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PostPosted: Tue Mar 07, 2017 3:42 pm 
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Bottle Rocket

Joined: Tue Mar 07, 2017 3:36 pm
Posts: 3
Hi,

Saturday my express 5:50+ was working fine, today I had no sound at 5w. 25 and 50 were the same, so I assume the 50w position has a problem as well.

Any suggestions were I should start looking ?

Thanks,

Walter.


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PostPosted: Tue Mar 07, 2017 4:41 pm 
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Mark IV
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Joined: Wed Sep 08, 2010 4:12 pm
Posts: 628
Location: Petaluma, California
lecossois wrote:
Hi,

Saturday my express 5:50+ was working fine, today I had no sound at 5w. 25 and 50 were the same, so I assume the 50w position has a problem as well.

Any suggestions were I should start looking ?

Thanks,

Walter.


Sounds like you may have a bad power tube. Swap the pair from left to right and see if you have sound in 5w. I'd bet you're running the amp off one tube right now...

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PostPosted: Wed Mar 08, 2017 5:55 am 
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Bottle Rocket

Joined: Tue Mar 07, 2017 3:36 pm
Posts: 3
Thanks for the quick reaction. I'll do the test this evening and buy a new set of power tubes if needed. I have a couple of questions though on how I should handle the amp :

1) Can I plug in those tubes myself ? I read something about the need to bias ?
2) We rehearse in a basement, which is not heated when we don't play and somewhat humid as well. Normally I leave the amp there (because it's not exactly fun to carry the amp). What is worse for the lifetime of a tube : keeping in a cold/humid place or transporting it all the time ?
3) I power on/off using both switches at the same time (power and standby). Somebody told me I should not do that, and first put in standby and wait a bit, and only then turn off the power, otherwise it negatively impacts the tubes. Is that correct, or doesn't it matter how I turn on/off the amp ?
4) I was also told when finished playing not to move the amp too fast, and first let the tubes cool down a bit. Any truth in that statement ?

Thanks for your advice.

Walter.


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PostPosted: Wed Mar 08, 2017 12:15 pm 
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Mark IV
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Joined: Wed Sep 08, 2010 4:12 pm
Posts: 628
Location: Petaluma, California
Hi Walter,

You can install tubes yourself. If using MESA power tubes there is no need to worry about bias, which is fixed in the design of the amp.

Amps are used in all types of environments and transported all the time...not to worry about what is worse for the lifetime of a tube.

ALWAYS power on first, allow the amp to warm up...then switch from Standby to On. (Be sure to read your user manual, too!)

I've never had an issue moving an amp too fast after shut down...clearing the stage if you're an opening act happens fast!

Thanks

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PostPosted: Wed Mar 08, 2017 12:50 pm 
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Single Recto
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Joined: Sat Jan 12, 2008 12:32 pm
Posts: 1271
Check your phase inverter/driver tube (V4, if it's similar to a non plus Express). It's used as a driver in 5 watt SE mode which places a higher demand on it.
The 5:50 that I used to own had a similar issue (though that amp did not have a 25 watt setting) and V4 was the problem.


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PostPosted: Sun Mar 12, 2017 8:02 am 
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Bottle Rocket

Joined: Tue Mar 07, 2017 3:36 pm
Posts: 3
Ok, checked the tubes and one was effectively physically broken. So I replaced them, and now 5w and 25w are working again, but 50w is still the same as 25w (when I switch I even notice that 50w is just a little bit less louder than 25w...). I have to admit that I've never used 50w before, so maybe this problem could have been there for a while.

Any suggestion on what could be the cause ?

Thanks,

Walter


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PostPosted: Sun Mar 12, 2017 1:55 pm 
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Mark IV
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Joined: Wed Sep 08, 2010 4:12 pm
Posts: 628
Location: Petaluma, California
lecossois wrote:
Ok, checked the tubes and one was effectively physically broken. So I replaced them, and now 5w and 25w are working again, but 50w is still the same as 25w (when I switch I even notice that 50w is just a little bit less louder than 25w...). I have to admit that I've never used 50w before, so maybe this problem could have been there for a while.

Any suggestion on what could be the cause ?

Thanks,

Walter


There is not a lot of volume difference between 25w and 50w (about 3db) - but you will notice a difference in clean headroom. Thanks

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