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Is bias setting necessary on matched tubes?

Hi Guys,

Just bought my first tube amp and it was delivered with broken/defective tubes. I just bought a matched quad of Genalex KT88's to replace them and was wondering if biasing is a must, or can I just "plug and play" them as they say.

I'm pretty much a newbie with tubes so any advice is really helpful.

Thanks!

Geoff
geoffcin
brf
1,715 posts
 
Yes, the bias will need to be reset. Make sure the bias pot is turned all the way down before turning on the amp. Let the tubes warm up for 10 minutes and then bring the bias up slowly to the recommended settings. With new tubes, check the bias again after a couple of hours playing time and again in a weeks time. Enjoy.
hanaleimike
125 posts
 
yes, and they will sound different at different bias settings.
dusty
60 posts
 
Unless your amp is of the "audobias" type (primaluna is one brand) then you will have to readjust the bias. Matched tubes just means that they are very similair in terms of operating characteristics. Important! If your amp has only one bias adjustment for each channel then it's recommended that you ONLY buy matched tube sets and replace them all when one goes bad. RAM tubes website has a good primer on matched tubes.
Cheers!
Post removed 
geoffcin OP
4 posts
 
OK, it looks like my amp the Mingda 368-b90 has manual bias adjustment, one for each tube. I've got a multimeter, but I'm about as new to tube bias adjusting as it gets. Is it easy to do? Where can I get info on how? I don't have any info on the specs save that I'm putting in a set of KT88's. (I think it came with 6550s) Should I just bring it to a guitar shop? Am I being a sissy for not wanting to stick my hands where I know not what? I really don't want to smoke a new set of Genalex Gold Lions or myself for that matter!

Thanks for your input!

Geoff
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