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  1. ViperZ

    Tannoy HPD 385A tweeter diaphragm replacement options

    Hi all, I bought a pair of Tannoy Berkeley with HPD 385/A in them, and one tweeter coil was repaired (now it is lower impedance compensated with resistor in series). I would like to replace the diaphragm with a coil, and Lockwood looks like the best replacement avaialble on the market. I also...
  2. ViperZ

    Velodyne ULD-15 subwoofer repair

    Hi all, I am going through my system repairing minor issues, and finally got to this Velodyne ULD-15 Series II subwoofer amplifier from 1985. I repaired it probably close to 20 years ago and it has worked great every since in my system. Last year I noticed that the subwoofer got a little...
  3. ViperZ

    ADC Accutrac 4000 repair

    (Many of you probably think - yes, another Accutrac 4000 not working... ) So I felt adventurous and got this Accutrac 4000 from a friend. It is missing the stylus, but everything else is there. What I have done so far: - Opened the bottom, axial 3300uF capacitor was leaking. Replaced all...
  4. ViperZ

    Disassembly of Marantz 1122DC?

    Hi all, could someone advise on the easiest way to access the selector board in Marantz 1122DC integrated amp please? The bottom of the amp does not come off. The amp is stuck on one input. So looks like selector shaft got disconnected somewhere from the selector on the board. Thank you.
  5. ViperZ

    Adjusting bias current in fixed-bias amplifier

    Hi all, I am almost done restoring a stereo amplifier from Rowe AMI jukebox, but would like to inquire about one remaining thing. First, I pushed the amp boards at rated 0.9V input with 14V output with no distortion. I pushed them further up to 30V output (didn't touch the preamp, as volume...
  6. ViperZ

    Help ID transistor and its substitution

    Hi all, I am working on this fairly basic amplifier, but of course I had to accidentally short something in one channel (channel output was low to begin with), so I had to replace both 2N3055 output transistors and their 0.47 Ohm emitter resistors. Unfortunately also shorted out the NPN driver...
  7. ViperZ

    Vintage Grado G cartridge stylus

    (I went through several threads on these carts, and tables, etc, but still can't figure this out, sorry). I have a tan-coloured Grado G vintage cartridge. Both coils measure equal, so it is a good cart. What is the correct replacement modern stylus for this cartridge? (I did clean out black...
  8. ViperZ

    Tube Buffer with known high input impedance

    Hi all, I am running Dynaco PAS-3 preamplifier with Dynaco MK-III monoblocks. I would like to split output of PAS-3 through basic RCA splitters and run second feed into Velodyne ULD-15 subwoofer amplifier (to compliment Magneplanar speakers low end). Unfortunately, ULD-15 input impedance is...
  9. ViperZ

    Sony TA-3650 - weird problem with volume

    Hi all, I have Sony TA-3650 integrated amplifier, which I rebuilt last year (one blown channel in the power amp). It has a "noisy" volume control - every time I click the volume control, there is an audible click in the speakers (much more in the left than in the right). I took apart sealed...
  10. ViperZ

    Rotel RA-1412 strange preamp problem

    I'll start documenting repair of my Rotel RA-1412 integrated amplifier. Sometimes it would just kick into protection randomly. Settings that I am measuring at: all tone controls are in 'out' position. AUX input is selected. I checked voltages on both power supplies, and all voltages are...
  11. ViperZ

    How to change a light bulb?? (pilot lamp in Harman Kardon A50K/A500)

    Well, that's embarrassing, but I can't figure out how to get to the pilot lamp (Type # 1847?) from inside the power button of Harman Kardon A50K (A500) integrated tube amplifier? Does the front panel have to come off? Or do I need to take the button body apart from the back (it has two metal...
  12. ViperZ

    Harman Kardon A50K integrated amplifier repair - help needed

    Hi all, I have been working on this integrated on and off for a few weeks now. It was in a very poor cosmetic shape, I cleaned everything up as much as I could. The power supply is completely rebuilt - new electrolytic caps and new diodes, all output DC voltages are good. I also replaced bias...
  13. ViperZ

    Sony TA-3650 pilot lamp wiring??

