[medium jim]

I'm in the final stages of tube burn in on my recently acquired amp, an ARC VS-110 and in the last week or so noticed that I was leaning to the right a little with my head as the soundstage was slightly to the left.   I immediately checked the bias and the left channel was spot on, the right channel had a couple of the 6550's that needed to be nudged up a couple of ma.   Damn, what a huge difference just a couple of ma's make, the soundstage was right again and since the tubes are about all the way burned in, the soundstage is more holographic and inviting. 

I cannot bely how important it is to check the output tube bias and get it as close as possible to each other tube as this will greatly extend the lifespan more so than biasing them on the light side.  ARC says change the output tubes every 2,000 hours (new production tubes), but I know from experience that with judicious biasing (in a push/pull setup) that the lifespan can be 5000 hours.  By keeping the tubes biased as close as possible the tubes don't have to work against each other. 

I check the bias every month or will if I notice a change in the SQ.  A little care and preventative maintenance will pay off in both life of the tubes and in better SQ Of course, I'm preaching to the choir!

Jim

[InfernoSTi]

Nice post, Jim!

I use self-biasing tube amps because I'm not so good with the multi meter!

Best,
John

[medium jim]

Nice post, Jim!

I use self-biasing tube amps because I'm not so good with the multi meter!

Best,
John

John: 

What amp do you have? 

Jim

[Captainhemo]

That is  a great little post.  Very  helpfull  to  anyone , like myself,  who is just sstarting out   with  a first tube amp.  Can' t wait for it to arrive 

-jay

[Maritan]

I'm quite anal, especially with electronics. I like to take care of things so they last me a long, long time. Here's what I do before every listening session:

I switch the pre-amp on, put it on mute. Then I switch the amp on and let it warm up for at least ten minutes. Then I check the bias of each output tube. Once I make sure everything seems normal, I commence the music.

This is probably way overkill, but I like making sure everything looks good every time...

Enjoy your VS-110! 

[Bob2]

I check the bias of each output tube. Once I make sure everything seems normal, I commence the music

Have you found much change in the bias from one session to the next? I usually check mine once a month....I may need to re-think that!
Thanks, Bob2

[Ericus Rex]

Jim,

IIRC, ARC drives their output tubes pretty hard.  They sound great this way but don't last so long.  You may actually only get 2k hours on them.  Whats their recommended bias current?

[Freo-1]

Jim,

IIRC, ARC drives their output tubes pretty hard.  They sound great this way but don't last so long.  You may actually only get 2k hours on them.  Whats their recommended bias current?

Agree.  I had a D115II that sounded great, BUT, munched on 6550's like candy. 

[medium jim]

Jim,

IIRC, ARC drives their output tubes pretty hard.  They sound great this way but don't last so long.  You may actually only get 2k hours on them.  Whats their recommended bias current?

Freo:

They recommend 65ma which really isn't that hard on a 6650 which is a 42 watt tube at full dissipation and at 65ma dissipates 27 watts.

E.R.:

I will find out how many hours I can get them to last....I checked the mutual conductance when they were new and will check them about every 6mo and at sooner intervals when they start to move towards weak/good.

Bob:

It only takes putting a multi meter on them, rather easy, so it is like checking the oil in your car on a regular basis.  It may be that if I don't see any changes month to month, I will reevaluate and just do so when I hear something different going on.

The tubes in my Marantz 9's had about 4K hours on them (NOS XF2 Mullards) and they still tested in the new range.  But, we are talking different tubes and different amps, so it will be a learning experience for me, but feel that it is a good primer for anyone new to tubes or otherwise.

BTW, you should always turn on the amp first and shut it down last!  Very important....otherwise you can pop a tweeter....

Jim

[Maritan]

Bob2 - Like I mentioned, I'm anal.  What I'm doing is probably ...no... most likely...no... definitely ...yup... completely unnecessary. But like Jim mentioned, it takes no more than a couple minutes to check the biasing of each tube when I start things up. If your tubes are stable and you don't feel like checking it, you'll be absolutely fine. Don't be OCD like me. 

Jim - I always heard the other way round. Turn amp on last and off first... Hmm... It looks like this might be one of those topics that there's a camp of people firmly entrenched on both sides of the issues with neither seeing the validity of the other camp.

I'll look at the VTL manual when I get home this evening to check what it says.

[JerryM]

BTW, you should always turn on the amp first and shut it down last!  Very important....otherwise you can pop a tweeter....

It's typically the other way around. Amp on last, amp off first. This prevents amplifying any on or off transients from up-stream gear.

