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GK Fusion Issue - do my tubes need replacing?

nonohmic

nonohmic

Dec 13, 2005
7,961
13,583
Land of Entrapment
#1
Hi all, all of a sudden I have a 'farting' or 'flapping paper' sound in my rig. I'd be surprised if I have damaged the cab, as I have never pushed the volume on my amp much past 9:00. And the Revsound is a little beast.

Also, I searched and one suggestion was to reduce the bass EQ and see if it still farts. Which it does.

It will also fart with the -14db switch engaged, if I dig in.

So, I think something is wrong with the amp. The 3 tubes all glow "normally" although I don't really know what normal is to be fair.

What else can I check? Thanks.

20240517_210108.jpg
 
#2
You said "GF" and I passed it by. First lift the amp off the cab, "farting" stop? Patch a cable from effects send to return amp back on cab, farting still gone the unused effects send jack is "dirty" get it cleaned by a shop or well versed tech in a music store (Caig DeOxit is the stuff to be used), farting back you may have a tube problem (you can also tap the top on the amp, NOT HAMMER on it and with the cable still in hear a rattle with the "fart").
 
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#3
Turn the master on full and work the Gain. Should clean up the sound and sound good between 1-2 on the Gain.
But, don't you only have pre amp tubes in that head? Preamp tubes last a very long time, mostly many years and usually only go one at a time which I found can also include a screaching, almost whistle type of sound.

Agedhorse could probably describe the symptons better? I haven't blown enough to claim any expertise.
 
#5
FWIW I had the same problem with the original version of this amp. Worked fine for about two years. I found that the middle preamp tube had failed and replaced just that one. The heater glowed fine but it had that smokey look of a blown tube. Went out right before a gig so I swapped it out on stage. It's been working fine but I carry a couple of spares just in case...
 
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#6
B-string said:
You said "GF" and I passed it by. First lift the amp off the cab, "farting" stop? Patch a cable from effects send to return amp back on cab, farting still gone the unused effects send jack is "dirty" get it cleaned by a shop or well versed tech in a music store (Caig DeOxit is the stuff to be used), farting back you may have a tube problem (you can also tap the top on the amp, NOT HAMMER on it and with the cable still in hear a rattle with the "fart").
Click to expand...

Ha, yes caught that and changed the title.

Still farting when I patch through the FX loop.

Aussie Player said:
Turn the master on full and work the Gain. Should clean up the sound and sound good between 1-2 on the Gain.
But, don't you only have pre amp tubes in that head? Preamp tubes last a very long time, mostly many years and usually only go one at a time which I found can also include a screaching, almost whistle type of sound.

Agedhorse could probably describe the symptons better? I haven't blown enough to claim any expertise.
Click to expand...

Thanks for the suggestion. Still farting at low Gain. And yeah tubes look like they're fine so I'm a little confused on it.

agedhorse said:
First, try the amp with another known good cabinet.
Click to expand...

Thanks. Agreed first port of call, was hoping to get a solution without having to hit up a music store though.

Anyways I unplugged and replugged everything in including my bass. And somehow it came right again. So serendipitously that's ruled out the cab. I guess I'll run at low gain for a while and see if the issue comes back.

I will say my setup is incredibly noisy. Unshielded 60s jazz with vintage single coils, and running through an extension cord and multi outlet from a house with 1950s electrical. Could excess noise cause things in the amp to go weird from time to time?

I'll grab my beater bass from work on Monday and see if that changes anything too.
 
#7
smokinjoe said:
FWIW I had the same problem with the original version of this amp. Worked fine for about two years. I found that the middle preamp tube had failed and replaced just that one. The heater glowed fine but it had that smokey look of a blown tube. Went out right before a gig so I swapped it out on stage. It's been working fine but I carry a couple of spares just in case...
Click to expand...

Oh interesting, thanks. I'll take the cover off and see what the tube glass looks like.
 
#12
nonohmic said:
Ha, yes caught that and changed the title.

Still farting when I patch through the FX loop.



Thanks for the suggestion. Still farting at low Gain. And yeah tubes look like they're fine so I'm a little confused on it.



Thanks. Agreed first port of call, was hoping to get a solution without having to hit up a music store though.

Anyways I unplugged and replugged everything in including my bass. And somehow it came right again. So serendipitously that's ruled out the cab. I guess I'll run at low gain for a while and see if the issue comes back.

I will say my setup is incredibly noisy. Unshielded 60s jazz with vintage single coils, and running through an extension cord and multi outlet from a house with 1950s electrical. Could excess noise cause things in the amp to go weird from time to time?

I'll grab my beater bass from work on Monday and see if that changes anything too.
Click to expand...

That doesn’t rule out an intermittent speaker or speaker cable.

nonohmic said:
Oh interesting, thanks. I'll take the cover off and see what the tube glass looks like.
Click to expand...

Don’t waste your time, a tube that’s lost its vacuum will not be intermittent, it will not work at all and won’t “heal itself”.
 
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#15
I don’t know the speaker connection type on the amp or the cabinet, but I’ve had multiple amps and cabs that connected with 1/4” T/S (or T/R to some) connections that sounded fuzzy at times that was cleared up by a twist of the cable in the jack.

Neutrik brand Speakons are so nice…
 
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