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Lets get Technical > All Things Tube All about preamp and power amp Tubes.

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Author Topic: MP1 - Developed very loud hum on tube settings  (Read 255 times)

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MR THUD

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    • MR THUD

Hi Guys,

Im really enjoying my MP1, but it has developed a problem.
On all the tube settings there now is a new loud hum (solid not pulsing and sounds 'transformer'y' ), you can play over the top of it and that seems to cancel it out to some extent. But it is way louder than the usual noise I have been used to with my MP1.

I tried relocating the racks and using a different power point and decent multi plug, but the noise continued.
I tried other input and output leads, but no change.
If you unplug the guitar the noise continues.
If you unplug the amp and other rack effects and only power up the MP1 and just use the headphone out, the noise continues.
I have some (possibly buggered) 12AX7 valves here, so I tried swapping out the two valves in the MP1 but the noise continued.

So, the status is that it appears to be fully functional, but now with loud '60Hz cycle hum'.. or something, but only on the Tube settings. On the solid state patches it operates as before with an acceptable level of 'different sounding noise' (i.e. normal).

Any ideas? or do I need to take to the ADA hospital (Assuming I can find a suitable service/repair guy in the Brisbane area).

Thanks in advance for any help!

Cheers,
Gerard.

PS... I just read through some old posts, it sounds possible that my issue could be due to caps on the tube board..
Will have a close look to see if I can spot any that look ruptured (I recall my old Marshall Plexi that had huge blue caps that were always exploding and leaving yellow crap everywhere. Not easy to miss!).
« Last Edit: Time Format by MR THUD »
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Micky

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Hi MR THUD,

I had the same problem.

MarshallJMP suggested me to change the three big capacitors on the tube board with high temperature version: problem solved.

Micky
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Harley Hexxe

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More than likely, it sounds like bad caps to me too.

      There are a few competent techs around Australia, I'm sure you'll find someone who can help set you straight.

Harley 8)
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I used to be ambivalent. Now, I'm just not sure...

MR THUD

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Thanks Guys!
Will take that advice as first thing to try, new high temp caps it is then.
Anyone know the model number for the better/ high temp caps?

In parallel I will try contact Mr JMP, as he has helped me source parts before and may have some for sale.
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MarshallJMP

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Mail me and I'll tell you what to order with your local electronics shop
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MR THUD

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Cheers, Philippe.
I have sent you an email and also attached some photos.
Hopefully they get to you ok.

Thanks!
G.
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