 例如,我可以燈絲供電用slow-start, B+供電沒有這機制但使用IDH rectifier做整流. |
bambino 正式會員 210.xxx.xxx.231 |
2025-04-03 16:04 |
| [#5012] 單端胆機同好會 喺網上搵到一啲有用嘅資料: https://www.dhtrob.com/overige/idh_vs_dh_rectifiers.php |
DY2036 正式會員 182.xxx.xxx.139 |
2025-04-03 17:02 |
| [#5013] 單端胆機同好會 The article basically says the type of rectifier (direct-heated vs indirect-heated) should match that of power tubes. for example, DH power tubes start to draw plate current soon after the amp is turned on. This current drawn put stress on IDH rectifier when its filament is still too cold to conduct current. So, it's recommended to use DH rectifier to match that of power tubes. I do agree with what's said here. But it does not cover the case when power tube filament is slowly heated up. When filament of DH power tubes is slowly heated up, its plate current drawn will be slowly cranking up. The demand of current from rectifier tube is also gradually increased. There's a little time delay when full amount of current is needed from the rectifier. Depending on how slow the power tube filament is heating up, you will have a choice to use IDH rectifier (which is NOT slow-started). Also, a low-uF first cap is always good for tube rectifier. |
bambino 正式會員 210.xxx.xxx.231 |
2025-04-03 19:41 |
| [#5014] 單端胆機同好會 #5005 把 Morgan Jones Valves Amplifier third edition 看了一次。 只找到這個電路圖。有standby 功能 4V。  |
WilliamsonAudio 正式會員 165.xxx.xxx.28 |
2025-04-03 22:35 |
| [#5015] 單端胆機同好會 Interesting note by EM Lab about the requirement of the grid resistor of the EML-2A3.. Note 11) These grid current values are the original RCA specifications, which EML also meets and guarantees. Though it can be observed that often significant higher values seem possible with old or new tubes, please keep well in mind, that the grid current creates a voltage across the grid resistor. This is a DC current, coming "from" the grid. So, the polarity of this voltage will off-bias the tube such that plate current will increase, above the intended value. In some bad cases, leading to thermal destruction of the tube. For this reason, manufacturers specify a maximum grid resistor, which value has to do with the quality of the whole tube, including clean materials, best vacuum, and safe thermal design. When tubes are new, grid current is usually at it's lowest. In order to operate safe, during the entire lifetime of the tube, these grid resistor values were specified by RCA. We adopted those values at EML, in order to prevent amplifier designers to build products around the (much better) EML specifications, but then historical tubes may sometimes fail in such an amplifier. Understanding this consequence, EML 2A3 may be used with 2x higher grid value resistors as RCA specified. So 1 Meg for Auto bias, and 100k for fixed bias. Grid current of factory new tubes is below 1uA. Rejection level for faulty, used tubes is above 3uA at 250V/60mA, and full warm up. |
johnnykmtang 會員 70.xxx.xxx.22 |
2025-04-04 15:40 |
| [#5016] 單端胆機同好會 It is true that a higher value grid resistor is salient to ensure Safe Operating Area, however we also need to consider the resistance and the tube's miller capacitance may cause unexpected HF roll-off in the circuit.  |
LaLaLam 會員 1.xxx.xxx.197 |
2025-04-05 08:12 |
| [#5017] 單端胆機同好會 功率膽軟啟動確實需要考慮與燈絲發熱時間、高壓上電時間相配合（原子粒整流，直熱整流膽，旁熱整流膽）。而通過控制功率膽的負柵壓來實現軟啟動是一種更通用的設計方法。這樣就不需要考慮太多燈絲以及高壓的時間問題。 例如一開機，845負柵壓就由-200V, 然後慢慢提昇。屏流也跟住一步一步提昇（例如0-70ma）。 |
WilliamsonAudio 正式會員 182.xxx.xxx.92 |
2025-04-05 09:05 |
| [#5018] 單端胆機同好會 是否這樣理解? #5015 EML 是講解Grid leak resistor（接地的），Grid current 對 bias 的影響。 #5016 是道出Grid stopper 對高頻的影響。  最後修改時間: 2025-04-05 09:23:50 |
WilliamsonAudio 正式會員 182.xxx.xxx.92 |
2025-04-05 09:22 |
