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Mesa Boogie F-50 combo - snap crackle pop
Mesa Boogie F-50 combo - snap crackle pop
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Old 13th February 2019, 12:56 AM   #1
KA1J is offline KA1J
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Default Mesa Boogie F-50 combo - snap crackle pop

It's not that bad, but it is there. My initial thought is either arcing in from the PS caps, possibly there is some varnish/crud in the pots and it's coming from there. Not firecracker loud, just light snaps & pops on no regular timing.

I just picked the amp up late last week and have tried replacing the tubes and that didn't remove the issue. The amp may be just fine; I thought I might remove the enclosure and deoxit all the pots/connections. If nothing else, it's probably time, the amp was made around 14 years ago. Even if not necessary, it probably wouldn't hurt to replace the existing caps with current ones.

Any gotchas or time saving suggestions with this particular amp I might not be aware of? FWIW, I'm accustomed to working on transmitting equipment with 5KV supplies with high current and I'm aware of the dangers surrounding working with HV. I have a healthy respect for working in these conditions.

Would someone have a schematic I might work from? That'll help a lot. Gravy would be one with test points/values & maybe a parts list for the components. If only a schematic is available, I'll be grateful.

I thought Mesa Boogies were point to point amps but inserting the tubes I see that's not the case. No biggie, for ease I just prefer point to point.

Thanks!
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Old 13th February 2019, 10:58 AM   #2
hex69 is offline hex69  Canada
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There it is:

Mesa Boogie F-50.pdf - Google Drive

If the new tubes don't fix your problem, you might want to have the caps in the power section checked out for proper readings.
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Old 13th February 2019, 12:16 PM   #3
KA1J is offline KA1J
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Hex, thanks so much! I'm going to see if I can find a photo of the power supply to know what kinds of caps, axial or pin, to order from Mouser and just re-cap the HV supply for good measure. I plan on keeping this amp so future proofing it is a good thing. I'll deoxit all the pots & it hopefully will deal with the little noises.

One thing that I was just made aware of is from my girlfriend, she has the best hearing of anyone I know, it's almost scary what she can hear that others don't. She said there's a repetitious sound, like a beep coming from the amp, she thought it was my phone beeping. I sort of hear a faint change in sound with the volume up that happens about every second. Not present with the input plug removed, so the cord is acting like an antenna. She said she could hear it two rooms away... She can hear a fly fart at 20 feet. Perhaps it's related to the noises I'm hearing but that one is regular, the ones I hear aren't.
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Old 13th February 2019, 02:24 PM   #4
Enzo is offline Enzo  United States
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Something I always check on latter day Mesas: the pots.

The 16mm pots mounted to the panel with wires to the board. grasp the metal cover on the rear of each and wiggle. ANy loose? If so, bend down the little tabs that hold the cover on. The cover is what holds the wiper assembly in place, Cover gets loose, the pot starts to lose contact.

Takes less than 30 seconds to check them.
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Old 13th February 2019, 05:49 PM   #5
KA1J is offline KA1J
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Thanks Enzo,

Other than simply removing the four screws holding the amp to the cabinet, are there any "hang-ups I should expect to encounter when pulling the amp out of the enclosure? I'm not expecting any but perhaps there are interlocks, something that needs to be attended to while removing? Always better to ask first than wish I had, later.
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Old 14th February 2019, 01:53 AM   #6
Enzo is offline Enzo  United States
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It is just a guitar amp, no hidden kill switches or other conspiracies. SOmetimes a chassis sticks to the tolex.

I don't know this model, but SOME Mesa amps have a big bolt up through the chassis in the middle underneath. It pushes against the roof of the cab to help prevent vibration. MAke sure there isn't one.

I find it sometimes helpful to turn the amp on its side. If I leave it upright, then I have to fight gravity. On its side, a loose chassis just sits on the side wall, then you can slide it out.

There may be anchored cables to reverb or speaker you may need to free.

Plain old common stuff.
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Old 14th February 2019, 04:16 AM   #7
KA1J is offline KA1J
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Thanks. Interesting you mention the bolt in the middle for added support. I removed the metal bar and lower back section and took a photo of the bottom albeit the tubes were in place. I found what might be the bolt area behind and in-between the two finals, but the bolt is missing. Looks like it was done long ago, there's some surface rust, or maybe it's wood showing, I'm not sure but here's a photo of it.

Click the image to open in full size.


I saw that hole when I first got it home and wondered what that might have gone to. Might this be where the bolt should be that you're talking about?

Thanks.
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