Mark IV loud hum.

[JPIndustrie]

Hey all,

I have a '92 Mark IV A Rackmount that I love, however it seems to have a loud, constant hum. Thing is, the severity of the noise is intermittent, I'll have some days where the noise is bearable and others where the noise sounds like a pack of helicopters near by. I'd like to get this amp to a point where it's as quiet as possible.

When I got the amp (around 2007), I retubed it with a full set of Eurotubes and I didn't remember it being that noisy then. I am however in a band that practices once a week and plays 1-3 gigs a month.

Is this a tube problem, or something else?

Thanks!

 

[GD_NC]

My Mark IV was humming earllier this summer. The problem was a loose power tube socket. It wasn't getting a good connection with all the pins.

There are probably a million other reason for humming, but that's an easy one to check.

If you have a local M/B tech you might just want to take it in for a tune up and some new power tubes. Probably well worth the $$ if you depend on it. Most hums are easy to fix if you can isolate the problem.

 

[JPIndustrie]

If you have a local M/B tech you might just want to take it in for a tune up and some new power tubes. Probably well worth the $$ if you depend on it. Most hums are easy to fix if you can isolate the problem.

I see. I think I know what you mean regarding a million different things, and that's what I was afraid of. :lol:

I was thinking of just buying a new set of tubes first, switching them out and seeing if the problem goes away. Would anyone recommend I do that first before seeking a tech?

I've heard the term 'tune-up' applied to amplifiers as some sort of 'package' deal that techs can do. I've been thinking of doing this also, anyone have a basic idea what gets done, and what the ballpark would be for a Mark IV? Just want to plan out so I would know how much cash to devote to it.



Thanks!

 

[GD_NC]

Sure. The local M/B shop here in Raleigh, NC charges $54. See FAQ #8 on the webpage for the details... http://www.madscienceworks.com/list.html

I had my Mark IV serviced there this summer. In addition they replaced a flakey pentode/triode switch (another source of noise) and repaired a bad LED. The grand total was about $75 which included parts.

Getting my amp serviced probably saved me money because he insised that my power tubes were fine and didn't need to be replaced. I would have spent $100 on new tubes NOT to fix the source of the noise.

 

[mgunstudios]

I believe a faulty power supply cap will let 60 cycle hum into the system. If it's old it might be worth doing a recap.

 

[primal]

My Mark IV had a hum that was like a plane taking off. Put in a new set of power tubes and the problem was gone.

I have read the unballanced tubes are a big cause of hum that can swell over time.

Try just going Class A and seeing if you still have the hum. If you do, provided you are using all 6L6 tubes, swap the outer power tubes with the inner ones and see if you still have the hum. If not, it is probably the tubes.

That was how I diagnosed it in mine

 

[stokes]

I believe a faulty power supply cap will let 60 cycle hum into the system. If it's old it might be worth doing a recap.

Faulty filter caps produce 120 cycle hum,not 60.There are so many possible causes of hum,you should take it to someone who can diagnose the issue,you can end up spending a lot of unnecessary $$ and get nowhere.It is very possible that 2 year old Euro power tubes need replacing anyway,but if that doesnt cure it,take it in.