How to Bias an Amp 2020

[@sam127001]

handy info to have - It was really interesting to see the waveform change on the scope as you changed the bias.

[@erpringle]

These guys want you to subscribe to their channel but they won't answer a simple question when you ask. I Appreciate it and I'm sure everyone else does too.

[@amplifiedparts]

Hi guys, we do not regularly check our comments on all of our KZbin videos. You can always give us a call at 480-296-0890 or shoot an email to [e-mail] and we will try and answer your questions to the best of our ability.

[@AlejandroFortheKIll]

Do you need to use high volumes on the power tubes to make the adjustment correctly?

[@gamesandguitars3901]

definitely a thing i need to learn because i cannot afford to pay someone else to do it for me

[@johnsimms3957]

I liked seeing the sine wave on the scope on this video. Anyway I like to fine tune the bias by ear while playing my favorite guitar with my favorite settings. I find I tend to like the bias lower than 70%. I believe 60% sounds better.

[@michaelevans3852]

There is no video online that shows how to solder a vintage RCA male plug. Could you make one please.

[@yahweh1x543]

Why are you not using insulated tools with such a high voltage available on the board?

[@preciseaudioblog]

Hi, great video. I have a Bugera V22 Infinium (with auto bias). It bursts the power tubes in days. Could be that auto bias is damaged? Thank you.

[@amplifiedparts]

Uh oh if you are going through power tubes that often something is definitely wrong! I would recommend taking your amp to a local tech to get to the bottom of the issue.

[@preciseaudioblog]

@@amplifiedparts I have taken it to 2 techs... none of them can fix it. Thanks for the fast answer. Cheers!

[@merqury5]

@@preciseaudioblog You probably have this problem still. Id say you need to take it to an actually educated service tech. This should be quite easily diagnosed by a competent person. A guitar shop random dude rarely has this. A radio or tv repair man is what u need.

[@preciseaudioblog]

@@merqury5 Thank you so much, I'll fallow your advice. Cheers

[@23skidoo46]

do you need to rebias if just changing preamp tubes?

[@amplifiedparts]

You should not need to rebias your amp when replacing preamp tubes.

[@beerwolf8518]

Is the plate voltage typically the same on each power tube or do you need to measure each power tube?

[@chriskilian2325]

Last time I did it both plates were within 1-2 volts of each other.

[@sadzidsmajkic6181]

If the tubes are well matched, the plate voltage can vary but only for a few volts up and down which in general doesn't really matter. What does matter is when you start to increase the current the plate voltage will drop, depending how much you turned (if your amp was set too cold) so in the middle of the process you may want to stop, redo your calculation and continue.

[@theczarofguitar2109]

what would happen if you tried to connect the multimeter to measure the plate voltage while the amp was on?

[@sadzidsmajkic6181]

Nothing, the multimeter would display the measured value of the voltage. I've done it a dozen of times.

[@redburner]

is the rebiasing process the same for the 2203x reissues? Also, do you need those tube probes that plug in before the tubes or can you just use a voltmeter?

[@erpringle]

Don't waste your breath, they don't answer questions.

[@katman11]

Yes I saw another video where guitaroligist just switches his volt meter to 200 ma setting and gets the plate current.

[@silasfatchett7380]

You can bias using just a multimeter, but knowing how to do it safely requires experience. Not a job for a novice.

[@sciencemansandera]

What is considered a standard fee to say take an amp someplace and have this done. Or does it go like a flat rate 50- 60 bucks an hour or something like that. I work mostly on instrument stuff and I’ve built cabinets but I wouldn’t mind buying the test gear to be able to tuneup and biased amps

[@amplifiedparts]

Different techs have different practices and rates, like the general market, fluctuate. We suggest contacting a few other technicians in your area to gather general pricing.

[@bc454irocz89]

If theres only 1 trim pot, does it even matter which tubes go back in what sockets?

[@sadzidsmajkic6181]

No, it really doesn't matter! Every amp which is fixed bias and have only 1 bias trim pot relies exclusively on how well the tubes are matched. So, you can put the tube from socket 1 to socket 4, it won't make any difference at all in operation. Cheers!

