just built a 50 watt 1987 using the metro amp instructions and parts from valvestorm,marstran, etc...
I'm trying to bias the amp according to georges instructions but I'm a little confused. It says to get a reading from V4 and V5 pin 1. But in the voltage chart, it says pin 1 and pin 8 are ground. I can't get a steady reading from pin 1, I've tried 2 different meters (including a fluke) and it either reads 0mv or it gradually increases or decreases in value from 0 to 60mv. Did I wire something wrong. I can get pin 5 to give me a steady reading, can I just use that for the bias?
Thanks for any help that may come my way. The amp sounds pretty darn good....and loud!
biasing question 50 watt kit
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rynugz007
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rynugz007
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Re: biasing question 50 watt kit
so, I finally got a reading from pin 1. Not sure what i did differently??? I did let the amp warm up quite a bit before I took any measurements and used my dads reliable multi-meter (mine is of the radioshack variety). I could only get the pin 5 reading to -38, and that was with the pot fully counter-clockwise. Which caused me to only see about 19 to 29mv on pin 1. After reading around on this here wonderful forum, someone mentioned changing the bias pot resistor to a lower value (i dropped it from 47k to 33k). POOF!!! i was able to get pin 1 and pin 5 in their normal ranges. I'll fire it up tomorrow and see if I hear a difference.