I'm so FU__ING pissed right now! Stupid so called "techs"!

[lespaul6]

Ive been doing my own biasing with the probe for some time now... its great and saved me a bunch of cash!

 

[crankyrayhanky]

Good move ditching that clown. You have a fleet of amps that need quality attention!

 

[ibenhad]

Hey man don't blame the tech, some guys bias with a scope. I think you needed to tell him you felt he was biasing cold. I have a scope and a bias rite and it is a personal preference to how you like your amps. You also should know what the plate voltage is before doing anything.

Lane from Marshall forum - To measure plate voltage, remove ALL power tubes from the amp and power it up (BOTH power and standby switches ON). Set your DMM to read voltage, and if it's not auto ranging, set it to the 500v (or higher) setting. Place the red lead of your DMM on pin 3 in any power tube socket, and the black lead goes to the chassis (ground). You should get a voltage reading somewhere in the 400s, generally.

WARNING: See my sig below!

Best of luck, and BE CAREFUL!

Some tubes like higher plate voltages than others and that can make a big difference in sound too. It is not as simple as lots of people make it sound. It's not as complex either if you have some basic electronics knowledge. As Lane says be careful. Lots of juice in there to make your hair stand up. Especially if you don't know how to discharge caps. If your poking around I always found a wooden chopstick works well. Peace and good luck.

 

[Racerxrated]

Ive been doing my own biasing with the probe for some time now... its great and saved me a bunch of cash!

What he said. Bias Rite=20 bucks. Doing it myself=priceless! Some of these amps come to me with ridiculous bias..50-60ma(!!) all the way down to 15ma like lowman..get them into normal range and MUCH better.

 

[MississippiMetal]

Measuring plate voltage with the tubes out is not an accurate measurement. When the tubes are in, the plate voltage is pulled down by the tubes to a degree relative to plate current regulated by the bias, so it will be lower. That's the voltage reading that you calculate your plate dissipation by.

And it's also worth mentioning that the amount of wattage the plate is dissipating is by no means an indication of how many watts the amp is dissipating through the speaker load. So If all 4 of your tubes are biased to dissipate 20 watts, that doesn't mean your total power on the speaker side is 80 watts.

To put it more simply, the wattage you calculate when biasing is nothing more than the amount of power those tubes are wasting as heat.

 

[benduncan]

I see that you have test points. What's the difference between using the test points with a multimeter and the Pro One device?

I'm pretty interested in learning how to biasing my own amps. I'm going to get some new tubes for my triple rec next week, it has test points and a bias pot. I didn't get around to looking into it yet, but I assumed that I could just use the test points

 

[glip22]

Local techs. I stopped using them for everything 16 years ago. I'm better than any one I met local aside from a couple. They are out there but you have to know who.

 

[richardt4520]

Thanks so much for posting this. Just bought one.

 

[Erock]

If you have multiple amps, it pays for itself quickly. You should also be checking each tube by the way. Unless they are perfectly matched, some tubes will read higher or lower. They are never perfectly matched IME. You want to bias it so that they are all within the range you want. It's a balancing act a lot of times. Do they make a quad version of that? I bought a bias rite br4 to avoid having to shut down to check each tube. It's kind of pricey, but a huge time saver.

 

[MississippiMetal]

As long as the tubes are decently matched, it's a waste of time checking each one in the 100+ watters. The reason being is in a typical guitar amp with a four-tube power section, it's really two pairs working in push-pull. Electrically each pair behaves as one big valve.

Hence, you only really need to check one tube from each pair, usually one outer tube and one of the inner two.

 

[glip22]

As long as the tubes are decently matched, it's a waste of time checking each one in the 100+ watters. The reason being is in a typical guitar amp with a four-tube power section, it's really two pairs working in push-pull. Electrically each pair behaves as one big valve.

Hence, you only really need to check one tube from each pair, usually one outer tube and one of the inner two.

If the OT sees each pair on the legs, does it pay to match the pairs as close as possible or will they still be imbalance? I test all tubes at the given PV and match the pairs. So , if tube 1-4 tests 36, 32, 33,30, I would pair up the the 36 and 30 for 66MA, and the 33, and 32 for 65ma. As far as the OT is concerned aren't my tubes now matched to within 1MA or will the tubes still be mismatched since the 30 and 36 ma are 5ma out?

 

[C1-ocaster]

Good for you man!
Learning a new skill is not just a money saver, it pays back dividends.

I've been lucky with the amps I kept cause they have built in test points and adjustment, both the Vengeance and PRS SE-30.
From what I understand Peavey has some amps with external test points and adjustment, but the points don't actually measure plate voltage.
They use some electronic scheme to get you in the ball park. It's still usable though and you can try a few settings to see if you like them.
But, if you like it really hot but the amp can't take it you'll burn the tubes.

The Vengeance it seems does read from the correct test point, Egnater did the work for the users and there are 2 test points and adjustments to adjust both sets of tubes independently, and that allows me to run different tube types.
Very cool.
The PRS has only 2 power tubes with test pts for each tube, but there is only one adjustment, so you have to balanced between them, and that really relies on having a good matched set.

As others have said players have preferences so some may like bias hotter some colder.
Having the ability to SAFELY adjust bias lets you try out different settings for different tone and feel.

Great job on your part.

BTW, how much does that thingamajig cost?

