clipping effect troubleshooting...problem solved.

[electrickn]

I'm having the power cut out on channel 3 and 4. Almost a "clipping" effect.
The harder I pick the more the sound drops out....to a very low volume.
I'm using two 8 ohm 2X12 cabs (one in a, one in b.) I'm even using two different power tubes in each channel. I've tried different cables, and different guitars. Effects loops are not engaged.
Does anyone have any ideas? Could a loose pre amp tube from shipping do it?
I checked the power tubes, but not all the preamp tubes....I'm not home now, so I can't try it until later, it's really bugging me..

 

[Tubegear Junkie]

I would check preamp tubes- yes.
Use process of elimination when troubleshooting preamp
tubes-helps you isolate the problem.

Seems to me you are experiencing rectifier tube problems.
you're getting excessive sag
Sag in the power supply- You hit a note or chord and the amp tries
to respond but the demand exceeds what the rectifier can supply
so the power sags.

just some thoughts...

Tubegear Junkie

 

[electrickn]

I would check preamp tubes- yes.
Use process of elimination when troubleshooting preamp
tubes-helps you isolate the problem.

Seems to me you are experiencing rectifier tube problems.
you're getting excessive sag
Sag in the power supply- You hit a note or chord and the amp tries
to respond but the demand exceeds what the rectifier can supply
so the power sags.

just some thoughts...

Tubegear Junkie

I initially thought that too, however channel 3 I tested with the 2 34's...and channel 4 I tested with 2 6l6's...same result.

 

[electrickn]

It's not the pre amp tubes, I just switched them all out.
It definately cuts out when more signal is sent in (on channel 3 and 4 only.)
If I let a hard strummed chord ring...it will come up to normal volume.....but then cuts out when I strum again.

 

[Tubegear Junkie]

I would look for D.C. leakage from a coupling cap.
A coupling cap is attached to the plate circuit of
every preamp tube so that A.C. signal can pass
but D.C. voltage is blocked. If D.C. is leaking from the cap,
the bias of the next stage is thrown off.

Tubegear Junkie

 

[electrickn]

I will do that now.
Thanks for the input, I appreciate it.

 

[electrickn]

I saw nothing that looked out of whack...I slid the chassis out a bit..(I'm no tech by far...but I didn't see any loose wires or bad soldering.)

 

[Tubegear Junkie]

Desolder the end of the coupling cap not connected
to the plate of the preamp tube and check from there
to ground with a voltmeter. If there is more than .25 volts D.C.
on the non-plate end of the coupling cap, then the cap needs replacing.
Remember, if D.C. leaks, it throws off the biasing on the preamp tubes
and causes very low power.

I don't know if this is what your experiencing, but that's how you
check for D.C. leakage from a coupling cap.

Tubegear Junkie

 

[electrickn]

I guess I have to bring it to a Boogie tech Monday...The seller is giving me crap saying "it worked perfectly when it left me," kinda stuff.
Anyone know how the Mesa warranty repairs work?

 

[edgarallanpoe]

I guess I have to bring it to a Boogie tech Monday...The seller is giving me crap saying "it worked perfectly when it left me," kinda stuff.
Anyone know how the Mesa warranty repairs work?

Dude...There is a whole lot that can happen to an amp when it is shipped. If it wasn't shipped, and you didn't notice it, then the seller could be telling you the absolute truth.

IIRC the amp should still be under warranty as the RKII is not that old of a design, that amp should still fall well within the warranty time frame. Boogie is great with that kind of stuff. Call them and see what they say.

Go easy on the seller. I have had this happen to me a few times...on both ends. UPS damaged a THD that I received and Fed-Ex buggered up a Dr. Z that I shipped all the way across the country. Dude gets the Dr. Z and has a meltdown, accusing me of all kind of silly ****. Z gets the amp and tells him that the damage was almost surely caused by shipping and not abuse or neglect. Idiot STILL wanted a major refund even though the amp was fixed for free. :roll:

 

[electrickn]

We're working together now...I got mad at him because he told me it was my problem and he didn't have to do anything about it...we're passed that...now I just have to wait and see the diagnosis

 

[edgarallanpoe]

We're working together now...I got mad at him because he told me it was my problem and he didn't have to do anything about it...we're passed that...no I just have to wait and see the diagnosis

That's good to hear. This is the risk we take when we buy from an individual and have something shipped. I hope it works out for you.

 

[rizboog]

I had the same problem, called boogie and after some trial and error, we found out one of the speaker cables was dying. Check it out.

 

[metal190]

Yeah, and like has already been said - one thing people love about boogies are the warranty. I had to have some work done on my old roadster. The tech basically called and got the warranty information from boogie himself and fixed the amp for free and boogie reimbursed the tech. I never had to do anything for it. So I certainly wouldn't sweat it.

As far as problems with shipment and potential problems with used gear, I think that has got to be the only reason why a lot of people still buy gear new. A lot more expensive, but a lot more peace of mind. Anyway, I hope it works out for you.

 

[electrickn]

I just got the amp back from the Boogie tech yesterday. Turns out it was the gain pots in channels 3 and 4. It was a full warranty repair (the amp is only a year old.) It took so long because Mesa shipped two bad gain pots...he had to send them back and wait for new ones. So, I'm pretty pleased...just can't wait to get it up to some decent volumes at practice tomorrow and the gig Saturday.