Posted by TubeCraft [ 207.106.24.98 ] on January 12, 2005 at 13:52:31:

Noticed the new amp I built is short on bass. I fire up the test tone CD, and sure enough, no reponse at 100hz. (Response at 1khz and 10khz seems pretty normal.)

Using a plain old VOM, I trace good response (test tone at 100hz) to the socket grid connection of the driver tube, a 5687. The 5687 has 170v on the plate (pin1), the cathode is at 7v(pin 3), running at 14.7ma. I measure a 5v RMS signal at the grid pin socket connection (pin 2).

There is little or no signal appearing at the plate (91mv).

Swap in several different tubes, 5687, 7044 no change.

Any ideas?

Rk=475r (bypassed 220uf) Rl=7k5 Grid=100k gain pot

Replies:

• Re: Today's Puzzler - Solved - TubeCraft 20:22:39 01/15/05 (3)
  • I do love the "solved" posts - Tnuctipun 10:20:14 01/18/05 (2)
    • Re: Here's the why! - TubeCraft 11:08:45 01/19/05 (1)
      • test first... - Tnuctipun 13:02:45 01/19/05 (0)
• Re: Today's Puzzler - colinhester 18:54:40 01/13/05 (0)
• Re: Today's Puzzler - Damir 07:06:44 01/13/05 (1)
  • Re: Today's Puzzler - TubeCraft 07:13:53 01/13/05 (0)
• Do you have grid stoppers? - BrownEyes 14:27:52 01/12/05 (2)
  • Grid stoppers- No change - TubeCraft 07:07:03 01/13/05 (0)
  • Re: Do you have grid stoppers? - TubeCraft 14:45:23 01/12/05 (0)