humming and crackling Marshall 2266 valve combo

Hi all,

I have a problem with my Marshall Vintage Modern 50 watt combo.

After a bit of playing, maybe 5 minutes, it starts crackling and humming.
Often at some point the hum becomes continuous, and I can disconnect the
guitar lead, turn everything down and it just keeps humming. The only
control that makes a difference is the master volume, and if I reduce
that, the humming gets louder.

Funnily enough the problem is sometimes induced by playing G, fifth
fret,fourth string. :-/

The amp is a tad over 6 months old, so its under guarantee - but not the
valves. I need to work out if this is a valve problem or not.

I've reseated the valves and swapped some about. It has 4 ECC83 (?)
pre-amp valves and 2 KT-66 power amp valves. I don't really want to
replace them and pay for a tech to balance them if the problem is

Any thought on how to detect where the problem lies?


All the best,
Angus Manwaring. (for e-mail remove ANTISPEM)

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