I am getting the impression that Nelson is putting more time and effort into design and building for projects around here than he might otherwise be doing for commercial Pass Labs and FW amps.
well, you never know ....... 🙂
point is , Greedy Boyz are dictating much faster turnout than Papa's commercial dealing ....... besides a fact that Papa is constantly cooking something for PL and FW
point is , Greedy Boyz are dictating much faster turnout than Papa's commercial dealing ....... besides a fact that Papa is constantly cooking something for PL and FW
Well, that's not a problem when you know how the part will behave in advance as I did. 🙂
Anyway, the Variac is simply a cheap and smart precaution / convenience that costs about as much as one of those VFETs.
It's only free advice, primarily meant to protect those who might not fully understand what they're doing and hook something up wrong. And, it allows you to work with a bigger variety of parts.
I'm sure NP will have something for you shortly. Wait and see.
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Yes, you are right about the costs for the variac and the SITs. I did not think about this.
Maybe at work we have a variac in the lab that I could borrow but at the moment it is just homeoffice since several weeks! So in any case I will first try the Vgs machting with const. DC voltage. And off course I am waiting for some new, nice surprises from Nelson, ZM and you.
Maybe at work we have a variac in the lab that I could borrow but at the moment it is just homeoffice since several weeks! So in any case I will first try the Vgs machting with const. DC voltage. And off course I am waiting for some new, nice surprises from Nelson, ZM and you.
As is also true for the K180's which by my experience are the closest match to the K77's first developed for audio use. Sadly, as you already know Tokin wasn't interested in SIT's for their audio performance like Yamaha, Sony, NEC, and Hitachi were when we were young and V-FET's were a new and exciting audio technology, albeit too expensive to keep producing against other cheaper technologies at the time. Their ability to switch large currents without the necessity for extreme process control made far more sense to Tokin and as such SIT production survived until just recently.
With that said you and others have clearly demonstrated how to use these sonic prima donna beauties for their triode like qualities and thank you so much for that!
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The trouble with matching Vgs with only one data point is that it will be possible to have two SITs with the same Vgs but differing Mu or Rd. Possibly measuring a few steps in the old fashioned manner would reveal more. 🙂
Ah, the problems we face.
I have a variac from tube amp building, but I've been hesitant in getting that Keysight oscilloscope...
However, I'd I gladly settle for a Tektronix or Rigol.
This hobby can get expensive and quite involved.
I have a variac from tube amp building, but I've been hesitant in getting that Keysight oscilloscope...
However, I'd I gladly settle for a Tektronix or Rigol.
This hobby can get expensive and quite involved.
Seems like what Mike is saying is that two unique parts could overlap at a similar point (area) but have two different set of curves (gain), coinciding. The tube guys don't seem to sweat this, but my experience is limited there. Perhaps it makes some larger difference at the currents being used.
Ideally, each and every Sit would be traced for a set of curves, but not every DIY'er is ready or capable of creating those curves, based on their particular investment. Conveniently enough though, most Sony in circulation are of the same grade. Tokin is another animal, if to be driven to max ability. But then again, NP says they look like Sony.
Ideally, each and every Sit would be traced for a set of curves, but not every DIY'er is ready or capable of creating those curves, based on their particular investment. Conveniently enough though, most Sony in circulation are of the same grade. Tokin is another animal, if to be driven to max ability. But then again, NP says they look like Sony.
As is also true for the K180's which by my experience are the closest match to the K77's first developed for audio use. Sadly, as you already know Tokin wasn't interested in SIT's for their audio performance like Yamaha, Sony, NEC, and Hitachi were when we were young and V-FET's were a new and exciting audio technology, albeit too expensive to keep producing against other cheaper technologies at the time. Their ability to switch large currents without the necessity for extreme process control made far more sense to Tokin and as such SIT production survived until just recently.
With that said you and others have clearly demonstrated how to use these sonic prima donna beauties for their triode like qualities and thank you so much for that!
very little known fact is that Yamaha called out the K180s as direct replacements for the K77, assuming towards the production sunset of the K77s. Which K180s were the right replacements, that I can only speculate....assuming Yamah did their internal matching before they slapped a Yamaha replacement part number on Tokin vfets
good point Michael
Looking at older designs such as the Yamaha B-1, for which Yamaha had an entire production line available to build parts for, yet their concerns with proper matching is evident and reflected in the circuit design of the B-1, where they allow for an additional bias balance of sorts, to account for minor variations among the already matched parts.
By that I mean using two variable DC supplies (or possibly even batteries for the Vgs supply) You could manually trace all the curves but you don't really need to. Just grab some data points on either side of your target operating point at the same Drain current.
On my Tokin THF-51S devices I can find the following numbers:
- 1X5906
- 1X5914
- 1X5946
- 1X5971
Looks really like individual serial numbers (not the lot code as I posted before), I have running numbers 1x59xx too. One could hope that they are from the same chip, even from the same area on the chip ...
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AlexRivera curve traced six THF-51S, purchased as unmatched, and got one perfectly matched quad and well matched pair.
https://www.diyaudio.com/forums/pass-labs/368651-while-they-last-42.html#post6588207
You can notice that serial numbers are very close (1X69xx):
https://www.diyaudio.com/forums/attachments/pass-labs/935931d1616775192-while-they-last-img_0890-jpg
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I guess we can only speculate on this: number of die per wafer, context with serial number, location in wafer, etc.
nice!
I wish I knew they would be that close. I took the hit ($$$$) on a couple of already matched quads.
I have not built a NP design or SIT amp, but I was very curious before the VFET lottery was announced, was excited to hear of it and joined but was not one of the chosen. I bought a "roughly matched" quad of THF-51S that I will stow away until this mystery project is announced. If it doesn't come to Pass (no pun intended) I will start from scratch. Thought I would make the investment while I still can, not cheap but surely less than I have paid for NOS tubes.
Thanks for the tip, Mr. Pass.
Thanks for the tip, Mr. Pass.
The pair that I got years ago are very nicely matched as are the K180 quad I got back then which is why more recently I bought a box for 20 more; out of that 20 I found 6 that barely met Tokin's K180 data sheet unlike my earlier quad which could easily be sub'ed for K77's in a B-1.