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PostPosted: Thu Feb 01, 2018 5:27 pm 
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Bottle Rocket

Joined: Thu Feb 01, 2018 5:11 pm
Posts: 4
Hi I am new to this board and kindly ask for some help understanding the Tube layout of the Mesa 50/50 rack power amp (mine was made in 1999).

2 Questions:
(1) Have I labeled the input, phase inverter, and power amp tubes correctly in the image below?
(2) If I only want to use channel A, can I remove 2 of the 4 6L6GC power tubes (that is, the 2 power tubes for channel B) and still use the amp? Or if two of the power tube sockets are empty the amp will not work at all?

Thanks so much for your help.

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PostPosted: Thu Feb 01, 2018 6:59 pm 
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Mark II
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Joined: Thu Mar 26, 2009 9:01 pm
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Location: Canada
Hi H.G.G.

Your tube designations are correct... Please find the tube layout below

Image

According to Mesa Fifty/Fifty Manual...

If you opt to use only one channel of the Fifty/Fifty with speakers connected to only one channel's output(s), you must turn the unused channel's Level control to zero! Otherwise the channel will be operating without a load, and damage to the tubes and/or the transformer will result.

Just to be on the safe side, I would put a load-box on the channel that is not being used.

Image

I hope this helps

Seeya

Joe

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PostPosted: Thu Feb 01, 2018 8:56 pm 
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Bottle Rocket

Joined: Thu Feb 01, 2018 5:11 pm
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Thanks so much Joe, for the very helpful info. I do have a load I can use on channel b.

However, what about if I physically removed tubes v6 and v7 (the power tubes associated with channel b)--can I still use channel a? Or will the amp not work if its missing 2 power tubes?

Thanks again,
HG


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PostPosted: Thu Feb 01, 2018 10:23 pm 
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Mark II
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Hi HG,

Yes you can remove the Power Tubes for Channel B and No damage will occur

I hope this helps

Seeya

Joe

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PostPosted: Mon Feb 05, 2018 12:34 am 
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Bottle Rocket

Joined: Thu Feb 01, 2018 5:11 pm
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Thanks again. If I remove the power tubes to channel b, does channel b still need a load to prevent damage to the transformer? Or no?


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PostPosted: Tue Feb 06, 2018 8:58 am 
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Mark II
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Hi HG

If you remove the channel B output tubes you don't need a load on Channel B Speaker output... Please let me know if I can help with any other questions.

Seeya

Joe

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PostPosted: Tue Feb 20, 2018 6:11 pm 
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Bottle Rocket

Joined: Thu Feb 01, 2018 5:11 pm
Posts: 4
Thanks a lot man, really appreciate your help.


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