Questions on tube amps

[Kriton]

As a tube newb, I have a couple of questions that I have researched and not been able to find the easy answers to:

Bias - how often can it shift, how often do I need to check for it, and why do I care?

Is it common to have gain differences between matched mono-blocs, right gain has to be higher than left to sound even? How do you measure right and left gain, can you do this on a meter, or is it more accurate by ear, or with stereo signals am I better off just leaving the controls even and chalking it up to separate channels?

Speakers and tubes - if it more likely for a tube set-up to fry my speakers than an SS set-up? Does anyone have a fool proof method to put fuses in the path between tubes and speakers to avoid a fry, and will it degrade the signal, what kind of fuses do you recommend, and will they work anyways?

Is it possible to minimize the tube hum, or is that just a part of the nostalgia that are tubes? I assume that the hum is only a problem when it actually is coming from the speaker and not just the tubes them selves? Can the hum vibration piss off (feedback?) a turntable that sits too close? How would you isolate the turntable within a reasonable budget?

OK, that is about it for now - any takers?

B

[Guest David H]

As a tube newb, I have a couple of questions that I have researched and not been able to find the easy answers to:

Bias - how often can it shift, how often do I need to check for it, and why do I care?

Is it common to have gain differences between matched mono-blocs, right gain has to be higher than left to sound even? How do you measure right and left gain, can you do this on a meter, or is it more accurate by ear, or with stereo signals am I better off just leaving the controls even and chalking it up to separate channels?

Speakers and tubes - if it more likely for a tube set-up to fry my speakers than an SS set-up? Does anyone have a fool proof method to put fuses in the path between tubes and speakers to avoid a fry, and will it degrade the signal, what kind of fuses do you recommend, and will they work anyways?

Is it possible to minimize the tube hum, or is that just a part of the nostalgia that are tubes? I assume that the hum is only a problem when it actually is coming from the speaker and not just the tubes them selves? Can the hum vibration piss off (feedback?) a turntable that sits too close? How would you isolate the turntable within a reasonable budget?

OK, that is about it for now - any takers?

B

You are asking tough questions. What amp are you running? Dyna mkIII?

Bias shift can depend on the amps age and duty, some amps shift monthly, and some maintain range for a year or longer. Probbly a good idea to check your amp every 100 hours of use until you get a feel for it.

You can set your left to right gain with an spl meter place in your listening position, then use a test tone fed through a Y adapter into both left and right channels. Then check balance and set gain accordingly.

If you are getting a hum from your amps, you could have a faulty or delaminated transformer, if the hum is from your speakers it could be a ground loop or a noisy electronic device located in close proximity to your amps, or possibly even sharing the same power ckt. I dont know how you have this set up, but cable boxes are notorious for causing system noise. Another trick to eliminating hums is to float the grounds if equipped by using 3 to 2 prong adapters, available at most hardware stores.

I have never had a tube amp blow speakers in the past because tubes tend to mush and distort rather than clip and cause damage like solid state gear. I am not sure it is necessary to fuse the speakers. I you feel the need to fuse them, I reccomend fusing at the input to the crossover.

[johnyholiday]

http://www.tubedepot.com/whisbipo.html

[Guest " "]

"Bias - how often can it shift, how often do I need to check for it, and why do I care?"

Bias can shift thru out the day as wall voltages change. Typically, the voltages tubes see are 3X wall voltages. So even a 5 volt wall voltage shift can cause a 15 volt voltage swing on the tubes.

Why should you care....if you checked your bias when your wall voltage was on the low side....but you biased on the high side...as wall voltages swing upward...you would be in an over bias condition....which would shorten tube life.

[garymd]

The bias on my VRDs shift slightly all the time but that could be due to the tubes. I try to bias when the wall voltage is on the high side. You get a feel for that in time. I check my Scott 299b about once a year but in 5 years, I've never had to adjust it.

As long as you have fuses in your amps, which you should, those will probably blow before any damage is done to your speakers (non-volume related blowing that is). I've blown quite a few fuses in one of my VRDs. I have no idea why (possibly the recifier tube?). It happens about once every 6 months.

I have the right channel gain slightly higher on my preamp to even things out. I just do it by ear. If you play a mono record you should hear everything dead center or if you know that the voice on a particular stereo recording should be dead center, it's easy to adjust by ear.

As far as gain, I've heard a number of ways to set your amp or preamp channel gain levels. It differs depending on what amp/preamp you're using. I have the gain on my BBX pre set to about 2:00. I could be wrong but I recall something about setting your volume control to 12:00 then turning your gain levels to the loudest you will ever listen. 2:00 seems to sound as good as any other setting I've ever tried so that's where I leave it.

[lighting guy]

I could be wrong but I recall something about setting your volume control to 12:00 then turning your gain levels to the loudest you will ever listen.

Gary,

FWIW, it's 2:00 that Mark suggests for the volume knob when setting the gain levels on the BBX.

D