Unobtanium for AFT Preamp?

[Dali]

That is just rambling, I'm not even really interested in doing it but I'm just curious.

AFT Preamp (https://www.pedalpcb.com/product/pcb346/) needs an OC139 very difficult part to find, so how people are expected to build the thing?

Or maybe the future building docs will have a list of easier replacements?

 

[benny_profane]

It's a modified rangemaster with input cap selection. Any Ge NPN BJT suitable for a rangemaster will work with this project. Part number is not relevant and is a reference to the part designated in the original build.

 

[Nostradoomus]

It's a modified rangemaster with input cap selection. Any Ge NPN BJT suitable for a rangemaster will work with this project. Part number is not relevant and is a reference to the part designated in the original build.

Truth! The guys at freestompboxes who traced it out had a measurement of 39hfe (unsure on leakage) on the OC139...hopefully a good candidate for the duds I get in bags of Russian Ge NPNs!

 

[manfesto]

I built an EffectsLayouts Beauregard (also a Bows) and used an MP38, works great! I did replace the emitter resistor with a 5K trimpot using a PedalPCB Trim pot adapter so I'd have an easier time biasing, might be a good idea to do with the Aft as well.

(Also, this circuit driving any of the Muff-derived circuits is really something special; I put the Beauregard in a combo box with a PedalPCB Ungula and it's *great*)

Trimmit! - PedalPCB.com

Trim pot adapter

www.pedalpcb.com