Amp tech/Bias question regarding bias probes

[maddnotez]

Looking at getting the Eurotubes newer ET One bias probe. I think i may have the old, very cheap version where its just the tube socket with wires that I attach to my own meter but I'd have to search for it and I really like how the ET one has it's own digital meter connected, I need dummy proof. Plus you can play the amp with it connected safely which is a huge bonus to me. (Can you do that with others?)

My problen is that the ET one only has one single octal head and this kind of bothers me. I could be wrong but I think back in the day they had one with 2 heads or even 4?

Im curious if this will be an issue for a complete noob like myself, I want to find a probe that has 4 heads so I can bias them all at the same time or at the very least 2 heads for basing in pairs. My ignorance makes me think wow, why would they not offer this? How freaking dumb......but im a noob and surely im missing something here.

I see other units out there with 2 or 4 heads together i could buy instead but the thing is I REALLY like the Eurotubes version with the digital meter that shows the plate voltage and plate current and all of that. Again, I want this as dummy proof as possible.

I have biased my own amps a couple of times before. I do not like doing it at all but im smart enough where I shouldn't die. Would much rather bring it to my local tech but im in a serious time crunch at the moment where doing it myself is the only thing that makes sense so yeah, was just curious about pros and cons with the ET One and doing one tube at a time and being able to play the amp with it connected vs biasing in pairs.

 

[greatmutah]

The ET one is probably fine. Does it take a little bit longer? Sure but bear in mind a couple things. Unless your biasing each tube individually you’re probably going to be doing either a pair at a time or all 4. Select one and get a read, check and set your bias and let it sit for a bit. Power down the amp and move the probe to the next tube. Check and measure readings. So long as nothing is red plating you’re good and as long as the tubes fall in range of +/- 5 mA of each other you’re good. That’s why we have tube matching these days, though how well they’re matched depends on the vendor.

 

[greatmutah]

FWIW my bias probe is a single octal socket from a bias master that George Metropoulos gave me at his shop and I set up a RCA adapter to run to my multimeter and it works great. I’m also doing one tube at a time.

 

[GuitarBilly74]

Most amps have a single bias pot for all tubes anyway. So as long as you have a good matched set, biasing it off one tube is enough.

 

[la szum]

Most amps have a single bias pot for all tubes anyway. So as long as you have a good matched set, biasing it off one tube is enough.

Yup. Which is why the "matched" set (duet or quad) of power tubes is important.

 

[Chocol8]

Yup. Which is why the "matched" set (duet or quad) of power tubes is important.

Hah! Thats what the tube vendors want you to believe. Might be true on high gain, because I never tested that, but I did do a test with Fender and Marshall amps with very closely matched tubes and modded to have individual bias adjustments. When listening and playing back to back, absolutely no one preferred super closely matched tubes/bias. Too close and too different are less desirable. A modest difference gives a little more extra sauce that is generally pleasing. Hifi would be different.

 

[GuitarBilly74]

Hah! Thats what the tube vendors want you to believe. Might be true on high gain, because I never tested that, but I did do a test with Fender and Marshall amps with very closely matched tubes and modded to have individual bias adjustments. When listening and playing back to back, absolutely no one preferred super closely matched tubes/bias. Too close and too different are less desirable. A modest difference gives a little more extra sauce that is generally pleasing. Hifi would be different.

well, you may not have heard it on your test, but there are definitely advantages with using matched sets. (btw, matched by industry standards is within 0-5Ma of each other).

First, say you bias your amp at 60% dissipation and the tube on the other side of that pair is much lower, chances are that tube is going to be close to its crossover distortion point.

Conversely, if you bias a tube and the other side is considerably higher, it may induce hum and put some strain on the grid resistors.

It's not a catastrophic thing as in "omg it will break". Not at all. It's all pretty safe and tube amps are more resilient than most people think they are. But these things you would ideally try to avoid.

As for tube vendors, their lives would be MUCH easier if they could just pick up any 2 tubes and ship it out. They really gain nothing by having to match them, aside from the extra work. They do it because it matters.

 

[Chocol8]

There was no such thing as matched sets when tubes where in their heyday. The vendors invented that shit as a way to charge more for the matching service and now most players think it's critically important. It's not! It's only important that they not be too far off.

Also, tubes matched when brand new may not be after 50 hours. The two sides of the OT aren't perfectly matched either FYI. If you really want perfection, you need to put in a bias adjustment for each tube, and you need to use an oscilloscope to set it. It's a shit ton of work and when you're done, you probably won't prefer it anyway.

 

[GuitarBilly74]

There was no such thing as matched sets when tubes where in their heyday.

This is technically true, but it doesn't take in consideration the fact that tubes were much better made and to much tighter tolerances. Back then, if you tested say, Sylvanias from the same batch numbers, they were pretty much what we call matched these days.

With what you get from the Chinese, Russian and Eastern European companies nowadays, matching is a must.

 

[maddnotez]

Good info here. I paid for the "matching" before even reading all of this haha.

 

[GuitarBilly74]

Good info here. I paid for the "matching" before even reading all of this haha.

who is charging you extra for "matching"??? most vendors don't.

 

[maddnotez]

who is charging you extra for "matching"??? most vendors don't.

Usually buy from the tube depot i believe

 

[Chocol8]

who is charging you extra for "matching"??? most vendors don't.

That varies, but most selling NOS do. It's a mix for new tubes, but if they offer it, it's baked into the price.

 

[maddnotez]

That varies, but most selling NOS do. It's a mix for new tubes, but if they offer it, it's baked into the price.

Well i just double checked tubedepot doesnt charge for matching power tubes but they do for preamp