This will be the first in a series of amp conversion posts that I am working on over the next few months. I will be showing how I go about planning out what i want to change on the circuit, the overall goal for the amp and the process of converting.
First up – Bogen Challenger PA Amplifier
I stumbled across this amp while looking through Facebook marketplace in search of transistors and other parts. It happened to be local and the price was right. Most of these solid state amplifiers go for pretty cheap, so I figured what the heck. It was a little bit of a “challenge” to find the schematic for this model. I could find plenty of copies of the reissue modern version online, but not this one. A quick search and Bogen appears to still be in business. So I sent over an email to see if they still had a copy in their archives and sure enough a day later I got a reply with the schematic!
Does this thing even work?
I contacted the seller to see if the amp worked at all, and they mentioned that it should still work ok. With that bit of info, I had two routes that I could go with this. 1) I could attempt to fix the amp, hoping that there weren’t any major issues, or 2) I could completely gut the amp and shove a low powered tube amp circuit in the chassis. After getting it home and putting it up on the bench, connected to my current limiter and dummy load (along with a bunch of alligator clips to monitor it and put signal into it), I fired the amp up. No magic smoke. No DC on the output. Sweet! Now time to put signal through it. Sure enough I had output to the dummy load, and a LOT of output. Enough so that my limiter lit up. We were in business.
My goal is to make this into some kind of guitar amplifier. So naturally I wired my guitar to the Mic 1 input to see how it sounded. Running it through my shop guitar cabinet the overall sound was kind of bland. The bass control added some decent low end and had a nice range. The treble pot didn’t really seem to add or take away much. Not sure if the pot was dirty or if it was adjusting frequencies that were more in the hifi range which would be past what most guitar speakers are capable of reproducing. So let’s take a look at the circuit and what can be done with it.
Next post coming up! Circuit Analysis of the Bogen Challenger C-100!