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Old 03-15-2010, 11:03 PM   #1
Join Date: Feb 2009
Posts: 50
bias settings jtm60?

I am playing through a JTM60, and i like the sound of this amp. a friend gave me a pair of new JJE34L's, suggesting they would much improve the mid-to-low end response. i am running sovtek EL34G's now, which i read negative opinions about, but i have nothing to compare them to, so i will give the JJ's a try (i REALLY liked what JJ's did for my fender).
my question:
should i rebias with the new tubes? i am familiar with the biasing process from re-tubing my fender, so no biggie there, except i am not familiar with the test points on the JTM are.
thanks in advance for any suggestions.
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Old 03-16-2010, 01:14 AM   #2
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Location: Outside of Chicago
Posts: 772
Re: bias settings jtm60?

Bias everytime you put in a different tube. Try the JJ's and run them for a while until you search around for some good old NOS/real old tubes. Nothing new can compare IMO to an older USA made tube.
I used to have one of those and it ran 510dcv's and I ran the bias at between .045 to .049 I think with some old RCA's.
Watch/check the boards on those. I got rid of mine because of too much heat damage. Don't put it up against a wall and run it for long periods and a little fan back there helps alot. Even if its one on the floor. Those tubes cook the boards.
Always Running Dirty on 10
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Old 03-16-2010, 01:24 AM   #3
Join Date: Feb 2009
Posts: 50
Re: bias settings jtm60?

thanks cuda, yeah the heat problem has already been addressed, i installed a fan.
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