Tone Vendor MK1 transistor options

[Song Naga]

Hi all,

I've got a Tone Vendor MK1 ready for transistors and I'm wondering if what I've got on hand might work. The BOM calls for an OC75 and a pair of 2G381's. I looked these up and the OC75 seems to have a minimum HFE of 55 and the 2G381's have a minimum of 75.

I've got a bunch of MP39A's and a pair of MA287's on hand, the MP39A's range from 14 to 49 HFE and the MA287's are 70 and 84 HFE. Are these in the ball park and worth trying out, or should I quest for some more appropriate transistors? Thank you for any input!

 

[leadfoot]

For MkI I've got these notes for hfe ranges:
Q1: 55 - 80
Q2: 65-100
Q3: 100-140

Also, replacing Q2's collector resistor (r5) with a trimmer to bias Q2 correctly can help.

That said, I'd socket the transistors so you can audition them for the best sound.

 

[leadfoot]

Since I mentioned MKI, here are the suggested specs I have for MKII:

Transistor	hFE	Leakage (uA)
Q1	60 - 90	< 200
Q2	70 - 120	200 - 400
Q3	110 - 170	100 - 300

 

[Elijah-Baley]

Small Bear shop has some different leakage:

Transistor Set - TB MK I PNP - Generic

New England's source for guitar pedals, pedal parts and electronics.

smallbear-electronics.mybigcommerce.com

Q1 hFE 70-85 Leak 150-320 uA
Q2 hFE 110-135 Leak 30-150 uA
Q3 hFE 100-120 Leak 20-120 uA

 

[Song Naga]

Also, replacing Q2's collector resistor (r5) with a trimmer to bias Q2 correctly can help.

Is there any value in also replacing R7 with a trim to bias Q3 as well? Is there an ideal voltage for the Q2 and Q3 collectors? I'm currently measuring -5.6V at the collector of Q2 and -7.0V at the collector of Q3.

The pedal does sound nice to my ears using the transistors I have on hand: currently I have a MP39A (49.1HFE) in Q1, an MA287 (70.2HFE) in Q2, and an MA287 (84.5HFE) in Q3. I know all these are below the suggested gain ranges so I may replace them soon with higher gain transistor.

 

[leadfoot]

I'm sure you could and I know AionFX has some suggested values for the readings on the transistors for what they consider spec. However, I generally just go by sound -- if I like the way it sounds, I call it done even if it is a mis-biased.

Here's a build report that has a lot of info: https://forum.pedalpcb.com/threads/tone-bender-mk-i-vintage-edition.14246/

 

[amorapotter]

Hi all,

I've got a Tone Vendor MK1 ready for transistors and I'm wondering if what I've got on hand might work. The BOM calls for an OC75 and a pair of 2G381's. I looked these up and the OC75 seems to have a minimum HFE of 55 and the 2G381's have a minimum of 75.

I've got a bunch of MP39A's and a pair of MA287's on hand, the MP39A's range from 14 to 49 HFE and the MA287's are 70 and 84 HFE. Are these in the ball park and worth trying out, or should I quest for some more appropriate transistors? Thank you for any input! - Yoplay -

The MP39A’s might be a little too low gain for Q1 unless you get one at the higher end of that range, but sometimes low gain can actually sound good in these old fuzz circuits.

 

[leadfoot]

I just finished off three TB style pedals a Tone Vendor MkI, Tone Vendor MkII and a Soul Vendor. I used 416A in Q1 and Q2 positions and a 410B in Q3 for all three and they fired right up and sounded great with no issues. The hFEs were around 60 - 80 for the 416As and low 100s in the 410B when measured with a DCA75 at 73*F in my office.