多謝Accphoto兄

小弟乃新手一名
有幸能於Accphoto兄手上接收其珍品，
ARC SP-10 Pre-amp一部，手工精巧，聲音甜美....
而是次交易乃為"四川賬災義賣"，
Accphoto兄不收分文，
着小弟把數仟圓機價，
全數捐住HSBC紅十字會賑災户口，
其善舉令小弟敬佩不巳，
試機時Accphoto兄亦教了小弟很多發燒知識.....
之後還多送兩支靚膽給小弟試聲，
所以小弟真的要主動在此留言.....
: ......多謝Accphoto兄..... :

對你Accphoto兄此舉深表敬意

100% 同意  

我煩了Accphoto "n" 次, 但佢依然好有心機慢慢解我聽我不明白的地方.

對他將自己的心血成品捐出更加令人佩服 ....

CAT

小事，小事，略盡綿力。

Really respect accphoto.


Dear accpohoto,

I got a question to ask, if we use lower Voltage for tube filamet what will happen? what's the effect of filament voltage to the sound? is it only inharge for amplification?

e.g for a 6.3v filamnet i use only 5V?

currently i'm running the 6x4 & 5687 at ~5V, them seems to sound normally.... so is it ok i just run them at 5V instead of 6.3V?

If using lower voltage, the tube may not operate at the optima performance, the sound may be very slow and strange. Do not suggest to run at 5V. Normally, we can run the filament at lower voltage say 6.1V but never run at 5V.

ok..thanks.

For filament, u prefer using AC or Dc? Some people say, using AC is better sound.... i also feel that running filament at AC seems sound more natural, noise is slightly higer but acceptable.

For A C or DC , it is really depend on what Signal Noise ratio you want.. For pre-amp, I always run in DC mode as it is more stable and less noise, For power-amp, i will run in AC.

if use AC for filament, u think the noise will be higher in the signal tube or rectifier tube?

Do u think using AC filament voltage at rectifier tube and use DC on signal tube filament is a good combination?

Rectifier tube must be AC. YOu cannot use DC for rectifier tube.For signal tube especially on the pre-amp, I normally running DC because it is quite easy to get hum if using AC. Besides, you do not need need to match the AC voltage of transformer to filament if using DC.

今天唔得唔多謝 Accphoto 兄杖義相助 .... 把有問題的 CARY KT 88 由頭驗到腳, 找出問題所在, 加以改善 .... 也給了我許多有用的意見, 使我得益不少 !

用了 Accphoto 兄整個下午 ... 真是不好意思 .... 實要在此表揚 Accphoto 兄的耐心, 對我這個什麼也不懂的人詳細的講解與分析 .....  

Dear accphoto,

you mean the filament voltage for rectifier tube must use AC not DC , any reason?

Attached is the power supply i recently made, still not completed. Do you think i shall parrallel all transformer & choke or made them 90 degree to reduce interference?

What is your recommendation while design the location to place the transformer, choke and capacitor? any special arrangement to obtain best sound?

For some rectifier tube like 5U4, the positive will come out of Leg 8, which is also the filamenet , it make things very complicated if you are running DC, For some tubes like 6X4, it is fine to run it in DC as the output is separated. But why border to run DC is AC is ok. Basically, I have never seen rectifier tube running DC filament.

Yes, Place of transfomer is good to have one vertical and one horizontal next to each other as this will cancel the EMI of the transformer.

Thanks accphoto!

So far never use 5U4G (direct heating type) as i'm a bit confuse on the connection. For 5U4G is it the output positive must be pin 8? can it be pin 2?

Doest it mean that the pin 8 will have  2 connection, 1 connect to the ac transformer , 1 to the B+?

Pin 2 & 8 need to connect to AC 5V, The B+ will be from pin 8.

TQ accphoto,

i got another question.

If i want to put in the bleeder resistor (to discharge the capacitor for safety purpose) which location shall i place it?

retifier tube ---L1---c1---L2---C2

Shall i connect the bleeder resistor in between rec tube and L2? or on the C1? or on the C2?

How justify what value of bleeder resistor to be use?

No, Bleeder resistor will normally connect to the +Ve and -Ve of the capacitor. So it mean you need two bleeder resistor if you are using  CLC, each one should be around 150K to 270K , at least 2W, better 5W depending on the voltage current. The smaller the bleeder resistor, the quicker the discharge time but the resistor will get hotter, so it is adverisable to use large "watt" for smaller value.

oh i see, if i use CLCLC, then i will need to use 3 bleeder resistor loh.

Thank you very much on the info.