#1
Hi,

My power tubes are starting to die. They have volume swells.

Now, I took my multimeter and hooked it up to the bias test (built into the amp), it gave me 15 volts. Now, isn't that quite low for a tube? The bugera-site said that tubes would typically run 30-40 volts.

Now, I haven't even ordered a matched pair of el84's. I really would like to know, how should I set my bias if the test voltage is 15v? Note: I haven't touched the bias since I bought the amp.

So, can I just slam some new tubes in there and re-adjust to about 15v with the bias test?
#2
Don't use the external bias point on Bugera amps, it does not give you a true reading.

You also want to set the multi meter to mA to measure the bias not volts. I highly suggest you buy a bias probe ($25 and well worth it) and it makes biasing very easy.
www.eurotubes.com/store/pc/viewPrd.asp?idproduct=149&idcategory=6
2002 PRS CE22
2013 G&L ASAT Deluxe
2009 Epiphone G-400 (SH-4)
Marshall JCM2000 DSL100
Krank 1980 Jr 20watt
Krank Rev 4x12 (eminence V12)
GFS Greenie/Digitech Bad Monkey
Morley Bad Horsie 2
MXR Smart Gate
#3
The bias current depends on the tube used and the amp circuit. It is not worthwhile to refer to a bias number that has no relevance to your situation. An "average" bias means absolutely nothing, and I'm not sure why Bugera would even mention it. You need to find the recommended bias value for your specific amp and bias accordingly.
#5
Using the bias probes? No. You would only have to pull the chassis if for some reason Bugera gave you bias points on the back panel but no way to adjust it from there, which seems unlikely. Can't say for sure without knowing what amp it is.

The bias probes plug into the tube sockets.
#6
I use a bugera v22. So I use a bias probe and connect it to the tube socket, then I can read the current that runs through the tube? And then I still turn the bias adjust knob to adjust the current/voltage? It seems really easy if my perception is correct.
#9
It looks like the V22 has a customer facing bias adjust knob. Not sure how accurate the test point is above the adjust pot. A bias probe as mentioned is the best way to go. You'll have to remove the tube cover but at least you won't have to go into the chassis itself - which can be dangerous.

But Roc8995 is one of our resident engineers so listen to his wisdom.

This may help a bit - or may be way too much
http://profile.ultimate-guitar.com/311ZOSOVHJH/blog/80083/

This seems pretty helpful as well but he doesn't ever make any adjustments.
https://www.youtube.com/watch?v=SStKuO1xE-U

Keep in mind, never play your guitar with the probe on. You can have the guitar plugged in but turn its volume all the way down.

Order matched pair of tubes
Install new tubes
Put probe on and take measurement
Take probe off and play the guitar
Put probe back on and make an adjustment
Take probe off and play the guitar
Put probe back on and make an adjustment
repeat as necessary

(that kind of thing)
Last edited by 311ZOSOVHJH at Jan 4, 2015,
#10
Quote by 311ZOSOVHJH

Keep in mind, never play your guitar with the probe on. You can have the guitar plugged in but turn its volume all the way down.


I actually wonder why that is like that.
#11
Quote by liampje
I actually wonder why that is like that.

because the power the tube makes is passed to the bias probe and it will fry the Multi meter and probe You only want to test the amp when it is on but not being used. And keep it hooked to a speaker or load while you do it
2002 PRS CE22
2013 G&L ASAT Deluxe
2009 Epiphone G-400 (SH-4)
Marshall JCM2000 DSL100
Krank 1980 Jr 20watt
Krank Rev 4x12 (eminence V12)
GFS Greenie/Digitech Bad Monkey
Morley Bad Horsie 2
MXR Smart Gate
#12
Quote by liampje
I actually wonder why that is like that.

I'm not the engineer here but I believe if you run a signal through the amp then your bias reading won't be accurate first of all. You want to see a nice idle current and let the number 'settle in'. More importantly however, is that the resistor used (at least in the cheaper probes) can fry if you play a lot while it is on. I just like to play it safe.

The probe I was using in my tutorial blog was the Eurotubes $25 probe. It works, but I blew mine doing that. Now I have a slightly better Weber probe ($60 ish I think). You may also want to make sure you have room for a tube probe (8 octel socket kind obviously) first as well.

Lastly, bias your amp with your ear and not a number
Last edited by 311ZOSOVHJH at Jan 4, 2015,
#15
Hi, been a long time since I last posted, but I had to add to what 311 and Robb are saying about not playing with the probe plugged in: there are some bias probe units out there that are a probe and meter in one, and at least one manufacturer (Bob at Eurotubes.com) says theirs is "designed to let you play with the probe in the amp" or something like that. Don't do it. It'll malfunction just like any other probe if you play with it plugged in.
Ibanez UV777 - Carvin TL60 & 727 - Jackson KE3
Splawn QuickRod - Mesa Stiletto & RoadKing - Peavey Ultra+ - Peavey Bandit
Some pedlulz & cabz


7 String Legion