Biasing a SVT-VR (has bias LED's)

[daz]

It's a newer SVT that has a biasing setup where there are 2 bias pots on the back, each one for three of the six 6550's. Then theres a balance pot. The manual is a no brainer for the bias on each side, but i don't know if theres a way to set the balance. You simply turn the bias pt on each side till the LED just lights. But the balance is to be set as follows from the manual...

insert a 40Hz signal, adjust the volume control for approximately 25 VRMS output, then adjust the balance control till the LED just lights

Now, i don't have a scope so i wanted to ask if it's ok just to set the balance so the pot is physically in the middle of it's range? I imagine the balance is there so you can balance the 2 sides, then set each side's bias. If thats the case i figure leaving in in the middle and just setting the 2 bias pots should be fine, no? If not, how could i set the balance w/o a scope?

[Jazz P Bass]

Nothing is noted about an oscilloscope
If you do not have a frequency generator, 40Hz is an open E (4th string) on a bass guitar.
The 25Vrms signal can be measured with a DVM hooked up to the speaker.
Set it to read Vac.

[daz]

Thanks much. Have a bass i can use too so that'll do just fine.

[SimTech]

Just to add a little here since a search for setting the balance pot lands here: if you did have an oscilloscope you would be looking for 70.71 volts peak to peak on the output. And yes that's ALOT of juice so if your doing this through a speaker it better be a good one and you will need hearing protection. Also be aware that 40Hz that loud can literally rattle the walls and shake the windows. Basically, this is gonna hurt you alot more than your amp. Be aware. Also if you're using a dummy load it better be able to handle ALOT of power. And it will get HOT quickly.

[Tom Phillips]

... i wanted to ask if it's ok just to set the balance so the pot is physically in the middle of it's range? I imagine the balance is there so you can balance the 2 sides, then set each side's bias. If thats the case i figure leaving in in the middle and just setting the 2 bias pots should be fine, no?...

I'll let you know that the Balance control on your SVT is for balancing the amplitude of the two out of phase signals from the phase inverter. That particular control does not affect the bias setting of the power tubes. The directions you described are similar to those for the original classic SVT. I'm surprised that they expect the amp's user to be able to make the adjustment and I'm skeptical that their LED system would work properly for that setting. The old directions instruct to do the test with a suitable dummy load connected to the output. Surly they must expect the same for the SVT-VR.