after getting DCA55, how to calculate bias resistors?

[dont-tase-me-bro]

is there a document or old thread that exists on how to do this?  I saw this calculator below, but figured there was more information out there.

http://www.diystompboxes.com/biascalc/ffbias.html

I wanted to order a DCA55 and a bunch of germanium, but didn't know what is contained in Small Bear's magic wand.

Thanks,
Pat

[Blues Healer]

have you read this:
https://www.smallbearelec.com/HowTos/FuzzFaceFAQ/FFFAQ.htm

Steve measures his transistor sets in an actual test circuit. I assume he uses math to figure out his resistor values.

in that article, he tells you exactly which gains work best in the circuit. The problem is that Ge gains vary a lot, so as he says, in order to keep costs affordable, he broadens the allowable gains, thus the tweaked resistor values. Note that those values are for the stock circuit, with fixed resistors. That is why a lot of folks nowadays use a trimmer -- it's adjustable!

anyway, I don't know the exact math he uses, but I measure my transistors for gain, set the bias, then LISTEN ... articles always mention that 4.5v setting, but as you know, actual voltage varies. In fact, I just got through testing an Axis circuit that sounded kinda crappy at 4.5v, but sounds great at 4.8v. Go figure.

anyway, I don't know if any of that helped, but the Peak tester is great for sorting transistors quickly, whether it's Ge or Si, NPN or PNP. you can also use it to verify the pin out if you have any doubts. That allows you to buy stuff like Small Bear's bulk trannies, and save some dough.

[dont-tase-me-bro]

Thanks.

I guess then, if I install transistors that are within the proper gain range per location, I wouldn't really have to tweak the resistor values for the most part.  I was looking at it wrong.

And if in doubt and my transistor was a bit off, I could either breadboard, or just socket the resistors.

I think I'm gonna order one tomorrow.

[dont-tase-me-bro]

and PCBs with trimpots will be key.  Nice, now I hunt for transistors

[culturejam]

I was going to suggest that the best way to bias a germanium transistor is with a trimmer. Even if you impeccably measure and calculate, those numbers are only good for whatever the ambient temp is in the room where you measured the trannies. Once the temp changes, the transistor gain changes, and then your bias resistor values are going to drift.

[dont-tase-me-bro]

Thank you for the info.  Just ordered some Russian transistors on ebay, after watching chrome sphere's tutorial on youtube.  I emailed New Jersey Semiconductor too.  It looks like they still manufacture germaniums.  Curious to see what they say.  According to their site, they have OC series in stock in NJ.  Being a fellow new jersey-er,  I probably get 10% off by using the secret handshake

[Blues Healer]

smallbear has a plethora of transistors, and he usually gives you some idea of the gain in each batch, and often the circuit they're best suited for

[TGP39]

Being a fellow new jersey-er,  I probably get 10% off by using the secret handshake

They stopped that years ago when the fat guy became governor.  Now you just have to bring some twinkies.

[culturejam]

I emailed New Jersey Semiconductor too.  It looks like they still manufacture germaniums.  Curious to see what they say.  According to their site, they have OC series in stock in NJ.  Being a fellow new jersey-er,  I probably get 10% off by using the secret handshake

Springfield is about half an hour from my house. Interesting.

[dont-tase-me-bro]

In stock at NJ semiconductor.  placed order today for a few different oc series, and I think some 2n.  Their online RFQ from kind of sucks, I could only add one thing, so it took several emails.  I felt bad I had to keep bothering the guy for a $100 order, but they don't have a cart on their website.

[dont-tase-me-bro]

They seem primarily b2b.  They asked me to send them a PO.  I drafted a letter, signed and scanned, and they took it with amex over the phone.

[culturejam]

If you don't mind, could you post (or PM me) the pricing? I could email them as well, but I'd rather not waste their time if it's definitely not going to work out.