Tube Bias Meter Questions

M

MetalThrasher

Well-known member
Thanks for the heads up on the amazon tube bias meter. Just bought one. I've never used a tube bias meter before, so does anyone have any tips, articles, or videos on how to do this? I don't want to fry myself! Also, what's the difference between biasing the tubes "hot" vs "cold"? Thanks!
 
MetalThrasher said:
Thanks for the heads up on the amazon tube bias meter. Just bought one. I've never used a tube bias meter before, so does anyone have any tips, articles, or videos on how to do this? I don't want to fry myself! Also, what's the difference between biasing the tubes "hot" vs "cold"? Thanks!
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Clip on how to use a bias probe…. It’s similar to the one you bought. Btw I bought one of these Black Friday ones too. It’s a good deal!!!



@MetalThrasher remember tube amps contain high voltages which can be lethal. I highly recommend learning about safety before diving into an amps chassis. It isn’t rocket science, but it can potentially save a person from a lethal accident.

Clip on basic tube amp safety:
 
napalmdeath said:
Really need the plate voltage, which is why I use a Eurotubes Pro One.
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@napalmdeath you’re right that they make a slick little device, but I’m super lazy. Having to unplug and plug for each socket is tedious.

I wish they’d make a setup with 4 sockets and a rotary switch like the TAD. I’d gladly hand my money over for that.

But for now, that cheap little Black Friday bias meter and my trust Fluke MM to check plate voltages at each socket and I’m set.
 
It's pretty straight forward to use. The probe sits between the tube and tube socket and displays current in mA. That's what is meant when people say bias.

In general terms about 60% max capacity give or take is a good place. You really don't want to exceed 70% then you risk blowing the tube and frying the amp. Biasing hot is pushing it closer to it's limit and cold is a lot lower percent of max. Aside from running it too close to max there's no hard rules on where to set bias. It depends on amp design, tube type, and desired tone.

The other part you need to know is plate voltage to calculate max current. Once you know the max current you can calculate whichever percent of max you want to set it at; be it 50, 60, 70 etc. percent max.

Im just linking this one video, but check out uncle doug's other videos on biasing. He has some really good in depth explanations.

 
Bossman415 said:
@napalmdeath you’re right that they make a slick little device, but I’m super lazy. Having to unplug and plug for each socket is tedious.

I wish they’d make a setup with 4 sockets and a rotary switch like the TAD. I’d gladly hand my money over for that.

But for now, that cheap little Black Friday bias meter and my trust Fluke MM to check plate voltages at each socket and I’m set.
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That's pretty much the same reason I got one. I'll get plate voltage from my bias pro and monitor current with this one. Much more convenient to monitor all tubes at once
 
This is all new shit to me! I want to learn how to do this and I'm sure you guys have a lot of experience but I'm just nervous about getting fried!
 
MetalThrasher said:
I really want to learn how to do this myself but I'm sure there's a learning curve. Anyone here know any good amp techs in central NJ?
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@MetalThrasher while you're waiting to find a tech who can help, check out YouTube clips.

There's a plethra of good YouTube channels which cover biasing and safety.

Doesn't hurt to listen/watch how these channels explain the process. It'll only arm you with more knowledge.
 
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10.00 dollar MultiMeter and the Probe you bought at Amazon will get you there ... Multimeter will allow you to check plate voltage ..... very easy to do . Just follow the simple safety rules ( like one hand in pocket ) I always go back to this vid from Eurotubes for reference .

 
The first thing I would do is to learn how to measure and set the bias on the current set of tubes, which are probably set up at least about right.

Before replacing the set of tubes, I recommend reducing the bias current to the minimum on the current set, as the new tubes can be steeper and before you get the idea, you will overload them unnecessarily.
 
Another thing to keep in mind is that the input voltage to the amp is good to know. I set bias on my amps and ones that come in for repair at 123VAC, as that is what the voltage runs in my house and my area in general. I set to about 60%, thinking that if the customer's voltage is lower, than it will still be above 50% and if its higher than 123VAC, then it should still be below 70%.

TLDR, wall voltage does affect bias, good to know, but if you are just getting started, don't worry about it.
 
The cheaper EuroTubes bias meters that go directly to a multimeter seem slightly unsafe to me. It looks like it is inserting itself between the tube and reading plate current directly off of it. If those bias probes were to be slightly out of the multimeter to where the metal is exposed at the banana plug, and you were to touch them, you're gonna get zapped by high voltage.

If you're handy with a soldering iron, look at the Bias Scout: https://tubedepot.com/products/tubedepot-bias-scout-kit

Nifty kit that lets you read cathode current safely with the appropriate resistors, as well as plate voltage.
 
Bossman415 said:
@napalmdeath you’re right that they make a slick little device, but I’m super lazy. Having to unplug and plug for each socket is tedious.

I wish they’d make a setup with 4 sockets and a rotary switch like the TAD. I’d gladly hand my money over for that.

But for now, that cheap little Black Friday bias meter and my trust Fluke MM to check plate voltages at each socket and I’m set.
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If there's only one adjustment for all tubes, you only need to plug into one socket. But yeah, if there's an adjustment per side, then yeah, you'll need the multi.. I have both. I can still use the Pro One to get plate voltage, either way.
 
napalmdeath said:
If there's only one adjustment for all tubes, you only need to plug into one socket. But yeah, if there's an adjustment per side, then yeah, you'll need the multi.. I have both. I can still use the Pro One to get plate voltage, either way.
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@napalmdeath you're 💯 right on the Pro One. I'm just lazy, so I prefer to just flip through each socket on a switch.

Fingers crossed EuroTubes is on this board. I'd hope they'd take my comment to heart.

I'd gladly buy a version of their meter with switching capabilities. I love how you see the plate voltage & current on 1 screen.
 
Code001 said:
The cheaper EuroTubes bias meters that go directly to a multimeter seem slightly unsafe to me. It looks like it is inserting itself between the tube and reading plate current directly off of it. If those bias probes were to be slightly out of the multimeter to where the metal is exposed at the banana plug, and you were to touch them, you're gonna get zapped by high voltage.

If you're handy with a soldering iron, look at the Bias Scout: https://tubedepot.com/products/tubedepot-bias-scout-kit

Nifty kit that lets you read cathode current safely with the appropriate resistors, as well as plate voltage.
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Huh, if that 40 - 70 milivolts are going to zap you, than be careful with 9V batteries. Those are capable of tearing you apart :)

But seriously. On that banana plug is a voltage, which is directly measured by the connected multimeter on 200 mV range. Under normal circumstances, this is a completely safe voltage. Potentially a bit more more dangerous is that recommended bias scout probe.

It is of course completely wise not to touch any potentially dangerous parts around you. It is also wise not to give any advice in a field in which one is not familiar and mistakes in it are life-threatening.

Totally bad and dangerous info, I didn't read the previous post carefully. Apologies to @Code001
 
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