Laney Nexus Tube amp bias, balance etc.

[Zouto]

Hi,
I got to retube a Laney Nexus Bass amp. In the Laney service manual I found no instructions for biasing and setting the balance. Any experiences with biasing and balancing that amp? There's sort of a bias LED lightshow similar to Ampeg's LED bias indicators.
Thanks for hints and help
Zouto

[g1]

If it is user adjustable, then it should be covered in the user manual:

edit: sorry, it is not in there. The lights are just to show fault (red) or signal present (blue).
Can you post the service manual?

[Zouto]

Sorry, I forgot, here are the links to the user manual:
https://www.laney.co.uk/uploads/7872...dc414ad774.pdf
and the service manual:
http://elektrotanya.com/laney_nexus_.../download.html

[Jazz P Bass]

Whoa!
(8) KT88's.

There appear to be 4 adjustment pots.
On Pg (1) there are:
VR1: Heater hum balance
VR2: Bias voltage adjust
Vr3: Output tube balance
Vr4: Input signal balance.

Laney_nexus_tube_nxt_Bias.pdf

Then, to confuse the issue, on Page 2 is another Vr1.
This appears to set the opamps to display the Red/ Blue status LED's.
I would assume this is a 'tweak' to be used after the bias has actually been set.

[nickb]

Ouch 34.5Kg -76lbs!!! Need some help getting that on the bench?

[Enzo]

Not quite up to SVT or Classic 400 territory, but still a beast.

[cfortner]

Hi,

old thread, but does anyone have a BIAS procedure for biasing this amp? Mine works well but one KT88 shows red, so I have to change it and rebias the valves.

Basically I know how to bias it, but may be there is a good description out there. At 1 Ohm-cathode resistor 50mV for 50mA current?

Thanks a lot

Chr.

[g1]

No reason to choose 50mA; but you are correct that 50mV across the 1 ohm resistor would indicate 50mA current.
It appears that if the bias is too hot, you will get red indicator lights, if it is too cold, you will get blue indicators. So somewhere between those will be ok.
I would check what they are all running at now and figure out the average.

But I don't think you can adjust for individual tubes anyway, just the whole set (VR2) and balance between top half and bottom half (VR3).
So if you are only replacing one tube, I would just leave it where it is, and if it is too mismatched with the rest of the set, you will have to try another.
If changing the whole set, rebias to the average that is measured for the current set (except the one showing red).