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About dave

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    incurable tinkerer
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  • Turn Table
    Pioneer PL L1000
  • Tone Arm & Cartridge
    Shure M75
  • SUT / Phono Stage
    834p tweeked
  • Digital Source 1
    Rotel RCD950 tubed
  • Digital Source 2
    Teknica tv tuner
  • Pre-Amp
    tubed dynaco PAT4
  • Power Amp/s
    ECL86SE, various diy
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    Wharfedale Dovedale
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  1. dave

    DC Offset different on both channels

    it could come from "un matched" transistors in the input diff amp, or maybe a leaking (dc) cap in the feedback circuiut. if it seems fairly stable wouldn't worry about it that much.
  2. dave

    Capacitor Tolerance

    They all sound fine (probably), but you need ESR (equivalent series resistance) to be truly useful, especially for power supply caps. I think tolerance is only important in filter circuits (as a gross generalisation). My cheap one, which I think was based on someone's home project, and then mercilessly cloned by the Chinese, measures ESR at the same time as capacitance.
  3. dave

    On the bench today.......

    Once upon a time I had a shortage of multiple input preamps. Being inspired by Lynn Olsen's Dynaco Pas re working I thought I got a good deal on a PAT4. You can imagine my disappointment when I found it was transistor, duh. Was wondering what to do with it, when I found that there are lots of upgrade kits, so I decided to convert it to valve with parts from Erhard audio. Been using for about a year and it's is very nice, but now on the bench for PSU work, as first attempt quite noisy. Heater supply diode noise primarily. The other work is the tone controls. The new design requires 100k linear, but trying to find concentric with the right diameter(s) spindle is proving to be difficult. I may have to settle for 50k and reduced range.
  4. dave

    Capacitor Tolerance

    Re caping is one of those mythical audio things people like to do. Yes electrolytic capacitors get old and dry out and go high impedance, yes paper in oil go leaky, yes some film caps of a certain age can do strange things, this is from my limited experience. Anyway maybe it's cooler in the UK and they last longer. Tolerance on caps are not very good, especially electrolytics. When describing test equipment it is nice to know make model. I have one that was £16,(probably a close relative of "LCR-T4 Component Tester Kit 9V with 12864 Green Back light LCD Display" on ebay) and it is very good but not very accurate on passives, I notice there is no tolerance Spec'ed on the above. Buy a few 1% caps and check its accuracy of you don't trust it.
  5. dave

    Identifying unmarked Transistor & circuit type......

    Result. Having a nicely documented circuit makes all the difference, and lots of web tweaks. If you post in the right place on DIYaudio you can communicate with the Pass himself. (Be warned), I was a bit taken aback when he responded in person to some of my slightly tongue in cheek comments.
  6. dave

    Identifying unmarked Transistor & circuit type......

    Switcher Cad is free, and an excellent simulator. I did what you did and then rearranged it to look like an amplifier. I have never done it like that before, I am looking forward to doing a few more now, like a fun puzzle.
  7. dave

    Identifying unmarked Transistor & circuit type......

    Spoiler alert, He says modesty. happy to delete...... My guess of the circuit. Drawn in LT switcher Cad.
  8. dave

    Multimeter Diode Test on Transistors - Results!

    2 points to me, I guessed the pnp and jfet from the PCB picture....
  9. dave

    Identifying unmarked Transistor & circuit type......

    Do an image search for "hitachi mosfet amplifier circuit" I would imagine it could be a derivative of one of those, due to the absence of big driver transistors, and temperature compensation. that would make the output devices complementary lateral mosfets...
  10. dave

    Identifying unmarked Transistor & circuit type......

    wow, is that it? you picked a good amp as a first project...... d
  11. dave

    Identifying unmarked Transistor & circuit type......

    In your multiple posts I may have missed it, but would it be possible to have a nicely lined up well illuminated photos of both sides of the amplifier board(s)
  12. dave

    Identifying unmarked Transistor & circuit type......

    The can is usually the collector for a bipolar transistor, see complementary emitter followers in link below:
  13. dave

    Getting active and never looking back

    As an incurable tinkerer I find building 2 amplifiers (for stereo) enough of a chore. Building 6 is not happening, in the foreseeable future. That said I intend to build some a active speakers with current output amps, I can't imagine it is possible to drive a passive crossover speaker with current unless the crossover has been designed to provide a constant resistive load. So I find passive to suit me better at the moment.
  14. dave

    Transistor Identification ?
  15. dave

    Transistor Identification ?

    Check if it is on the primary side of the transformers. If it is in the soft start it is probably mains, would be personally wary of it and leave it alone, put some insulation round it so you don't zap yourself. If it is working the amp should power up without any big clonk noise. If it is on the secondary it could be part of a protection circuit that shorts the transformers to blow the input fuse. Get your competent friend to work out what's going on. Appreciate that the mains side is not my area of expertise. That it seems to be mounted in a chocolate block sounds a little DIY, or stuck on as after thought. Also it is probably not remotely in the signal path during normal operation.