Laney KLIPP question

[Bernardduur]

Hey all!

I recently got in the posession of a Laney Klipp amp; great little amp with a great loud tone. When I got her first she blew the house fuses as some idiot wired the primairy winding of the PT to ground (???)

I fixed that; now she works fine with a voltage over the powertube plates of around 600V and a bias of -52V

Problem: after a while 2 of the powertubes begin to burn bright red and blue and the sound vanishes. My best guess is that, as these amps put a lot of strain on the plates, the tubes are just not capable of delivering the goods that long.

Would replacing the powertubes with some better suited tubes (for example JJ's KT77's) do the trick?

Second question: as this amp is a present for my band's guitarist, can I improve the amp more? I was thinking of a cap change (already done), replacing the 470 ohm resistors with some newer versions and replacing the 5.6 ohm cathode resistor with individual ones (one for each tube). Any more?

Here's a schematic of the unit. Mine does not have a choke but a 500 ohm, 10W resistor. Also the PSU section is slight different

Note: I am a beginner in the amp-knowing so I take all opportunities to learn

[VacuumVoodoo]

The KLIPP, as you found out, puts around 600V on the power tubes plates. The old EL34 were good for this, new production need a little tweak to the circuit.

1. change screen grid resistors from 470 Ohm to 1 Kohm
2. put individual 1Ohm resistors in power tube cathodes instead of the common 5.6.
2. put a 22kOhm trimpot in series with th 56Kohm resistor in the bias supply
3. move the upper end of the 220K resistor in the bias supply to the left of stdby switch. This will put bias voltage on power tube grids as soon as you power the amp up and eliminate plate current surge when you go out of stdby to play.
4. adjust bias with the trimpot to measure ca 25-30mV over the 1 Ohm resistors

I've done this to a number of KLIPPS with good results.

Also:

Clean power tube sockets or ven replace them with ceramic ones, many KLIPP amp have traces of arcing on the sockets between pins.

When doing this mark the ends of PT primary with a piece of tape to identify which end goes to which socket - the PT leads are not color coded and it's easy to get the phase wrong when reassembling with huge self oscillation as result.

Try to find NOS RFT EL34. KT77 will probbaly work too but I haven't tested them at higher than 500V.

Good luck

[Bernardduur]

The KLIPP, as you found out, puts around 600V on the power tubes plates. The old EL34 were good for this, new production need a little tweak to the circuit.

1. change screen grid resistors from 470 Ohm to 1 Kohm
2. put individual 1Ohm resistors in power tube cathodes instead of the common 5.6.
2. put a 22kOhm trimpot in series with th 56Kohm resistor in the bias supply
3. move the upper end of the 220K resistor in the bias supply to the left of stdby switch. This will put bias voltage on power tube grids as soon as you power the amp up and eliminate plate current surge when you go out of stdby to play.
4. adjust bias with the trimpot to measure ca 25-30mV over the 1 Ohm resistors

I've done this to a number of KLIPPS with good results.

Also:

Clean power tube sockets or ven replace them with ceramic ones, many KLIPP amp have traces of arcing on the sockets between pins.

When doing this mark the ends of PT primary with a piece of tape to identify which end goes to which socket - the PT leads are not color coded and it's easy to get the phase wrong when reassembling with huge self oscillation as result.

Try to find NOS RFT EL34. KT77 will probbaly work too but I haven't tested them at higher than 500V.

Good luck

Thanks!