White noise problem

[toneseeker911]

Was at a recording last weekend and I suddenly realized that my Mark V was making this whooshing white noise in ch3 (all modes) . This is even after I bypassed the effects loop and master at 11.
I came home and swapped all the preamp tubes one by one with a good one but to no avail. I also swapped out all the power tubes and still no luck in eliminating the problem. Also the problem is present in ch2 and ch1 too if I turn the master high enough (which I would not do normally) even for a recording.

Does anyone know what the issue could be ?

Thanks

 

[screamingdaisy]

Does it still make the whooshing noise if you unplug your guitar lead?

 

[toneseeker911]

Yep, even with nothing connected to the input jack, it makes the noise. I've swapped speaker cables, speakers, bypassed effects loop, turned off reverb.
And the frequency of the noise changes with the tone control. It is loudest in ch3. ch1 is second loudest with an added hum. Everything seems to point to a preamp tube problem... aargh.
Anyway, I'm taking it to a mesa authorized amp tech today. Will let you know how it turns out.

 

[toneseeker911]

Just an update on this issue.
Took my amp to a tech. There was no real problem that he found. He just removed all the tubes and cleaned out the sockets. Voila, the background sound was back to normal.

Just played it out at a gig this weekend and it was back with its monster tone !

 

[boogieman60]

good idea to use dielectric grease...just a little on each tube prong. also aids in tube removal. My MkV going on 3 years..very few tube issues. always there.

 

[mace]

good idea to use dielectric grease...just a little on each tube prong. also aids in tube removal. My MkV going on 3 years..very few tube issues. always there.

What is a good brand of grease to use on mesa tubes? I too have this weird noise problem in my 2 year old Mark V. I swapped all 12AX7s, also changed out 6L6s and it didn't make any difference.

I went to the trouble of measuring the noise with a decibel meter for future reference. Like the original poster ch3 is loudest and ch2 the quietest with ch1 in the middle (with no guitar plugged in).

Method: Each channel's master level set to same SPL level for a given Output setting. I bypassed the effects loop, no reverb, no EQ, 10W mode, each channel on middle setting (fat, crunch, mk4). Here are the dB measurements (without and with guitar plugged in):

dB ch1 , ch2 , ch3
No Guitar
Output 7 o'clock Baseline, all channels were 50 dB
Output 12 o'clock +12 , +4 , +24 dB

Guitar
Guitar volume zero, Output 12 o'clock +14 , +11 , +31 dB
Guitar volume 10 , Output 12 o'clock +15 , +18 , +33 (note: most of this volume increase in ch2/3 was 60 cycle hum, not hiss/noise)

So, one can see that channel 1 has more noise than channel 2, which is surprising since channel 1 is low gain.

Also, the guitar adds noise to the high gain channels but I could tell most of that 60 cycle hum, probably to be expected.

Similar results for different speaker and speaker cable.

Similar results for 45W and 90W modes, pentode/triode ch3 and tube/rect @ 45W on ch1/2. No real difference to the above in 10W mode.

I'd like to try to get this amp back to normal myself and not send it in. Maybe cleaning the contacts or using some grease on the tube prongs will help. How does one clean the sockets? Any recommendations on dielectric grease? Thanks for any advice.

Regards,

Mace

 

[boogieman60]

Just use any good automotive dielectric grease made for electrical connections. I like the clear stuff..they make some real gooey grade for bulbs.. too messy. Just a little keeps the pins and sockets from forming that white powdery deposit.