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apehead 27th December 2006 02:07 PM

bias adjust installation, bogen mo-100a mo 100a quicksilver
2 Attachment(s)
Hello everybody,

Glad to be back, and with a new question concerning the best bang for buck amps... Bogen! I've been playing my bass through an EL-34 retro-fitted MX-60a (originally designed for 8417's) and I'm nothing but impressed. There is some noise as you begin to crank the gain up with the high- pass filter engaged, and I would like to remedy that if possible, but the main focus of this thread concerns another Bogen I purchased and have yet to hear. It is a MO-100a that is in need of some TLC. It came with a quad of 8417's, one of which is visibly bad, and the other three are a mystery (I don't have a tube checker). The only modification I've done thus far is replacing the broken two-prong power cable with a proper, safety-grounded power cable. Now, I would like to add a bias adjust circuit. I've included the schematic, and I need some advice as to where/what should be added. The only adjustment i can find is called "Balance" and I assume its used to favor one side or the other in the power section. I plan on converting this amp to 6550's in the future, considering the fact that 8417's are extinct, and the ridiculously high plate voltages on this thing are more compatible with the 6550 than the 8417 (I think, correct me if I'm wrong). I took a look at the Quicksilver 8417 monoblock schematic (according to the Triode website, the are quite similar) but the schematic i was looking at only has a pair of 8417's, and seemingly no bias adjustment. So, I am a little confused and a little over my head. Please help a lowly noob out!

apehead 27th December 2006 02:08 PM

2 Attachment(s)
Also, here is the Quicksilver amp schematic I've been using as a reference

apehead 27th December 2006 02:13 PM

Mo-100a manual
I now realize how tiny the Bogen schematic is. This may help.

MO-100a Manual

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