How to bias your VH4 w/DMM - attention lethal volts inside !

  • Thread starter Thread starter duesentrieb
  • Start date Start date
Okay. I took the fuse out that is located on the back of the amp and it was most certainly toast. In the fact that it was brown glass instead of clear like the other three.

If I understand you correctly, there is another fuse inside the amp that could also be blown? Or are you referring to the dead tube that took out the fuse it's connected to?


Just so we're clear, the strange reading I was getting from the OT for the bias is indeed being effected by the fuse, correct?

Thanks so much!
 
Hi there,
I know that the preffered plate biasing are 50 mA for 5881, 60 to 70 mA for 6L6 and EL34 and finally 80 mA for 6550, KT66, KT88.
I would like to swap my EL34s to KT77s and i dont know the correct biasing for this kind of tubes.
Could anyone help me?
Thanks a lot!
Gabe
 
Bias them likem EL34s 30mA/tube. When reading off the cathode (bias rite) add 5-10% to this value.
 
Hi Duesentrieb,

Thanks a lot for this tutorial.

I had one question, when you turn the amp on and then get the amp out of standby, and of course attached to a cab (for the load), do you have your master volume set to 0 before you adjust the bias trimmer?

Also I believe this multimeter will work for me to do the biasing, but just wanted to know from you if it is in fact good.
I will have to buy croco wires as well.

http://www.canadiantire.ca/AST/browse/4 ... ?locale=en

You can zoom in on the multimeter too to see the readings but I think its good. Also with this multimeter, I would assume that I connect the red wire connector in the middle connection of the multimeter, and the black connector in the bottom connection?

And I noticed in your video you say to put the red croco in the middle of the OT and the other wire in either the top or bottom of the OT, however in your instructions with the pictures, you mentioned to put the black croco in the middle and the red croco in either the top or bottom of the OT. Im just a bit confused and wondering if you can clear this up for me.

Thanks and hope to hear from you soon.

Mark
 
Set DMM to read 200mA (grey area), red probe middle, black on top. Then hook the crocos to the probes and the other sode of the crocos to the OT pins.
 
Hi Duesentrieb,

Thank you for the information about the master volume and the (200 ma) settings on the multimeter.

So for final confirmation, Red probe is connected to the middle slot of the multimeter and black probe is connected to the (10A) connection of the multimeter (top connection) and not the COM connection of the multimeter (bottom)?

And the red croco connects to the middle of the OT and black croco connects to either top or bottom pins of the OT?

Thanks again.

Mark
 
great read and great video...I have a herbert that Im getting ready to bias for the first in a few weeks but i think Im going to buy a bias rite. Are they advantages or dis-advantages using a bias-rite instead of a multi-meter?
 
Hey folks, rather new here but getting a warm welcome, thanks. I've got a VH4S with 6l6 tubes and want to switch to E34L tubes. I got my tubes in house, and before I put them in I thought I'd take a quick look inside, I opened the amp up and lo and behold there is no bias trimmer. Going by the tutorial here the bias trimmer should be the one by the midi board, the hum trimmer is in the upper right hand corner of the PCB. The Hum trimmer is still where its supposed to be but in place of the bias trimmer I have a resistor. I received the tech manual from Peter which covers how to repalce a hum trimmer with resistors but didn't see anything about replacing a bias trimmer with resistors or vice versa. Anyone with any knowledge on what resistor value I would need to properly bias my VH4S for EL34s? Or should I repalce the resistor with a new bias trimmer, if so what value?
 
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