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  1. Replies
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    2,971

    The story that I heard was that the Stones...

    The story that I heard was that the Stones brought their English Hiwatts to the States and they did not work, so they switched to Ampeg for the US tour.
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    874

    I replaced the MJ21194's with MJ15024's and that...

    I replaced the MJ21194's with MJ15024's and that took care of it.
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    4
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    874

    Yes, I specifically added that cap to stop the...

    Yes, I specifically added that cap to stop the oscillation, but it did not help.
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    4
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    874

    Crown DC300A Oscillating

    I have a DC300A on the bench that one channel was folding the top half early into a load. I couldn't get the original 2N5804 driver transistors, so I used a pair of MJ21194 transistors as...
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    1,061

    They can be used in Wah pedals. ...

    They can be used in Wah pedals. https://www.youtube.com/watch?v=lL9ToDSFz0E
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    11
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    889

    Yes, I changed the driver transistors. When I...

    Yes, I changed the driver transistors. When I ran each amp against ground, the amp that I just fixed was ok, whereas the one that I did not fix had the buzzing on it's output.
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    11
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    889

    I forgot something. One of the 15V rail caps,...

    I forgot something. One of the 15V rail caps, C24 blew up in the original amp failure. I replaced it along with C25. Could the regulator IC2 be compromised because of that?
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    889

    I just did the latter test, as it was easier. ...

    I just did the latter test, as it was easier. Grounding either one of the power amp inputs increases the hum quite a bit. Grounding both completely eliminates the hum. Looks like the preamp/power...
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    11
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    889

    No, I have not. What will that show me?

    No, I have not. What will that show me?
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    889

    This might be a later version. The power amp...

    This might be a later version. The power amp schematic only shows one of the power amp stages. If you look on the upper right, it shows that it is hooked up in bridged mono with another power amp B...
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    11
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    889

    Oops! Here they are: 44824 44825

    Oops! Here they are:

    44824

    44825
  12. Replies
    11
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    889

    Buzzing solid state bass amp

    I've had 2 different bass amps do this lately. This one is a Madison Abraxas amp that had a blown up output stage, as someone ran the output of another amp into this amp's output. The amp runs 2...
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    807

    Yeah, it's really weird. It doesn't make sense.

    Yeah, it's really weird. It doesn't make sense.
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    750

    This apparently works better:...

    This apparently works better: https://tubeamplifierparts.com/turret-eyelet-boards/fender-style-circuit-boards.html/
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    807

    The customer just brought in a footswitch for the...

    The customer just brought in a footswitch for the amp. And if I plug in the footswitch, the pump circuit no longer sputters when it is activated. In fact, if I plug in a stereo cable with nothing on...
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    6
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    750

    Here's the boards, pick your version:...

    Here's the boards, pick your version: https://tubeamplifierparts.com/turret-eyelet-boards/fender-style-circuit-boards.html/Fender-Bassman-style-circuit-boards-c9635850
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    3
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    807

    Peavey Encore 65 - Pump circuit sputtering

    The Pump knob causes a sputtering sound, with no input, when it's turned up above 2 or 3. I've swapped tubes, and that doesn't make a difference. I replaced the 51V zeners, thinking they might be...
  18. Replies
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    1,014

    I just re-capped one yesterday and it exhibits...

    I just re-capped one yesterday and it exhibits the same issue. I thought maybe I had a bad cap, but I paralled a new cap on each filter cap (one at a time) and it did not make a difference. I...
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    2
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    766

    Yes, the limit LED comes on when the tweeter...

    Yes, the limit LED comes on when the tweeter output is in Limit mode. Yeah, I guess they let the woofer clip, not exactly bulletproof, I guess.
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    766

    Mackie SRM650 Not Limiting

    I have a Mackie SRM650 on the bench with new PCB's, and the LF output does not go into limiting, it just goes into clipping. Has anyone else observed this? The HF output limits as expected. ...
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    1,485

    Randall, How old are those ARS caps? Any idea?

    Randall, How old are those ARS caps? Any idea?
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    1,032

    I charge $45 each as a diagnostic fee, just to...

    I charge $45 each as a diagnostic fee, just to look at the amp. If it's super easy, I might give the guy a break on that, but if I have to pull the amp apart, not really.
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    2,849

    Try a different speaker cabinet, if you can. How...

    Try a different speaker cabinet, if you can. How does the power amp output look on the scope? Do you have a Dummy resistor?
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    1,196

    Peavey 6505 Plus Channel Switch Popping

    I've seen this in some of these amps where the first few times you switch between Rhythm and Lead channels, you get a massive pop out of the speaker. And then after about 5 channel switches, the pop...
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    904

    Thanks Enzo. I'll look into the grounds and...

    Thanks Enzo. I'll look into the grounds and re-check all of the soldering.
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    904

    Roland PM-30 Oscillating

    I've got a Roland PM-30 that has ultrasonic oscillation (667Mhz) on all of the speaker outputs, and this is not a switching power supply. The unit came in with both fuses which feed the 5V rail...
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    598

    I figured it out. Q35 basically acts as a...

    I figured it out. Q35 basically acts as a switch. It grounds the input of the triangle wave generator at IC5, which turns it on.
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    598

    JC-120 Chorus Question

    The manual says that there should be a 25Vpp triangle wave at the output of IC5, but I am getting a very small output at that point and VR1 does not affect it at all. Can someone explain how the Q36...
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