1970 BMP - SPT 87-103 trannies or hfe info & specs sought.

Thaxt · Post by **Thaxt** » 24 Jun 2010, 09:17

As the (very happy!) owner of a 1970, Triangle Era Big Muff Pi, I have scoped out & recorded the components many times, for breadboarding mods,etc, & possible cloning. The ones that throw me (as to where to get exact specs, or better still, to find) are the (4) SPT 87-103 transistors.

Also: the diodes on this one read: GY 918 (or GY 816, looking upside down?)

The trannies sport a "T" mark on the opposite side of the part #, who's right end inflects upwards - like a kind of fancy script "T"... & the diodes have a kind of 'lightning', "S" shape , before the #'s "918"

I've heard that the "GY" refers to "Made in Guyana", but, I'm not sure how true this is.

Anyway, I'd be looking for anyone who has info as to where I can get the rare SPT 87-103's, or, @ least, an exact rundown on their specs, particularly
their hfe...which I'd say is pretty high. What they say about these Muffs is certainly true of this one; it has one beautiful tone, & one heck of a bass transient impact. & much more sustain than any of my mods, try as I have to use all suggested improvments.

rrhoads33 · Post by **rrhoads33** » 26 Jun 2010, 12:22

GY sounds strange to me. Is it possible, that it means (or originally meant) "BY" instead?

That would simply mean, it's a silicon rectifier diode.

The actual type of the transistor doesn't change the sound noticeable. The hFE of the transistor is way more important.

If you want to make really authentic BMP clones, you may also use one of these trannies: http://www.kitrae.net/music/music_big_muff.html#Mojo

Cheers

Thaxt · Post by **Thaxt** » 21 Jul 2010, 20:46

The important descriptive term w my (particular) 1970 Traingle Muff would best be "dynamic" - it responds most dynamically, especially with initial transient impact, & in a very bass-heavy way. While highs are compressed (as usual) by the 500pf caps, it still is a very "hard-hitting" Muff, w notes & chords, seems much better than subsequent models. It has an onboard EQ-dynamism that I'm not sure is there in many others. I do think I bought one heck of a prize w this thing.

I have put this down to the SPT 87-103's, as well as its using large input & feedback loop caps ( 2.0 & 1.0 uf electrolytics). It just seemed that a rapid response by the trans. (hi-speed switch types) might have been responsible for this,too.

Are you sure this transistor spec doesn't affect dynamic response?

I wonder if breadboarding a clone using other high speed switch type trans. might yield some info/results? I don't think (have to re-check those datasheets) that the typical 2N5133s or 5088/9s ,etc, etc, are described this way, pondered if there is any relevance to this spec.

mictester · Post by **mictester** » 22 Jul 2010, 05:33

Thaxt wrote: Are you sure this transistor spec doesn't affect dynamic response?

Not at all. The "speed" of the transistors won't have the slightest effect on the "dynamic response" - you'll be choosing from transistors the go up to 100 MHz or ones that go up to 400 MHz! The capacitor values will have most effect.