Most of us bottleheads progress through various cycles of valve euphoria and end up applying our minds, budgets and families to the need to understand the essence of the pleasure that valve amplified music gives us. Whether we do so by collecting old equipment, repairing or restoring it, pontificating on its design or performance limitations or just keeping the couch thief at bay while listening to our favorite box of glowing bottles, we end up at some stage listening for hum, whoosh, noise or a "black" background. Our glowing bottles have the limitation of being noisy with respect to their solid state counterparts and despite excellent design effort, the "ultimate black" background is seldom achieved. For most of us it is not an issue and we continue enjoying our music from within our individual constraints and remain satisfied...... for a time. Complacency however is not in the nature of the audio enthusiast, we swop boxes, fiddle with cables, move speakers and even beg borrow or steal fine pieces of audio kit from the likes of KK and Co to improve our sound.
So why the rambling. Being one of the above with an itchy rear end, a instrument nut and a dislike for noise, I started looking at hybrid front ends for a phono stage. A valve in a totem pole configuration with a jfet as the input, significantly reduces input noise and has become a subject of interest. Out of this in turn, came the awareness of the legendary Toshiba 2SK170 jfet and its prowess in various designs worldwide.
So I went on a mini quest to find these devices and see what was so special about them. First stop was my old friend and yours, Alan Hobkirk who has a stash of most thinks interesting in his store room. As expected Alan had a little packet of jfets that I used as a reference. These were tested and compared to the specifications. A good start. Now as most of you know, these jfets are rare as hens teeth these days so where next. I next contacted various old favourite valve and component suppliers, (not in SA) as well as eBay and AliExpress.
I got 4 jfets from each of six suppliers and sat down to do some measurements (naturally). All devices were marked correctly and I've included a pic with a genuine and fake
Running various sets of graphs, it was very clear that there were two distinct sets of parameters. (See pic below). One set matched the manufacturers data and the other did not. It appears that the fake jfets either come from the same manufacturing source or are another legitimate jfet relabeled as a 2SK170 BL. How many suppliers provided original jfets? Only one (from the US).
While we all know that there are fake devices out there, there are also good ones. I guess we are all obliged to do our homework thoughly if we are to get what we want without wasting time and money.
Mods. Not sure where this should go so please move as necessary
[/URL][][/img]
[/URL][][/img]
So why the rambling. Being one of the above with an itchy rear end, a instrument nut and a dislike for noise, I started looking at hybrid front ends for a phono stage. A valve in a totem pole configuration with a jfet as the input, significantly reduces input noise and has become a subject of interest. Out of this in turn, came the awareness of the legendary Toshiba 2SK170 jfet and its prowess in various designs worldwide.
So I went on a mini quest to find these devices and see what was so special about them. First stop was my old friend and yours, Alan Hobkirk who has a stash of most thinks interesting in his store room. As expected Alan had a little packet of jfets that I used as a reference. These were tested and compared to the specifications. A good start. Now as most of you know, these jfets are rare as hens teeth these days so where next. I next contacted various old favourite valve and component suppliers, (not in SA) as well as eBay and AliExpress.
I got 4 jfets from each of six suppliers and sat down to do some measurements (naturally). All devices were marked correctly and I've included a pic with a genuine and fake
Running various sets of graphs, it was very clear that there were two distinct sets of parameters. (See pic below). One set matched the manufacturers data and the other did not. It appears that the fake jfets either come from the same manufacturing source or are another legitimate jfet relabeled as a 2SK170 BL. How many suppliers provided original jfets? Only one (from the US).
While we all know that there are fake devices out there, there are also good ones. I guess we are all obliged to do our homework thoughly if we are to get what we want without wasting time and money.
Mods. Not sure where this should go so please move as necessary
