Hfe measurements for transistor sets

[eldredracing]

I thought I'd finally build a proper Fuzz Face, so I bought a few NKT275 sets from this address:

http://store.eleb.cz/en/germanium-transistors/11-nkt275-fuzz-face.html

When I received them, all of the Q2 trannies were 96-103 hfe instead of the stated 120-140 and leakage was 230-340uA.  I used both my Peak and the Keen method to test and they were consistent.  On the transistor packages, the notes say:

hfe@Vce=2V, Ic=1mA, 1kHz: 122
Icbo(uA)@Ucb=2.0V@77degF: 3.3

DCA55 reading:
hfe=100
Leakage Ic=.23

Would these testing conditions make all the transistors gain read higher than what I'm finding with my meter?  Just want to know why they would all test low.

[rocket88]

Hey man. Just a couple of things. First, the temperature will have an effect on the gain and leakage readings you get, so if the temperature was higher where the company is their readings will be higher then yours. Second, is you should know those aren't NOS nkt275's. I don't know where those ones came from, but they've shown up in the past year and have been sold as NOS nkt275's, but they are nothing like them. Some company is either making them currently or are old copies of the famous ones that everyone is after still. That doesn't mean they won't sound good, but they will not sound the the NOS ones.

The NOS ones are short and fat, while these look like AC125's and such.

NOS NKT275:


The "Vintage" NKT275:


With all that said you caN still use them. In my experiments with fuzzfaces, the "holy grail" hfe isn't the end all be all, and I've built many a fuzzfaces with much lower hfe, like in the 50's and they sounded fantastic.

Also, I noticed that on this companies site in the description it says that you get a matching pair of AC128's, not nkt275's. Which is strange to me.

[Travis]

I thought that those were NOS but made by a different manufacturer (tungsram?).

Either way they aren't the NKT275 we're looking for.

To make matters more confusing, I think mammoth sells some actual current production "reissues" which are of course way off from the original. These are the ones that EHX and Dunlop used

[eldredracing]

Thanks for the help guys.  He agreed to take them back, but they have to be shipped overseas.  I'm just disappointed they didn't read what was stated on the page.  I wanted to compare to my favorites from our friendly Bulgarian ebay seller.

[dbat69]

Damkit

I've got some of those "vintage" NKTs from minifux.  Ohh well, I'll have to stick with the Russians from Bulgaria .... hmmm sounds like a Bond movie

I thought I might have been able to see what all the mojo fuzz is about but alas twas not to be.

Thanks for posting the pics Zach , at least I now know I've been done  and not to buy more from minifux

[Travis]

Again, I'm pretty sure these are NOS, just not the brand that we're looking for.

Also, the reissue NKT275 looks almost exactly like the real ones so look out.

You're probably not gonna find any real newmarket NKT275 at this point. If you do good luck cause if you post here to check if they're real they'll be gone if they're legit

[rocket88]

Anytime. I don't want anyone to get swindled and screw out of their hard earned cash by being deceived. Travis, I'm not sure if they're are really vintage or not, I had ways read that the skinny ones were the reissues. I didn't know that the short fat ones were being remade. This is really going to mess things up for us.

[Travis]

Yeah the skinny ones in the OP are not the reissues. Those should be NOS but again not the desirable brand or part

This is what the reissues look like (gut shot of an EHX pedal)


My suggestion for the guys that are new to this germ obsession is to just not even try to get NKT275. The chances of you actually getting the real deal are ridiculously slim

[rocket88]

oh shit. those look damn near identical to the real deal ones i've got. that's really fucked up.

[Travis]

They aren't really intended to be sold as NOS, they're supposed to be new "reissues". But people would easily buy them mistaking them for NOS

These have been around for years btw. The OC81D reissues look real also but they have the DSI logo which makes them easy to spot

[motterpaul]

Guys, I mentioned my experience on the 'Bay where I got a bundle of AC125s.

I saw a thread at Madbean where someone mentions these are sold in three different lots: IV, V and VI:  http://www.madbeanpedals.com/forum/index.php?topic=11715.msg106079#msg106079

he says for HFE:

IV - 50-100 hfe
V - 75-150 hfe
VI - 100-150 hfe

My lot is marked VI. Now I have been measuring and I am finding HFEs of 110 - 135, leakage of .40 to .82

I still need to figure out what these are ideal for. I have yet to try any fuzz so I don't know. Also, I need to find out how the leakage figures in, in terms of usage. It seems that most people are primarily concerned with HFE - but they always want to know the leakage, too.

Interesting about the NKTs - I bid on quite a few of those but never got any. I am supposed to have some Mullards coming from Turkey, though (I think they are OC77s but I would have to look it up).

[dbat69]

Thanks for the heads up Travis, I'll certainly give up looking for any more 275s
I got some of those reissue OC81Ds from minifux, although I had sussed out that they were a reissue by DSI

[tjdracz]

dbat69 wrote

and not to buy more from minifux

Had nothing less than a very good experience with minifux. As long as you're not trying to get NKT275 which are unobtanium or even stay away from AC128 you can get pretty great deals on the other transistors which are great, GC series, Japanese ones etc Plus combined shipping always, he doesn't screw you over.

Think lots of people got cross with him as they were complaining that HFE values were not what was stated in the eBay description. Truth be told, he only gives datasheet values if anything.

The skinny NKT275 are DSI-made, 99% sure. Reissue, not necessarily NOS (how old has it be to be NOS? Who knows?). Still will sound as good (or as bad) as the real deal. Heard people had good experiences with them. As long as you don;t pay obscene ammount, you should be good (and it's a good chance that minifux ones will be cheapest out there, loving no buy it now auction style)

Anyone that tells you that only NKT275 will give you sweet sweet Fuzz Face is plain bull****

Now, back into hibernation for me...