AmpTalk.com

[gregor77]

I have a Mesa Boogie Rocket 44. It works great for a few minutes and then starts cutting out - losing 75% of its volume and crackling loudly. I am broke and looking for a way to fix this myself. Any ideas from my colleagues here would be greatly appreciated. thanks!

[tw001_tw]

You just described how my friends jcm800 sounded right before he had
to replace the output transformer. Instead of "after a few minutes", it
eventually turned into "as soon as he turned it on".

now, it might be something like an output tube or tube socket. If you are
confident you can (and sure you want to) resolve it yourself, I'd start by
seeing if you can borrow a test/working set of tubes. Then I would do a
visual inspection of the inside of the amp. If nothing noticeably wrong, I
would try to isolate if the problem was in the preamp or the power amp -
thats easy if you have an effects loop. I would then take resistance readings
for the potentiometers (easy & quick ). If all is normal at this point, I would take
voltage readings on all the tube socket pins and comparing them to
known good values for the tube/pin - as long as they are in the ball park,
you could consider it good (as voltages will vary from amp to amp). (let the
amp warm up before taking the readings). But like I said, it kind of
sounds like the output transformer.

let us know, and if there are any follow up questions, let us know too..
good luck.

[gregor77]

[gregor77]

I replaced the last preamp tube (furthest from the input) and the crackling seems to have been eliminated. Thanks for the tips!!!

[tw001_tw]

[gregor77]

The small transformer started smoking - the wire coming out of it was glowing red and smoking. So I guess this transformer is toast. Any ideas?

[tw001_tw]

[gregor77]

The transformer that smoked was the small one that is located on the right hand side of the amp as you view the amp from the back side.

I replaced the tubes with EL84's I scavenged from my 30 watt Peavey Classic 30. I bought those tubes in a matched set from J&J.

Did mixing these two tubes with the Mesa EL 84's cause the transformer to blow out???

Is there a website that offers downloads of Mesa schematics?

BTW, estimates for repairing this amp are running as much as $400, which is more than I paid for the thing. So any help with fixing this is greatly appreciated, since i can't pay a tech pro to do it. Thanks.

[tw001_tw]

Been a while! I was hoping you had it all solved by now.

Mixing the el84's would not have done that
I checked at the usual schematic sites... I can't fine your model.

Check your PM.

-tw

[gregor77]

I can't access the PM (not authorised) is the message I get, even when signed in. I checked the FAQ and didn't find anything there to solve the problem. I'll keep trying.

[tw001_tw]

You have to have 10 or 11 posts to send a PM. I thought since I sent you
one, you could access it. 1 or 2 more posts to go

[gregor77]

I 'll stick around and keep checking as I post. Thanks!

[gregor77]

Thanks! BTW, wires from the speaker input jacks run to the small transformer-like device that was smoking. See photo.

[img]http://www.flickr.com/photos/33266605@N02/?saved=1[/img]

[tw001_tw]

The transformer in question is the output transformer.
The green and yellow ones look like the OT secondaries - the blue and brown
are coming form each 'side' of the power stage and the red is giving the
OT its high voltage. I don't see a reverb transformer in the pictures.

back to the original plan. replace the OT transformer. You going to do it,
or have it done at a shop?

<edited>
while you have it out, do you see any burnt or blackish components (since
its out of the chassis) ?

[gregor77]

I might try and do it, but I'll have to learn how to safely proceed because I haven't done this before. Are the Weber transformers good? Can you recommend a good brand of replacement transformer?

I haven't seen any other blackened components inside. Thanks for your input!