[marvda1]

i had one tube amp manufacturer say bias the tubes with no signal going thru the amp and another say use low volumn music playing.  which is the correct way?

[SteveFord]

Preamp on, no signal is what VTL says.

[kingdeezie]

I would think, and I am no expert, that it might be dependent on the type of design and the manufacturer of the amplifier.

The cheekiest thing to say here is to check with whatever company makes your amplifier.

I have Manley's and they say to bias the tubes with no signal, and the preamp off. I follow their bias procedure.

[Freo-1]

The old Dynaco MK III owner's manual I had all those years ago did state that the bias should be set with no input (music) signal present. 

I think most bias setups are designed to be adjusted with no input signal.

[avahifi]

In general, when the amp is amplifying a signal, this will increase the bias reading.  Thus I would suspect that setting bias while the amp is seeing a signal would give a faulty reading (high).

The problem with the advice to set bias while the amp is generating an output signal is just how much signal should it be playing?  Unless you had the amp attached to a scope, how would you know how much signal is the right amount?

Regards,

Frank Van Alstine

[decal]

i had one tube amp manufacturer say bias the tubes with no signal going thru the amp and another say use low volumn music playing.  which is the correct way?

The "best" way is the way the manufacturer of your amp recommends. They built it, they should know. Good luck. 

[Ericus Rex]

Biasing without music playing is the standard, so do that unless you amp manufacturer recommends otherwise.

[marvda1]

this is what the manufacturer says: " set the volume at lower level (less than one quarter). i guess you could take this as no signal present or with a signal.

[Steidl Guitars]

set the volume at lower level (less than one quarter).

Does the amp have a volume control?  If it does, they might mean you should set the volume to low, with no input signal.

[marvda1]

yes, it is an integrated. i tried doing it with the siginal and the readings kept jumping around, then i tried with no signal and the volume set low and got great readings to set the bias.

[Steve]

In general, when the amp is amplifying a signal, this will increase the bias reading.  Thus I would suspect that setting bias while the amp is seeing a signal would give a faulty reading (high).

The problem with the advice to set bias while the amp is generating an output signal is just how much signal should it be playing?  Unless you had the amp attached to a scope, how would you know how much signal is the right amount?

Regards,

Frank Van Alstine

+1. Nicely put Frank.

Cheers.