Biasing

nikolas812

Ok heres the deal. I got my first tube amp today and installed new tubes and biased them at 42millivolts. Now the manual says to set the bias between 36-44 mv's. Ok. Well a few hours later I decided to check the bias again and they are 40 now and not 42. Again I am new to all of this. But I turned them up to 48mv's and wow! Its the amp I thought I was buying initially. Everything was increased ten fold. Not only is it louder but it sounds much much better musically. What should I do? Is ok there? Or should I back it down to the recommended max of 44mv's?

Edit: Also it wasn't making any real volume until about the 12 o' clock mark at 40mv. Now its doing pretty good at 8 or 9 o' clock.

HB27

Biasing your tubes high will decrease tube life substantially. New tubes will vary on the bias. When I install NEW OLD STOCK tubes I check them every half hour or so for the first couple of hours. Later I check them every couple of hours and check them for color to make sure they don't over glow. After a couple of days I'll only check them a couple times a week. If they're stable and holding bias where they're supposed to I only check them every month or so. If still stable, leave them alone unless you notice your sound changes.
I've found the new issue tubes can be unstable and if I have to use them I check them regularly.
HB

Systems

Back it out Homie. Don't set that bias so high...go for the lower end. You tubes will require re-biasing when new....and as they are used. Back that plate voltage back to the lower side of the recommended setting. I know it sounds louder. But what you may really need are more efficient speakers. Have fun!

What tubes are you using?

Chuck

beardog03

I agree...
Put the bias were it should be....keep the plate voltage were it should be...

If you want, you can change tubes , get more efficient speaks, and try some MIT cables to let the juice really flow !!!

If you keep the plate voltage too high, you will shorten the life of your tubes and quite possibly your amp..

you can always run her on the high side of the recommended bias.......just not much past the highest recommended number, if at all (past)

It will take awhile for your tubes to settle in, but when they do, you will know it, and by that time you will have gotten in sync with the sound and output of your amp....



or will have changed tubes !!

(and will continue to until you find the right sound and synergy)


Just my .02
"Cary" on..;)

HB27

When ordering tubes deal with a reliable and knowledgeable dealer. REQUEST tubes and signify the bias and PV you need them for. Not all tubes are created equal. You and your gear will be happier in the long run. Eventually you'll get to know your gear and tubes and be able to choose for yourself. Some may think this is "overboard" but matching your gear is critical.
HB

beardog03

I never thought about that, but it makes sense to me...

nikolas812

LOL! You guys are a little late. I posted this about a month ago.:D Any way shortly after I posted this question and didn't get any responses I backed it down to about 37-38mv across the board.

Harry you mentioned tubes glowing brighter than others? I think I have a power tube glowing brighter than the other three power tubes. What does that mean? They are JJ's EL34's from thetubestore.

You can see that the second power tube from the left looks a little brighter than the rest. I don't know if it is the angle or if it is really brighter than the rest but it is bugging the hell out of me.

Also the boxes my tubes came in had the number 34 on all of them. Is this what they are ment to be biased at? If so should I get new tubes? Because the recommended bias on my amp is 36-42 I think.

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mhardy6647

As long as the plates aren't glowing red, you're probably OK.
Assuming this is a fixed bias amp, what really matters is the current, not the voltage. At any rate, the designer and/or distributor of the amp has determined a bias voltage region that should yield safe and sane bias current. Don't second-guess the mfgr/designer/distributor, unless you feel like stocking up on EL34s.

HB27

Nick,
I had the same tubes in my Dynaco ST70 when you were here. They all "glowed" a bit different. Keep an eye on the bias and keep it in manufacturers specs. From what I've found these are some of the unstable tubes I've run into.
Put them on your tester (ya gotta have a tester) and see where they stand. If ok, I wouldn't worry about it too much.
There's a lot of better sounding tubes around than the EH and JJ. (If you're leaning that direction)
The Svetlana winged C will match up good in your Jolida and they're a pretty good sounding tube and according to some guys "in the know" they're just going to get better. I'm a Mullard EL34 XF1 and XF2 freak but you'll pay $300-$600 for a NOS quad of them. I try to buy the XF2 singles with the B code cheap and put quads of matching tubes together. I cut the price more than half that way on them. I've ended up with a dozen or so mismatched XF2s laying around. I'll eventually match them up and I don't mind stocking a couple extra sets of good tubes.
HB

HB27

Nick,
Another thought on the glow. Clean your sockets and tube pins and tighten up the contacts in the sockets if they're loose. Just take a pick and lightly put them back in shape to assure good contact.
Make sure to unplug the amp for an hour or so to make sure it bleeds down before working on it. That still doesn't assure safe contact with the pins. Just make sure you don't ground yourself to the amp when doing it and you'll be fine.
HB

Joe08867

The 34 on the box describes the tube inside. EL34 or 34 for short. I had JJ's before. To inconsistent for me. I used to double order and then play the match game with a tester. Got crazy after a while.

Just make sure your voltage is set correctly and wathc that the plates don't get red.

HB27, That is always a good idea. I have done that on all of my tube stuff.

nikolas812

What plates!?:o:confused:

The JJ's always seem to creap up on the mv's for some reason. I will check them again later tonight to see if there has been any change since the last bias.

dragon1952

I just lost my first tube since I started in tubes about 3 yrs ago. It was a JJ KT88. I was sitting at my computer, which is in the back of my music room, and all of a sudden the right channel went distorted. I got up real quick and saw one of the tubes entirely lit up inside like a light bulb. Kinda scary, especially since it was dark in the room. I doubt if this tube had more than 1000-1200 hrs on it. In the meantime I stuck the original Chinese issues in there and I tell ya, it sounds sweet. I wonder if that tube had been degrading the SQ for awhile now.

Joe08867

If anything inside the tube except the filiments themselves turn red you have to cut back the voltage.

It just means there is to much heat being generated and it will cause a premature failure.

Plus when they are to hot they don't always sound as good.

Nice piece of equipment by the way.