[@skaboosh]

the repetitive riff is a kind of mini torture bwahahahaha

[@Joejoe-nt3gc]

I have an ampeg j12t that will not break up…and i dnt see any pots.. tubes are brand new and working …

[@erpringle]

What happens if you go to set your bias and there's not enough when you turn the trim pot to reach your mv? What I mean is, when I turn the bias adjustment pot there is not enough adjustment to reach 36 mv. I have a vox night train 50 with el34's and it's got an bias adjustment pot for each power tube but it usually takes about 3 sets of tubes to get a pair that will bias hot enough. I think I have to change a resistor or something like that or maybe even the bias pots. I need more adjustment in my bias pots. How would I fix that. Is there something I need to tell the guy where I buy my tubes? Any help would be appreciated.

[@nikonmikon8915]

You should definitely check the voltage and re-calculate before assuming you're out of range. Your voltage on the plates will change as you change the current and you should re-calc to see where you're at (50% 60% 70% etc). If you find that after calculations it's still out of range you can modify the bias circuit to allow for more range. You can google how to do that, but if you can't figure it out, send a reply here.

[@sciencemansandera]

I don’t know the guys name might have to see if I can find it but there is a guy on KZbin that seems to be an expert in these Marshall amps he has complete re-wiring Circuit to correct Marshall 900s which I guess have a known issue. He would probably be the guy to find an ask a technical question because he seems to understand electronics really well. I do somewhat but I usually just go by following directions or trying to match up parts to what their values are supposed to be I would like to get back into it in one a lot more electronics is fun stuff.

[@luperziohaadam4043]

Nothing registered on the meter

[@waynegram8907]

What is the standby switched purpose for to just to wait for the power tubes to warm up and then the standby switch turns on the plate and cathode voltages, but why need a standby switch?Biasing tubes at 80% and 90% wears out the power tubes faster? less life expectance?

[@erictripton]

Uhm, you can forgo the cost of bias probes and meters... all you need is a multimeter.

[@peakAV]

The nub comments are hilarious. Don't be scared to 1) own and 2) maintain a tube amp. It's not hard...

[@snakepitsam]

I will just do solid state

[@dickieradd]

Yeah I thought you could just change the tubes out in 4 mins. This convinced me, I'm runnin' my JCM 2000 to the ground and then selling.

[@jfxberns]

1) You don't show how the bias probes are connected--though you do show them being removed. 2) You show the signal on the oscilloscope, but you don't explain what points the problems are connected to to get that signal. 3) What volume setting do you use to test? 4) I see a waveform on the oscilloscope. Do you need an input signal to do the biasing? Remember, this is for beginners!

[@Purplexi]

A JCM 800 on four?

[@amplifiedparts]

Our video room isn't sound proofed well enough to go louder than that here in the office! 😂

[@merqury5]

I cringed from the bare finger handling of these tubes. The finger marks will be there for ever one the oven has been on a while.

[@jgabora]

and that matters because....?

[@merqury5]

@@jgabora Beacuse that how we who were trained on tubes during our education learned it. Maybe these simple amps wont suffer tolerances that bad, but remember tubes were once used in computers.

[@brianbianchi8028]

@@jgaborathe oil in your hands can burn up from the heat of the tubes and melt them

[@kahlrhoam6769]

New sub & that was elegantly demonstrated. 👏🦡

[@robertcallahan7061]

And then I'll sound like Jeff Beck ?

[@robertyoung1777]

Too dangerous for an inexperienced technician. High voltages present in tube gear are the end of you if you come in contact with them. Hire someone who knows what they are doing. It ain’t worth it to try it yourself.

[@davesims6517]

My "Incredibly matched" power tubes were off by 9ma; Never again! And what is going on with that horrible sounding guitar in the background; it sounds like two wasps mating in a paper cup.

[@chriskilian2325]

9ma isn’t too bad at all. Actually a “mismatch” of 9ma will benefit the sound overall by enhancing harmonics. A real mismatch is of 20-30 MAs

[@davesims6517]

@@chriskilian2325 I've heard all about the apparent even order harmonic enhancement of mismatched tubes, and think it's exaggerated. 9ma is too much in my case, because it was causing significant redplating In one of the tubes, and I'd rather not have them wear at different rates.

[@chriskilian2325]

@@davesims6517 well my “matched” pair of tubes are 6ma apart right now. Just saying this to illustrate that “matched” tubes doesn’t mean they are clones. It just means they won’t be 15-30 MAs apart. Right now I have one set for 60% and one at 68% and I like the sound. Ultimately your ears have to decide how hot or cold. I wouldn’t go over 70%. Then it would probably red plate

[@davesims6517]

@@chriskilian2325 I hear you. The one that's red plating is doing it at 65 percent dissipation, so that particular tube that I have is definitely a high current tube.

[@chriskilian2325]

@@davesims6517 what tube is this?