300B trible parallel single end 35W power amplifier

Years of experience bring very nice things to life,

This project is a continuation of the Kurt Kr52bx project but with std 300b that operate well within their specs and limited to a reasonable power.

High power mono blocks are always in demand, so that was on my mind since I didn’t want to venture anymore in tubes costing hundreds of euros and burning up very fast with companies that don’t honour there warranty think of Krenterprise and Kraudio and AVVT and Emmissionlabs and probably the same tubes are sold under other brand names but it is always the same, and imagine this especially with 3 per channel if you need that guarantee.

Triple is like the name mentions based on a triple Parallel single ended configuration of 300B’s, the circuit is simple and uses standard design principles, nothing exotic and is well measured, with the Boully 88 I learned to my own surprise that measurements help fasten the optimising procedure and that indeed good measurements often are confirmed by listening as being better but not always as long as they haven’t been obtained by extra circuitry.

I also wanted to use the C3m in this design ( and in a few new designs as well ) as this little tube is sexy and even on the datasheet it looks extremely promising, the problem with this tube is its low gain , a µ of 10 as a triode, rather relegates it more to an output power tube , maybe for a new project putting 10 in parallel and making a Push Pull amp.

2 configurations possible, triode or penthode, will try both .

The output transformer, I stick with Lundahls as they are excellent, I haven’t really heard better ones yet and this is no compliment just in vain. The LL1627 was chosen as 3 parallel 300B’s can easily be loaded with 600 ohms , this is connection ALT D or eventually ALT C, and the low inductance of 9H is not a problem as the 3 300B’s don’t need much , the frequency graph confirms this, from 14Hz full power is obtained this is excellent.

The driver stage also uses a Choke loaded configuration, a LL1668/25ma for optimum loading, the benefits are tremendous, so I stick with this technology .
An Elna and a mkp capacitor and a Dale resistor fulfil the cathode requirements.

If used as a penthode , the LL1668 is paralleled with a 82K resistor for improved linearity,
And a zener reference is used to bias and supply current to the 2nd grid, the cathode resistor is changed by adding another 560 ohm resistor in parallel and the trick is done, the gain approaches a µ of 35 , which is sufficient for any pre amp.

As coupling caps I used std mkp and sink foils 630 volt rated.

Resistors std ceramic where it doesn’t matter and Top quality Dale where necessary.

The high voltage is a mere 400 volts on the 300B’s and they are not pushed to extremes, 65ma per tube. Should give a 20 Watts of output power at very low distortions and long life as well. For the start up there is a relais sequence, this is absolutely necessary as with the choke input filter. The voltage can rise to 700volts if you forget the stand bye switch and the capacitors cannot handle this ( I learned the hard way ) .

This is a little circuit powered with the 6,3 volt and uses a timer that always counts 30seconds before powering up.

Design considerations :

What Load to choose, a load of 600 ohms to 8 ohms , gives high power ( 35 watts )but horrible distorion , see the flat sinuses , and this starts at 10 watts see charts
With a Load of 1K2 to 8 ohms , distortion falls to extreme low levels and power is 15% less ( 24 watts ) , but signal looks clean all the way .

I measured on ALT D 50 watts with loads of distortion , relatively clean with 12,5 watts but overall not satisfying , lots of 2nd harmonic and lots of 3rd harmonic ect , can be a very good match if you need that added distortion for listening to older recordings that lost some of their harmonics !!!!!!!

I measured on ALT C , 38 watts of relatively clean output power , same 50 watts with loads of distortion , but below 38 watts very clean signal , ( at 38 watts the grid is swinging to 0 above we are in class A2 ) bandwith is excellent see graphs

多年的經驗為生活帶來了美好的事物，

該項目是Kurt Kr52bx項目的延續，但是std 300b在其規格範圍內運行良好，並且限制在合理的功率範圍內。

總是需要高功率單聲道模塊，所以這是我的想法，因為我不想冒險花費數百歐元，並且非常快速地與那些不尊重那裡的公司一起燃燒保證想到Krenterprise和Kraudio以及AVVT和Emmissionlabs以及可能相同的管子都以其他品牌銷售，但它總是一樣的，如果你需要這種保證，想像一下這個特別是每通道3個。

Triple就像基於300B三重並行單端配置的名稱一樣，電路簡單，使用標准設計原理，沒有異國情調，並且很好地測量，使用Boully 88我自己驚訝地發現測量有助於優化程序和確實良好的測量通常通過傾聽確認更好但不總是只要它們沒有通過額外的電路獲得。

