Now I didn't go as far as measuring and matching gain and leakage (as much as possible), but here's a comparison of a few Q3 transistors for a Tone Bender MKIII - all the same setting, just swapping Q3 on the breadboard.
Why? I saw someone on Facebook poking fun at an eBay seller in Thailand over what they thought were fake OC71. I bought some as the seller looked legit to me, as did the transistors - so I tested them yesterday, and it turns out they are real, so I promptly ordered more.
Lines on a screen don't replace ears, but as you can see, they are quite similar. There are definite differences in harmonic content, with the 2nd and 4th being the most obvious. On the scope, the waveforms are very similar, with hard-to-pick differences.
I could talk about the sound, but it's very subjective...
Unbranded OC71
Valvo OC75
Mullard OC81
can you say the name of the seller on ebay you used?
ReplyDeleteSure - the ebay seller is papanohn1, and there's some available right now. Please note that I have no association with this seller.
ReplyDeletehello, this Multi Function Tester Tc1, Can it measure leakage with good results? thanks
ReplyDeleteHi Andy - I have a post about it somewhere here. Try looking under tools, or search for tester. Short answer is yes. They’re great for $20
Deletethanks! I got some Germanium NPN and I want to mount a Tonebender, which schematic version do you recommend?
DeleteWhat better trio to get a great tonebender?
Follow report with Geofex tester
Item - HFE - LEAKAGE mA
01 - 116 - 0.082
02 - 113 - 1.015
03 - 79 - 0.566
04 - 113 - 0.607
05 - 69 - 0.562
06 - 90 - 0.983
07 - 97 - 0.672
08 - 121 - 0.716
Thanks
Personally I like the DAM Fuzzsound III layout, but that does have a slightly bigger cap in the high pass filter, so it’s not an exact copy of the originals. It does sound great.
DeleteLooking at my layouts I just realised that I haven’t posted a layout for a MKIII using standard vero. I probably should do that as not everyone will want to go point to point or have access to 0.15” vero.
In terms of transistors, MKIII Tone Benders will work and sound good with almost any germanium transistor. I’ve tried a lot on the breadboard, and found that most work just fine.
I’d suggest putting the two withe the lowest hfe up front for Q1 and Q2, and then the highest hfe with moderate leakage in Q3. So maybe number 4 or 8. If you have a breadboard, I would solder some jumper leads on and test a few in Q3 to see what you like.
One of my favourite MKIII has all OC45 transistors, which are low hfe and leakage, and I really like it. These are never recommended and are the wrong spec according to everything online. It’s a little less aggressive / not as tight sounding as normal, and the best way I can describe it is soft and spongey - still has a lot of fuzz.
Good luck.
Oh and don’t forget to flip the electrolytic caps and the germanium diode for a regular Power supply (not positive ground) - guessing you already know this, but just in case…
Deleteyes I know about the electrolytic inversion, thanks!
DeleteI'll try MKIII Tone Benders, what's the biggest leak I can have in the circuit?
I’m yet to find a germanium transistor that doesn’t work in Q3, and that includes some quite leaky OC75. They just have a different texture to the fuzz or noise levels. But to answer your question, anywhere in the 400 -900uA range will be fine. These are without a doubt the easiest Tone Benders to make.
Deletethanks \m/
Delete