Tweet
Kalamazoo Model 2 cathode bypass problems - hiss and MORE hum!!!
I just bought a Kalamazoo Model 2 recently and have been slowly going through it. First I swapped out the two prong for a grounded three prong plug, moved the fuse to where the old plug hole was in the back and added a power switch to the front panel. Worked great. Then I went through the input jacks and fixed the issue of all of the resistors being wired straight to the 12AX7 pins causing serious stress and snap crackle pops. Definite MUST for these as the front panel flexes so much.
There is a bit of hum that's always there. When not plugged in to either input the hum is the same no matter if the volume pot is at 0 or 10. It's not too annoying though and I'm OK with it. On 10 no other sounds but the hum. I still haven't replaced the filter caps yet, but I did try to add cathode bypass caps across the power tube and pin 8 of the 12ax7. Straight away I noticed a huge difference in overall volume early on, definitely more gain. But that hum is now LOUDER than before and when I turn the volume up to between 8 and 10 there is a noticeable hissing noise. The bypass caps I used are Mallory 25//25 caps I had pulled from a silverface Bassman someone had failed at making into a Twin like head. I checked the capacitance and they were both between 23 and 25. The polarity on each cap was correct and I even second guessed myself and switched them around, same thing. Took them out of the circuit, back to before. Alligator clipped just the power tube cap, hiss there more hum. Alligator clipped just the 12AX7, hiss there more hum. What could it be? Do you think it's the caps I am using? Is the hum that's always there just getting louder with the cathode bypass mods on account of the increase in bass frequencies?
There is a bit of hum that's always there. When not plugged in to either input the hum is the same no matter if the volume pot is at 0 or 10. It's not too annoying though and I'm OK with it. On 10 no other sounds but the hum. I still haven't replaced the filter caps yet, but I did try to add cathode bypass caps across the power tube and pin 8 of the 12ax7. Straight away I noticed a huge difference in overall volume early on, definitely more gain. But that hum is now LOUDER than before and when I turn the volume up to between 8 and 10 there is a noticeable hissing noise. The bypass caps I used are Mallory 25//25 caps I had pulled from a silverface Bassman someone had failed at making into a Twin like head. I checked the capacitance and they were both between 23 and 25. The polarity on each cap was correct and I even second guessed myself and switched them around, same thing. Took them out of the circuit, back to before. Alligator clipped just the power tube cap, hiss there more hum. Alligator clipped just the 12AX7, hiss there more hum. What could it be? Do you think it's the caps I am using? Is the hum that's always there just getting louder with the cathode bypass mods on account of the increase in bass frequencies?
Comment