Just got the Bugera 1990... (JCM 900 copy)

butterguitar · 10-12-2009, 01:50 AM

All i have to say is....WOW! What a fantastic sounding tube guitar amp!!!
It sounds great out of the box, and best of all it sounds very similar to a jcm900! Fantastic 80's metal tones, no need for a tube screamer with this amp.

My only thing is, should I set the bias for this amp? I don't know how to check it (my tech used to maintence my last tube amp, but he has since moved). What is a normal bias rate? What will happen if the bias is set too low or too high?

bro blue · 10-13-2009, 11:40 PM

I have a Bugera 6260 and a 333. There are places to bias inside the amp using a voltage meter. The bias settings are available on the web. You shouldn't have to bias the amp unless you change power tubes. Remember, tube amps, even if they have been turned off and disconnected for a while, may still contain lethal voltages. Lethal as in "it will kill you dead."

T-Bird · 10-14-2009, 12:36 AM

Hi.

Congrats on the NAD.

While the bias shouldn't shift, with modern bulk tubes it will. IME for the first 20 hours or so of operation. If the tubes have been propery burned-in the bias shifts less if not...

Huge, huge + 1 for NOT to poke around in the internals of Your amp if you don't know what you're doing.

Regards
Sam

butterguitar · 10-14-2009, 12:49 AM

Quote:

Originally Posted by bro blue

I have a Bugera 6260 and a 333. There are places to bias inside the amp using a voltage meter. The bias settings are available on the web. You shouldn't have to bias the amp unless you change power tubes. Remember, tube amps, even if they have been turned off and disconnected for a while, may still contain lethal voltages. Lethal as in "it will kill you dead."

How do I drain the voltage from the amp before working on it?

bro blue · 10-14-2009, 01:12 PM

You'll find a couple of good links here:

Tube Amp Mods - SAFETY Questions - Guitar Noise Forums

If you are just checking the bias with a voltage meter and turning the bias knob (if it is set up to adjust like mine), you shouldn't have to discharge the filter caps although it is still a good idea to do so in almost all cases. The caps should not be visable if you are just looking at the power tubes and bias adjust knob.

Here is a link to the spec sheet I use:

http://www.behringerdownload.de/_Bug...9-10_Rev.1.pdf

If you still have the stock power tubes in it the bias point should not have drifted much. They may have been over/under biased from the factory, though. If you replace the power tubes you have to replace them with a matched set, you shouldn't just pick a tube here and there.

MartyStrat54 · 10-14-2009, 09:49 PM

Why do you feel the bias has drifted? You stated that the amp sounds fantastic and that to me means the bias is right where it needs to be.

TPR · 10-14-2009, 10:12 PM

Butter,
Like Bro said, you do typically want to drain the filter caps before working inside the amp. However, you can't do that when biasing because the bias reading has be taken while the amp is on. Also, before biasing you need to find out what the plate voltage is, which of course requires the amp to be on.

There's already a wealth of info about keeping safe and about how to do the biasing, so I won't go into that except to say - Don't work with both hands inside the amp! Keep one away from the amp at all times. If you have one hand on the chassis or other ground point and the other hand touches a high voltage point, it might be the last amp you ever work on.

I don't know anything about the Bugera, so the above info assumes that it has an adjustable bias that can only be accessed after opening the amp up.

By the way, if your bias is too high your tubes will burn up fast. If it's too low, your tubes will last forever, mainly because the amp will sound so bad you won't want to play it.

There's a bias range, but you would need to find it by knowing the plate voltage of the amp and the max dissipation rate for the tube.

And if I haven't already worn out this post, one more thing. If you can find a tech, checking the bias should be pretty cheap. That would let you put off the learning curve for a bit. If you have to do it yourself, take your time learning so you don't get zapped or damage the amp.

Cheers.

TPR · 10-14-2009, 10:22 PM

Quote:

Originally Posted by MartyStrat54

Why do you feel the bias has drifted? You stated that the amp sounds fantastic and that to me means the bias is right where it needs to be.

I dunno, some guys seem to like running pretty damn hot, to the point where they're burning through tubes pretty quickly. Take it a little further and I'd be worried about damaging the amp. Is that paranoid?

butterguitar · 10-15-2009, 01:13 AM

Well like i said the amp sounds fine right now but I just want the amp to run at the peak performance. I got everything set up correctly now. I just gotta figure out what ohm setting to run my halfstack at lol

TPR · 10-15-2009, 09:05 AM

Quote:

Originally Posted by butterguitar

Well like i said the amp sounds fine right now but I just want the amp to run at the peak performance. I got everything set up correctly now.

OK, I hear you and it's probably all good, but at least make sure you aren't red plating the tubes after running the amp for awhile. It's the easiest thing in the world to check while in normal operation. Cheers.

