Hello All,
A friend brought over a non working CB head. I found one of the emitter resistors (2.7ohm/10watt) had broken loose on the power transistor nearest to the filter caps. After reattaching it, I powered it up with my variac and light bulb current limiter. I got sound through the speaker but nothing from the input. After poking around with my chopstick for a while I found that the red wire from the preamp to the power amp board had popped loose. When I powered up I got bass guitar through the speaKer. The sound was slightly distorted at first. The sound gradually got more and more distorted, like overdrive had been kicked in. During this time I kept an eye on the light bulb limiter which would glow very brightly when I would hit a note on the bass. After about five minutes the two amp breaker in my variac tripped. I plugged straight into the wall to see if I could see what if anything was gettiing hot. Ouch!! I got smoke off the power board. After checking caps and resistors I found nine resistors that were out of spec, as well as three large caps, a 250mf/64v ( read a constant 839 ohm in circuit, but not out of circuit) and two 1000mf/50v. I checked the filter caps (in circuit with a DVM) and I thought they looked good. When I got all the parts replaced I once again plugged the amp into the variac. As I brought the voltage up on the variac I got an ever increasing loud buzz coming out of the speaker, the higher the voltage the louder the buzz. Next I checked the power transisitors (2n3055) and found two that tested bad on my transistor checker. I replaced the two transistors and when I brought the voltage up there was no sound at all through the speaker. I checked the rectifier and it looks ok, but when I re-checked the filter supply caps, this time disconnected from the circuit, they both read open. The transformer reads and looks good. Does this now sound like a filter cap problem? Would it be a good idea to replace the rectifier as well?
