11-11-2017, 07:28 AM
Thanks, Journeyman. What Ampeg do you have?
I have completed the Ampeg GuitarAmp and put it back together. It looks and sounds so good. I thought I needed a tube on the tremolo circuit, but I had actually pulled a lead loose on the coax to one of the tremolo pots on the back of the amp.
I cathode biased each 6V6 tube independently so that they put out a more balanced power dissipation. This required a bias resistor of 500 ohms for one tube and 680 ohms for the other. These are 10 watt resistors. The PD for each tube is now 10 watts.
Also, I had replaced the linear volume pot with a "audio" pot. This made the amp get way too loud too early in the 1-10 scale. I put the original linear 1 Meg pot back in and that works great.
I attached 3 photos. Two show the finished amp. The other pic is a chart of the calculated power dissipation (PD) at three test points using 300, 470 and 770 ohm cathode bias resistors on each 6V6. By plotting the PD points, I could choose the nearest resistor to even out the PD between the two tubes to close to, but less than 12 watts. I ended up with 500 and 680 ohm 10 watt resistors giving me about 10 watts on each 6V6 tube. I do not consider myself a electronics expert, so this all comes from reading and watching you tubes. YouTuber "Uncle Doug" was especially helpful.
I have my Gemini VI on the bench now. I am updating the power cord to a 3-prong and changing out several old electrolytic caps.
Larry
I have completed the Ampeg GuitarAmp and put it back together. It looks and sounds so good. I thought I needed a tube on the tremolo circuit, but I had actually pulled a lead loose on the coax to one of the tremolo pots on the back of the amp.
I cathode biased each 6V6 tube independently so that they put out a more balanced power dissipation. This required a bias resistor of 500 ohms for one tube and 680 ohms for the other. These are 10 watt resistors. The PD for each tube is now 10 watts.
Also, I had replaced the linear volume pot with a "audio" pot. This made the amp get way too loud too early in the 1-10 scale. I put the original linear 1 Meg pot back in and that works great.
I attached 3 photos. Two show the finished amp. The other pic is a chart of the calculated power dissipation (PD) at three test points using 300, 470 and 770 ohm cathode bias resistors on each 6V6. By plotting the PD points, I could choose the nearest resistor to even out the PD between the two tubes to close to, but less than 12 watts. I ended up with 500 and 680 ohm 10 watt resistors giving me about 10 watts on each 6V6 tube. I do not consider myself a electronics expert, so this all comes from reading and watching you tubes. YouTuber "Uncle Doug" was especially helpful.
I have my Gemini VI on the bench now. I am updating the power cord to a 3-prong and changing out several old electrolytic caps.
Larry