#1
I'll try and keep this brief. I have a Bugera V55 head that's on its 3rd set of tubes. The first change went smoothly and I had my friend who owns a multimeter help me out. We didn't have an RCA cable but we were able to get a reading from the bias test point regardless (red probe in socket, black on screw for ground). This time around, visited the same friend and the voltage reading was all over the place. Also, when we made connection there was a slight pop/spark and the tubes would glow brighter and the idle hum would increase. For fear of bodily harm, I opted not to mess with it any further and took it home. Sounds alright, and operates fine (no redplating, etc).

Took the liberty of buying my own digital multimeter to verify it wasn't something dumb we were doing there. I took the recommended procedure of attaching an RCA plug to the probe ends this time as well. Once again, connection with the bias test point would induce increased hum and tube glow but no reading. I moved the bias pot a bit with no luck. Even without the meter hooked up I can tell moving it increases the idle but I don't see any visual change in the tubes and any audible differences are subtle. Is it possible we fried the test point/pot?

Sorry for the long winded rant, just looking for some guidance.
SLAP energy drinks ftw.
Last edited by ianae86 at Aug 16, 2011,
#2
those test points can't be trusted

there are other ways to check the bias but they are more dangerous

i'd take it to a tech or exercise your warranty

or ask these guys:

https://www.ultimate-guitar.com/forum/showthread.php?t=845438&highlight=bugera+bias
#3
If the Bugera's are anything like Peavey's then the bias points are a joke. I've read that they don't even read the right thing if they are even reliable at all. You need a bias probe or directly measure the current on the tubes themselves by getting into the guts (not recommended).

Just for times sake, were you measuring amperage and in the right range?

EDIT
I wouldn't even begin to recommend opening the chassis to measure the bias. You should get a bias probe to attach to your DMM and do it that way. Just takes removing the tubes to do so.

i.e. https://ssl.eurotubes.com/cart/index.php?page=view_products&category_id=108&sub_category_id=109

But I am sure others sell them.
Last edited by Sputnik1 at Aug 16, 2011,
#4
Quote by Sputnik1
If the Bugera's are anything like Peavey's then the bias points are a joke. I've read that they don't even read the right thing if they are even reliable at all. You need a bias probe or directly measure the current on the tubes themselves.

Just for times sake, were you measuring amperage and in the right range?


Thanks for the quick replies. I had it set on DC volts, per the Bugera bias PDF.
SLAP energy drinks ftw.
#5
Quote by ianae86
Thanks for the quick replies. I had it set on DC volts, per the Bugera bias PDF.

Ok, nm. You were doing it correctly. When you use a bias probe you read in amps and do a calculation. But there is a recommended amp bias range.
#6
Quote by Sputnik1
Ok, nm. You were doing it correctly. When you use a bias probe you read in amps and do a calculation. But there is a recommended amp bias range.


The tricky things with the Vseries is that their tube sockets are not accessible without removing the entire chassis. The first time we used the recommended range on the Bugera PDF and it went well. My main concern now is that their doesn't seem to be much difference in turning the bias pot besides audible hum, and that the tubes kick into bright glowing mode when the meter is connected. I actually shut if off once because I thought I started to see redplating when the meter was connected
SLAP energy drinks ftw.
#7
Quote by ianae86
the tubes kick into bright glowing mode when the meter is connected. I actually shut if off once because I thought I started to see redplating when the meter was connected



not good

I have a bias probe like the one posted above. They don't last forever because the resistor used can fry. I also have a biasing blog 'for my amp' if you find it helpful. You can remove the chassis as long as you don't touch anything on the inside. There is also a heat sink 'mod' that can be done on the older versions of these V amps. It is fairly well documented.
#8
I guess my main concern is I wonder what is getting bridged when that meter is connected that would cause the idle to increase so much. I might actually look into taking it in to have it "properly" biased. I just want to make sure that its dialed in properly as opposed to having it tuned by ear like it is right now. I just don't want to drop a lot of money on such a cheap head.
SLAP energy drinks ftw.