B52 amps? tell me about em

[drewl]

So I have a 2x12 B52 amp for routine tune up.
Seems to be a cross between Mesa and Valvestate amps. They even make SS amps that look like Marshall Valvestates.

3 channel, tube or ss rect. 8 preamp tubes, quite versatile and better sounding than Mesa IMO. and alot cheaper.
wonder why they're not more popular.......

[StratTone]

I have no idea. They do sound really good and look built really well. I bias one up for a buddy the other day. The only problem is they have the switching on the back that throws the bias WAY crazy if you don't know what you are doing.

[Amp Kat]

They have some switching issues with the channels and fail quite easily with tube shorts much like the Marshall DSL 2000. They do sound pretty decent when working properly but that's the main problem. They don't work very long with out problems. I also don't care for the way that AT112 sits in the cabinet in the back and the reverb is very sensitive and over vibrant. Other than that they are ok. Just like anything else, you get what you pay for !

[StratTone]

To be honest though the problem lies in the comsumers no knowing what they are doing. If they put it in class a the bias sky rockets. Especially if they put in new power tubes that draw more current than stock. They really should put more accurate adjectives on switches other than "diode", class ab, class a. People don't know the effect on voltage swings when they make a switch and could be running an amp at over 100% plate dissapation.

[drewl]

This one is running 4 6l6's -Cathode Biased!
I assume to avoid the bias problem you mentioned.
I could see where different rectifier's would cause biasing problems
B+ with tube rect= 400v
B+ w/tube & diodes= 420v
B+ w/diodes only = 460v

[StratTone]

Don't get me wrong it is a cool feature but you really need to know the effects before messing with it. I really want to snatch a AT100 up while there cheap. My buddy picked on up for $250 shipped and I like it. I have high end amps as well but I like to "think" that I can hear tone no matter the price. Hell I'm digging my Crate V1512....... Another killer cheap amp. I tell people all the time that if you played my V1512 you will still hate crate......but no this one.

[drewl]

Alot of Mesa's can switch between rectifiers, but they're usually biased so damn cold it doesn't make a diff.
Like I said, this one's Cathode biased so it removes the user error factor.

[StratTone]

Alot of Mesa's can switch between rectifiers, but they're usually biased so damn cold it doesn't make a diff.
Like I said, this one's Cathode biased so it removes the user error factor.

Very true about the Mesas but the B-52 does have a bias pot. I'm sure someone will be tinkering.

[clintronics]

Just repaired one yesterday. The 470 ohm grid resistor fell from the PCB. This one didn't seem to have much solder if any holding these resistors in.

[drewl]

I was mistaken, I thought I checked for this but it's switchable between fixed and Cathode biased, and yes it does indeed have a bias pot that could be messed with by the wrong person.

As far as the boards, these things were definitely engineered by a computer guy!
multiple boards with little plugs to connect the multitude of wires between boards....

[Euthymia]

I had one in here that had been badly trashed in an unguided attempt to repair it. The Rectifier-style head mentioned earlier.

Boards hangin' out of it, etc.

30 minutes to fix the original problem (roasted screen resistor) and then a couple of hours to fix the other stuff that was inflicted on it.

Looks like the same package designer that does the Behringer amps designed it: all of these flimsy-ass connectors everywhere. I spent a goodly amount of time fixing (or eliminating) broken cheap connectors.

Everything about the construction/assembly screams "made in china," but I actually was surprised by how good it sounded after I got Humpty back together.

Sound: 8
Support: (they sent me a schematic for free) 9
Reliability: 4
Serviceability: 4

[danielh8139]

Hello i have a b-52 at100 and i want to put some winged 'c' 6l6 tubes in it. I found a repair shop that took one in that was cooking hot after these tubes were installed and they said it was due to a negative voltage supply problem in the bias system. They used the high voltage 2ndary to supply the bias range and the rectifier provided voltages for solid state functions left intact. Now any 6l6 can be used. Can you tell me how to do this ? They wont. They wont me to ship it to california.

[Amp Kat]

Hello i have a b-52 at100 and i want to put some winged 'c' 6l6 tubes in it. I found a repair shop that took one in that was cooking hot after these tubes were installed and they said it was due to a negative voltage supply problem in the bias system. They used the high voltage 2ndary to supply the bias range and the rectifier provided voltages for solid state functions left intact. Now any 6l6 can be used. Can you tell me how to do this ? They wont. They wont me to ship it to california.

Try this down at the bottom of this page. Can't understand why they had to revert the bias from it's original tap. Something not right here but that explains why they are having so many problems with tube failures and screens blowing up which I repaired one of those also that had blown to pieces and had black crap all inside it from something exploding inside.

http://people.cornell.edu/pages/mt24...switching.html

[drewl]

Well aside from installing a fan over the rectifier as per B52's instructions, that one I repaired has been working fine.
I didn't know it then, but the owner is a friend of a friend.

[flem-1957]

B52 A112 control circuits

Be aware that there is a voltage tripler circuit that supplies 17VDC to a 3 terminal regulator, LM7812 to supply relay switching power, and control for "dirty" and "clean" modes. The diodes in the tripler can fail, and you are stuck in "dirty" mode. Check the capacitors in the tripler circuit, and if you have an ESR tester for your caps, check them for leakage.
Also, the B+ Caps go south, for some reason, poor quality, and will cause some 6L6 trouble when they go.