heyniceguy
11-01-2006, 01:17 PM
Chapter 3. This one has been a mystery to me since i got it in 2002.
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UNIT: Dr. Blade Subtortion Converter Pedal (circa 1990)
UNIT TOPOLOGY: Ugly black distortion box. Uses 12AX7, TL072 for gain stages, 1N34A for a clipping stage, 7805 in power stage with 2 1n4148's at pin 2 so that output of chip is ~6.5V, AC powered and rectified for +12V/+0 operation, 5 knobs: Bass/Treble/Tube Gain/Volume/"Incision".
PROBLEM: Didnt power up. Now it does. Distortion is ugly/splatty/mis-biased sounding.
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So this thing would even power on. Here's what i had to do so far (for the succor of future forum goers that may find this helpful) to get it to where it is now:
1) Checked transformer. Good.
2) Replaced fuse.
3) Replaced blown 12V zener diode which was rectifying the raw 15V from the transformer-AC/DC rectifier.
4) Replaced 2 NPN transistors with higher current ones that were feeding the circuitry from the zener diode output.
RESULT: Pedal powers up. Success! But when i play through it, the distortion is splatty and gated sounding. Immediately i think if a mis-biased tube. So heres what i did:
1) Swapped tube. No change.
2) Checked that 7805 output was exactly/close to half of Vref. Vref = 13V. Vb = 6.5V. Damn close.
3) Changed dual opamps. No change.
This is the extent of my knowledge with tube-based pedals. Im an EE grad from UF, so as you can imagine, the majority of my know-how is with Solid State stuff.
Does anyone have any insights or places where i can find faqs/info on 12V operation of tubes (starved plate, i think it's called)?
---------------------------------------
UNIT: Dr. Blade Subtortion Converter Pedal (circa 1990)
UNIT TOPOLOGY: Ugly black distortion box. Uses 12AX7, TL072 for gain stages, 1N34A for a clipping stage, 7805 in power stage with 2 1n4148's at pin 2 so that output of chip is ~6.5V, AC powered and rectified for +12V/+0 operation, 5 knobs: Bass/Treble/Tube Gain/Volume/"Incision".
PROBLEM: Didnt power up. Now it does. Distortion is ugly/splatty/mis-biased sounding.
---------------------------------------
So this thing would even power on. Here's what i had to do so far (for the succor of future forum goers that may find this helpful) to get it to where it is now:
1) Checked transformer. Good.
2) Replaced fuse.
3) Replaced blown 12V zener diode which was rectifying the raw 15V from the transformer-AC/DC rectifier.
4) Replaced 2 NPN transistors with higher current ones that were feeding the circuitry from the zener diode output.
RESULT: Pedal powers up. Success! But when i play through it, the distortion is splatty and gated sounding. Immediately i think if a mis-biased tube. So heres what i did:
1) Swapped tube. No change.
2) Checked that 7805 output was exactly/close to half of Vref. Vref = 13V. Vb = 6.5V. Damn close.
3) Changed dual opamps. No change.
This is the extent of my knowledge with tube-based pedals. Im an EE grad from UF, so as you can imagine, the majority of my know-how is with Solid State stuff.
Does anyone have any insights or places where i can find faqs/info on 12V operation of tubes (starved plate, i think it's called)?