Laney amp problem

[frosty55]

Can anyone shed some light on a problem with a 50 watt Laney head?
I run an AOR MK 2 head through a new 2x12 cab with Celestion G12T-75 speakers.
When I play through it at low volume, the treble is there. Turn the volume past 12 o clock, it dissappears.
I have had the amp checked out by an engineer, and new valves put in, along with a bias check. any ideas chaps?
Thanks.

[oc disorder]

Hi Frosty 55
I presume you mean the preamp volume ?
That has a 1n cap and a 220k resistor between the wiper and the "hot side"
from the preceding stage.
Its kinda like a loudness control on a Hi-Fi or the bright ? mod on a guitar volume.
The idea is that the highs can pass through the capacitor and the resistor
when the volume is turned down to compensate for lack of edge (bite?)
until the volume is turned up when the path through the volume control becomes more attractive (less opposition/resistance)than through the 220k
and the 1n cap.
The master (main not pre-amp) seems to have a switchable capacitor on
it in the same way as the pre-amp master.
I presume it is in a pull switch arrangement.
Does that help compensate for the lack of treble in the pre-amp master when it is over half way ?
All the above is based on the assumption it is the pre-amp volume in AOR mode not the gain or the main "power amp" volume.
I have attached the schematic (schematic Heaven post 70's amps) in case someone else would like to comment.
It was drawn 20 years ago ! Seems like only yesterday.......
Only seen one this end of the world.
Someone forgot to plug in the speakers and fried the o/p transformer.
Because of the range of output tappings the output is not shorted when there is nothing plugged in. So always double check this before you turn it on!
Good sounding amp though.

[frosty55]

Its not the pre amp volume thats the problem.
I always have the pre amp up full, its when I raise the master volume up to halfway, the top end dissappears.

[guitician]

The Master also has a "TOP" switch. Are you using it? That will loose effectiveness as that control is turned past 12:00.

[frosty55]

Lane AOR50 mk.2

Exactly where is this master "top" switch?

[oc disorder]

"Exactly where is this master "top" switch? "
On the master vol control. You pull it.
Unless the pots have been replaced without pull switches
both masters ,bass and middle should all have pull switches for additional boost.
See the users manual
http://www.laney.co.uk/manuals/A50-A...0Issue%201.pdf