Tubes...........

dhart86

I am getting very much into tube amps. Love the the sound of tubes in my music. Like one of the brothers here says, "Tubes add soul."
Even while I am still developing my knowledge base ....... I'd like to know what is meant when people say a tube won't bias.

Also, what damage is done by a tube not holding bias?

thsmith

some amps require that you bias to the required voltage for the tube. In this case you do not need matched tubes. If a tube will not bias to the specified voltage or will not hold a steady voltage setting the tube is bad. This can present itself with no impact to amp or take out the biasing resistor or possible other damage.

Some amps auto bias and requires you do nothing.

SOme amps have a bias meter or require you use a multimeter.

My Anthem Amp 1 has test points for a meter and a screw you set per power tube.

My Wright Amp has a built in meter and has a screw per power tube to adjust.

Hope that helps and I have provided no bad info.

mhardy6647

Never heard of 'em; did Fee Waybill have anything to do with these "Tubes"?

http://en.wikipedia.org/wiki/The_Tubes

;-)


either way you look at it, your amp's got sand in it. Whether it's semiconductin' or just enveloping (in the form of glass); it's there... and it's all good. Good stuff is good stuff.

An old, tired output tube may not be able to attain/hold its proper operating points (plate current, bias, grid voltages, current) - it's usually pretty obvious (the tube will be operating 'too cold' or 'too hot'); in the latter condition, the plate will dissipate so much power that it'll start to glow red hot ("redplating") - this is bad; very bad.

The concept of bias is related to the fact that we're trying to amplify an AC waveform - it goes above and below zero volts - but electrons only have one kind of charge ("negative", in the formalism that traces back to Benjamin Franklin*). We trick the tube into doing this by offseting the signal from zero ('bias') - this lets us amplify the whole AC waveform (MUSIC!) without the need for anti-electrons ;-)

For a primer on tube operation, see http://archive.anthemav.com/oldsitev1/pdf/taste.pdf
or the intro sections of any RCA tube manual - e.g., http://www.tubebooks.org/tubedata/RC20.pdf (big file and slow server for D/L, but well worth downloading a tube manual or two - www.tubebooks.org is an outstanding resource!).

* Old Ben Franklin knew he had a 50-50 chance of being right; he guessed... and later physics determined that he guessed wrong.

cstmar01

thsmith wrote: »

some amps require that you bias to the required voltage for the tube. In this case you do not need matched tubes. If a tube will not bias to the specified voltage or will not hold a steady voltage setting the tube is bad. This can present itself with no impact to amp or take out the biasing resistor or possible other damage.

Some amps auto bias and requires you do nothing.

SOme amps have a bias meter or require you use a multimeter.

My Anthem Amp 1 has test points for a meter and a screw you set per power tube.

My Wright Amp has a built in meter and has a screw per power tube to adjust.

Hope that helps and I have provided no bad info.

Nicely put. When I had the VTL's they all had points in order to test for the bias and then adjust as needed. Also depending on the amp if you adjust the bias of one tube it can affect another tubes bias depending on how it is designed. Some are independent of others.

I would always bias at first every month to check (I was paranoid) but know other people who would check every 6 months or so. Sometimes it can be bad if something goes out of bias and then can damage different part of the amp or sometimes it can have no affect.

I also have to add that if you are going to be doing a lot of tubes I found a tube tester helped in understanding the life of the tubes in the amp. For me it was a MaxiMatcher however there are others out there. I liked it as I would test normally each month and record the life of the tube so I could have an idea of when to replace. Some people will just say they know they blew a tube and just replace then but I like to know ahead of time when to switch out. Also doing so and just waiting for a tube to fail can also damage an amp. I guess mine the fuse would go before hand but I never wanted to take a chance.

Also different tube amp designs will have different tube life spans.

Good luck!

dhart86

thsmith wrote: »

some amps require that you bias to the required voltage for the tube. In this case you do not need matched tubes. If a tube will not bias to the specified voltage or will not hold a steady voltage setting the tube is bad. This can present itself with no impact to amp or take out the biasing resistor or possible other damage.

Some amps auto bias and requires you do nothing.

SOme amps have a bias meter or require you use a multimeter.

My Anthem Amp 1 has test points for a meter and a screw you set per power tube.

My Wright Amp has a built in meter and has a screw per power tube to adjust.

Hope that helps and I have provided no bad info.

