Herbert tube bias....HELP!!!!

[monkeyking67]

Hi,im about to bias my herberts tubes for the first time...I bought the bias rite meter but im not sure how to do it....it states on the Diezel tech corner that the pairs are 1-6,2-5,3-4......does this mean that channel one (clean) goes with tubes 1 & 6.......ch. 2 with 2 & 5.......ch. 3 with 3 & 4?????? not sure how that end works...
will take any advice before attempting this....thanks guys

 

[D-Rock]

You might have better luck in the Deizel forum. Check the RigTalk index page. Good luck.

 

[Dale B]

Hi,im about to bias my herberts tubes for the first time...I bought the bias rite meter but im not sure how to do it....it states on the Diezel tech corner that the pairs are 1-6,2-5,3-4......does this mean that channel one (clean) goes with tubes 1 & 6.......ch. 2 with 2 & 5.......ch. 3 with 3 & 4?????? not sure how that end works...
will take any advice before attempting this....thanks guys

The entire power section works with every channel on the amplifier. Tubes 1 and 6 are controlled by one bias pot, Tubes 2 and 5 are controlled by one bias pot and Tubes 3 and 4 are controlled by their own bias pot. Each channel doesn't have its own power section. I remember seeing that false information being spread around the net by some people after the Herbert hit the market several years ago. It's just not so. The VH4 Stereo head has two different power sections. The Herbert isn't an amplifier that can be set up for channel specific power tubes like the Mesa Road King. The Herbert is geared more along the lines of mixing power tube types within each pair in order to blend power tube type qualities together.

Also, when you're biasing the amp, be very careful when adjusting the bias pots because they are extremely sensitive. A little turn does a whole lot. One thing I noticed when adjusting the bias of one pair of power tubes is that adjustment had an effect on the other pairs. If you hear the amp humming or see any extremely high cathode current values, put the amp in standby until you're able to focus on the particular pair that isn't within the specified range you're shooting for.

Lastly, the amp will sound its best if you stay within the cathode current ranges that Diezel specifies for the amp. Also, those ranges are there because the bias pot is extremely sensitive with power tubes that have more natural plate current draw. EL34's won't be quite as sensitive. 6L6GC's will be a little bit more sensitive. KT88's, 6550's and KT66's will be VERY sensitive. Be careful.

Good Luck!

 

[monkeyking67]

Nooooooow I get it....I really appreciate your help......Thanks Dale!!!!!!!