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  1. Replies
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    Ashdown Mag300 blown output stages.

    Default VI limiter/ SOA protection For push pull Amps.
    Hi all
    I have recently been getting a couple of Ashdown MAG300 bass amps with blown output stages.
    All due to either shorted speaker cables...
  2. Replies
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    For me, its JJ's. I buy them from CE...

    For me, its JJ's. I buy them from CE distribution. When I do use them, I always make sure the screens are 2k2 5W, and add 3000V flyback diodes to the plates.
    Never had an issue!
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    The fix is easy. Use slightly longer cables and...

    The fix is easy. Use slightly longer cables and place the box closer to the input of the amp far away from the power ttnsformerh side.
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    Opamp circuit DC offset

    Good day all
    I have built this circuit as part of a little audio mixer.
    Im getting a 200mV DC on the output pin. Opamp is not oscillating at all, actually perfectly clean DC.
    I have tried...
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    here are the documents I have been using to get...

    here are the documents I have been using to get to my list.
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    Hi Guys I know this is a very old thread. But i...

    Hi Guys
    I know this is a very old thread. But i think starting a new thread might be a bad idea.
    I'm in the process of compiling a list of things to do to convert a Jcm 900 dual reverb to EL34....
  7. Hi Spunkymonkey I know this is sn old thread....

    Hi Spunkymonkey
    I know this is sn old thread. With regards to the Heatkit scope from a post a couple of years ago. Could you explain in more detail how you routed the twisted heater wires.
    Did you...
  8. Bridge rectifier diodes have been known to go bad...

    Bridge rectifier diodes have been known to go bad in these amps. Replace them all and stand them off of the board.
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    Sticky: I'm only seeing this thread now. There is a fix...

    I'm only seeing this thread now. There is a fix for this. I have been doing on Blues jnr's for the past two years.
    It is due to lead dress. The cream boards where the worst.
    Solder a 100p capacitor...
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    Thanx for sharing my article :) I rebuild lots...

    Thanx for sharing my article :)
    I rebuild lots of these amps. Unfortunately the damage on this board is extensive. I haven't seen one with so much damage.
    Yikes!!
    Its probably fixable.
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    Thank you Chuck H. Please do share.

    Thank you Chuck H. Please do share.
  12. Replies
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    Speaker - amp attenuator topologies.

    I want to design and build an amp speaker attenuator. It will go between an amp and its speaker. I have been looking at L pads that parts express sells.
    But before i delve into building it I...
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    I found the problems. Wave was clipped on the...

    I found the problems.
    Wave was clipped on the bottoms.
    Decided to bias G &S at 1/2 supply.
    Then added a diode on Gate. Problem solved.
    Thank you all.
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    881

    I will check and report back. Client only brought...

    I will check and report back. Client only brought it back today
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    P channel JFET as audio switch

    P channel JFET as audio switch
    Hi.
    I recently built a 4 channel audio switch for a client. I was in a rush.
    I decided to use a circuit described on the net “Audio switch notes”. It uses a P ch...
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    Thank you for replying. I tested both in...

    Thank you for replying.
    I tested both in circuit. It seems like the free running frequency is a bit lower on the AN version. Go figure...
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    UC3842AN vs UC3842BN

    Working on a Mackie SRM 450 V2.
    It uses a UC3842AN.
    I only have the BN TYPE. What are the differences between the two?
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    I believe they are TDA8954 if I remember...

    I believe they are TDA8954 if I remember correctly.
  19. The final say/ Question on Output transistor matching.

    I know a lot has been written on the topic of parallel output devices.
    But, after repairing over 100 power amps of varying makes in the past two years, i have started once again questioning the...
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    The problem with standby switches is that they...

    The problem with standby switches is that they mostly switch DC. This is much worse than AC switching. I have implemented Rod Eliott's approach with much success....
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    Randall. I have exactly the same issue you...

    Randall. I have exactly the same issue you described. Did you fix it? What was the solution?
  22. Thanx for all the help guys. I managed to track...

    Thanx for all the help guys.
    I managed to track down the issue. When I cup my hand over a specific output valve the oscillation disappears. So it seems I have a faulty KT88. Will have to replace all...
  23. Did some further testing today. I think I might...

    Did some further testing today.
    I think I might have a faulty output transformer.
    I can hear it ticking when the instability happens at higher volumes.
    How do I test it?
  24. C14 wasn't installed on this particular amp, but...

    C14 wasn't installed on this particular amp, but adding it didn't make any difference
  25. Do you think I should try removing it?

    Do you think I should try removing it?
  26. I will check on Monday!!

    I will check on Monday!!
  27. Trace Elliot V4 bass amp oscillation issue

    I have this amp for repair.
    See attached schematic.
    It has 4x KT88's as outputs.
    Tubes test fine on my tester.
    All filter capacitors test good.
    Managed to get sound from it, but it has one last...
  28. Hi JM. Completely forgot. This issue has been...

    Hi JM. Completely forgot. This issue has been resolved. I have Modded almost a hundred of these units until now. Not one comeback. The info on the mod has been sent and reviewed by Montarbo HQ. lets...
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