BHK Preamp tube rolling

so new to tubes…these are the ones I got before the war…

So true. There was a point in time when they were made in England, not Russia, and they came in small sizes and big sizes too.


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The KT88’s are sweet. Especially with a CJ!!!

They certainly were and just as nice with the 11A’s successor the Pr. 140. But it got to the point where having to sometimes manhandle an 85 lb. amp got to be a little too much for me so it was sold.

Sorry to derail the thread.

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A few years ago there was quite a bit of discussion about possible benefits of using the 5 mA setting for 12AU7 type tubes vs. the default 4 mA setting in the BHK Preamp. But reading through hundreds of posts in this thread I haven’t found any recent discussion about this. Did a consensus develop that there was no benefit to that or …?

Welcome to the community @pinwa

BHK Preamp Bias - Audio Components / Preamplifiers - PS Audio

You can also use the search magnifying glass. There are other threads that discuss bias voltage side by side with other topics such as tube rolling.

I did try a variety of search terms without getting any helpful results.

I find using Google to search the site to be ore effective.

The format is, for example:

site:psaudio.com “bias voltage”

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The Google is the way.

The late venrable BHK said " The intent of the bias or tube operating switch was to allow for the use of the 12AU7 and the 6922 family of tubes. For the 6922 types, the current was set for 5 mA and for the 12AU7, 4 mA."

I tried 5mA with 12AU7, and it gave more of everything, but after two tracks, I felt tired, nervous, and wanted to turn the system off. You can try for yourself and see which one sounds better in your system.

Agree, the 5ma is just a bit more “in your face” from a soundstage with 12v; I preferred the 4ma setting with them.

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Thanks. That actually doesn’t result in anything helpful but I was happy to learn that you could restrict a google search to a specific site.

“more of everything” is a good description of what my limited experience has been with 5mA and 12AU7 tubes. It may become fatiguing over time but for the moment I am enjoying 5mA with GE JG-5814WA tubes and my Aric Audio Super 300B SET. But I have almost a dozen tubes I am going to roll in and the reason I asked if a consensus opinion had developed is because I don’t want to listen to each tube twice.

As an aside, I have also found there is a difference using the RCA output from my DAC versus the XLR output of the DAC into the BHK. RCA is smoother, less detailed in the top end, and probably a bit more pleasing for female vocals. XLR has that more of everything quality. The differences are noticeable but modest. I am using Harmonic Technology Pro Silway cables with both.

Good news :+1:t2:

After how many hours do you recommend changing the tubes? I last changed 2 years ago and I just looked, over 6000 hours. It seems Ive lost a bit of gain. Is that a sign to change? No idea what is in there now. But I see 4 spare sets of tubes in my box. I will be ordering more haha. Your help is appreciated!!

Noise. If I detect an audible increase in the noise floor, I start thinking time to replace. I don’t recommend any canonical rule of thumb for hours of on-time to replacement. A good set of tubes can last a very long time indeed. It isn’t overly unusual for tubed gear to run on the same set for a decade. Be lucky enough to get tubes from a particularly good lot and you can forget about fretting over a usage counter. If they are still quiet and provide enough gain, stick with them. You’ll likely be better off since the set you replace them with may not be from a strong lot (manufacturing variation from lot to lot does matter). Grading only characterizes beginning of life, doesn’t characterize longevity.

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MUCH appreciated Owlsalum! I ordered a pair of matched gold lions after reviewing the last parts of this thread. But I will hold off on doing the replacement. THANKS!

When facing the BHK Pre from the front; is the tube on the right the one for the right channel?

Yes!

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Guys, if you want the best tubes for your BHK Pre, buy ECC80 Philips D getter Pinched Waist WK6 or WK4 codes. They blew out of the water every 12au7 I tested and I got all of them :slight_smile:

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