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Old 29th October 2005, 05:42 AM   #11
Enzo is offline Enzo  United States
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The simple test is this: plug a guitar cord into the effects send jack, then plug the other end right back into the effects return jack. If this restores the sound, then the return jack needs service.

The effects loop is essentially a break in the line between the pramp output and the power amp input. When you are NOT using it, there are contacts in the jacks that carry the signal past them. When you plug into them niormally, these contacts open and the signal must travel out, through the effects unit, and back into the return to finish the trip. If those contacts get dirty or bent or whatever, then they won't pass the signal when they are NOT in use.

Do this test.

Also do the other half of the test I mentioned the other day. You already plugged into the return and got sound. Run a cord from the effects send to the input of some other amp. We do this to see if the preamp is putting out a signal. if it is, then the loop jacks aalmost have to be where the trouble is. If there is nothing coming out the effects send, then the preamp has a problem.
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Old 30th October 2005, 03:26 PM   #12
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I did as u said and put a cord in the send and the other end in the return and got sound back. thank you very much for all your help.
my other question is do i need to replace return loop jack or just clean it.
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Old 1st November 2005, 02:56 AM   #13
Enzo is offline Enzo  United States
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You need to clean the cutout contacts in the return jack. if you cannot get at them or cannot successfully clean them, then you replace the jack.

Sometimes you can squirt cleaner in the jack, them probe a plug in and out a few times to move things around. Some of the cleaner might bribble into the contatcs and you might get away with just doing that.

Otherwise, I don't recall that amp specifically, but many GK amps use the Switchcraft jacks with the gray tombstone shaped top. On this top there shuold be a number like RN112APC or something close. Pop the gray top out and look at the exposed contacts. Note when you plug something in that it pushes the tip contact back a ways. There is another contact that was touching the tip contact, but now it is no longer touching. That is the dirty contact. Get between it and the tip contact and clean that surface. That will cure it or not. If not, replace the jack.
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Old 2nd November 2005, 10:44 AM   #14
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Thanx ENZO you have been a great help.
may all your wishes come true.
thanx
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Old 20th December 2005, 08:29 AM   #15
jeyvi is offline jeyvi  Philippines
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hey guys...

i need help too..

i recently bought an 800RB head...

though when i plugged it in a Behringer 410 cab 4 ohms...
and when i turned it On... white smoke came out of the box and knobs...

so i quickly turned it Off and looked inside... the wires on the mains plug has melted.

damn... help me!
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Old 12th January 2009, 10:33 PM   #16
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hello, does somebody know the value of C1 and C4 that I don't understand it well in the supply schematic?
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Old 24th March 2009, 03:16 PM   #17
drewl is offline drewl  United States
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Kinda' hard to see but on the 400rb the supply looks the same C1 and C4 are 561pf, looks like they're there to prevent oscillation.
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Old 2nd June 2010, 01:10 PM   #18
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Default GK 800RB schematic request

Hi
Not sure if this is the correct place to post, but does anyone have the 800RB schematic please
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Old 3rd June 2010, 08:58 PM   #19
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Go back thru this post, near the beginning someone uploaded them. Not far to go at all
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Old 3rd June 2010, 09:27 PM   #20
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Red face 800rb schematic

oops-so it is Dooh!!!
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