'Laney Klipp 60' keeps blowing the same power tube.

[EstynEstyn]

Hi,

I have a Laney Klipp 60 (schematic: http://www.prowessamplifiers.com/sch...s/klipp_60.jpg) that keeps blowing the same power tube. Other than the blown tube, that I've replace twice with the same outcome, nothing else is obviously damaged. What else should I check?

Thanks.

[Gtr_tech]

Check to see if theres negative voltage at pin 5 on *both* pwr tube sockets. It should be the same on both. You can check this with no tubes in but the amp will need to be in "play" mode (off standby) since bias is obtained from a resistor tap off the plate supply winding. If -v is missing, check the 220k bias feeds, then the 10k grid stoppers. If those are ok and you have -v at both #5 pins, any of 3 things could be happening....

1 - the socket connection is not making reliable contact....clean/retension the socket receptacles.

2 - leaky coupling caps at the phase inverter plates can cause the bias voltage to "creep" toward ground making it less negative and idling teh tube closer to dangerous levels of current. Bias voltage should stay stable after a few seconds.

3 - I'm looking at the schem, and if that says "-30v" for teh bias into the feeds, thats not nearly enough. Some tubes may be able to take that at a real low plate supply, but we're talking serious plate v here....near 600v. Theres no way -30v is even close. At that plate voltage, I'd want to see them idle at around 27ma for roughly 16w idle plate dissipation.


This amp apparently has no balancing resistors on the series connected filter caps...thats a no no.

Since this thing uses "kill yer ass dead" plate supply, I'd recommend you take it to a professional to be dealt with. If you have no electronics experience and no knowledge of high voltage safety....don't screw with it.

On a positive note....it has potential to be a real Mar$hall killer.....