Some years ago I switch from DN2540 to IXTP01N100D (due to the first item unreliability at high -near 400V- voltage) ... and never look back.
Ixys is more robust and fortunately better in tonality.
I use this type everywhere -as HV device-, except PSU (CCS).... I have a bunch of DN2540.
As "lower" device in CCS I use (TO92) DN2540.
In Ale's gyrator (I have some) -where "lower" device forward transconductance (Gfs) and reverse transfer capacitance (Crss) are the most important things- I regularly use
5-10 mA range: 2SK170 (Gfs: 22mS),
10-30..40 mA range: (TO92) DN2540 (15mS), J310 (8mS).
Gfs is mostly determinate output impedance, so -for me- this is more important than Crss.
Ale suggest to use BF862 (45mS), or BH111 (640mS). Both of them is good for lower output impedance.
I have some AOT1N60 (900mS!), I will try it... when I have a little spare time.
Ixys is more robust and fortunately better in tonality.
I use this type everywhere -as HV device-, except PSU (CCS).... I have a bunch of DN2540.
As "lower" device in CCS I use (TO92) DN2540.
In Ale's gyrator (I have some) -where "lower" device forward transconductance (Gfs) and reverse transfer capacitance (Crss) are the most important things- I regularly use
5-10 mA range: 2SK170 (Gfs: 22mS),
10-30..40 mA range: (TO92) DN2540 (15mS), J310 (8mS).
Gfs is mostly determinate output impedance, so -for me- this is more important than Crss.
Ale suggest to use BF862 (45mS), or BH111 (640mS). Both of them is good for lower output impedance.
I have some AOT1N60 (900mS!), I will try it... when I have a little spare time.
Hi Béla, there are many compromise decision to make when choosing the lower FET. The high transconductance isn't only needed to reduce the output impedance, but also to improve the bootstrap and minimize the impact of the input capacitance of the FET. This is important on the MOSFETs which tend to have a high Cgs.
As the gm is proportional to the square root of the drain current, you need to maximize the drain current for best GM. What I have found is that at higher drain currents the rds of the DN2540 drops which impacts the high impedance reflected to the valve, in a CCS in particular. Hence, there is always a trade off. I try to look for a high gm at the operating current of the FET as well as low cgs and crss.
If a FET is design with high gm at high current, not necessarily is best match at lower current in the gyrator based on my experience.
As the gm is proportional to the square root of the drain current, you need to maximize the drain current for best GM. What I have found is that at higher drain currents the rds of the DN2540 drops which impacts the high impedance reflected to the valve, in a CCS in particular. Hence, there is always a trade off. I try to look for a high gm at the operating current of the FET as well as low cgs and crss.
If a FET is design with high gm at high current, not necessarily is best match at lower current in the gyrator based on my experience.
check out the 17 pages here:
http://www.diyaudio.com/forums/tubes-valves/38248-new-dht-heater.html
there are a number of posts reporting sound quality changes with parts substitution, mainly the R1 for a Mill NI WW, and your favourite flavour of film cap....for example I really liked an old yellow Hovland or a Dueland
many more disturbances to your contentment field await
Blimey! There was a quite significant gain in naturalness with a change from stock R1 resistors to Mills.
I just might have to try out the capacitor mod now.
Can somebody teach me to find the outer foil of an unmarked capacitor? I have a Fluke multimeter and an old analog oscilloscope and that's about it.
Observing Inner and Outer Foil of Some Popular Capacitors – Jimmy's Junkyard
check out the 17 pages here:
http://www.diyaudio.com/forums/tubes-valves/38248-new-dht-heater.html
there are a number of posts reporting sound quality changes with parts substitution, mainly the R1 for a Mill NI WW, and your favourite flavour of film cap....for example I really liked an old yellow Hovland or a Dueland
many more disturbances to your contentment field await
Blimey! There was a quite significant gain in naturalness with a change from stock R1 resistors to Mills.
I just might have to try out the capacitor mod now.
Can somebody teach me to find the outer foil of an unmarked capacitor? I have a Fluke multimeter and an old analog oscilloscope and that's about it.
Maybe it's you?
Have you tried putting the cap next to a mains lead? Or a cheap SMPS?
LOL, as they say nowadays. Yes, maybe, but I finally did manage to get a difference by taping the capacitor to a mains lead WITHOUT touching the capacitor. Verified by using a marked Jensen paper oil.
The russian K40-9 paper oil was easy, and not following any direction of the lettering by the way. The k75-10 and the FT-3 on the other hand was very difficult to measure. I will try some more later.
The russian K40-9 paper oil was easy, and not following any direction of the lettering by the way. The k75-10 and the FT-3 on the other hand was very difficult to measure. I will try some more later.
You are right. I tested a few more and sure enough there wasn't any set direction related to the text. Everyone needs to be measured. From now on I'm using a marker on every capacitor.
He-he! Great stuff has always been made by obsessive persons.
I had some Vitamin Q's in my stash and they are just fabulous. 400V by the way. My search for output caps are over. To top them I probably have to go Duelund or Jupiter.
However there is a small matter of hookup wire. For now I'm running with some OEM silver plated stuff bought from HifiCollective, but I've been wondering if there is something to be gained with going all copper or all silver. Is Jupiter silver in cotton something you folks have tried? Or perhaps Cardas copper?
I had some Vitamin Q's in my stash and they are just fabulous. 400V by the way. My search for output caps are over. To top them I probably have to go Duelund or Jupiter.
However there is a small matter of hookup wire. For now I'm running with some OEM silver plated stuff bought from HifiCollective, but I've been wondering if there is something to be gained with going all copper or all silver. Is Jupiter silver in cotton something you folks have tried? Or perhaps Cardas copper?