After a long time waiting, finally I got this transformer on hand – myself. This is the Ultimate Level 4 Power Transformer from J&K Audio Design. You can read some detail here and here.
My first impression was: Heavy! Each of this power transformer has around 4-4.5 Kg of weight (need to find my scale to measure it right).
My second impression was the build quality. It has sturdy cover and excellent easy to solder turret. The transformer cover reminds me of old Tamura transformer (not exactly the same, but a bit similar).
The turret on High Voltage power transformer. I ordered 320 and 240 VAC option for High Voltage purpose. A bit high for pre-amplifier usage, but be noted that I’m using Choke Input most of the time on my application.
Below is the Low Voltage or Filament transformer. Nothing really special, only standar 6.3 VAC windings and 0-4-5 VAC rectifier winding to cover most common 5V rectifier and classic 4V RGN/AZ rectifier.
The benefit of having two separate High Voltage and Low Voltage transformer is you can always switch them on separately (Low Voltage should come first). Once the tubes are pre-heated enough around 60-90 seconds, then the High Voltage could be switched on (manual or automatic with delay relay). Many people don’t believe this kind of old trick, but for the sake of longevity of our old tubes, then this is nothing.
Be noted that the mains wiring should be arranged properly in order to make sure the High Voltage power transformer can’t be switched on if the Low Voltage/Filament power transformer is not switched on yet.
Edgar
December 9, 2014 09:50No need separate transformer just to switch ON heater first before HT. I’m sure you know that.
Auw Jimmy
December 9, 2014 10:25Hi Edgar,
Yes, you are right. There are several approaches which we can take to turn on the heater first, then followed by the high tension.
Off course we can always put extra switch on the DC out after the rectifier (but not many switch will last long used in DC – except some industrial one).
We can also put the switch in the secondaries before the rectifier (make sure you have good enough switch, as we are playing with higher than mains voltage – even at lower current).
Or another approach is to cut on the Ground. Theoretically speaking, even the high voltage is there but the Ground is cut, then the current will not flow. Mean circuit will not be powered ON.
And you are right, I’ve been there 🙂
Actually I plan to have separate article to discuss that approaches, and why I choose this different approach to have separate transformer. Maybe later, as I need to take some photo first to support that article.
Thank you.
DHTRob
December 14, 2014 17:13Jimmy,
Interesting topic. Preheat rectifiers versus Cold start.. When using directly heated (dh) rectifiers, preheating them will result in maximum current demand from both capacitors and signal tubes when high voltage is applied. This results in a current peak and high voltage peak.
Cold start (just one on/off switch) will take care of instant current demand of signal tubes and the voltage peak. When directly heated power tubes are used, operational temperature of the filaments will be reached at about the same time. So more hand-in-hand. Current draw from capacitors will remain at a too low cathode temperature. This was no problem at that time since only low-uF capacitors were available.
When indirectly heated (idh) rectifiers are used, current draw from capacitors and dh power tubes will be present at a too low cathode temperature. Current draw from idh-power tubes will go hand-in-hand.
My experience is that it is best to use dh-rectifiers in solo dh-tube circuits, and idh-rectifiers in solo idh-tube circuits. Use of type power tubes (dh vs idh) dictates more or less type of rectifier. Sow when a mix of idh-tubes and a dh-power tube is used, it is best to use dh-rectifier since these will demand highest current.
Maybe a bit long story, but I hope this will be of any help for your PSU.
Rob
Auw Jimmy
December 22, 2014 22:20Hi Rob,
Thanks for sharing, mate!