| [#5019] 單端胆機同好會 extracted from #5015 by EM Labs "..........please keep well in mind, that the grid current creates a voltage across the grid resistor. This is a DC current, coming "from" the grid. So, the polarity of this voltage will off-bias the tube such that plate current will increase, above the intended value. In some bad cases, leading to thermal destruction of the tube. ......" 1) ".....a DC current, coming "from" the grid......" It's actually electrons, not current 2) ".....the polarity of this voltage will off-bias the tube such that plate current will increase, above the intended value...." Grid leak electrons actually flow this way, Cathode -＞ Grid -＞ Grid Leak Resistor -＞ Cathode Bias Resistor -＞ Cathode. Current flows in opposite direction. Electrons flow from low voltage potential to high potential. (e.g. from signal ground 0V to cathode, approx. +70V for 300B in self-bias configuration) While Current flows from high voltage potential to low potential (e.g. from anode to cathode) As electron flows from grid to ground via grid leak resistor, yes, a dc voltage develops across the resistor, but in an opposite direction. The resistor lead that connects to grid should be more negative, compared to the other end. As a result, grid dc potential should be more negative and the tube should be more negatively biased. Plate current should drop instead. I am afraid this theory alone does not explain why a tube can malfunction due to grid leak current (or electrons). correct me if i am wrong. |
bambino 正式會員 210.xxx.xxx.231 |
2025-04-05 11:40 |
| [#5020] 單端胆機同好會 grid current 有點複雜。可以參考下面。比較長，要花時間才能看完。 https://www.diyaudio.com/community/threads/amplifiers-that-exceed-grid-leak-resistance.261130/ There are 3 types of grid current Current flowing into the grid is known as POSITIVE grid current • When the cathode is heated a cloud of electrons forms around the cathode known as a “space charge” • Some of these electrons gather at the grid. These electrons then flow out of the grid which is the same as saying that current flows into the grid. • This positive grid current generates a voltage across the grid leak resistor (Rg1) • This voltage makes the grid more negative which ADDS to the bias • If the grid leak resistor is large enough then this positive grid current can generate the entire required bias – This is known as “Grid Leak Bias” POSITIVE grid current is a low level phenomenon and can easily be overshadowed by NEGATIVE grid current Current flowing out of the grid is known as NEGATIVE (or REVERSE) grid current • Negative grid current can be caused by 1. gas ioniszation current 2. leakage current (grid to cathode) 3. grid emission (from grid being heated by the cathode, screen or anode) • gas ionization current dominates with the other 2 being low level effects • As electrons accelerate “up” the tube from cathode toward the anode, some of them collide with residual gas atoms. This collision is energetic enough that it strips an outer orbit electron from the gas atom which turns it into a positively charged ion. • The positively charge ion accelerates back “down” the tube toward the cathode • Some of these positively charged ions collect at the grid (which is usually the most negative potential of any tube element). Electrons must flow into the grid to neutralize these ions which is the same as saying that current must flow out if the grid • This current generates a voltage across the grid leak resistor. • This voltage makes the grid more positive which SUBTRACTS from the bias and results in increase tube current. • This effect is proportional to tube (anode) current and so is worse in power tubes • This effect also is worse in old “gassy” tubes. • This is why there are always 2 specifications for maximum Rg1 values. One value for cathode (auto) bias where the increased current is opposed by an increased bias due to increased voltage drop across the cathode resistor, and another smaller value for fixed bias where there is no action to oppose the current increase. The mechanism