madbeanpedals::forum

I'm working on an old board for the El Guapo fuzz. I bought 2 2N3565 transistors and decided to check their HFE before soldering them in. I found that they're wildly different. One was about 500 and the other one was maybe 290ish. Any recommendations on which I should put in Q1 and Q2?

Looking at s few older posts, over seen things like the 5088 and 3904 suggested. Is there something about those 3565 Si jobbies that's desirable for that circuit?

From a post regarding the Pepper Spray

Quote from: midwayfair on June 02, 2014, 08:23:04 PM
2N5088, 2N3904, etc.

However, in some circumstances, the 2N3565 seems to produce a slight octave effect, and this has only been observed in older (and lower gain) pieces. In other words, I wouldn't worry about it and would just use any transistor with hfe ~200-300.

Like I said, I always assumed Si BJTs were a bit more on the plain jane side of characteristics and that Germs were the magic beans.

Is there any reference as to what the original needs/wants?

I only bought the 2N3565 because they were available and look cute, but I'd put whatever transistors are of a favorable hfe value in instead.  I don't know anything about this circuit  either 🤷

Quote from: harryklippton on February 05, 2023, 03:25:12 PM
I only bought the 2N3565 because they were available and look cute, but I'd put whatever transistors are of a favorable hfe value in instead.  I don't know anything about this circuit  either

Look cute....


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The pragmatist in me would say split the difference, but the original datasheet has a min of 120 and max of 750 which puts you at 435. ¯\_(ツ)_/¯

Maybe socket it and try a few different values? ~200 and ~500 to see what results you get/like the most?

Small sample sizes here

Out of 70, the motorola 3904s I have hit mostly 140 or 170 (scattered in between).
(https://i.imgur.com/sCJTcbz.png)

The name-brand (Fairchild I think?) 5088s actually do sit right around 430 (from the 6 or so pieces I have left)

But the Tayda mystery surprise varieties are almost a linear line of non-matching indecision.
(https://i.imgur.com/qT6dcAr.png)

One other thing I just thought of: in some analysis of the Superfuzz circuit, the bias trimmer was so you could adjust for the difference in hFE values for the "matched pair" since I don't think they could match precisely (or bother to match them). But, *sigh* the pics I've found of the el Guapo don't seem to show a trimmer.

(https://i.ebayimg.com/images/g/I-0AAOSwEUFgihX8/s-l1600.jpg)

I also thought about the Madbean LETFA, but it simply suggests using the 3565s. My brief skim didn't show values in the documentation.

Interesting. Bean's LETFA does have a trimmer for the same reason.

(https://i.imgur.com/DA2UTFs.png)

https://www.madbeanpedals.com/projects/archives/1590A/LETFA.zip