| ampage Tube Amps / Music Electronics |
For current discussions, please visit Music Electronics Forum. |
ampage archive
Vintage threads from the first ten years
Runaway Bias
 6/5/2000 1:52 AM |
|
Casey4s | Runaway Bias A few minutes ago I finished putting together my newest DIY. It is an Ampeg SB12 clone/variation.I am useing a Stancor PT 375-0-375 with a pair of GE 6550's, and a GZ34. I am getting 535v on the plates with no tubes, which is well within limits for these tubes. The first thing I tried to do was bias the amp. With a swamp probe, I am reading 180+ ma! I put a 25k bias pot in the circuit, and lowered the 56k bias resistor to 50k when I put this together. The pot dosn't seem to have any affect at all. Pin 4 on the power tubes reads 534v and pin 5 reads -40.5 volts. That's with no tubes into an 8 ohm 160 watt resistive dummie load. I am getting ready to start trouble shooting this thing, so does anybody have any thoughts? Thanks ... Casey4s |
|---|---|
| Replies: |
| R.G. (1) did you get the pinout right? |