@edward78 said:
my multimeter is new and is from KAIWEETS.
Model number?
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I’m still only able to get to 129m V but that is close enough. The trim pot is now maxed out on the left channel (before it was the right), so it seems that the problem is related to the tubes.
Did the amp come to you with all the new tubes installed in the tube sockets already?
IMO, you have a problem with the amplifier. Could be just the power tubes???
You need to be able to directly contact the repair shop that fixed and re-tubed the amp. Going through the Dealer and Distributor just doesn’t work!
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It would also be nice to have a bit of headroom on the bias adjustment in case I ever want to go above 129m V for whatever reason.
Every time the amp, (amplifier) is playing music the power tubes are using up their life. For the VT100 II the average tube life is around 1500 to 2000 hours, going from memory. (YMMV)... The harder you push the amp the shorter the life of the power tubes. Over setting the bias voltage above specs, 130mV, will use up tube life faster.
Hopefully the new 6550 tubes were pre burned in, at least 48 hours, 72 hours is better. Bias for the power tubes was then checked, set again before the amp was shipped to you. IF the power tubes were not pre burned in then the bias voltage should be checked after the amp has been playing music for a few to several hours.
You should have been advised to check the bias on the power tubes again after hooking up the amp to your speakers. Reason is the repair shop AC mains voltage may be higher or lower than your nominal AC mains voltage. That will have an impact on the bias voltage setting.
Depending how often you listen to music, and how hard you push the amp, will determine how often you check the bias on the new power tubes. The bias is not set once and then forgotten... If you listen to music everyday, for say a couple of hours each day, with the new tubes you might want to check the bias again after a week or two. If the bias voltage measures the same without having to adjust it then you might want to check it again in about 4 weeks. If the bias voltage measures good then you might then check it every other month. Your usage of the amp will determine how often you will need to to check the bias. After the tubes get a few hundred hours on them you may find you only need to check the bias every six months.
What you will find as the power tubes age, (from playing music), you will need to increase the setting on the blue trim pots to raise the bias voltage to 130mV. Usually near end of life of the power tubes the tubes will not hold a bias.
FYI, when checking, setting, the bias for the power tubes the amp should be allowed to stabilize without any signal applied for at least 30 minutes. Therein after first being turned on or after listening to music.
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