#1
I am having a issue with my jet city jca20h. The amp when turned completely on, is making no sound at lower volumes. When turned up further to I can hear what I would describe as a buzz with the undertones of the of the guitar's sound. So far I have tested the cables the input and output jacks and the power tubes which along with the preamp tubes are fresh out of the box as I first diagnosed this problem as worn out tubes. There are no nearby amp service locations so I desperate for some help.
#2
How long have you had the amp?
Did it start doing this outta the blue?
Is the guitar's volume knob turned up? Have you done any work on the guitar recently?
Make sure you have the cabinet hooked up to the correct speaker jack.
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#3
about two years and yes it did happen out of the blue. I checked it with 3 different guitars no luck. Finally yes it is I tried both 8 ohm jacks same thing no luck
#4
Have you had the amp turned on without a speaker cabinet hooked up?
What kind of speaker cable are you using?
Are the power tubes all glowing?
Endorsed by Dean Guitars 07-10
2003 Gibson Flying V w/ Moon Inlay
2006 Fender All-American Partscaster
SVK ELP-C500 Custom

1964 Fender Vibro Champ
1989 Peavey VTM60

[thread="1166208"]Gibsons Historic Designs[/thread]
#5
Quote by Flux'D
Have you had the amp turned on without a speaker cabinet hooked up?
What kind of speaker cable are you using?
Are the power tubes all glowing?


1 Never
2 Its kind of a cheap cable but it does work to drive the cable with my other amp fine.
3 All of um are glowing.
#6
Power off and unplugged before checking anything.
HIGH VOLTAGE INSIDE!! BE CAREFUL!!
Check for blown fuses.
Check for bad/broken solder joints.
New tubes can sometimes be dead (though not often, it does happen).

You can also try to clean the tube pins:
Spray contact cleaner (CONTACT CLEANER, NOT WD-40...EVER), on tube pins and insert and remove several times from the tub sockets.

You can also use contact cleaner on the various pots, spray a little inside and turn the pots (Volume, tone, and other pots).

Contact cleaner evaporates quickly, but I still prefer to wait awhile before powering up after using it. In any case, you don't need very much to clean. a few squirts will be fine.

There could be other things wrong, but those are the first things I would try.
#7
Does your amp have an FX loop?

Try plugging your guitar into the return and see if you can hear it.
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#8
if the tubes are glowing we know that there is not a blown the fuse in the PT is okay (i am about 98% sure, maybe back me up)

i had an HT fuse blow on me before, they are internal. but i don't remember the symptoms. i had an HT fuse fail to blow and melted some shit in an amp.
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#9
Quote by trashedlostfdup
if the tubes are glowing we know that there is not a blown the fuse in the PT is okay (i am about 98% sure, maybe back me up)

i had an HT fuse blow on me before, they are internal. but i don't remember the symptoms. i had an HT fuse fail to blow and melted some shit in an amp.


I had that problem with a Valveking I worked on a few years ago.
The Mains fuse was fine, but one of the internal fuses (I forget which one exactly) was dead.
And it was one of those white fuses, not the glass type where you can see a fried wire.
Last edited by CodeMonk at Dec 6, 2013,
#10
Quote by CodeMonk
I had that problem with a Valveking I worked on a few years ago.
The Mains fuse was fine, but one of the internal fuses (I forget which one exactly) was dead.
And it was one of those white fuses, not the glass type where you can see a fried wire.


my fuse was opaque black. i had to get a meter to test it and found it was fine. amp wasn't fine thouogh.

it is an Ampeg Lee Jackson head. not a bad sounding amp. to be honest i am not even sure i remember what the dirt sounded like. i may have some really old clean clips of it somewhere.
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Quote by andersondb7
alright "king of the guitar forum"


Quote by trashedlostfdup
nope i am "GOD of the guitar forum" i think that fits me better.


Quote by andersondb7
youre just being a jerk man.



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2017-04-13 RUN AWAY from COMPUTERS!!! TCE? RANT ALERT!!!
2017-03-02 - Guitar Philosophy 1001- Be Prepared For the Situation (Thursday 2017-03-02)
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Resentments and Rambling from a Guitar Junkie
---> http://trashedengineering.blogspot.com/
#11
+1 to check the HT fuse.

I actually just had that happen to my AC30 last week... Turned it on, worked fine, came back an hour later, turned it on again, and nothing!

Turns out, in my case, with the AC30, when you use the stby switch it stores some energy then when you flick it, it goes straight to the rec tube causing fast wear. Killed a brand new JJ in a week which caused the HT fuse to also blow.


And it only took me 3 fuses to figure it out!

Now I no longer use my stby on that amp. Very poor design.
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#12
opened it up and was unable to locate any fuses. Also I replaced the one under the power jack. Still not working.
Last edited by foxmagic at Dec 8, 2013,
#13
I honestly have no idea man

All I can say is take it to a friend who's good with electronics/guitar stuff or to your local amp tech. Jet City doesn't have any common problems AFAIK and we've ruled all the common stuff out.
Endorsed by Dean Guitars 07-10
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2006 Fender All-American Partscaster
SVK ELP-C500 Custom

1964 Fender Vibro Champ
1989 Peavey VTM60

[thread="1166208"]Gibsons Historic Designs[/thread]
#14
Quote by Flux'D
I honestly have no idea man

All I can say is take it to a friend who's good with electronics/guitar stuff or to your local amp tech. Jet City doesn't have any common problems AFAIK and we've ruled all the common stuff out.


Thanks for the help I appreciate it.
#15
im having the same issue too but i cant find the fuse? same amp jca20h, can someone point out where it is for me, i can't find info on this anywhere.