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previous: A.Colman Thanks to Scott and MB for the repl... -- 10/25/2000 10:06 PM View Thread

Re: Not making sense?

10/25/2000 10:54 PM
Re: Not making sense?
I have a chb35 but haven't opened it or worked on it yet.  
Looks like regular unbalanced inputs on the bogen though . . .  
A simple mod for the Bogen; I would suggest using mic#1 as the guitar input, replace the .1/100 input cap with a 33K resistor, adding a 1.5K resistor between pin 9 of V1A and ground, while also replacing the 470K leading to pin 7 with a 100K instead.  
This will change the original grid leak bias of V1A to cathode bias, using commonly seen values for a guitar input stage.  
You would still be able to connect both a monophonic CD and tape deck to aux1 & aux2, plus use V1B with mic#2 for vocals or magnetic phono (monophonic also) input according to the switch position.  
Nothing else would actually *require* changing, but any of the components between V1A and the speaker can be expected to effect the tone if changed from the original values. Also somewhat lower dropping resistors in the power supply leading to V1A would give you higher voltages on your guitar input tube, to make it operate more similarly to common guitar amps.  
If you do have more than two thumbs, like I feel sometimes, it might be best to let an experienced tubehead work on it, especially with regards to safety and avoidance of fatal electrocution. Even with a simple modification, one false move and . . . zap!  
If yours has an input transformer between the XLR connectors and the input tube it could be bypassed during a rewiring job to resemble my suggestions, or you could even add a switchable guitar input to select either one.  
ten big thumbs up,  

A.Colman Thans MB, i'll print this and show ... -- 10/25/2000 11:44 PM