Marshall 4104 bias ?

[patnemo]

A friend of mine was given a jcm800 4104 50 watt head from a combo & was told it kept blowing fuses, which it did. After inspecting all of the tubes, one of the power tubes had a cracked base & the index key on the bottom was completely gone, the tube was indexed wrong...i rotated the tube & its been fine. my question is the only tubes i have around to replace these with are new 6l6's. i popped them in & the bias probe & they read about 24-25 ma....the tubes in there read 34-35 ma with the probe, which look like 6550's, there is no marks on them. can i safely bias 6l6's in this amp? is there a bias setting i should shoot for? im not to familiar with the 800's
thanks
pat

 

[patnemo]

I don't think you'll be able to bias that low for the 6L6's. Even if you wanted to use EL34's you would need to have a resistor changed in there.

how low...they read 24-25 ma ea. when i checked with the probe? should i just tell him to get new 6550's & keep the amp biased around 34ma.

 

[Everlone]

I had a 4104 and I used E34L's. The EH tubes it came with were crap. I don't think 6l6's would be doable. Plus, its a Marshall. It NEEDS EL34's.