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    Eden WT800C Power Amp module failure

    When is the last time you've encountered a simple SS power amp module fail, taking out EVERY transistor in the circuit? Besides that a handful of resistors, both zener's, leaving behind three 1N4148...
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    I have a pair of NiCd batteries in a vintage...

    I have a pair of NiCd batteries in a vintage General Radio 1564A Sound & Vibration Analyzer (1/3 Oct, 1/10 Oct, All Pass) that I bought used in Aug 1992 for $40 at a Radio Amateur's Technical Swap...
  3. While none of the replacement pots have that tap...

    While none of the replacement pots have that tap for the 120pF cap, no big deal, as placing one from CW to W terminals pretty much does the same thing. I hadn't seen this pot before......nice to...
  4. Repairing a Hewlet-Packard 6227B Dual Tracking Power Supply

    While working on the SWR SM900 last week, and setting up the remaining power amp modules from a boneyard SM400 to work in the SM900 chassis, I was powering up that amp module from an external...
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    It may be this 'dinosaur' of a Sony Mavica camera...

    It may be this 'dinosaur' of a Sony Mavica camera that I've been using mimics the shutter speed issues enough so that taking a picture of multiple sweeps, or dual displays on a spectrum analyzer that...
  6. This morning, after looking at the companion PCB...

    This morning, after looking at the companion PCB that had burnt thru the fiberglass, I found the fan circuitry is completely isolated from the heat sink. The head of the corner screw adjacent to...
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    Tektronix 466 Portable Storage Scope

    54655

    I'd start with reading thru the attached Instruction Manual for the Tek 466 Storage Scope. While I don't own a 466, my bench scope is a Tektronix 7633 Storage Scope, which unlike the...
  8. Everything changed when Ch 1 Heat Sink was screwed onto chassis!

    After removing the Nidec fan wires, and removing the temporary 2nd stage 1000uF filter cap, I shaped the leads of that cap, added a touch of RTV to glue it into place, soldered it in, then...
  9. SWR SM900 Fan Circuit issues (older series)

    Having opened up a client’s older SWR SM900 amp, the 2-pair quasi-comp output stage variety (four 2SC3265 Sanken MT200 pwr xstrs) and having the larger single EI power xfmr, I found the rear heat...
  10. Tackling the re-wiring of your hollow body Tele look-alike

    It's often the simplest circuits that those of us who are involved in very complex amplifier circuits and such make the most mistakes. And, when the build is so space-constrained as yours sounds, I...
  11. I think those Elmwood Sensor (or Equiv) Thermal...

    I think those Elmwood Sensor (or Equiv) Thermal Switches (mounted below the heat sink PCB) are 55 Deg C COR, while the ones in series with the output from the module are around 80-85 Deg C. I...
  12. Fender Blues Deluxe Reissue Rev A Schematics

    54517
  13. Thread: Nichicon EOL

    by nevetslab
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    Well, this just sucks big time!! I use those ALL...

    Well, this just sucks big time!! I use those ALL THE TIME...I just don't buy production qty. I absolutely hate it when Corporate bean counters decide Nobody should be using thru-hole parts, and...
  14. OK, now I'm following ya. The Grid resistance...

    OK, now I'm following ya. The Grid resistance path is typical of most amps....1M + the 68k resistors, one used to form the 6dB attenuator on the lower input jack. The 'normals' on the input jack...
  15. You're right........with the Treble Ch volume at...

    You're right........with the Treble Ch volume at zero, it IS dull sounding. So, it sounds like this is normal.
  16. I did check the shorting contacts on all four...

    I did check the shorting contacts on all four inputs, and they all measure ground, until interrupted with a plug.

    "if the passive input is open it will receive high freq content via capacitive...
  17. Ah, ain't that grand to hear a common 2N5551 has...

    Ah, ain't that grand to hear a common 2N5551 has 3 flavors, without being a different prefix. I've never encountered any of the non-EBC pinout versions with the 2N prefix. We'll see how long that...
  18. Marshall 1987x Plexi HF leakage via High Treble Vol Pot when plugged into Normal Ch

    I have a Marshall 1987x Mk II Plexi 50W head on the bench, doing preventative maintenance. After swapping out the power tubes and re-biasing, next checking to see if everything works, I find going...
  19. I've always thought a separate MEF Forum category...

    I've always thought a separate MEF Forum category such as this would be useful. It would certainly make it faster to search for something you came across in one of the maintenance or design forums...
  20. I hear ya on that! I gather you didn't buy those...

    I hear ya on that! I gather you didn't buy those parts out of normal distribution. 40V sure is way shy of their rated 160V Vceo!
  21. I too never allocated funds for a Tek 576 or...

    I too never allocated funds for a Tek 576 or better Curve Tracer. I had bought a B & K Precision 501A, one of the only two B & K Precision instruments I ever bought, and while it's limited to 100V...
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    Now THAT ^^^^ is my idea of a proper capacitor!!

    Now THAT ^^^^ is my idea of a proper capacitor!!
  23. The output protection relay circuit (schematic on...

    The output protection relay circuit (schematic on a different page) opened, so there wasn't DC on the output. Those TO126 parts that were on the individual U-shaped heat sinks were the pair I had...
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    With the value of 200 on the polystyrene cap,...

    With the value of 200 on the polystyrene cap, that could well be 20pF, where 201 would 200pF, 202 being 2nF and so on. I've been burned by those assumptions before, thinking it was 200pF.
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    Revised Traynor YBVA-1A Preamp tone circuits

    Now, I haven't yet built this onto a new circuit board. My Traynor still has a modified stock tone circuit installed, with this revised circuit needing the time to build it up and iron out the...
  26. Yamaha P2150, Output DC level near max V+, no shorted xstrs or open resistors

    Having a Yamaha P2150 Power Amp on the bench, whose left channel had it's output latched up near full V+ voltage, but not drawing current, I pulled the module after disconnecting the Hi Current...
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    Traynor YBA-1A Bass Master Tone Stack response curves, stock

    The stock Traynor YBA-1A's four tone controls ARE quite limited in what they do. I haven't finished revising mine, but when I first got it back up and running, I was very disappointed in how little...
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    Have you removed C1 10nF/1kV across the AC input...

    Have you removed C1 10nF/1kV across the AC input terminals of the bridge BD1? Does it matter whether you switch into Full (250VAC) or Half (180VAC) when switching out of Standby? With R2 lifted out...
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