Ultravalve Bias check...How Often

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trackball02

Ultravalve Bias check...How Often
« on: 11 Mar 2011, 06:52 am »
I finally got my Ultravalve today. The combination with the Avastar and Zu Soul Superflys is incredible. Just hooked it up to the 16 ohms taps and the sound is phenomenal and beyond words. Thanks AVA, it was worth the wait. I'm one very happy customer.

I ran the voltage check with initial power up right out of the box and came in at about 2.1 v which did not change after after 15mins. It was not problem adjusting to 1.6v for both channels. Are there specific intervals on when to recheck the bias in the future? Any recommendations?

Wayner

Re: Ultravalve Bias check...How Often
« Reply #1 on: 11 Mar 2011, 01:00 pm »
I've done considerable research on the Ultravalve's biasing. I have built a dual bias voltage meter and have watched the behavior for some time now.

 

The real story is that 1) the bias is line voltage dependent, and 2) should be set after the amp has been on for several hours. I have purchased a Kill-A-Watt meter (available at Radio Shack) and that device constantly monitors incoming line voltage.

It usually takes about 3 hours for the bias to fully bottom out, so your initial setting will be a small amount off. At start up the bias usually starts out at around 1.7-1.8 volts and slowly migrates downward with time. When you finally set the bias to 1.56 volts, the line voltage should be at 120vac. As the line voltage varies, so will the bias, but should always reference 1.56 when the line voltage is at 120.

After setting the bias, you should not have to monkey with it for some time. I'd say to recheck it after 3 to 6 months.

One strange behavior to be aware of is that when you adjust one channels bias up or down, the other channel with change conversely. In other words, as you might change the left channels bias down by .1 volts, the right channel may go up by .03-.04 volts. Using 2 volt meters will quickly show the results I am describing.

I have also found some small size knobs that I have set-screwed to the bias adjustment pots, to make them "finger" adjustable. I found the knobs at a local Ace hardware store.

So basically it is set it and pretty much forget it, rechecking about every 3 to 6 months.

Wayner

pelliott321

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Re: Ultravalve Bias check...How Often
« Reply #2 on: 11 Mar 2011, 04:02 pm »
Wayner
cool little device you built!  can you calibrate the two meters against one voltage?
Could you spend some time explaining what we are adjusting when making these changes.
Aren't we measuring voltage across a resistor which in turn is changing the current to the tube?


Wayner

Re: Ultravalve Bias check...How Often
« Reply #3 on: 11 Mar 2011, 04:37 pm »
The 2 meters are identical but share the same 9 volt (DC) power supply. They have been calibrated together, using a quality 3rd meter to calibrate the other 2. They can measure from 1 to 20 volts dc.

As far as biasing voltage and all the fun stuff that happens down stream I will let Frank explain it as this is a Frank question. I would probably get something goofed up with my explanation. I am not a circuit wiz.

Wayner

trackball02

Re: Ultravalve Bias check...How Often
« Reply #4 on: 11 Mar 2011, 06:46 pm »
Thanks for the advice Wayner. I'll recheck today and then go for every 3 to 6 months. This is my first tube amp, and it is not very difficult to maintain. I was concerned that the bias needed to be checked more often.
Jay

avahifi_lj

Re: Ultravalve Bias check...How Often
« Reply #5 on: 11 Mar 2011, 07:02 pm »
Hi:

The proper bias for the UltraValve is 1.6V.  The Ultimate 70, which is built in the Dyna 70 chassis, is 1.56V.  You should be fine with the lower setting, however.

Larry

trackball02

Re: Ultravalve Bias check...How Often
« Reply #6 on: 13 Mar 2011, 03:49 pm »
I rechecked the bias yesterday and it looks and sounds fine.

I noticed that one of the EH 6CA7 tubes is glowing brighter than the other 3. The top filament is at least 50% brighter than the others. I moved the tube from front the back, and the problem stays with that tube.  Does this mean that the tube is bad or is this just a normal variation?

avahifi

Re: Ultravalve Bias check...How Often
« Reply #7 on: 13 Mar 2011, 05:22 pm »
Note that the filament will look much brighter or dimmer depending upon which side of the amp the tube is on.  They point different directions on each side.

However I would keep an eye on the "bright" tube and check the bias setting more often. It may be OK, but it is possible it may not be.

Regards,

Frank

trackball02

Re: Ultravalve Bias check...How Often
« Reply #8 on: 13 Mar 2011, 06:51 pm »
Frank,
I'll move the right channel brighter tube back to the front and keep an eye on it and check the bias more often. As mentioned perviously by Wayner, since the right and left channel bias are related to each other, what will be the earliest bias change that I'll notice if the front right channel tube goes bad?

I also agree with Wayner's observation that is takes several hours for the bias voltage to bottom out.

Thanks,
Jay

pelliott321

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Re: Ultravalve Bias check...How Often
« Reply #9 on: 14 Mar 2011, 04:35 pm »
Frank i would like to know like to know what are we actually measuring with meter at 1.6vdc.
which element of the tube is being biased.

rlee8394

Re: Ultravalve Bias check...How Often
« Reply #10 on: 14 Mar 2011, 09:02 pm »
You're measuring 1.6 volts across a 16 ohm resistor. The resistor is between the cathode of the output tubes and ground potential. This equates to 100 milliamps if current for the pair of output tubes, thus 50 milliamps of current per tube.

Hope this helps,
Ron

trackball02

Re: Ultravalve Bias check...How Often
« Reply #11 on: 27 Mar 2011, 02:51 am »
Frank,
Just a follow up. I have been listening to the Ultravalve for about 70 hours. The bias has been rock steady at 1.6 volts.
By the way, call me crazy, but I think the burn-in has improved the sound of this amp. It was great to begin with but it now is phenomenal.
Thanks for building a great product.
Jay

simon wagstaff

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Re: Ultravalve Bias check...How Often
« Reply #12 on: 27 Mar 2011, 01:34 pm »
The U70 is amazing. I may change other things in my system but I couldn't imagine anything that would sound better than my U70.

:)

tipatina

Re: Ultravalve Bias check...How Often
« Reply #13 on: 15 Oct 2019, 11:31 pm »
One bias question, with speakers hooked up?

avahifi

Re: Ultravalve Bias check...How Often
« Reply #14 on: 16 Oct 2019, 12:14 am »
Yes, set bias with speakers connected and volume all the way down.

Frank

tipatina

Re: Ultravalve Bias check...How Often
« Reply #15 on: 16 Oct 2019, 01:53 am »
Thanks Frank, It worked out well. Love this thing!

Kw6

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Re: Ultravalve Bias check...How Often
« Reply #16 on: 20 Nov 2019, 08:17 am »
Does the Ultravalve have more tube magic than say a Prima Luna Prologue Premium? I like the fact Ultravalve has tube rectification.

avahifi

Re: Ultravalve Bias check...How Often
« Reply #17 on: 20 Nov 2019, 10:45 pm »
Much of the Ultravalve magic is our unique use of independent regulated power supplies for each plate of each small signal tube.  We do this in all our preamplifiers and power amplifiers too, solid state, hybrid, and tube designs.