Duocast Ge specs

[Trevlett]

Hey guys,
My first time working with a germanium Transistor.
Q2 of the Duocast requires a OC71, I'm looking for an alternative at my local supplier.
He needs the following info to help..

• Voltage ratings
• Hfe
• Leakage

Any recommendations?
Thanks
Trev

 

[Cybercow]

Most any PNP germanium with low leakage will suffice. Just be aware of the pinouts.

 

[TheSin]

I used a GT2308 on mine and it sounds great!

 

[okstateblues]

GT-OC71 Mullard | Discrete Semiconductor Products | DigiKey Marketplace

Order today, ships today. GT-OC71 – Transistor from Mullard. Pricing and Availability on millions of electronic components from Digi-Key Electronics.

www.digikey.com

I used one from digikey in mine. If you aren't in a rush.

 

[ch ra]

OK, so seriously gain and other specs mentioned by the OP doesn't matter? It just has to be germanium???

How much is a reasonable price to spend? I've seen single OC71s going for $10. Does anyone have a better source? Even an eastern european seller that might do a multi pack for use in rangemasters or other similar circuits?

 

[benny_profane]

Aim for hFE~=70–110. The part number is irrelevant. The OC71 has so much mystique surrounding it that has driven up the price (that and it’s been OOP for decades). Unless you’re getting guaranteed gain and leakage specs, I’d be willing to bet all OC71 devices were previous cast offs that are now being sold. Save your money: Socket the transistor and try out any PNP Ge in the gain range with low leakage.

 

[caiofilipini]

What is considered to be low leakage in this case?

 

[benny_profane]

I usually go by RG Keen’s advice with fuzz face transistors when thinking about leakage:

How much leakage is too much? 100uA is common, 200 happens pretty often. More than 300uA means the device is suspicious, and more than 500uA I would say is bad.

http://www.geofex.com/article_folders/ffselect.htm

 

[caiofilipini]

I usually go by RG Keen’s advice with fuzz face transistors when thinking about leakage:




http://www.geofex.com/article_folders/ffselect.htm

Thanks!

 

[ch ra]

@benny_profane @PedalPCB do you have recommendations for a reliable, inexpensive source of unobtanium germanium transistors? Here's a couple I found on flea_bay:
https://www.ebay.com/itm/P30-30-Vin...rentrq:d9541f5b1730aaa32b80a3d6ffffe39f|iid:1

Transistors for sale | eBay

Get the best deals on Transistors when you shop the largest online selection at eBay.com. Free shipping on many items | Browse your favorite brands | affordable prices.

www.ebay.com

 

[benny_profane]

Those would most likely be fine. Small bear has plenty of options too. Don’t get hung up on the part number. It really doesn’t matter for this circuit. You just want moderate gain and low leakage devices. SBE will have the specs listed and you can choose what device sounds good to you.