    Hi all, Can someone please post a photo of the connections where the pilot lamp is wired in their Sony TA-3650? Mine is missing the bulb (someone cut it off), and power supply wiring is different from the manual. I bought a new correct neon bulb, just need to know where to wire it. Thank you!
  14. ViperZ

    Sony TA-3650 integrated amp - light hum problem

    Hi all, I recently repaired Sony TA-3650 integrated amp with a blown channel. Now that it is working and DC offset is solid, I noticed that both channels hum/buzz evenly and slightly, but it is noticeable from 1-2 feet. I replaced two smaller electrolytic caps in the power supply, it didn't...
  15. ViperZ

    Help me troubleshoot Rotel RA-713 integrated amp

    Hi all, I have this integrated amp. The amplifier circuitry is fully working - I can trace sound all the way to the relay contacts, DC offset is a couple of mV on each channel. The relay works too - I can trigger it externally. The whole protection circuit is turned off - D903 is not biasing...
  16. ViperZ

    STK0039 - pinout question?

    Hi all, I'm working on Technics SA-300. Right channel gets significantly distorted at higher volumes. I found an equivalent schematic of STK0039 power module, but it shows only 6 pins being used 0/1, 2/9 and 3/8. SA-300 uses 7 pins from this module. 7th pin is Pin 5. On a good channel, pin 5...
  17. ViperZ

    Help - Technics SA-303 balance pot problem

    Hi all, I have this Technics SA-303. Sounds great from both L and R speakers (after I completely disassembled it into pieces and cleaned all pots and switches with contact cleaner). The receiver does not respond to the balance pot being moved. Balance pot is a 3-terminal pot, and measures...
  18. ViperZ

    Pioneer SX-650 - troubleshooting power amp board

    Hi all, I finally found some time to play with another receiver. This will be Pioneer SX-650. Original symptom was - relay clicking on and off. - measured all power supply voltages - all correct - measured all voltages to the power amp board - all correct Right channel DC offset = 0.41V...
  19. ViperZ

    Pioneer SX-750 protection circuit troubleshooting

    Now that I happily finished my SX-650, the SX-750 that I had in my system decided to act up and shut off the protection. It worked for a couple of hours, then protection turned on. Now the protection kicks in after 1-2 minutes at most. DC offset is ok on both channels - 30-50mV. Bias measurement...
  20. ViperZ

    Pioneer SX-650 protection circuit troubleshooting

    Got this Pioneer SX-650 stuck in protection. All power supply voltages are as per manual. Relay itself seems ok. Output modules are not shorted. DC offset is around 30mV in each channel. Started going through protection circuit. Q11 and Q12 have their 0V on each base (no DC offset in each...
  21. ViperZ

    Transistor substitution help please - MPS 6729

    I have Motorla MPS6729 burned out in my amplifier power supply control circuit. Can somebody please recommend a good substitute (beside NTE129)? Other versions of the same circuit (Carver M-1.5t power supply triac optoisolator control) use MPS U60 or MPS A93, but they seem quite different from...
  22. ViperZ

    Technics SA-5760 - one channel repair

    It's time for me to start my winter project (that I bought last winter lol). I wanted to start a thread to document progress. Technics SA-5760 with wrong (10A) main fuse blown. Replaced the fuse (8A FB) and turned it on (stupid), some resistors on the power board started to smoke. Somebody...
  23. ViperZ

    Repairing Crown XLS-602 amplifier - need help

    Hi all, A Crown XLS-602 has failed in a local church, so I'm trying to troubleshoot it and get it back up and running. All power supply voltages are present. No speakers and no inputs connected (happens with connected load/input too). Level potentiometers are set at zero on both channels. So...
  24. ViperZ

    Apt Amplifier Model 1 amplifier question - buzzing

    Hi all, I rebuilt Apt Power Amplifier Model 1 amplifier, but have this weird condition that I don't understand. When no input is connected, there is loud buzzing (transformer-like) through only the right channel (it's much quieter in the left channel). As soon as I connect RCA input from my...
  25. ViperZ

    Marantz 2240B - blown outputs - bad potentiometer??

    I have had this 2240B for a while - one channel had blown output transistors and a couple of resistors. So I replaced the parts, check the voltages without outputs - get weird voltages on the drivers (i.e. 5.5V instead of 5V, etc) Turns out that pot that adjusts bias current seems to be the...
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