Sola Sound - Tone Bender Mark I (1965)  [schematic]

Discussion regarding early stompbox technology: 1960-1975 Please keep discussion focused and contribute what info you have...

Re: Sola Sound - Tone Bender Mark I (1965)

Postby pietro_moog » 16 Dec 2019, 18:30

Hi guys.
Recently i was really into Doyle Bramhall II, and in his Reverb interview he talked about the Zonk Machine as a secret weapon.
So i decided to build a Tone Bender MK1 just to see what it is.
I didn't have fancy 60s transistors, so i used some russian ones. They say you need leakage for MK1, but these are very low.
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Re: Sola Sound - Tone Bender Mark I (1965)

Postby pietro_moog » 16 Dec 2019, 18:58

I adjusted a few resistors and caps, and the Q3c voltage is like -8.05v
I don't what to make of Q2C: it really depends from the voltage divider, so i tried 180k (-1,2v) and 430k (-5v); i don't know what i like more, i can't decide.

Q1 is the strange one: it has very low hfe and leakage, but everything works. i tried to reach the suggested voltage (around -1v) changing the bias resistor, but i only get to -0,4v with a 4,7M resistor. There is a noticeable effect though, it doesn't SAG anymore.
With 1M on Q1B i had a HUUUUGE Sag, i wasn't expecting this (but i like it).
Is this suppose to happen?
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Re: Sola Sound - Tone Bender Mark I (1965)

Postby pietro_moog » 16 Dec 2019, 19:00

I forgot: my transistors are

Q1 = MP40B, 30hfe, 20mA L

Q2 = gt308b, 64hfe, 5mA L

Q3 = MP42 , 52hfe, 50mA L
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Re: Sola Sound - Tone Bender Mark I (1965)

Postby Manfred » 16 Dec 2019, 20:29

Hfe depends on collector current at which current Hfe was measured.
The unit for the leakage current is certainly Microamps not Milliamps.
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