Need schematic Laney L20

[fredcapo]

Hi. I need a schematic for a Laney L20. Thanks.

[mozwell]

L30 may be close enough

[fredcapo]

Thanks. But I don't see it when clicked...

[Enzo]

Yeah, the link won;t work for me either, probably have to reload it with a different size.

[g1]

For the L30, try here: LANEY - amplifiers head combo drawings - schemes drawings schematics - schemes drawings schematics | GuitarElectric.eu

[fredcapo]

Thanks. Those L30s seem to be solid state. This L20 is running a quad of EL84/6BQ5 (one of which is redplating). It is a Laney Lionheart L20.

[g1]

If you swap around the output tubes, does the problem stay with the tube or with the socket?

[oc disorder]

I gather this amp has all 4 EL84's in parallel in a supposedly single ended class A set up. Yep single ended with 4 !
Its the big brother to the Lionheart L5 the schematic of which is here http://music-electronics-forum.com/t19978/
Time for new tubes I'd say

[fredcapo]

Put in a new quad and the same socket starts to redplate. Didnt take it apart yet so dont know about the output stage config. A schematic would be nice.

[Jazz P Bass]

The L5T is a single EL84, Class A.
The L20T is a quad of EL84's in parallel.
Also Class A.
http://music-electronics-forum.com/a...-schematic.pdf
In Parallel means just that.
The plates will be commoned.
The cathodes also.
The grids will have there own resistors but still commoned.
That leaves the screens.
They will have there own resistors commoned to the B+.
So if all of this is true & no faults are found (bad connections, open resistors) check the socket itself.
There could be carbon tracks on the surface from a previous tube blowout.

[Enzo]

I'd pull the power tubes and take voltage readings on the empty sockets, in particular look at the control grid pin on the affected socket.

[fredcapo]

Thanks. Yes it's the grid on that tube. Appears to be open, though I can't see what is on the other side of the pcb. Will have to pull the board out. When my voltmeter is on the grid it doesn't redplate.