evh 5150 III issue

[mniel8195]

hey guys i am not sure if i have always had this problem but when i turn on the effects loop on my evh III i notice a slight hum compared to when it is not on. I am running clean power and 100 % new cables as well as a isp decimator g string through the front of the amp and the back. Should i change a preamp tube and if i have to which one? Also i have biased this amp quickly in the past and just set it to 30 ma. I would like to check the plate voltage. What is the easiest way to do it on this amp? I have all of the correct tools to do the job!

 

[311boogieman]

free bump day


My guess is a that it is a preamp tube. Swap out that tube with one of the other ones in the amp or get a new one. I recommend JJs. What brand(s) are in there now?

Looks like it is V7 according to this:
http://www.docstoc.com/docs/9861175/EVH ... Tube-Chart

You should be fine with 30ma but if you need further help biasing the amp - check out this tutorial (similar amp set up)
http://splawnfans.proboards.com/thread/ ... g-tutorial


Edit
I also found this helpful thread just now:
viewtopic.php?f=3&t=112027

 

[SFW]

My 5153 is slightly noisy when the loop is active. It has always been that way.

 

[nwright]

Change the loop tube. I had a hum that disappeared when I got rid of the jj in there.

Ive said it before but I had 4 of the 8 12ax7s in my 100 were microphonic or noisy when I got my amp.

 

[mniel8195]

i have a bunch of jj preamp tubes so i will switch slot 7 thank you