.50 cal + bias resistor value and location.

[billygoat]

Can someone tell me what the standard value is for the bias resistor in a .50 Caliber +, and where it is located on the board. If you can just give me the number that is silk screened on the board, i can find it.

I have a feeling my amp was modded. My tech said it was, and I am going to put a new set of tubes in it. I want to replace them with something close to what I have, which may be the original boogie tubes!!! Red GT/Boogie's

If someone can recommend a tube number (ie. the hotness) for these 6l6's that would be great!

Thanks

Nik

 

[Boogiebabies]

The stock bias circuit from the schematic shows a red wire from the PT being used as a LV tap. It has a 47K resistor, a 1N4007 diode set to block positive voltage and then an 82K and 62K tied together. From Russ B's .50 Cal the best I can tell is that the red wire connects to the board where the 47K resistor is mounted to the board standing up. The diode and the 2 other resistors are just below the third green 220uf / 100V electrolytic cap. Also, there may be a 33K before it hits the two 220K resistors that end up going to pin 5 on the power tube. Pin 5 should read -47V. If it does, then it's stock.

Russ B's great pics are listed under a Mesa search at http://acplink.com/
Many thank to Russ.


http://www.tubefreak.com/cal50pow.gif

 

[RussB]

Here's a couple pics...I added a resistor in parallel...I seem to remember running the Valve Arts (shuguang) 6L6's at around 35mA.