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    Excellent, thank you!

    Excellent, thank you!
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    Thanks everyone. It's for the Mackie FR...

    Thanks everyone.

    It's for the Mackie FR M1400i I am working on in this thread:

    https://music-electronics-forum.com/showthread.php?t=49370&p=537573#post537573

    The schematic is in that...
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    Rectifier substiture?

    I'm trying to find a substitute for an obsoleted rectifier, SF304 (see attached datasheet). Does this look like a good substitute?

    FFA60UP20DNTU
    ...
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    So I've spent some more time with this amp and...

    So I've spent some more time with this amp and found out that apparently by DMM's diode setting is not working. I used a different one and now I appear to be measuring a short on half of D7 (center...
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    Sorry I haven't responded in a while to this...

    Sorry I haven't responded in a while to this thread. I had a lot going on and a desperately need vacation that put this on the back burner. I'm back and still trying to figure this out.


    ...
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    Maybe I misunderstood The Dude's post. I...

    Maybe I misunderstood The Dude's post. I measured the + and - binding posts of each channel for a short.




    I THOUGHT by removing the 10A fuses I eliminated the power transistors, but since...
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    That's what I thought, but when I test it that...

    That's what I thought, but when I test it that way I get "weird" results.

    According to the data sheet I included in the first post the center leg is a common cathode or anode, depending on which...
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    Thank you for your response. I tested the 1N5404...

    Thank you for your response. I tested the 1N5404 diodes on the 80V rails (D1, D6, D9 & D12) and they all tested fine, ~450 in one direction, open in the other using the diode test mode on my DMM. I...
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    Mackie FR M1400i blowing main fuse

    After you guys helped me out with my Peavey CS800S I thought I could tackle anything (just kidding), but I'm trying to solve a Mackie FR M1400i that blows the main fuse as soon as it's powered on. ...
  10. I sent the tubes back as I mentioned in the last...

    I sent the tubes back as I mentioned in the last post and the folks from Tube Depot sent me a set with their 24 rating. It was a big improvement! I was measuring 28-29mA @ ~370V vs the 41-43mA @...
  11. I noticed that the boxes that the tubes were in...

    I noticed that the boxes that the tubes were in were marked "37" so I emailed the folks I purchased them from and asked what, if anything, that marking meant. They responded that they test them at...
  12. I can't wrap my head around this. I know you...

    I can't wrap my head around this. I know you "lose" .7V when passing through a diode, but it doesn't seem intuitive, at least to me. So if you start with, in this case, +15.7V and pass through a...
  13. I'm not concerned about the voltage I'm measuring...

    I'm not concerned about the voltage I'm measuring (370V), but I am about the current (41-43mA). It seems like every EL84 guitar amp goes over the 300V max for EL84s, but all the things I've seen say...
  14. I used an Amp-Head bias probe. These guys don't...

    I used an Amp-Head bias probe. These guys don't seem to be around anymore so here's the archive.org capture:
    ...
  15. Still Wrestling with a Crrate GT500H/VC50 bias

    I'm still playing with that Crate GT500H that I was asking about HT fuses on a while back:

    https://music-electronics-forum.com/showthread.php?t=47617

    As described in the previous post it had a...
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    Yes it does. :) I really thought I was in over...

    Yes it does. :) I really thought I was in over my head on this one once the simple stuff didn't fix it. Well, actually I was, but you guys saved me. I learned a lot on this one.

    Thanks again.
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    It took along time, but I finally had a chance to...

    It took along time, but I finally had a chance to work on this again. I installed the new MJ15025 & MJ15024 power transistors and 2N5415 & 2N3440 voltage gain stage transistors, as well as...
  18. So of course I didn't have amp 1/2A fuses laying...

    So of course I didn't have amp 1/2A fuses laying around and now that Radio Shack is no longer around in my area I need to order some. But I do have some Buss MDL 3/8A, 250V (slow-blow). So...
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    I checked all of the resistors that were not 1/4w...

    I checked all of the resistors that were not 1/4w carbons, as I have plenty of those, and went ahead and placed the order. When I receive the parts I will install and report back.

    Thanks for...
  20. The only things I can see are: 1/2A 250V 312...

    The only things I can see are:

    1/2A 250V 312 around the metal on one end
    nothing wrapped around the metal on the other end
    on one end what looks like an LF as kind of a logo, I'm guessing...
  21. The blown fuse appears to be fast acting. I only...

    The blown fuse appears to be fast acting. I only see a little bit of thin wire in there, not the coil I'm used to seeing in a slo-blo.
    In my limited experience, slo-blo seems more common as well,...
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    Thanks again! I added the 2N5415 and 2N3440 to...

    Thanks again!

    I added the 2N5415 and 2N3440 to my Mouser order. I'm not sure what else I should check, caps, etc., or am I at the point where I should just place the order and install everything...
  23. Fast Acting or Slow Blow on B+ in Crate GT500H/VC50?

    So while you guys have been helping me with a Peavey CS800S in the "Other Amps" forum I picked up another project, a Crate GT500H. The GT500H is supposed to be the same as the VC50 (Vintage Club),...
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    I finally had time to go over this one more time....

    I finally had time to go over this one more time. I checked the resistors suggested (as well as all of the flame proof and big ceramic ones, I have plenty of 1/4W resistors so if I discovery any bad...
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    I finally had a chance to pull the power xstrs...

    I finally had a chance to pull the power xstrs yesterday evening and measure them. It was easier than expected. I just flipped the board over, soldapullt the leads and went back and forth trying to...
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    Thanks again nevetlab, I will lift the...

    Thanks again nevetlab,

    I will lift the resistors you suggest and check. I'm pretty convinced all of the power xstrs are cooked, but maybe I'll get lucky. I'm thinking that at some point, either...
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    I took the readings from the base to emitter and...

    I took the readings from the base to emitter and base to collector, but I didn’t differentiate, so I can’t tell which order I listed the values in. I didn’t look up which were NPN vs PNP but tried...
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    I finally had a chance to start really digging in...

    I finally had a chance to start really digging in last night/this morning. Here's what I've found so far, and I believe it doesn't look good:

    I started with checking Q120 and Q121 and the diodes...
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