Aft preamp Trouble

[princeofyams]

Hey guys,

I’ve been working on a couple aft preamps and ran into the same problem with both:

When engaged, the signal only seems passes through if I’m playing hard; and then it quickly fades back out, almost like a noise gate with the settings cranked.

I did opt to use a OC140 rather than the 139’s but I didn’t think it would matter so long as the Collector and Emitter were in the right places.

Please let me know if you see anything obvious:




Thanks

 

[princeofyams]

**Does it on both settings

 

[JamieJ]

I had this with mine because the transistor was in the wrong way round. Double check the pin outs.

 

[princeofyams]

I had this with mine because the transistor was in the wrong way round. Double check the pin outs.

Did you also use a OC140?

 

[JamieJ]

I think I used an OC139.

 

[PAGOON]

I’m having this trouble right now and I ended up using the oc140 as well.. both transistors are mullard black glass… I used another oc140 that had 88hfe and that sounded choppy and cutting on and out and was unusable just like the 0c139 I’m. The one that works well is a 0c140 with 77hfe would ten hfe make such a difference or is the other two transistors I have bad? I switched the oc139 around the pinouts must be different from other mullard black glass transistors I have used … but I like the sound out both transistors so I’m going to install a toggle switch so I can switch from oc139 and oc140.