Mesa 50/50 problem
Dicky Clark
of the channels has gone off. I dont think this is tube related as when its
running they all apear to be the same healthy colour. I have also changed the
pre amp tubes and this does not seem to have made any difference. Any one got
any ideas????? Any help is much appreciated.
Keep Rocking,
Dick...@aol.com
nospam
If you haven't tried already, swap the power tubes on the dead side with
the power tubes on the working side, this will help narrow down the problem.
Good Luck,
Chuck
Dicky Clark <dick...@aol.com> wrote in message
news:20000820170335...@ng-ck1.aol.com...
Montie Merciless
in with just a cable not being used could cause problems.
BK
have no idea how they have risen to the level they have. The manual for this
amp is riddled with laughable nuggets. (a quote from it: "Sometimes a tube
will "short-out" intermittently, turning red-hot all over the large metal
plate inside". "But usually a momentary switching off of the Standby or
Power switch will enable the tube to straighten out its electron flow and
return to proper operation.")
You should also avoid their comment that it's "OK to operate the amp with
one of the channels not connected to a load......as long as you have that
channels Vol. control turned down".
If operating it mono you should zero the control *and* connect a dummy load
at the very least. The output jacks are not a "shorting-type" nor do they
terminate into an internal load when not connected.
Changing the preamp tubes of the non-functioning side was a good move,
however, I would not recommend just swapping out the power tubes for a
"let's see what this does" gorrilla-troubleshooting-approach. Why risk
damaging a set of tubes or further damaging the amp by nailing it with full
line power?
With both outputs connected to a cab. and the amp on, do you hear any noise
or "blow" coming from the "dead" channels speaker or is it totally silent?
Do you hear any noise when taking it off standby? Do the power tubes on this
side seem to be operating at the same temperature as the working side? If
the tubes are defective, they shorted and most likely took out the screen
supply by exceeding the rating of the 470/ 1W g2 limiting resistor(s).
Each channel shares a common power and bias supply. Unless there's an open
connection (to the dead channel) you can basically rule-out a supply issue.
If the dead-side tubes seem to be getting as hot as the working side and you
can hear slight noise from the speaker, you could have a small problem (like
an input jack or control-related issue).
If you are able (qualified) to troubleshoot internally, I have a schem. for
this amp if it will help. Take it to a tech. if you aren't one. If you do
need new power tubes (and don't purchase the "STR-420" directly from
Boogie), you will need to have the amp biased properly.....regardless of
what the manual says)
LV is matching Fenders "color spec." he may also be doing this for Boogies
as well.(?) Give him a shout.
Good Luck,
Bill
David
> You should also avoid their comment that it's "OK to operate the amp with
> one of the channels not connected to a load......as long as you have that
> channels Vol. control turned down".
I am considering a 50/50 and would rather run it mono with a 1x12 3/4
tuned back cabinet rather than stereo mode. Both the 50/50 and 2:90
manuals state what you just mentioned in addition to turning the
presence all the way up, but the 2:90 manual states its better to not
run an input signal into the unused channel. Why should I have problems
with running in this fashion? There are basic amplifier theories, then
there are the "custom" power amps of today (such as boogie), I'm just
curious if you actually know the internal schematics of the boogie
stereo power amps to back up your claims. How can I create a dummy
load inexpensively without an extra cabinet? Ideally I would like to
run a 50/50 and Triaxis into a Mesa Celestion 30 1x12 3/4 tuned back
cabinet in mono. I think this would be an ideal setup for small to
medium size gigs. Thanks.
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David
> one of the channels not connected to a load......as long as you have that
> channels Vol. control turned down".
I am considering a 50/50 and would rather run it mono with a
1x12 3/4 tuned back cabinet rather than stereo mode. Both the 50/50 and
2:90 manuals state what you just mentioned in addition to turning the
presence all the way up, but the 2:90 manual states its better to not
run an input signal into the unused channel. Why should I have problems
with running in this fashion? There are basic amplifier theories, then
there are the "custom" power amps of today (such as boogie), I'm just
curious if you actually know the internal schematics of the boogie
stereo power amps to back up your claims. How can I create a dummy
load inexpensively without an extra cabinet? Ideally I would like to
run a 50/50 and Triaxis into a Mesa Celestion 30 1x12 3/4 tuned back
cabinet in mono. I think this would be my ideal setup for small to
David
Perhaps you should read the post a second time before posting.
Questions are indicated with a question mark (sorry can't resist being a
smart ass on this).
But I'll spell it out:
Why should I have problems running a Mesa Boogie stereo power amp in
mono without a "dummy load" on the unused channel using the specified
method stated in the manual for the power amps? (vol level at 0,
presence at max, no signal on unused channels input)
and
How can I create an inexpensive dummy load without carrying around
another speaker cabinet?
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Ken Gilbert wrote:
>
> In article <39A6C253...@nowhere.com>,
> David <nos...@nowhere.com> wrote:
> > > You should also avoid their comment that it's "OK to operate the amp with
> > > one of the channels not connected to a load......as long as you have that
> > > channels Vol. control turned down".
