TRANSISTORS NEEDED

Despite three days of searching, being the proud owner of the DIY f5 circuit boards, I am still unable to come up with the transistors for a simple f5 build. Any ideas are welcome. I have searched as many threads as I can stand, and still am unable to come up with a source. Help!!!
 

kasey197

Member
2009-09-08 9:29 am
Despite three days of searching, being the proud owner of the DIY f5 circuit boards, I am still unable to come up with the transistors for a simple f5 build. Any ideas are welcome. I have searched as many threads as I can stand, and still am unable to come up with a source. Help!!!

The only tough ones to get are the input JFETs and amongst other places mentioned above, you can get them from spencer at fetaudio.com - I believe many have bought from him. Not cheap but they are the originals.
 

6L6

Moderator
Paid Member
2010-10-22 6:43 pm
Denver, Colorado
If you need a full kit (all the transistors in one package, and his Jfets are genuine) I would happily suggest Hannes, his Forum name is " h_a " Search and send him a message.

I have bought from him before, he is great to work with.

Buzzforb has really nice output transistors.

The little ones in the limiter circuit are available by the bazillion at all the normal distributors.
 
Essentially the only place you can be assured of getting genuine 2SK170/2SJ74 is from Spencer at Fetaudio.com

Ebay is all fakes.

The ZTX450/550 and IRFP240/9240 are easy - Mouser, Digi-Key, etc...
I bought matched k170/j74 of ebay (Hong Kong) for a F4 I build for a friend and had no problem with them.

The key word is "assured."
Fakes may work, but may not be optimal.
 
The 2SJ74 may very well be perfectly within tolerance for IDSS.

NONE of the ones I got from ebay or from other asian sources are genuine, there is a thread here about fakes, look for it, there are examples of the JFET fakes. Also some USA suppliers are just passing along fakes from asia.

The problem is mostly going to be the 2SJ74. The 2SK170 being offered may or may not be a real 2SK170, but it is easier to make N ch JFETs and the ones being offered work and curve trace ok.

The J74s I have obtained DO NOT match at all when curve traced.
The gains are different, as is the linearity.
But it is a functioning JFet, just not a Toshiba that is anywhere near a compliment to the K170.

This is not a low noise circuit, or one where low noise is required, so that aspect does not matter.


The performance of the amp in terms of harmonic distortion will be altered by the difference between the P & Nch JFETs in the front end. The amp will function regardless.

Hannes probably has legit parts. Spencer I have no information about.

Beyond this, it is apparent that JFETs and through hole parts in general are becoming rare quickly, and may end up being more difficult to source than tubes! Ironic.

_-_-bear
 
I concur with Bear. The K170's and SJ74's I've purchased through eBay in the past couple years were revealed as fakes on a curve tracer, even if their Idss happened to be within spec. I can confirm that Spencer's product looks genuine when curve traced. Unfortunately, he has been raising prices as things become scarce (can't blame him, supply and demand). Maybe Linear systems will one day bring their sj74 to market, but don't hold your breath.
 
This is also our finding.

A team member of XEN who has the best equipment in the Team (R&S UPV) did extensive measurements on LSK170 compared to 2SK170.
As a result of his measurements, we immediately bought a life time stock of Toshiba devices from Japan even at premium prices.
(This supplier is now also out of stock.)

While most of the LSK170s meet noise specs, their distortion in a typical circuit is higher than 2SK170.
And they also need to be operated at much higher Vds than the Toshiba's.

So even though we are fully aware of the possible (since 2005?) availability of the LSJ74s, we shall continue to want to use Toshiba's in our DIY lifetime.
You only need to compare the annual budget for process development at Toshiba, to say the total turnover of Linear, to understand why.

And look around in all Japanese (as well as elsewhere) semiconductor manufacturers.
Who else has ever managed to put out a low-noise, high-Yfs P-JFET ?
Only NEC, years and years ago (2SK163 / 2SJ44).

A few years from now, Toshiba FETs will just become like NOS tubes from Telefunken etc.
You can still get new equivalent tubes from Russia or China these days, but they are just not the same.


Patrick