Tubes for Nagra VPA

Thanks for you guys help.
I have just bought used pair of VPAs and have listened only 3 days, actually around 10 hours, and using them with Meridian G08 CDP & Clearaudio TT, Nagra PL-L preamp and B&W Signature 805 speakers. And also, My VPA has only XLR input and they provided adapters to use single ended input.
Up to now, the performance of VPA is a little fall short of my expectations. therefore I doubt tubes life and want to know how to set the bais.
To "Kleech", please send an email to "bwv1004@hanafos.com" regarding setting the bais. I found a black button to the side of the volt meter and 4 screws in the left panel, but I do not know hot to used them to set bais.
Thanks again you guys help and look forward to further information to set bais.

JWK

JWK, I received your email but I'll use some Audiogon bandwidth and reply here as the bias adjustment seems to be a FAQ that has been asked before and in fact another Audiogoner helped me out with this as well.

For this adjustment refer only to the red arrow on the meter and with a small screwdriver access the pots through the top two (of the four ) holes on the left side of the amps.

Have the amps idling in "mute" mode. By default, the front tube is monitored. The red arrow should be sitting on the green zone on the left of the meter. If not, adjust bias with screwdriver through the uppermost hole. Depressing and holding down the black button next to the meter monitors the rear tube. Adjustments to this are made through the second from the top hole. Again adjust to have the red needle in the middle of the green zone while the black button is continuously depressed. Repeat for the other monoblock.

I would expect that these should work quite nicely with your Sig 805's. What is it that is lacking? My guess is that it isn't your tubes or the RCA/XLR adaptors. Have you tried hooking the speakers up through the 4 ohm taps?

Tangram I'm using them with Wilson Sophias and very happy with the results. The Nagras offer better dynamics and bass control on these than some Rowland monoblocks I was using before. Occasionally when I want to zone out to some chamber music I bring down the Guarneris from another system. This combination simply sings but the Wilsons are the more versatile speaker.

I checked ex-owner's bais setting when MUTE mode and found that the red arrows are below the green zone. Therefore, I moved red arrow to the middle of the green zone in accordance with Kleech's instruction on the above. And then, I moved speaker cables to 4 ohm taps from 8 ohm taps and connected Discovery Essence XLR interconnects between Nagra PL-L and VPA.
The result was very impressive, my disappointment for the VPAs was almost disapear and I could listen my favorate Keith Jarret Trio and Casandra Wilson with satisfactroy. Thanks for your help ~~~

[p.s] To Kleech, I have one more question that what is the role about the rest two holes on the middle of left side of the amps. And have you ever changed input tubes (E182CC and/or ECC83) to the famous NOS TFK, Mullard, Amperex, etc ?

JWK, I have no clue what the other two holes are for. Just don't stick anything in there while the amps are running! Perhaps someone reading this could fill us both in.

I have left the tubes alone in these amps. In general, swapping out tubes in your preamp may offer more sonic bang for the buck.

the other two holes are for hum adjustments