Have fun,

Jerry

[medium jim]

You all are correct, I did write it backwards...it helps to check what you write before hitting the submit button For the record, I do turn the amp on last and turn it on first....

Jim

P.S.

Only use a plastic screwdriver to make bias adjustments!

[Ericus Rex]

65mA does sound high to me based solely on experienc.  I'm used to KT88 amps that bias around 40-50mA.  At any rate, I'd be very interested to see how many hours you do get from your tubes.

[medium jim]

65mA does sound high to me based solely on experienc.  I'm used to KT88 amps that bias around 40-50mA.  At any rate, I'd be very interested to see how many hours you do get from your tubes.

Many amp makers employ higher ma settings in order to get more watts out if them.  A 6550 is capable if around 120ma, so 65ma really isn't that much in the scheme of things.  The original tubes were still in the amp and I would bet had several k's of hours on them and still tested in the good range.  In fact, one of the input tubes started to glow funny, which was also the original tube.  The recommended change point for the 6N1P is 4000 hours. 

27 watts / 42 watts = 65% (approximately)

My guess would be that the original tube set had around 4-5k hours in them, but this is only an educated guess.

Jim

Add Note:

The baseline for the new tubes was 112 on my Eico 667 using the newest calibration/settings and the ones that I pulled 94, with 80 borderline weak/good. 

[SteveFord]

I only bias my amps once or twice a month because I'm lazy and they don't really seem to need it.  Most changes seem to be due to voltage changes from the power conditioner - it would be nice if it would stay steady but nope...
medium jim is right in that you get so used to the sound of your system that any change can be pretty noticeable.
Trying to come to grips with a change in preamp is murder - it's close but not quite right...

[medium jim]

I only bias my amps once or twice a month because I'm lazy and they don't really seem to need it.  Most changes seem to be due to voltage changes from the power conditioner - it would be nice if it would stay steady but nope...
medium jim is right in that you get so used to the sound of your system that any change can be pretty noticeable.
Trying to come to grips with a change in preamp is murder - it's close but not quite right...

Steve:

My AC runs pretty clean and consistent between 115-120.  An advantage of the Eico 667 or most decent tube testers is that you an check the current draw/feed on them.  It is a great tool, a decent Tube Tester if you have tube gear.   

I only pull a tube or so every now and then to check them.  Unfortunately, my current amp uses a modern designed Russian tube for the front end and I don't know of any affordable tester for them...I would have to get a maxi matcher or similar.  Will change them at the same time I do the output tubes to be safe....

Jim

[Bob2]

Maritan,
Nothing wrong with being fussy about your gear. Probably most people here are. I look at your experience and try to learn what and why. Being anal, I don't think that's the case.  Although I have been involved in this hobby for over 50 years I'm learning everyday so reading about how you operate your gear gives me perspective.
All I know is every day I'm digging it more and more.
Rock on !
Bob2

[medium jim]

Here's yet another "Preaching to the Choir", the beauty of tube gear is that by changing tubes or even capacitor values, you can adjust the tone/sound to the point of being like a new system altogether.   Sure, it takes being a little fussy or anal, but it really is fun and worth it.   SS or Class D you merely turn it on and listen which has its own rewards I suppose.

Jim

[jlafrenz]

Checking my tube bias is something I need to get in the habit of doing more regularly. Typically when I sit down to listen, I am ready to listen and don't want to mess with things. It really doesn't take all that long to do though.

With my amp, the manual give a range to which the tubes need to be biased to. Is there any benefit to setting them at the lower/higher end of the range? Or is this just something the manufacturer does to make it easier for the end user to get the bias close for all tubes?

[medium jim]

Checking my tube bias is something I need to get in the habit of doing more regularly. Typically when I sit down to listen, I am ready to listen and don't want to mess with things. It really doesn't take all that long to do though.

With my amp, the manual give a range to which the tubes need to be biased to. Is there any benefit to setting them at the lower/higher end of the range? Or is this just something the manufacturer does to make it easier for the end user to get the bias close for all tubes?

I used to advocate biasing on the low side, that was until I spoke with Audio Research and was told the differences...if you bias on the cool or low side, the amp will be more in Class B and not as dynamic or as fast.   Some like this, so for them, bias lower and the tubes will last longer....I used to bias my Marantz's on the low side and liked them, but I now wonder what they would have sounded like at full bias.   

I started out my new amp at 63ma (recommended is 65) as this is where the tubes initially settled into...however, I biased them at 65ma about a month ago and really liked it and when a noticed that I was leaning a little to the right to center the sweet spot, I checked the bias and a couple of the tubes for the right channel were at 63ma....after nudging them back to 65, all was good again. 

Jim