ram's head transistor choice

[evildead222]

I got a rams head put together except the transistors.  I got some bc547's laying around.  Are they close to bc550's?

[midwayfair]

This is a complicated answer but hopefully it'll be useful.

First, once you get above ~100hfe, the differences between transistors become very, very small except with huge changes in hfe. hfe 300 isn't vastly different from, say, hfe 800 except in special circumstances.

Second, take a look at the BMP schematic and you'll see that the gain is not maxed out on the transistors used. The emitters aren't grounded, and the collector is hardly smashed; additionally, the 470K/100K voltage dividers on the bases could also be increased to get more gain out. Hitting certain bias voltages might help achieve certain sounds, but you'd want to compare with a known good sounding unit. (6V is good.)

Third, always read the datasheet. If you didn't do that yet, then lesson learned for next time! If you did, it's polite to link to the one you used. Here's a perfectly cromulent one: http://www.ece.usu.edu/ece_store/spec/BC547.pdf

You'll notice that it's a little difficult to answer your question: You need to tell us which designation is on the transistor (A, B, C). But the numbers generally line up with the other transistors in that series. And FWIW, that series is VERY consistent, quieter than a slew of other transistors, and sound quite good.

[evildead222]

I jammed them in there and they sound good.  I don't understand half of the stuff you just said, I'm still learning.  I just read a bunch of stuff on muffs and transistors. It sounds smoother and more like a rams head with bc547's than the 2n5089's i had in before.

[pryde]

I jammed them in there and they sound good.  I don't understand half of the stuff you just said, I'm still learning.  I just read a bunch of stuff on muffs and transistors. It sounds smoother and more like a rams head with bc547's than the 2n5089's i had in before.

The 550's are lower noise transistors than the 547's. Even though the 547's sound ok I would be open to try some others (I hope you socketed them). Try some 2n5088s if you have them as they are a bit lower lower gain than the 5089's.