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Maybe they just added the "+" on the early 400+ and used the same faceplates then. Because that pic below is a 400+ with a 6.25A fuse and thus doesn't...1 Photo
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Did a full cap job on this amp now. Also disconnected the PT and checked: couldn't find a fault there, either.
Think I've found the answer, though:...
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Did some more measurements with the varistors disconnected:
Max current at power on / standby off: 6,5A (out of 25 sample measurements)
...
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Measured mains is 235V. No abnormal hum. Supply, bias and heater voltages check out.
Good hint on those varistors. I remember that I have replaced those...
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I use ESKA cartridge fuses rated for 250V and 3,15AT (=timelag/sloblo).
https://www.eska-fuses.de/en/fuses-a...es/cartridge-f...
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It is in 230V configuration and has been for the last 15 years.
ThereŽs no ground filter switch on this unit and never has been, I would guess the schematic...
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To clarify: I'm talking about the MAINS FUSE on the front panel of the amp, not the MAIN fuse on the socket or plug.
Schematic calls for a 3A SLO-BLO...
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Mesa/Boogie 400 keeps blowing mains fuse
The amp blows the mains fuse when you switch on the power (standby is in off position).
If I cycle it 10 times, it will be blowing the mains fuse 9...
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You're right. I've did that in the meantime. And it is a diode indeed!...
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But aren't other components the same or even more affected by thermal stress during manufacture and should thus show coiled leads as well? I'm thinking eg...
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Replacing the pot did it. Out of tune sound is gone.
Thanks for the help guys!...
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Guyatone GA-1200 guitar tube amp
On the hunt for a schematic for this seemingly rare tube amp.
Guya Co Ltd
Made in Japan
Stereo guitar amp with tremolo & reverb
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Help identifying this component / labeling?
It is the part circled in blue. From a Guyatone GA-1200. It is probably a diode since it is downstream a 56V tap from the PT and there is a RC node following...1 Photo
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The pics IŽve attached are labeled. YouŽll see the label if you hover or click on a pic.
So, the first pic is the BBD out adj, where going after the...
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Good call on the pot! Connections were good, but resistance was all over the place while turning. Will order a new part and replace.
However, the bad...
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That's what I've done to get those oscope screen shots attached above. The component numbers fit with p.2 of the schematic linked above....
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Roland JC120 Vibrato Problem
Amp works fine and chorus sounds good.
However, when I switch to vibrato it works but sounds very out of tune. "Vibrato Speed" knob works....4 Photos
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Hello JM,
could you reupload the mod schematic or specify the position of those 4k7 resistors? One each after the .68 coupling caps?
...
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Hmmm, I used an ECC82 as in the schematic in Merlin's book. I probably must've had a mistake in there somewhere.
Interesting idea with paralleling two...
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