How do you bias your amp?

I was an electronic engineer, so do my own tech work, and also for friends / acquaintances.
Generally I’ll fit 1 ohm resistors to power tube cathodes to sense their current. That can be too much of a PITA with pcb mounted sockets, in which case I use the OT primary winding resistance method (removing the phase splitter tube to prevent oscillation). But that method’s not ideal with 4 tube amps; if concerned I’ll swap tubes around to attempt to assess how well matched they are.
With fixed bias amps, set idle current to 30 to 35mA per EL34 or 6L6GC, 18-20mA per EL84 or 6V6. Multiply current by HT voltage to verify that the resulting idle dissipation is reasonable, below 18W or 8.5W.
For cathode bias, getting idle dissipation down to the limiting value is usually the issue; whilst bearing in mind that the absolute limit will be higher than the design max limit, which will in turn be higher than the design centre limit. If it does need lowering, then that’s often due to the HT voltage being excessive, so better to reduce that (eg with lossier rectifier or sag resistor) than tinker with the bias resistor value.

Multi-meter here. I gave up one the ear thing years ago because, simply, in A-B'd recordings, my amp (EL84s) had to idle at less than 55% to make any difference in tone. So, 60 - 65% maximses tube life with no tonal trade off. I just don't see any reason to run hotter than that.

Haha, but to be fair, if you know your amps REALLY well, and you’re getting reasonable tube life, you’re probably not far off.

Electronic Engineer, Awesome. I knew you were good but didn't know about the engineer aspect of your knowledge. Years ago I was not wanting to pay for what they wanted for even a simple bias probe so I bought, sockets, 0.1 % 1 ohm resistors and made my own. If I had actually owned a tube amp instead of just working on them I would have incorporated the resistors and test jacks or if it was a Quad power tube setup I would just use one set of Jacks and a rotary switch to switch between all 4 tubes .

I built a twin bias probe with meters in a little cabinet and it works great for my 6V6 amps.

For the EL84 amps I have a Weber Bias probe that plugs right in.

You apparently have very acidic skin chemistry. Try cleaning your hands with Hand Sanizer each time before you play and maybe at the break and then wipe your strings down when through. If that doesn't help then I don't have a clue.

Some of you might remember a magazine called Guitar Shop from many years ago.
Amp builder, George Alessandro, wrote an interesting article about biasing amps and balanced (Matched) tubes.
At that time Mr. Alessandro offered a bias meter, which had dual meters, where you would plug your tubes into the sockets which are plugged into the amps sockets.
I contacted him and ordered one which I have used successfully ever since.
On the front of the enclosure is a chart that provides the reference values for the most common octal-type tubes utilized in amplifiers.
It's quite a useful tool.

LTB; I believe that it was priced at about $90.00. During our telephone call I remember George complaining that he thought that the price was too low.



ibb.co/6mHkgsd

I use bias rite bias probe that has 4 sockets so I can do up to 4 tubes at once0 Fenders with 6L6's I go 65% at 36ma. Marshals with EL34's I go 33ma 65% alos. Sounds good and can get 60 four hour cranked gigs out of my tubes

That was my method, too.