 

[C1-ocaster]

As long as the tubes are decently matched, it's a waste of time checking each one in the 100+ watters. The reason being is in a typical guitar amp with a four-tube power section, it's really two pairs working in push-pull. Electrically each pair behaves as one big valve.

Hence, you only really need to check one tube from each pair, usually one outer tube and one of the inner two.

If the OT sees each pair on the legs, does it pay to match the pairs as close as possible or will they still be imbalance? I test all tubes at the given PV and match the pairs. So , if tube 1-4 tests 36, 32, 33,30, I would pair up the the 36 and 30 for 66MA, and the 33, and 32 for 65ma. As far as the OT is concerned aren't my tubes now matched to within 1MA or will the tubes still be mismatched since the 30 and 36 ma are 5ma out?

I'm sure someone with accurate knowledge will answer this.
I believe 5% variance is acceptable to be considered "matched".
So 33 and 36 would be around 10%, and 30 and 33 would also be 10%.
Both sets too far out.

That said, I have read that mismatched tubes can actually sound better given that the variance may add more harmonic complexity that may be pleasing. 5 to 10ma difference may be a good thing.
Matched sets would be a cleaner reproduction, and better for hi-fi amps where true reproduction is what is needed and wanted.

That is of course "idle" draw. Once you start playing the bias goes all over the place.
On the Vengeance I leave the meter plugged in just to watch what happens.
But I'll sit down and wait for the correct answer.

 

[jharpersj]

This is what I LOVE about my carol ann amps (among other things like the tone) they have a built in bias monitor, I actually adjust my bias in 2 seconds for every room I play. I can now tell whether the voltage in the room is making my amp hot or cold just by playing it, two seconds later I am back to where it should be. I wish every amp had this feature. No trips to suck techs anymore (although my tech is awesome as well)

 

[stratotone]

By the way, there's a wide range of bias that will 'work' - you might want to play with your bias amount, not exceeding the tube's ability to take it of course, but just going to 70% or whatever may not be the best sounding bias to you. Then once you find where your amp sounds best, you can remember it or write it down and next time you have to retube, you can get back to that point.

 

[MississippiMetal]

As long as the tubes are decently matched, it's a waste of time checking each one in the 100+ watters. The reason being is in a typical guitar amp with a four-tube power section, it's really two pairs working in push-pull. Electrically each pair behaves as one big valve.

Hence, you only really need to check one tube from each pair, usually one outer tube and one of the inner two.

If the OT sees each pair on the legs, does it pay to match the pairs as close as possible or will they still be imbalance? I test all tubes at the given PV and match the pairs. So , if tube 1-4 tests 36, 32, 33,30, I would pair up the the 36 and 30 for 66MA, and the 33, and 32 for 65ma. As far as the OT is concerned aren't my tubes now matched to within 1MA or will the tubes still be mismatched since the 30 and 36 ma are 5ma out?

No you're doing the right thing. They OT doesn't "see" the tubes so much as they "see" each other and the OT's reflected load. Keep in mind a-a impedance halves when you have four tubes vs two because each pair is in parallel. Because they are in parallel, they operate as one current valve. Between two tubes on one side of the OT primary, the individual values make no more a difference than the individual values of two resistors in parallel. Electrically it's one component. a-a impedance for four valves is only 1/4th of a single tube because each pair is also basically in parallel with the other pair in addition to each tube being in parallel with the valve on its side.

 

[mmolteratx]

90% of techs are a complete joke. Most know barely more about electronics than your average guitarist, and almost none have any real technical knowledge beyond hearsay they've read on the internet and regurgitated. I get a kick out of talking to them about basic electronics topics. I've had several cost me considerable money after a few amps were sent to buyers and supposedly damaged in transit. When I get them back, it's always something stupid simple like a loose ribbon connector or a PC mount socket that needs to be reflowed that somehow they fail to catch.

 

[Erock]

As long as the tubes are decently matched, it's a waste of time checking each one in the 100+ watters. The reason being is in a typical guitar amp with a four-tube power section, it's really two pairs working in push-pull. Electrically each pair behaves as one big valve.

Hence, you only really need to check one tube from each pair, usually one outer tube and one of the inner two.

That's good to know. I was using the amp-head dual for years to check the pairs that way, but never felt completely comfortable not knowing what each tube was doing. Good to know I don't have to stress when I can't get that one tube to play nice, lol. I didn't think of matching the pairs that way either, thanks Gary.

 

[Racerxrated]

I have had a few amps that I've picked up at guitar center online and knowing I can take them back within 30 days gives me a nice tryout period. EVERY single one had an off bias, and once I put the bias rite to work it was like night and day. I think they just take amps in and like a used car put a price on them immediately without even checking them....

 

[RACKSYSTEMS]

As long as the tubes are decently matched, it's a waste of time checking each one in the 100+ watters. The reason being is in a typical guitar amp with a four-tube power section, it's really two pairs working in push-pull. Electrically each pair behaves as one big valve.

Hence, you only really need to check one tube from each pair, usually one outer tube and one of the inner two.[/quote

Well not really, testing each tube is good because It tells you each socket is working correctly and you haven't blown a screen grid resistor. Also many many times matched sets of tubes are not matched at all. It's good to check. Also you guys really should have a variac also so you can set the wall voltage to 120v or what ever voltage for the country your in. Then bias away. Also don't totally follow the rules listen to the amp at different bias settings. Most 100 or 50 watt el34 or 6l6 amps use a range of 30 ma to 40 ma.. Anywhere in there is fine if you like the sound.