Baising Tubes? TK Meteor content

[heady dude]

I really dont know much about this subject and was wondering if you are supposed to bias the power tubes according to the power rating labeled on them?
Ive got a TK Meteor and the amp builder(Mr. Baretll) recommends biasing at 33m/a. Now I have a matched quad of EH 6v6Gt's that have a power rating of 27, what would happen if I biased the amp at 33m/a and not 27m/a? Would getting a matched quad of 33 rated tubes make a huge difference in the sound of the amp?
Also M2 owners what tubes have you found sound the best in your amp? Ive been using EH, but have heard that Svetlanas are supposed to sound very nice.

[SatelliteAmps]

I don't think the EH power rating is the mA draw bias rating. I think that is more of a matching number. Any decent working 6V6 should be able to be biased at 33mA or 27mA or anywhere in between.

[heady dude]

Really, I was told that it is the recommended m/a number that the tube should be biased at.

[rockon1]

Whats the plate voltage? Bob

[Structo]

Yes as Bob alluded to you can't just arbitrarily throw out a bias number for all amps with the same power tube.

The bias current is dependant on the Plate voltage on the tubes. Voltage x Current (not the bias) = Watts.

So say if you have an amp that gets 350vdc on the plates that would be a bias range of around 17ma to 24ma with 24ma being at 70% dissipation.

Here are some handy bias charts for different power tubes with the plate voltages listed.
http://members.shaw.ca/house-of-jim/Html/bias_tables.html

[Structo]

Also I should add that knowing the plate voltage is good in that you can safely bias between the lower (50%) bias current and the highest (70%) and listen to the amp and see which one sounds the best.
Bias isn't a one size fits all. It depends where you run the amp at gig volume, what kind of breakup you want and how long you want your power tubes to last.

If Mr. Bartell told you to bias these new 6V6's at 33ma, that tells me he must be using a lower voltage power transformer because according to the table, if 33ma is 70% dissapation, the amp is only getting 250-275 volts on the plates.

[heady dude]

Im not sure what the plate voltage is, Im not even sure how to check it. So the number that is written on the power tubes(power rating?) does not have anything to do with what you bias the m/a to, its only decided by the plate volatge?
The builder told me to bias it to around 33, thats where I got that number. He did not even mention the plate voltage. The Meteor has an external bias port, Im not sure if this is why he didnt mention checking the plate voltage.
You guys have to excuse me Im a total noob when it comes to this stuff.

[heady dude]

Structo that could be it. Does each individual amp have its own plate voltage reading?

[rockon1]

Im not sure what the plate voltage is, Im not even sure how to check it. So the number that is written on the power tubes(power rating?) does not have anything to do with what you bias the m/a to, its only decided by the plate volatge?
The builder told me to bias it to around 33, thats where I got that number. He did not even mention the plate voltage. The Meteor has an external bias port, Im not sure if this is why he didnt mention checking the plate voltage.
You guys have to excuse me Im a total noob when it comes to this stuff.

The number on the tubes doesnt have anything to do with biasing. If the builder told you to bias it around 33ma the plate voltage must be pretty low- under 300 volts

Structo that could be it. Does each individual amp have its own plate voltage reading?

Every amp has a plate voltage reading. If your unsure about this stuff taking its reading could be deadly so I wont go into it. I trust the builder gave you a ma setting that correlates with the amps plate voltage. Like Structo stated the plate voltage must be around 250 volts to be set at 33ma

12 watt tube / 250 plate voltage = .048 ma max dissapation X 70%= .0336 or 33.6 ma 70% idle dissapation. Bob

[heady dude]

The number on the tubes doesnt have anything to do with biasing. If the builder told you to bias it around 33ma the plate voltage must be pretty low- under 300 volts

Ok thanks for clearing that up



Every amp has a plate voltage reading. If your unsure about this stuff taking its reading could be deadly so I wont go into it. I trust the builder gave you a ma setting that correlates with the amps plate voltage. Like Structo stated the plate voltage must be around 250 volts to be set at 33ma

12 watt tube / 250 plate voltage = .048 ma max dissapation X 70%= .0336 or 33.6 ma 70% idle dissapation. Bob

Yea Im not going to attempt to do any internal readings, I know the caps can hold a lethal charge even when not plugged in.

