I replaced my Bugle Boy 5AR4 with a NOS GE 5V4 and the center tap voltage dropped by 10 Volts from 445 to 435 which I expected. With the voltage drop I got a bias reading of 32ma. I reset the bias to where it was when using the 5AR4, which was 36ma. Should I bias hotter with the 5V4 in there Or leave it at 36ma? It sounds pretty good as is............
Post by muzacman02 "Jamie" on Nov 22, 2010 21:05:14 GMT -7
The specs call for no more than 38Ma I 'm pretty sure , But biasing hotter wont hurt the amp it just may eat tubes up faster, I went with the 37.5 on my last set and it was On the money both tubes were the same. Hope this is helpful. ;D
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Post by Phil (aka Phil) on Feb 12, 2011 11:03:00 GMT -7
You should bias the amp for the specific tubes that are in use in the circuit. I usually bias mine at 60-70% ID (idle dissipation). For example most EL34's are rated at 25W, the GT EL34LS was a 30W tube.
Myles made up this cool XLS spreadsheet a while ago...you just put in the plate voltage and the tube's plate dissipation rating and it'll tell you the %ID.
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