LesPaulopolis · 10-15-2009, 01:46 PM

Quote:

Originally Posted by butterguitar

Well like i said the amp sounds fine right now but I just want the amp to run at the peak performance. I got everything set up correctly now. I just gotta figure out what ohm setting to run my halfstack at lol

16 ohm tap on amp
high power
mono cab input
16 ohm tap on cab

Oze · 11-07-2009, 03:45 AM

Hey all....greetings from Downunder

I own a Bugera 1990 and there's no need for rebiasing out of the box...HOWEVER..
You CAN download a document from the Bugera website as a .pdf with step by step instructions

10-12-2009, 01:50 AM	#1 (permalink)
butterguitar Junior Member Join Date: Sep 2009 Location: Las Vegas Posts: 29	Just got the Bugera 1990... (JCM 900 copy) All i have to say is....WOW! What a fantastic sounding tube guitar amp!!! It sounds great out of the box, and best of all it sounds very similar to a jcm900! Fantastic 80's metal tones, no need for a tube screamer with this amp. My only thing is, should I set the bias for this amp? I don't know how to check it (my tech used to maintence my last tube amp, but he has since moved). What is a normal bias rate? What will happen if the bias is set too low or too high? __________________ Bugera 1990 Crate Blue Voodoo Cab w/ Celestion 75's Crate g1600xl Marshall MG w/ MC412 Kramer 1984 Epiphone SG Double Neck OLP MM1 Guitar Yamaha Pacificia

10-13-2009, 11:40 PM	#2 (permalink)
bro blue Senior Member Join Date: Aug 2009 Location: Southern USA Posts: 142	Re: Just got the Bugera 1990... (JCM 900 copy) I have a Bugera 6260 and a 333. There are places to bias inside the amp using a voltage meter. The bias settings are available on the web. You shouldn't have to bias the amp unless you change power tubes. Remember, tube amps, even if they have been turned off and disconnected for a while, may still contain lethal voltages. Lethal as in "it will kill you dead."

10-14-2009, 12:36 AM	#3 (permalink)
T-Bird Senior Member Join Date: Jul 2009 Location: Finland (Northern Europe) Posts: 214	Re: Just got the Bugera 1990... (JCM 900 copy) Hi. Congrats on the NAD. While the bias shouldn't shift, with modern bulk tubes it will. IME for the first 20 hours or so of operation. If the tubes have been propery burned-in the bias shifts less if not... Huge, huge + 1 for NOT to poke around in the internals of Your amp if you don't know what you're doing. Regards Sam

10-14-2009, 01:12 PM	#5 (permalink)
bro blue Senior Member Join Date: Aug 2009 Location: Southern USA Posts: 142	Re: Just got the Bugera 1990... (JCM 900 copy) You'll find a couple of good links here: Tube Amp Mods - SAFETY Questions - Guitar Noise Forums If you are just checking the bias with a voltage meter and turning the bias knob (if it is set up to adjust like mine), you shouldn't have to discharge the filter caps although it is still a good idea to do so in almost all cases. The caps should not be visable if you are just looking at the power tubes and bias adjust knob. Here is a link to the spec sheet I use: http://www.behringerdownload.de/_Bug...9-10_Rev.1.pdf If you still have the stock power tubes in it the bias point should not have drifted much. They may have been over/under biased from the factory, though. If you replace the power tubes you have to replace them with a matched set, you shouldn't just pick a tube here and there.

10-14-2009, 10:12 PM	#7 (permalink)
TPR Senior Member Join Date: Sep 2009 Posts: 161	Re: Just got the Bugera 1990... (JCM 900 copy) Butter, Like Bro said, you do typically want to drain the filter caps before working inside the amp. However, you can't do that when biasing because the bias reading has be taken while the amp is on. Also, before biasing you need to find out what the plate voltage is, which of course requires the amp to be on. There's already a wealth of info about keeping safe and about how to do the biasing, so I won't go into that except to say - Don't work with both hands inside the amp! Keep one away from the amp at all times. If you have one hand on the chassis or other ground point and the other hand touches a high voltage point, it might be the last amp you ever work on. I don't know anything about the Bugera, so the above info assumes that it has an adjustable bias that can only be accessed after opening the amp up. By the way, if your bias is too high your tubes will burn up fast. If it's too low, your tubes will last forever, mainly because the amp will sound so bad you won't want to play it. There's a bias range, but you would need to find it by knowing the plate voltage of the amp and the max dissipation rate for the tube. And if I haven't already worn out this post, one more thing. If you can find a tech, checking the bias should be pretty cheap. That would let you put off the learning curve for a bit. If you have to do it yourself, take your time learning so you don't get zapped or damage the amp. Cheers. __________________ '91 JCM 900 Head w/ EL34s '68 Bassman Head- Blackfaced Hand Built 2x12 Classic 30 Gibson LP Studio w/ PAFs Epi LP Standard w/ G 57s The usual assortment of pedals and stuff

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10-15-2009, 01:13 AM	#9 (permalink)
butterguitar Junior Member Join Date: Sep 2009 Location: Las Vegas Posts: 29	Re: Just got the Bugera 1990... (JCM 900 copy) Well like i said the amp sounds fine right now but I just want the amp to run at the peak performance. I got everything set up correctly now. I just gotta figure out what ohm setting to run my halfstack at lol __________________ Bugera 1990 Crate Blue Voodoo Cab w/ Celestion 75's Crate g1600xl Marshall MG w/ MC412 Kramer 1984 Epiphone SG Double Neck OLP MM1 Guitar Yamaha Pacificia

11-07-2009, 03:45 AM	#12 (permalink)
Oze Junior Member Join Date: Nov 2009 Posts: 1	Re: Just got the Bugera 1990... (JCM 900 copy) Hey all....greetings from Downunder I own a Bugera 1990 and there's no need for rebiasing out of the box...HOWEVER.. You CAN download a document from the Bugera website as a .pdf with step by step instructions

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