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Old 08-26-2018, 10:16 PM
birdland birdland is offline
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Join Date: Aug 2016
Location: Bay Area, Northern California
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Default REF150 Tube Bias is increasing!?

Hi:

I was going to post this as a reply to the coupling caps topic but since the last post there was 2 years ago, I thought I'd post this as a new thread.

Does anyone know what failure due to the teflon coupling caps looks like?

I decided to check the bias on my power tubes in my REF150 and I found that the front tube of the right set power tubes on the left channel was reading 70mV! The last time I checked which was only a few listening sessions ago, they were are 64/65mV. The left side of the left channel were reading exactly what I set them to awhile ago.

The right channel had the same problem. The front tube of the right set of power tubes was reading 75mV!

I lowered the bias to 63mV and then checked the rear tube which was more than 64mV and then I went back to the front and it was already at 67mV.

At this point, I just turned off the power.

Could this increase in biasing voltage be due to the coupling caps starting to fail? My local tech mentioned that I should check my bias periodically because when the coupling caps fail, they do not take very long to completely fail.

Thanks,
Walter
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Digital W4S DAC-2v2SE, W4S Recovery powered by Uptone Audio LPS-1, OPPO BDP-105; Office: iFi micro iDAC2 Home Office: iFi nano iDSD with iPurifier2
Analog Rega Planar 2 (original) heavily modified; Benz Micro Ace; Aesthetix Rhea phono pre-amp
Pre-amp/amp Audio Research REF 5SE, Audio Research REF 150, Martin Logan SL3s, Shunyata Research power cords throughout
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