^^^^^Yeah man, that was a big help!!! You explained it in a way that makes sense to my mind (limited knowledge and experience)

I've got 2 amps. The Rogue st 90. I believe it has screws for each tube w/ built in meter.. (4x KT-88)

The other is a Yaqin Ms 300 Set (integrated amp) It has 300b power tubes with test points, requiring a multimeter.

dhart86

mhardy6647 wrote: »

Never heard of 'em; did Fee Waybill have anything to do with these "Tubes"?

http://en.wikipedia.org/wiki/The_Tubes

;-)



either way you look at it, your amp's got sand in it. Whether it's semiconductin' or just enveloping (in the form of glass); it's there... and it's all good. Good stuff is good stuff.

An old, tired output tube may not be able to attain/hold its proper operating points (plate current, bias, grid voltages, current) - it's usually pretty obvious (the tube will be operating 'too cold' or 'too hot'); in the latter condition, the plate will dissipate so much power that it'll start to glow red hot ("redplating") - this is bad; very bad.

The concept of bias is related to the fact that we're trying to amplify an AC waveform - it goes above and below zero volts - but electrons only have one kind of charge ("negative", in the formalism that traces back to Benjamin Franklin*). We trick the tube into doing this by offseting the signal from zero ('bias') - this lets us amplify the whole AC waveform (MUSIC!) without the need for anti-electrons ;-)

For a primer on tube operation, see http://archive.anthemav.com/oldsitev1/pdf/taste.pdf
or the intro sections of any RCA tube manual - e.g., http://www.tubebooks.org/tubedata/RC20.pdf (big file and slow server for D/L, but well worth downloading a tube manual or two - www.tubebooks.org is an outstanding resource!).

* Old Ben Franklin knew he had a 50-50 chance of being right; he guessed... and later physics determined that he guessed wrong.

WOW..........guess I really gotta get my learn on

Thanks Mhardy

dhart86

cstmar01 wrote: »

Nicely put. When I had the VTL's they all had points in order to test for the bias and then adjust as needed. Also depending on the amp if you adjust the bias of one tube it can affect another tubes bias depending on how it is designed. Some are independent of others.

I would always bias at first every month to check (I was paranoid) but know other people who would check every 6 months or so. Sometimes it can be bad if something goes out of bias and then can damage different part of the amp or sometimes it can have no affect.

I also have to add that if you are going to be doing a lot of tubes I found a tube tester helped in understanding the life of the tubes in the amp. For me it was a MaxiMatcher however there are others out there. I liked it as I would test normally each month and record the life of the tube so I could have an idea of when to replace. Some people will just say they know they blew a tube and just replace then but I like to know ahead of time when to switch out. Also doing so and just waiting for a tube to fail can also damage an amp. I guess mine the fuse would go before hand but I never wanted to take a chance.

Also different tube amp designs will have different tube life spans.

Good luck!

Thank you cstmar01

Is it normal for the tube bias to fluctuate or slide by a digit or two. For example....my tubes are set to bias at 0.80v
If I check the bias in a few days it could be 0.81 or 0.78.

So my question is, if I set it at 0.80v should it remain consistently at 0.80 or is it ok if it moves by a point or two?

heiney9

They will fluctuate. Within 10mV is about normal. Your fine, nothing to be concerned with.

george daniel

Don't get obsessive with tube bias-- set it,,check it and monitor ocassionally/when indicated-- otherwise you will go crazy-- just ask Tom(trietz),, you can bias a tube to death!!

dhart86

heiney9 wrote: »

They will fluctuate. Within 10mV is about normal. Your fine, nothing to be concerned with.

Phew!!!!

Thank H9....glad you guys know your $h_t

dhart86

george daniel wrote: »

Don't get obsessive with tube bias-- set it,,check it and monitor ocassionally/when indicated-- otherwise you will go crazy-- just ask Tom(trietz),, you can bias a tube to death!!

George..........That....is what I wanted to hear..Thanks

cstmar01

heiney9 wrote: »

They will fluctuate. Within 10mV is about normal. Your fine, nothing to be concerned with.

Yep, it can change with your line voltage changing etc. I know mine would change a little but as long as its close your fine. If its WAY off then yes I would check things out and rebias but like H9 said around 10mV is fine.

Mike Reeter

dhart86 wrote: »

^^^^^Yeah man, that was a big help!!! You explained it in a way that makes sense to my mind (limited knowledge and experience)

I've got 2 amps. The Rogue st 90. I believe it has screws for each tube w/ built in meter.. (4x KT-88)

The other is a Yaqin Ms 300 Set (integrated amp) It has 300b power tubes with test points, requiring a multimeter.

If your Stereo 90 is a Magnum version, I highly recommend the Tung-sol KT-120's, they will bring out the best of the Rogue.

dhart86

Mike Reeter wrote: »

If your Stereo 90 is a Magnum version, I highly recommend the Tung-sol KT-120's, they will bring out the best of the Rogue.

Naw mike, only got the standard STereo 90. Would like to upgrade one day