Help! Old Thomas Organ/Dunlop crybaby typical npn transistors aren’t working

[Jbassfunk775]

Hey guys, I'm hoping that someone on here has come across this issue or maybe has some insight into these old wah's.  Basically it's an old 2 ("4117" printed) transistor Crybaby from the Thomas Organ/Dunlop Transition era back in the late 70's-early 80's, w/the "stack of dimes" inductor. Really a pretty simple circuit.. And minimal off board wiring; no Led, Non-true bypass, battery power only etc. which really makes things easy to troubleshoot.

  **Heres my problem; I removed the original transistors (I did it so long ago I can't remember exactly why) and based on information gathered by R.G. Keen the "4117" printed on the transistors was actually a parts reference number for Thomas Organ. Keen had to go really deep to hunt this info down (he's actually cataloged an impressive number of these ancient parts). Anyway,  long story short he recommended simply replacing these with a modern medium-low gain npn 2n5088/2n3904. I tried both and neither worked am I missing something here? I understand that these old wah pedals aren't exactly the most popular topic, and I've considered just replacing the circuit board entirely.. But I'd be psyched if could get this working again, it's been collecting dust on my bench for probably 2 years now so.. Thanks in advance!!

[Jbassfunk775]

*EDIT* I mistakenly wrote "4117" they're actually "5117" transistors, Apologies. I also wanted to post some photos and the schematic but my WiFi is down and I can't post icloud pictures until I  get my IPhone connected to WiFi.. But I will asap

[willienillie]

The "5117" was a shortened version of the Thomas Organ part number (86-5117-1 from memory).  They were actually Sprague 2N2925 transistors.  They came in TO-98 package originally, then switched to TO-92 toward the end of the Thomas period, but were still the same transistors.

The pinout was ECB, whereas 2N3904 and 2N5088 have EBC pinout.  So in order to use those transistors, you have to twist two of the legs.  Pretty much any NPN will function, but for the correct tone and sweep, you need to be mindful of the gains (hFE).  I like about 415 in Q1, and 260 in Q2, but those numbers are pretty rough, I don't have a very accurate measurement system.

[Jbassfunk775]

-Hey @willienillie thanks so much for the info, I know from experience it's not easy to come by!!

Apologies for the belated response.. I put this wah project/repair aside for a while and I'm only now picking it back up again. My general knowledge & understanding of the circuit and some of the key components (both vintage & modern) is definitely better than when I originally posted this.
So anyway after fussing with the old PCB and trying to make a decision about the correct transistor (I actually tried a couple varieties i.e. MPSA18's as well as 2n3904's & failed with both).. I just ordered a new PCB from Tonepad.com which is nearly an exact copy of my old one. Which I'll then repopulate with new components, minus the inductor which I salvaged from the old board.

Based on your advice and their popularity in boutique/repro wah's I decided to go with a lower hfe variant of BC109 transistor. If I remember correctly they were CDIL- BC109B (Indian manufacturer) which the datasheet had listed between 200-400 hfe. I'm wondering how many transistors you had to buy, and then test. To get ones in the specific hfe ranges you mentioned for Q1 & Q2?? I only bought about 10 BC109's from smallbear.. They're old Germanium's and too pricey to buy batches of 100+ like some people do

[willienillie]

BC109s are silicon, not germanium.  The gains I mentioned are what sound good to me with the stock circuit values, of the vintage Thomas Organ wah circuit.  You can change resistor values in certain spots to make the circuit work with a wider variety of transistor gains.