Help!! - Loud incessant squealing sound coming from tube amp

M

majorbase

Sep 2, 2024
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3
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#1
Hey guys,

While playing through my amp yesterday (GK MB Fusion 800), all seemed to be going well until I changed the gain option from 1 (clean) to 2 (overdrive). This resulted in a loud, high pitched droning squeal coming from the amp, that remained even when switching back to the original gain setting.

In terms of troubleshooting, I’ve tried the cab (the drone persists through headphones), tapping the 3 preamp tubes (has no effect on the sound), removing the tubes/reseating (also has no effect) - as well as having the bass plugged/unplugged/different bass (still squealing in all scenarios)
I’m completely at a loss as to what this might be.

There don’t seem to be any other online threads that regard something like this, and due to the price of local amp technicians i’m treating it as a last resort of sorts.

Any help would be greatly appreciated
 
#2
Hmm. I have no advice but something similar happened with my ancient tube guitar amp the other day… it was just sitting there turned on but I wasn’t playing anything and then all of a sudden, it started squealing. I turned it off, let it cool down a bit, then turned it on again and the problem disappeared.
 
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#5
majorbase said:
Hey guys,

While playing through my amp yesterday (GK MB Fusion 800), all seemed to be going well until I changed the gain option from 1 (clean) to 2 (overdrive). This resulted in a loud, high pitched droning squeal coming from the amp, that remained even when switching back to the original gain setting.

In terms of troubleshooting, I’ve tried the cab (the drone persists through headphones), tapping the 3 preamp tubes (has no effect on the sound), removing the tubes/reseating (also has no effect) - as well as having the bass plugged/unplugged/different bass (still squealing in all scenarios)
I’m completely at a loss as to what this might be.

There don’t seem to be any other online threads that regard something like this, and due to the price of local amp technicians i’m treating it as a last resort of sorts.

Any help would be greatly appreciated
Click to expand...
That sounds like it might be a tube calling for help. Have you tried swapping in a replacement 12AX7, one at a time, in each position?
 
#6
Remo
majorbase said:
Seems to be the most likely route.. any input on what may be causing it?
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Remote possibility that it’s a tube, and iirc they are fairly involved to change due to the compact packaging. I can think of 40-50 other possible causes, which an experienced, qualified tech will be able to identify.
 
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#7
I've been MIA around here for a while. I still feel like a broken record saying this; any amp with series effects loop jacks if you experience volume drops, squealing, popping, thumps, crackles try looping the effects send and effects return jacks with an instrument cable and see if it clears. Just by inserting a plug may break the micro corrosion known as "fretting" in the low voltage/low current contact. Newer sealed or enclosed jacks see this less but can still have it happen. Either way a good instrument cable will bypass those internal contacts. If it returns (without the cable still in use) you may need a good tech to PROPERLY clean the jacks (not an expensive process). Swapping tubes is the next step as a "tube tester" is near guaranteed not to find this type of fault in a tube. Many other possibilities as agedhorse said, but those are the basics and tapping a tube while in operation (ONLY use a wooden orange stick gently) is viable but not recommended for a user. One slip can turn an inexpensive repair into a financial disaster.
 
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#11
majorbase said:
Hey guys,

While playing through my amp yesterday (GK MB Fusion 800), all seemed to be going well until I changed the gain option from 1 (clean) to 2 (overdrive). This resulted in a loud, high pitched droning squeal coming from the amp, that remained even when switching back to the original gain setting.

In terms of troubleshooting, I’ve tried the cab (the drone persists through headphones), tapping the 3 preamp tubes (has no effect on the sound), removing the tubes/reseating (also has no effect) - as well as having the bass plugged/unplugged/different bass (still squealing in all scenarios)
I’m completely at a loss as to what this might be.

There don’t seem to be any other online threads that regard something like this, and due to the price of local amp technicians i’m treating it as a last resort of sorts.

Any help would be greatly appreciated
Click to expand...
That’s not really a “tube” amp, but a hybrid with three preamp(only)tubes.
 
#13
Get the amp to a GK authorized repair shop. I would hope a company of that size maintains a problem/solution database that all their shops have access to. I can almost guarantee GK has seen the problem before and know exactly what the (I suspect exceedingly simple) fix is. There may even have been a tech bulletin released to those shops informing them of that problem. If you insist on using your "local repair store," maybe they can email that Jason guy at headquarters and get some quick guidance.
 
#15
eniac said:
Get the amp to a GK authorized repair shop. I would hope a company of that size maintains a problem/solution database that all their shops have access to. I can almost guarantee GK has seen the problem before and know exactly what the (I suspect exceedingly simple) fix is. There may even have been a tech bulletin released to those shops informing them of that problem. If you insist on using your "local repair store," maybe they can email that Jason guy at headquarters and get some quick guidance.
Click to expand...
Should have mentioned - my local repair store handles the exclusive authorised repair for GK, Ampeg, Markbass, etc…
 
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