of NEGATIVE grid current, reducing the bias, increasing the current, increasing the negative grid current, reducing the bias etc. etc. round and round, then boom is called thermal run away and is what causes a lot of power tubes to self destruct. This is made worse by the fact that Rg1 values in most guitar amps ignore the recommended maximum Rg1 values. This is done so as to not load down the output of the phase splitter too much. This is usually compensated to some degree by biasing the output tubes at 70% of rated maximum dissipation, that is, reduce the tube idle current by 30%. That allows use of an Rg1 value of about double the recommended maximum which is based upon running the tube at 100% of its dissipation rating. This helps at idle but does not help much when running the amp with full signal. So NEGATIVE or REVERSE grid current is something you really need to watch in power tubes. It can be a problem in small signal tubes as well, particularly high mu triodes which led to the RDH "Rule of Thumb" that for high mu triodes (like 12AX7, 6SL7 etc.) that Rg1 should be no more than 3 times the anode load resistor for cathode bias and no more than twice the anode load resistor for fixed bias. Those familiar with 12AX7 circuits used in guitar amps will note that Rg1 is often ten times the anode load resistor value. This is because one of the defining characteristics of a 12AX7 which actually makes it ideal in guitar amps is unusually low NEGATIVE grid current. The above also explains why grid leak bias does not work with older gassy tubes. The negative grid current from the gas ionization opposes the positive grid current needed to establish the grid leak bias. Grid current is statistical in nature, that is to say that as well as developing a DC voltage across Rg1 it also develops a noise (hiss) voltage across Rg1 which is then amplified by the tube. Low Rg1 values not only give you a more stable bias point but also lower noise. You can think of this as the lower Rg1 shunting the grid noise to ground. There is one more type of grid current, GRID RECTIFICATION Current. When the grid is taken positive with respect to the cathode the grid to cathode circuit starts to look like a forward biased diode. Current into the grid increases with more positive voltage and usually this has the effect of clamping the positive going signal at the grid. The current also charges up any interstage coupling (DC Blocking) capacitor and this is the root cause of blocking distortion. Cheers, Ian |
WilliamsonAudio 正式會員 182.xxx.xxx.92 |
2025-04-05 19:12 |
| [#5021] 單端胆機同好會 Regarding the 300B grid current, my understanding is that:- The grid current will appears when the signal is very large that portion of the signal gets to the positive potential. With this positive voltage appears at the grid, there will be small amount of current from the grid. The current will be stored at the coupling capacitor which lower the grid-cathode potential. Then, the bias voltage will be changed. The electric charged to the capacitor will be dissipated through the grid resistor (say 100~250K). This is the reason why there is a limit of the grid resistor maximum value to avoid such issue. Using the Inter-stage transformer or Grid Choke would prevent such instability because the inductor would have very low DC resistance and won't store the grid current at all. 最後修改時間: 2025-04-05 19:25:47 |
johnnykmtang 會員 70.xxx.xxx.22 |
2025-04-05 19:17 |
| [#5022] 單端胆機同好會 最近出外，依家睇返DHT燈絲分析 用過AC及DC點300B, Hum AC 約4.4mV, DC non regulated hum 0.8mV, 但沒有感覺AC會靚声咗，相信前人推介AC係耐用方面，要对300B燈絲正負对換去做成耐用，我盡量唔加額外SS線路，我方式係左右300B燈絲正負焊時不一樣，用家只須每兩三個月互換300B就燈絲正負反轉，唔使焊過，當作保養事項，唔記得都冇事，反正正負不立刻对換也不會短時間有任何事 211, 845必須做高壓延遲45秒，211,845 燈絲未熱時浪湧可以令瞬間电流高過250mA, 最嚴重可以衝斷輸出牛初級，300B燈絲未熱就唔會咁嚴重，好多外國市面300B機都沒做高壓延遲 最後修改時間: 2025-04-05 21:33:04 |
niceday009 正式會員 182.xxx.xxx.214 |
2025-04-05 21:16 |