我也想在這個設計中使用C3m（以及一些新的設計），因為這個小管很性感，甚至在數據表上它看起來非常有前途，這個管的問題是它的低增益，μ為10作為一個三極管，而不是將其更多地放在輸出功率管上，也許是為了一個新的項目，將10個並聯並製作推拉式放大器。

2種配置可能，三極管或penthode，將嘗試兩者。

輸出變壓器，我堅持使用Lundahls，因為它們非常出色，我還沒有真正聽到更好的那些，這並不是恭維，只是徒勞無功。選擇LL1627作為3並聯300B可輕鬆加載600歐姆，這是連接ALT D或最終ALT C，9H的低電感不是問題，因為3 300B不需要太多，頻率圖證實這，從14Hz全功率獲得這是非常好的。

驅動級也採用了Choke加載配置，LL1668 / 25ma可實現最佳負載，效益極高，因此我堅持使用這項技術。
Elna和mkp電容器以及Dale電阻器滿足陰極要求。

如果用作penthode，LL1668與82K電阻並聯，以提高線性度，
並且使用齊納基準電壓來偏置並向第二柵極提供電流，通過並聯添加另一個560歐姆電阻來改變陰極電阻器並完成技巧，增益接近於35的μ，這對於任何前置放大器都是足夠的。

作為耦合帽，我使用std mkp和630伏額定電池。

電阻器std陶瓷無關緊要，高品質的Dale必要時。

300B的高壓僅為400伏特，並且它們沒有被推到極端，每管65馬力。應該在非常低的失真和長壽命的情況下提供20瓦的輸出功率。對於啟動，有一個繼電器序列，這與膽電阻輸入濾波器一樣是絕對必要的。如果你忘記了單獨的開關，電壓可以上升到700伏，電容器也無法處理（我學到了很多方法）。

這是一個用6,3伏電源供電的小電路，並使用一個定時器，它在上電前總是需要30秒。

設計注意事項：

什麼負載可供選擇，600歐姆到8歐姆的負載，提供高功率（35瓦）但可怕的失真，看到平坦的鼻竇，這開始在10瓦特看圖表
負載為1K2至8歐姆時，失真降至極低水平，功率降低15％（24瓦），但信號看起來一直很乾淨。

我測量了ALT D 50瓦，失真負載，相對乾淨，12.5瓦，但整體不滿意，大量的二次諧波和大量的三次諧波等，如果你需要增加的失真來收聽，可以很好地匹配丟失了一些諧波的舊錄音!!!!!!!

我測量了ALT C，38瓦相對乾淨的輸出功率，相同的50瓦負載失真，但低於38瓦非常乾淨的信號，（38瓦時網格擺動到0以上，我們在A2級）帶寬非常好看圖表

Distortion measurements :

Alt D
1 watt 10 watt 30 watt
2nd harmonic 1,4% -37dB 5,1% -26dB 12% -18dB
3rd harmonic not measurable 1% -40dB 4,8% -26dB

Alt C
1 watt 10 watt 30 watt
2nd harmonic 0,7% -43dB 2,5% -32dB 4,5% -27dB
3rd harmonic not measurable 0,3% -51dB 1% -40dB

This was all measured with the C3m in triode connected, for 17,5volts ( 19Watts on Rload ) I need 6,5v input voltage on the C3m’s grid!!!!
A tube pre amp can deliver this without a problem, for transistor pre amps more of a problem.
C3m connected in penthode, just 1,5v is needed on its grid for same swing on load.
First I was afraid I needed Rx // to the choke because the gain of a penthode is the slope ( mA/v ) multiplied by Rl, since the choke is not a linear Resistance but a frequency depended one. I was afraid this would alter frequency graph a lot, but actually there is 3 x 83K in parallel from the negative bias so there is a Rx already of 27,5k approx.

Penthode connected, signal looks very slightly worse, gain is much improved. I have not listened yet to this configuration because while writing the report it became clear to me that people who will own this will also own a tube pre amp and that one can certainly drive 10volts peak at least without a problem.

Monoblock configuration on a not too big chassis, good looks and easy to build, I’m in love with it .Its nice to have an amp of this quality without having 1250 volts on its plates , as an accident can always occur and 400 volts on the plate is rather easier to work with then 1250, however I still advice everyone to be extremely cautious as this is no joke with the big capacitors in place.