Thanks for the help.

[Nolatone Ampworks]

Note that the Meteor is cathode biased, which usually doesn't involve an adjustment, so Mr Bartel is doing something that shouldn't be confused with setting fixed bias.

You should be able to dial up more than 70% dissipation with cathode biased. That 70% thing is a safety margin for fixed bias.

[KeithC]

If you can get your tubes biased at 33 per what Mark says you'll be golden.

Your only problem with the tubes would be if the sweep of the bias pots wouldn't let you get at that 33 that he recommends but I highly doubt that.

[rockon1]

Note that the Meteor is cathode biased, which usually doesn't involve an adjustment, so Mr Bartel is doing something that shouldn't be confused with setting fixed bias.

You should be able to dial up more than 70% dissipation with cathode biased. That 70% thing is a safety margin for fixed bias.

Ahhhh.... that makes more sense. The PV could be up at 400v and still be at 100% dissapation. Intersting cathode biased with individual adjustments.

http://www.toneking.com/products/meteorII/index.html#specs

Nice looking amp!

heady dude- set them at 33 and forget it! My mistake I didnt realise its a cathode biased amp. Cathode biased amps generally idle at max dissapation -much higher than fixed bias. Bob

[Structo]

OK I didn't realize it was cathode biased.

That isn't usually adjustable, so why are we discussing bias current?

Or does this amp have adjustable bias?

[rockon1]

OK I didn't realize it was cathode biased.

That isn't usually adjustable, so why are we discussing bias current?

Or does this amp have adjustable bias?

This one is and it looks like it has an adjustment for each tube too! Nice set up. Bob


http://www.toneking.com/products/meteorII/index.html#specs

[heady dude]

Mark makes some killer amps, I just wish I knew more about how the darn things worked.

Yes rock you adjust each tube individually.

I talked to a buddy again and he seems to be sure that ideally you are supposed to bias the tubes according to their power rating. So if your amp is supposed to be biased at 33, then you get a matched set of tubes with a power rating of 33.
Is this not correct?

[rockon1]

Mark makes some killer amps, I just wish I knew more about how the darn things worked.

Yes rock you adjust each tube individually.

I talked to a buddy again and he seems to be sure that ideally you are supposed to bias the tubes according to their power rating. So if your amp is supposed to be biased at 33, then you get a matched set of tubes with a power rating of 33.
Is this not correct?

Well Ive already been tripped up once with this amp in this thread but I cant see ( as SatelliteAmps stated ) that number being any more than a matching system of the tube vendor or tube manufacturer-unless you got them from the manufacturer of the amp and he states to set the amp to 33. Bob

[HCStraub]

Mark makes some killer amps, I just wish I knew more about how the darn things worked.

Yes rock you adjust each tube individually.

I talked to a buddy again and he seems to be sure that ideally you are supposed to bias the tubes according to their power rating. So if your amp is supposed to be biased at 33, then you get a matched set of tubes with a power rating of 33.
Is this not correct?

No, it is not correct. The 'power rating'(or whatever the numbers signify) written on your tubes is MEANINGLESS in your amp circuit other than it shows that they operate close to each other. That is it. You don't buy tubes based on 'power ratings'.....
The builder designed the amp to run on 6V6's, he took 6v6 tube spec's, took the voltages in the amp and set parts values based on that data. He then put several sets of tubes in his amps, tested several bias settings to dial in the best tone of the amp. Then he made a suggested bias setting....33ma. The numbers written on your tubes have no bearing on how you set the bias on your amp. The amp was designed to sound best running 6V6(any match pair of 6v6 tubes) tubes at 33ma.
You need to read the notes above(some very smart people wrote them, amp designers who KNOW what they are talking about) and then go out on the net and read up on how tubes work, bias settings, and some basic amp design notes. There is a lot out there, it seems like you are interested in understanding more....read up on it. It will make you better informed when you are buying tubes/amps and working with a tech.

[heady dude]

Thanks for setting me straight guys. HcStraub you are right, Ive got some reading to do.