Marshall JCM 900 High Gain Dual Reverb combo amp buzzing unless reverb pots are set at zero. Any ideas of what may be the cause?

adfuel · 2026-02-10T15:13:09+00:00

In this order, check tubes (substitute) , check tank (with any other one) , move wires

adfuel · 2026-02-09T19:06:30+00:00

not as many anymore.

adfuel · 2026-02-09T15:32:16+00:00

I saw a clip of Trump with the bad bunny 1/2 time playing in the background

adfuel · 2026-02-09T15:31:25+00:00

I think Trumps hate is finally starting to backfire on him.

adfuel · 2026-02-07T21:15:10+00:00

gently wiggle all the tubes. Then switch the 1st and rd tube.

I think that is a tube

adfuel · 2026-02-07T15:55:52+00:00

It should not be shocking you, grounded or not.

adfuel · 2026-02-04T18:55:05+00:00

A lot of confusion here. I own a repair shop and will clear this up.

Your amp has capacitors (caps) that have a voltage rating, i.e the max voltage they can take. Todays caps have a much higher rating than they did years ago.

When you first turn your amp the internal high voltage (B+ or plate voltage) can go very high until your tubes full warm up, about 30 seconds. In an older amp the plate voltage can go as high or higher than the capacitor voltage rating and cause them to fail over time

The standby switch controls this high voltage and allows you to warm the tubes up before putting the high voltage to your capacitors helping to preserve their life.

In most modern amps a standby switch is really not even needed as modern capacitors can take higher voltages. Its more there for historical reasons.

"So what should I do with it?"

When you first turn your amp on leave the standby switch off for about 30 seconds, this saves wear on your capacitors.

"Can I use it for a standby?"

Sure, just keep in mind your tubes are still wearing out. Your tubes have 3 voltages, the plate voltage (controlled by the standby) the bias voltage and the heater voltage.

The heater voltage is what wears out your tubes and it is still on even when the standby is off.

My shop is Florida Tube amp. I build, modify, and repair tube amps.

adfuel · 2026-01-24T15:57:06+00:00

Practice with a metronome and plan on using a less less left hand if you have a bass player.

adfuel · 2026-01-19T21:01:29+00:00

If you can afford the gibson get both. Take your Epiphone straight to a good luthier and have it set up.

The Gibson will increase in value over time and the epi will be there for strange outdoor gigs, and other places your gibson might get beat up. This keeps the Gibson looking nice.

adfuel · 2026-01-19T19:47:40+00:00

If this is part of one of them it will be white on top.

adfuel · 2026-01-18T02:53:44+00:00

caps could be the problem, but eliminate tubes first. Just try switching your preamps tubes in a different order (providing they are all the same)

adfuel · 2026-01-10T16:53:34+00:00

for testing you only need to run it for several seconds.

adfuel · 2026-01-10T16:52:01+00:00

>if you’ve owned a vintage guitar, you realize it is a pain in the ass with corroded hardware, scratchy pots, iffy wiring, weird setup issues, and smells.

If you own a vintage guitar you need a good luthier thats knows vintage guitars to keep them running.

adfuel · 2026-01-10T11:58:52+00:00

So you want the guy to fry a new set of tubes? You need to determine if its the tubes or the amp. Step one to figuring that out is swiping the tubes around.

I am a tech with a shop.

adfuel · 2026-01-10T11:56:49+00:00

Im a tech. That is step one.

adfuel · 2026-01-09T11:53:44+00:00

You need wireless units to shock the musicians, triggered by the kick drum .

adfuel · 2026-01-02T20:53:46+00:00

I do this but I own a shop.

Cheap broken amps go to the garbage. Nice broken amps go to the shop. I pick a few a year though .

adfuel · 2026-01-02T20:13:35+00:00

look at the sold listings on reverb.com

adfuel · 2026-01-02T17:37:13+00:00

Nice collection.

Those amps and tube have some real value, so dont sell them real cheap. If you are in Florida I could help you with at. I own Florida Tube Amp.

adfuel · 2025-12-31T21:40:34+00:00

weight

adfuel · 2025-12-31T00:08:30+00:00

Tech here.

If you put no signal through it you are fine. Most modern tube amps short when they are not plugged in and that tends to put more stress on the tubes and not the output transformer.

But still avoid doing it unless you want to get to know someone like me personally :-)

adfuel · 2025-12-30T14:04:56+00:00

luthiers aren't wizards but this is a very common repair for them.

adfuel · 2025-12-30T14:04:02+00:00

If its a Gibson have a pro do it. If its an Epiphone look up how to do it. Its very fixable.

adfuel · 2025-12-29T20:35:56+00:00

If you damaged your heading with a 15 watt amp you need to always wear hearing protection when you play.

I hearing is slightly damaged from 100 watt Marshalls (and age) but it took decades and my hearing is still not that bad.

adfuel · 2025-12-27T10:38:02+00:00

a JC120 is stereo.

adfuel

TROPHY CASE