失真測量：

Alt D
1瓦10瓦30瓦
二次諧波1,4％-37dB 5,1％-26dB 12％-18dB
三次諧波不可測量1％-40dB 4,8％-26dB

替代C.
1瓦10瓦30瓦
二次諧波0,7％-43dB 2,5％-32dB 4,5％-27dB
三次諧波不可測量0,3％-51dB 1％-40dB

這一切都是用連接三極管的C3m來測量的，對於17.5伏特（Rload上19瓦特）我需要在C3m電網上輸入6,5v電壓！
管前置放大器可以毫無問題地提供這一點，因為晶體管前置放大器更具問題。
C3m連接在penthode上，在其網格上只需要1,5v，以便在負載上進行相同的擺動。
首先，我擔心我需要Rx //到扼流圈，因為penthode的增益是斜率（mA / v）乘以R1，因為扼流圈不是線性電阻而是頻率取決於1。我擔心這會改變頻率圖很多，但實際上從負偏差並聯3 x 83K所以Rx已經達到了27.5k左右。

Penthode連接，信號看起來非常差，增益大大提高。我還沒有聽過這個配置，因為在編寫報告時我很清楚，擁有它的人也會擁有一個電子管前置放大器，而且至少可以毫無問題地驅動10伏峰值。

Monoblock配置在一個不太大的機箱上，外觀漂亮，易於構建，我很喜歡它。很高興有一個這種質量的放大器，其板上沒有1250伏特，因為事故總是會發生400伏特然後我會建議每個人都非常謹慎，因為這對於大電容器來說並不是一個笑話。

The Schematic :

Measurements of triode versus penthode connection

The left is the penthode connected C3m and the right is the triode connected version, output voltage is the same but gain is not.

Powersupply considerations :

LCLC

Choke input, for best possible current spike control

Massive 1000µF Siemens power reserve and hum killer capacitor bypassed by a 0,47/630v Mpp Xicon for best HF control

Again a choke for filtering, a LL1673/10H

Black Gate for the output circuit , a 2 x 100µF is used , the audio returns through this capacitor so it is highly critical here , and is well spend money .

The diodes are BYV26E types , they currently belong in the group of fastest soft recovery diodes and are excellent.The new CREE shottky high voltage diodes offer no advantage here because the current is to low.

For the filament rectification, parallel 1N5822 Schottkys are used, I tried 10A/100v schottkys but they loose to much voltage and voltage dropped to 4 volts which is too low .
Also a choke is used to reduce the current spikes, and a 10000µF/35v Hitachi is used, the audio is shunted through this one and an extra mkp back .

Negative bias supply is used to supply the 20v 125mA filament power to the C3m, then a doubler boosts this to 140v DC for use of negative bias to the 300B’s.
DC measurements :

NEVER run the high voltage power supply line without tubes as a load , this will damage the Black Gates and the Siemens , always use the stand bye switch or disconnect from first choke.

All 300B’s are polarised at -85 volt for starters
Filament voltage = 4,8volts under full load
See schematic

供電考慮因素：

LCLC

扼流圈輸入，實現最佳電流尖峰控制

大容量1000μF西門子動力儲備和嗡嗡聲殺手電容繞過0,47 / 630v Mpp Xicon，實現最佳HF控制

再次成為過濾器，LL1673 / 10H

輸出電路的黑門，使用2×100μF，音頻通過這個電容返回，因此在這裡非常關鍵，並且很好花錢。

二極管是BYV26E類型，它們目前屬於最快的軟恢復二極管組並且非常出色。新的CREE shottky高壓二極管在這裡沒有優勢，因為電流很低。

對於燈絲整流，使用並聯的1N5822 Schottkys，我嘗試了10A / 100v schottkys，但是它們鬆散到很多電壓，電壓降到4伏，這太低了。
此外，還使用了一個扼流圈來減少電流尖峰，並使用10000μF/ 35v Hitachi，音頻通過這個和一個額外的mkp背部分流。

負偏置電源用於向C3m提供20v 125mA燈絲功率，然後倍頻器將其提升至140v DC，以使用300B的負偏壓。
直流測量：

切勿在沒有管作為負載的情況下運行高壓電源線，否則會損壞黑門和西門子，始終使用備用開關或斷開第一個扼流圈。

對於初學者來說，所有300B均為-85伏極化
在滿負荷下，燈絲電壓= 4.8伏
見原理圖