TH30 50Hz hum

[Magor74]

Hi there

I have a problem with my TH30 and 50Hz mains hum. I use a Gibson Les Paul Jnr with P90’s (prone to this sort of thing I know) However I also have a Humbucker equipped guitar which reacts the same way.

Just to explain, I have enough years experience (ha ha !) to know that guitars placed near amps make noise, I can accept that, no problem.

However what I'm finding is that my amp is far more susceptible to guitar hum than it ever was in the past. i.e. my TH30 never used to hum like this no matter how close my guitar was to the amp.

Its like a shielding/ground issue??

Do you think this is to be expected?

Two local amp repairers think its perfectly normal, however like I say, the only reason I started out on this fault finding exercise is that my amp never used to make any noise, even if I sat right next to it. But now I have to sit a good 3 metres away for the amp to behave 'normally'. Here's a video of it

http://youtu.be/6Yr0a1Zs1vw" onclick="window.open(this.href);return false;


I’ve swapped out all power tubes for brand new matched pairs and it makes no difference whatsoever.

I’ve also changed all Preamp valves and I get varying results, sometimes it’s quieter but not for long. The PI valve seems to get a black deposit around its base pretty quickly (couple of hours). I don’t know if this is related.

Can someone confirm for me the TH30 tube layout, I’m starting to suspect the graphic on the back of my amp is printed incorrectly, possibly!?

[a.hun]

Hi Magor74 . Welcome to the forum.

TH30 layout here:
http://forum.orangeamps.com/viewtopic.php?f=3&t=42244" onclick="window.open(this.href);return false;
(see also p. there for fuller explanaition / correction.)

What do you mean about the PI valve getting a black deposit around it's base? The valve itself - ?outside ? inside? Or the valve socket? Could you post pictures of this? Sounds odd.

Hum can be as simple as a dirty input socket, or a bad pin contact on one of the valve bases. Worth cleaning all jack sockets once in a while, just using an electrical contact cleaner spray. You can spray this onto a jack and insert / pull it a few times as the stuff evaporates. For valve bases you need to make sure you use a NON lubricating cleaner, one which evaporates completely leaving no residue. You do much the same, just spraying the stuff on the valve pins and carefully replacing them a couple of times to clean the valve socket contacts too.

That 's what I'd be trying first anyway. Of course it might be a completely different problem, grounding or component failure, other possibilities too, most of which would need a tech to diagnose and sort.
http://www.geofex.com/ampdbug/hum.htm" onclick="window.open(this.href);return false;

And you're right by the way, if it didn't used to hum like that then there is now something wrong. Those techs are plain wrong on that. Modern Orange amps are very quiet and hum free when working properly!!!


Andy.

[Magor74]

Thanks for the confirmation I'm not going crazy! I'm getting fed up with amp repairers telling me its "normal for a tube amp". As you say modern Orange amps can be almost silent, mine was previously.

Thanks for the cleaning tips, I will definitely try that with the inputs & tube sockets. The input could be especially dirty as I tend to play in bars/pubs, where cables can be lying around on the sticky beer covered floor etc.... Actually the issue did appear after playing a bar where our singer spectacularly spilled beer over my FX & guitar & cables. The amp was untouched, however I guess the input may have gotten bunged up with dirt as I had to hastily swap guitars and re-arrange /unplug FX.

I hope its something simple like that. The TH30 is built like a tank so I'm hoping/assuming the components haven't failed in some way.

The black deposit is inside the tube, around the bottom of the Phase Inverter tube base. It forms a dark ring, I'll take a pic when I get home later, the sockets look fine.

By the way, (if I remember correctly) I'm using Marshall 12ax7 in the Dirty Channel sockets and a TAD in the PI tube socket and it sounds amazing, just flipping noisy!

[Blue Notes]

Mine had a bad hum as well, put a new 12AT7 in and she's nice and quiet now.