Question about Behringer BXR1800H Ultra Compact 180 Watt 2 Channel Bass Amplifier Head

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What is the bias setting for the bxr1800h - Behringer BXR1800H Ultra Compact 180 Watt 2 Channel Bass Amplifier Head

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Its the internal Voltage settings on the input gain.
Balancing it with current power setting sis a must.
what is the bias setting for the bxr1800h - 25320532-ow2wnwjtjj33rhn4gshzhkfw-4-0.png

Posted on Dec 23, 2014


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How do I bias the output tubes?

The adjustment method varies from amp maker to amp maker. if you're unfamiliar with the procedure, you're better off to take it to the shop and get it done right. If you really want to do it your self, VHT has a meter they sell for about $100 online so you can see where you're at and then you adjust the bias trim pot inside your amp to balance them out to where you want them.
But again, you're best off leaving it to a pro.

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The bias voltage goes to the output tubes only. These go into the larger tube sockets.

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Fail capacitors how to replace


If capacitors are electrolytic types, then they have polarity + and -, and always are a mark on the pc board and it could be marked with either the "+" symbol or "-" capacitor has a mark itself that denotes polarity also, the most common mark i have seen is "-" running from top all the way down at a side of cap, you just have to buy them same voltage and capacitance rating and install them verifying TWICE the correct polarity and you are done, Mouser electronics has a wide stock of electrolytics, but remember polarity otherwise you will get a very big pop.

Oct 27, 2013 | Behringer BXR1800H Ultra Compact 180 Watt...

1 Answer

Behringer BXR1800H blown fuse?

Might be a fuse, yes. It will require to open the unit to service. Do lights still come on? Have you tried headphones with it?

This unit takes a 100-120V T 6.3A H 250 V SLO-BLO fuse. They can be found at Radio Shaft. ;) Good luck!

Oct 26, 2012 | Behringer BXR1800H Ultra Compact 180 Watt...

1 Answer

Hello I have GK 1001 bass amp that stoped workirepng. I removed it from the case to get at the circuit board. Once I got down to the component level I descovered that several of the power transisors...

Yep... happens all the time. That is why I cold start an amp like this with an incandescent lamp in series to act as a current limiter. I will tell you what is wrong. You did NOT go back far enough in finding the bad parts. Also some that were not shorted MAY have been degraded. The real problem lies in the driver transistors and the bias regulating circuit and the transistors in that area. This amp has a mass number of components and there are many that if they fail they wipe out a bunch. When you think you have it repaired run it a while with a 150 Watt light bulb in series with the power input cord. Here is your schematic:

Scroll down to the link "Get Manual" and click to download. In the schematic there are over twenty transistors involved with power output and bias stability. This is one of the most complex amps I have seen. They get voltage capability by having two series banks of transistors to each voltage rail. The biasing network is a nightmare!!! Pot R28 sets the rest bias which you measure between J5-1 and J5-2 which is 1/3 of the rest current across a total of .4 ohms... whatever it is supposed to be. Q3, Q7, Q16 and Q17 are ALL real critical to the biasing as well as the smaller Q12 and Q13 and all the others. The problem when you have a feedback amplifier is if any of these components are sick, the feedback will still attempt to balance the amp even though it sloowly fries other parts. Frankly, this is going to be a miserable one to fix. Use the light bulb trick and a Variac. There are a few voltages marked n the schematic USE THEM TO CHECK the operation. When certain transistors go, they will take a bunch with them... NOTICE the FUSIBLE resistors up near the rails a couple stages back... need to check all of those and replace with IDENTICAL ones if they are blown or way off value. There are a lot of Zener diodes that ALL need to be checked as they afect the bias levels. You will need nearly full voltage during checking which really makes it tough. With the light bulb if too much current is drawn from the line the light will light absorbing the power line voltage. The light should remain off when repaired AND voltages should be near what is shown on the schematic. I would expect to see half the rail voltage across each of the sets within the banks when at idle. Good luck... from an electrical engineer with 50 years exp.

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1 Answer

Do 4-10 devilles need to have the bias adjusted when replacing tubes?

When replacing the two output tubes you should check the voltage at TP26 or either cathode pin of the power output tubes to ground. Set the bias by adjusting pot R82 to 60mv which is 60 ma across the 1 ohm metering resistor. This coresponds to 30 ma per tube. Changing other tubes requires NO adjustment.

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1 Answer

My Epi valve jr v3 burns up jj el84 tubes, but the solvteks work it the amp or the tubes?

Check the bias on the tubes! Some brands can run with bias set wrong. Also some amps have 4 output tubes and people don't know that MATCHED pairs have to be seperated to each side of center of the group of four tubes.
You probably only have a single EL84 tube in your unit.
I could not find the schematic for this unit... IF the plates of the EL84 are coloring, the bias is set wrong. The plates should remain BLACK and not coloring to dull red or orange. Telling if the tubes are "burned up" can only be done with a tube checker or electronic test equipment or by seeing a bright purple glow between the elements.
Now this is supposedly only a 5 Watt unit so that means it is for LOW volume practice only... If you overdrive this small amp you can PROBABLY burn almost any tubes you put in it. The sound you can expect out of this will not be louder than most of the consumer boom boxes at full volume.
If you overdrive and "flattop" the unit the power tube will overheat and fail... this amp runs the tube in "Class A" which makes failure under overdrive more likely than in Class AB or B. I can't go into the engineering details other than to say at volumes above the design the output transformer will saturate and the tube will have to dissipate way above its ratings.

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2 Answers

Fender Hot Rod Deluxe Volume Fluctuations. My amp (fender hot rod deluxe) will occasionally have volume fluctuations when I'm playing. The changes usually occur when I've moved my setup from one place...

First thing would be try another guitar with the amp. This will eliminate if it's a problem with the guitar or the amp itself. If the guitar is working properly then check all the tubes to be sure they are all seated into there slots completely. Depending on how much use they have been played it may be a good suggestion to then replace your tube's. Occationally the tubes will start loosing power, making sound fluctuate up and down or distortion sounding static in background noise. You will notice a big difference with newer tube. But remember the bias must be set correctly to match the new tubes so they won't over heat. You can check out youtube for setting the bias. Anyway this is my suggestion and I wish you good luck.

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1 Answer

The valves on my Marshall TSL 122 are getting to hot.What might be the problem? Can you get me the scheme for that amp?

Probably the bias is set wrong... Please note that when installing MATCHED pair tubes, the tube pairs usually go at opposite ends of the strings, that is one on either side of the center of a set of four.

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1 Answer

No volume.

Are the tubes bad? Do they light up? Check the tubes and install replacements if necessary. If it's a preamp tube that went bad, just replace that one tube. If a power tube went bad then replace the set of power tubes. Be sure to get a matched set when replacing power tubes, and to bias them.

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