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  1. SO I'll admit I don't really know what I'm doing...

    SO I'll admit I don't really know what I'm doing here but I found the issue, it was in U3A not U3B. Reduced the value of r28 (470k) and the problem disappeared. I know enough to understand I have...
  2. WOoOf, I was looking at u6, don't know what I...

    WOoOf, I was looking at u6, don't know what I was thinking.

    I'll test the AC points with the 1k signal as suggested, but my guess is that I need to increase the gain to the IC stage u3, would my...
  3. I actually did sub in a in4148 just to check, it...

    I actually did sub in a in4148 just to check, it was definately just the JFET :)



    Ah yes, well, while it does sound like what you'd imagine an Eric-Clapton-flavored turd to be, I believe it...
  4. One other issue I'm having now that all the...

    One other issue I'm having now that all the switching elements and crosstalk are fixed is a sort of crossover-esque distortion on the drive channel. I did replace both the IC and one of the LED's...
  5. Ahh, ok! the diode was measuring under, about...

    Ahh, ok! the diode was measuring under, about .3 instead of the other in4448's .55, so I wrongfully assumed. I understand now that lifting one leg of the diode was just a way to break the pathway...
  6. Enzo, thank you, this has helped immensely. ...

    Enzo, thank you, this has helped immensely. Turns out it was cr29, lifted one leg and everything functions as it should, switching and all. Still no reverb but perhaps that's because q5 feeds u5...
  7. Thanks Enzo! I didn't catch that, thank you for...

    Thanks Enzo! I didn't catch that, thank you for the correction.

    SO I think I understand what we're looking for now! U4 controller does indeed switch between 15/ -15 supply voltage for the...
  8. Hey Enzo, Thanks! All the low voltage rails...

    Hey Enzo,

    Thanks! All the low voltage rails are 15/-15 after replacing he bad ICís.

    The channel symptoms are as follows:

    Clean setting: clear Ďcleaní signal comes through speaker, ...
  9. any ideas of how to start troubleshooting those...

    any ideas of how to start troubleshooting those summing circuits? Iíve proved the signal
    Extensively and all I can really surmise is that it doesnít properly pass q4
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    Found it! Now that we have a correct PCB schem,...

    Found it! Now that we have a correct PCB schem, I went back to the other suggestions by Enzo, checked the ACTUAL resistor/cap he meant, (r3/c3). They measured fine, but there was no continuity to...
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    Here, found the correct PCB...

    Here, found the correct PCB version:https://music-electronics-forum.com/attachment.php?attachmentid=23933&d=1371880709

    And another similar...
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    I think it is the correct schematic, I could be...

    I think it is the correct schematic, I could be wrong though.

    Page title: ABM output board
    Project: Bass Magnifier

    Thereís text at the bottom to leave out tr3/tr6 c21/c211 on the 300 watt...
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    Hey G1, good thinking. Iíve already done that...

    Hey G1, good thinking. Iíve already done that and thatís what made me test for AC at the output in the first place... I saw an arc across the speaker cable when plugging it in! As soon as you add...
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    So, Output pot measures well, no AC on the...

    So, Output pot measures well, no AC on the output DI or the turner line output. The mute seems like it functions, No AC on the output until the first relay click during startup.
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    Thanks Glebert! Will check those and get back.

    Thanks Glebert! Will check those and get back.
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    Thanks Enzo. I donít have a scope, but I do...

    Thanks Enzo. I donít have a scope, but I do have an audio probe. The resistor is intact and measure a pretty well.

    Perhaps thereís an other way to check the rails??
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    Mick, youíre definitely onto something. AC...

    Mick, youíre definitely onto something. AC disappears when I disconnected the preamp board, grounding the input has no effect though. Resoldered c16/c15 and everything around r18 to no effect. ...
  18. Deluxe 112 Plus crosstalk / switching issues

    Got a highly abused Deluxe 112 plus that Iíve been working on for a couple weeks on and off. Didnít make any noise, replaced Q7, power amp springs back to life, But no sound from front end....
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    Ashdown Evo Mag 300 pulling current

    http://bee.mif.pg.gda.pl/ciasteczkowypotwor/SM_scena/Ashdown/Ashdown_MAG300_schem.pdf

    Hey yíall,

    Have a strange issue. Working on an Ashdown Mag 300, shows bright on the limiter WITH load, ...
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    Maximum load resistance for this amp is 8, so...

    Maximum load resistance for this amp is 8, so (57x57)/8 = 406, increase it a sprinkle to account more a maximum clipped load and somewhere around 425-470 is appropriate?
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    Unfortunately the hugest I have is 10w. 270,...

    Unfortunately the hugest I have is 10w. 270, 330, and 350 at the only low ohmage ones. This leaves me with very little options, so perhaps I should just mouser the correct parts.

    Also, you can...
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    The largest matched assembly of 10watters I have...

    The largest matched assembly of 10watters I have on hand is 2x350ohm, for a combined 175 ohm 20watt. I also have a 2.7k/270r pair of 10 Watts I could use, for a total of 245r, 20w. Would his be...
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    This was very helpful. Thank you all for your...

    This was very helpful. Thank you all for your knowledgeable replies. Chuck, good catch! With no jack plugged in, it would be in parallel, however with the jack’s shorting lug lifted, it only...
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    Aha! So itís a matter of Ďpeaksí through normal...

    Aha! So itís a matter of Ďpeaksí through normal
    operation? The screens will remain more constant while the draw of the plates will vary with a wider degree? This is honestly beyond my...
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    Thanks! 3A seems reasonable and I will go with...

    Thanks! 3A seems reasonable and I will go with that. Is there an accompanying explanation of WHY they see abuse above the chart ratings?

    Also, can you give any insight about the 270 ohm dummy...
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    So the ground disconnect was verifiable, I...

    So the ground disconnect was verifiable, I removed the ground fuse and hardwired it to ground. I guess before I was asking if a disconnected ground reference would account for all the previous...
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    Thank you for your reply- after your comment...

    Thank you for your reply- after your comment about the fusing system it led me to examine the three fuses... one is a 8a mains attached to primaries, one is a 6a screen fuse.... and one is a 2a...
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    Here are the supplies, sketched. There is a...

    Here are the supplies, sketched. There is a diagram of the KT88 too from earlier5673756738
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