problem with my Mark III

[Haith]

hey guys!
I'm new to the forum i thought maybe you guys could help me out with my problem
last month i was changing the preamp tubes in my mark III amp,when i finished changing the tubes,turned the amp on..no sound was coming out of it! i kept checking the knobs and the guitar cable but when i saw the back of the amp OMG! it's not connected to the speakers!! ****! :evil:
then when i turned it on probebly i had to crank the master volume up to 7 to hear anything and a gain loss in the lead channel occurred....
just changed the power tubes yesterday but nothing happend
what could happen when you turn your amp without a speaker?
do you guys think i should change the preamp tubes again?
some people told me that the transformer is dameged i'm not sure,how can i know though?
of course i don't know anybody here who can fix tube amps since there are no tube amps here for sell in my country...
this is my first tube amp i didn't know such a small mistake could result in damaging the amp!

thanks

 

[Nomad]

Try replacing the preamp tubes one at a time and check the amp each time.

You can toats the output tranny without a load but dont give up yet.

 

[Buddy]

Is it a combo or a head ?
The reason I ask is , sometimes the combo speaker wire will break off at the speaker terminal and cause the consternation you describe .

What happens with an unloaded output transformer is that it "see's" an INFINITE resistance and tries to drive it . This can result in an open , shorted ,or partially shorted winding . There can be smoke , sometimes not .

...And even in Antarctica you can find a tube tech .

 

[Nomad]

Agrreed.


Haith where are you located. Maybe your close to a board member.

 

[stokes]

The output jack should be a shorting jack.That insures if you do run the amp without a load you wont fry the OT immediately.It is far worse to run it into an open load.Put your old tubes back in and if the amp works okay,replace them one by one till you find the bad one.I am talking about the preamp tubes here.If all the new preamp tubes work okay with the old power tubes then you know you have a bad power tube.

 

[Haith]

Is it a combo or a head ?
The reason I ask is , sometimes the combo speaker wire will break off at the speaker terminal and cause the consternation you describe .

What happens with an unloaded output transformer is that it "see's" an INFINITE resistance and tries to drive it . This can result in an open , shorted ,or partially shorted winding . There can be smoke , sometimes not .

...And even in Antarctica you can find a tube tech .

it's a head

Agrreed.


Haith where are you located. Maybe your close to a board member.

I'm from kuwait

how long was the amp on and standby off (up position) and speaker unconnected?

turning the amp on with standby on (down position) and speaker unconnected is ok AFAIK b/c there is no DC current going thru the circuit, only the heater filaments in the power tubes are running.

I once left a Diezel einstein at a store on (standby off) with no load for about 1-3 min's while I figured out how to hookup the cable in the back to the cab, and it worked fine...

1 minute with the standby off and about half minute with standby on.

The output jack should be a shorting jack.That insures if you do run the amp without a load you wont fry the OT immediately.It is far worse to run it into an open load.Put your old tubes back in and if the amp works okay,replace them one by one till you find the bad one.I am talking about the preamp tubes here.If all the new preamp tubes work okay with the old power tubes then you know you have a bad power tube.

I'll try to change the preamp tubes,i'm gonna expirement with preamp tubes only since i changed the power tubes after the accident,i think they are okey..

hopefully i'll update this thread soon

thanks guys!

 

[Nomad]

Good luck and let us know how it turns out. There may not be that many tube amp techs over there.

 

[stokes]

As long as the output jack is the shorting jack that is supposed to be there,your OT should be okay.Even with an open load your OT is capable of surviving a 30 second blast.

 

[Restless Rocks]

The Marks have seperate 8ohm and 4ohm taps on the OT so it doesn't use shorting jacks.

 

[stokes]

The Marks have seperate 8ohm and 4ohm taps on the OT so it doesn't use shorting jacks.

Oh,yeah,but I still think the Mesa OT should stand up to it,if it was only 30 secs.

"have you tried a 30 sec blast?"

Nah,that must be an L.A. thing,we do things much faster here in NY!