> >
> > I am considering a 50/50 and would rather run it mono with a
> > 1x12 3/4 tuned back cabinet rather than stereo mode. Both the 50/50
> and
> > 2:90 manuals state what you just mentioned in addition to turning the
> > presence all the way up, but the 2:90 manual states its better to not
> > run an input signal into the unused channel. Why should I have
> problems
> > with running in this fashion? There are basic amplifier theories,
> then
> > there are the "custom" power amps of today (such as boogie), I'm just
> > curious if you actually know the internal schematics of the boogie
> > stereo power amps to back up your claims. How can I create a dummy
> > load inexpensively without an extra cabinet? Ideally I would like to
> > run a 50/50 and Triaxis into a Mesa Celestion 30 1x12 3/4 tuned back
> > cabinet in mono. I think this would be my ideal setup for small to
> > medium size gigs. Thanks.
>
> just what exactly is the question here?
>
> kg
> --
> I know that the twelve notes in each octave and the varieties
> of rhythm offer me opportunities that all of human genius
> will never exhaust. --Igor Stravinski
>
> Sent via Deja.com http://www.deja.com/
> Before you buy.
Ken Gilbert
BK
The reason that you didn't understand this is because it is part of a mess
that I posted to earlier. I've read this guys post and if I catch his drift,
he wants to operate this stereo Mesa "mono" and leave the other channel
disconnected. The Mesa manual says that it's OK to operate it this way as
long as you zero the unused control. I do not agree with this "advice" so I
wrote the "top side" of his post that he carried up here from the original.
Here are my reasons: first of all (if the schematic is true to the "real"
circuit), the input jacks are not a shorting type. The owner could be an
anal nut about keeping the control down, but throughout any given night it
could be "bumped" by mistake or turned up by some "helpful" knuckle head.
Regardless of its line-level sensitivity, it could sit there all night
oscillating and work the hell outta the tubes & tranny. Second, ......and
here's where I'll take a real ass-whooping.......even though the control is
nulled "I" think that a certain degree of flyback ~could~ still occur if
the power/ standby were cycled when the cathodes were up to temp.
Furthermore, if you owned this and really were concerned about the hangin'
channel, why not just pull the output tubes......or all the tubes out of the
channel not being used? (extra cautious, think, think, think....yeah, I
guess that would be OK....it would raise voltages....but) BTW, (to David)
the circuit of this amp is about as "straight-forward" and vanilla as it
gets.......so there are no magic parts inside.
So that's my crap rap,
Straighten me out (if bent) so I can file it away for next time.
Thanks,
Bill
Ken Gilbert
everything will be ok. if that's what the manual states, then i'm SURE
it's been done before, and i've never heard of an angry mob of MB users
who got screwed by the manual. so it probably works fine.
if you wanted to REALLY be ultimately careful, just go to rat shack,
pick up a suitable 8R resistor, and wire it across the output jacks.
that way even if there IS some signal being reproduced by the finals it
won't be operating into an open load.
as far as his "smart ass" reply to my honest offer of assistance, he
can go fuck himself. i don't owe anybody anything, especially not
people with shitty attitudes.
David
Thanks for the reply. Sorry if you think I had an attitude. Its just
that I hate meaningless replies, repeating myself, and pointing out the
obvious. Thanks again.
Ken Gilbert wrote:
>
> honestly bill, if there's no signal going to the output tubes then
> everything will be ok. if that's what the manual states, then i'm SURE
> it's been done before, and i've never heard of an angry mob of MB users
> who got screwed by the manual. so it probably works fine.
>
> if you wanted to REALLY be ultimately careful, just go to rat shack,
> pick up a suitable 8R resistor, and wire it across the output jacks.
> that way even if there IS some signal being reproduced by the finals it
> won't be operating into an open load.
>
> as far as his "smart ass" reply to my honest offer of assistance, he
> can go fuck himself. i don't owe anybody anything, especially not
> people with shitty attitudes.
>
> kg
>
> --
> I know that the twelve notes in each octave and the varieties
> of rhythm offer me opportunities that all of human genius
> will never exhaust. --Igor Stravinski
>
> Sent via Deja.com http://www.deja.com/
> Before you buy.
--
Danny Russell
David wrote:
>
> Thanks for the reply. Sorry if you think I had an attitude. Its just
> that I hate meaningless replies, repeating myself, and pointing out the
> obvious. Thanks again.
Don't power up a tube amp without a load connected. It's a costly
bad habit to get into. The part about "no output" sounds good in
theory, but in reality tube power sections employing a negative
feedback loop (a good majority) will have a tendency to go unstable
without a load tying them down. If the output does go unstable,
(into oscillation) then suddenly it's going to be producing full
power into an open load and something's likely to smoke in short
order. Also who's to say that a sudden burst of AC line noise
wouldn't generate "signal" in the preamp? Some amps use a shorting
jack in the output which is better than open. Your best, cheapest
precaution would be to have least have 10 watt, resistive dummy load
connected. -Danny
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