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resurrecting a Heathkit Fuzz - questions about old components

Discussion in 'Burnt Fingers DIY Effects' started by jhundt, Jul 1, 2017.

  1. jhundt

    jhundt Doctor of Teleocity

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    I am trying to bring my old, original Heathkit TA-26 Fuzz back to life. It works, but the fuzz effect is mostly horrible. It breaks up, and sounds like a noise-gate thing is happening. Blatty and farty might describe it. I know that this is to be expected, to a certain extent, with a 1.5V powered 2-transistor Fuzz from the 60's; but I also know that this is not the way it sounded when I built it. It was actually pretty cool in its day.

    What I am wondering is this: can old transistors "go bad"? and if they do, will they make sounds like I described? I will be re-soldering all joints, and checking component values as I go. There are a few electrolytics I will probably replace... but I don't know anything about transistors or how to tell if they are working properly.

    I can't even believe how bad my workmanship was in 1968, when I was 14!

    [​IMG]
     
  2. luckett

    luckett Banned

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    It sounds like your bias is off. Check the voltages on the transistor legs.
     
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  3. jimbo735

    jimbo735 Tele-Afflicted

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    Did they ship that all the way over there back then.
    I just bought one to use on some recording, I live not to far from the old factory building.
    I'm seeing mods for this to help with the volume drop,the r10 and r12 can be changed to 10k I believe to balance it out better or add a boost to the output.
    Good luck.
     
    Last edited: Jul 2, 2017
  4. NotAnotherHobby

    NotAnotherHobby Tele-Afflicted

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    If the bias voltages are correct, the next question to ask is: what's going into the pedal? Is the signal amplified prior to it hitting the fuzz? If it is, you'll get the same gating effect. That thing is made to work with a relatively tiny signal coming in. If the signal levels are too high, you'll basically get the same effect.

    Likewise, a crappy battery or a corroded battery lead will do something similar as well. It is an old pedal. There may be rust on some contacts somewhere.

    Edit: And yes, transistors sometimes do go bad over time.
     
  5. jhundt

    jhundt Doctor of Teleocity

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    thanks, I'll try that today.
    no, I got this one when I was a kid, delivered to Oakland CA. I have been reading those mod threads; I'll probably try the 10k resistors.
    yes, there is a whole lot of corrosion. I think I will disassemble it; clean everything; test each component and replace if needed; and rebuild. Maybe that will solve the problem.
     
  6. mictester

    mictester TDPRI Member

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    The transistors are very unlikely to be faulty. I'd check all the soldered joints first, then change out the electrolytic capacitors (be careful about the polarity of the caps). I built one of these a while ago (just out of curiosity) and it's a great sounding fuzz. It's worth increasing the 1k resistors (R10 and 12) - I used 4k7 at both sides - to get slightly more than unity level through the box. I also used a "Millennium" Indicator with a DPDT footswitch to show when it was on (not that you'd miss it, but it's nice to know before you begin to play!).
     
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  7. jhundt

    jhundt Doctor of Teleocity

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    thanks mictester, and welcome to the forum. I am going to try the larger resistors, after I clean it all up and test/replace the components. I checked the transistor voltages today, and they seemed to be pretty close to those specified on the schematic. My "1.5 Volt" source is actually about 2.3 VDC, so all the voltages were about 50-60% higher. I don't know enough about transistors to say for sure that this is NOT a problem, but I read some posts on other forums where guys were building this design and running it successfully with 9 V.
     
  8. NotAnotherHobby

    NotAnotherHobby Tele-Afflicted

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    It's not a problem. Battery voltages vary based on how "fresh" they are.

    I now highly suspect corrosion on the battery terminals. Rust acts as an insulator. Voltage will show fine when applied (as it is the potential difference between the voltage source poles, but current flow will be artificially limited or "starved" causing the transistors to "work harder" to pass the signal.

    The first thing I'd do would be to clean or replace those before anything else to eliminate the possibility of there being a problem at the source.
     
  9. jhundt

    jhundt Doctor of Teleocity

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    that's what I'm going to do... but first I need a massive clean-up of my workbench. Too many projects going, I can't even find the surface anymore!
     
  10. NotAnotherHobby

    NotAnotherHobby Tele-Afflicted

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    Oh...do I ever know the feeling...
     
  11. jimdkc

    jimdkc Friend of Leo's

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    I'd replace all the electrolytic capacitors first. That'll probably bring it back...
     
  12. dogwatermike

    dogwatermike Tele-Meister

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    Did the Fuzz ever sound good?

    I built a HealthKit guitar amp in '68 or '69 when I was 15 or so....it sounded bad then (ice pick).... and it sounds bad now!!! A tube amp years later made the difference for me!

    I like your story about fixin' it up! Let us know how the project goes!
     
  13. jhundt

    jhundt Doctor of Teleocity

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    Mike - I built a Heathkit guitar, a Heathkit amp, and this Heathkit fuzz. I think the guitar probably sounded good, but I wanted a Strat so bad I never appreciated it fully. The amp was definitely not a very nice-sounding thing, though it looked OK. I replaced it with a black-face bassman and 2 12" Radio Shack speakers in a home-built cabinet. The fuzz might have sounded OK. I can't remember using it to tell the truth. And I never used any other effects since then. Maybe it was so bad it turned me off to effects?
     
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