B52 AT100 Class A failure
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B52 AT100 Class A failure
B52 AT100 tube amp on the bench. Works fine except blows internal fuses in class a mode. Checking the big 15w resistor in circuit measures no resistance at all. I have another resistor I ordered, anything else I should be looking for?
Owner/luthier of Flintrock Guitar Shop, Flint, MI.
Owner of Hawkins Effects Pedals
Owner of Hawkins Effects Pedals
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Leo_Gnardo
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Re: B52 AT100 Class A failure
Everything we need to know is in that headlineflintrock wrote:B52 AT100 tube amp on the bench. Works fine except blows internal fuses in class a mode. Checking the big 15w resistor in circuit measures no resistance at all. I have another resistor I ordered, anything else I should be looking for?
heh, heh, heh.... No resistance at all? Meaning open circuit or zero ohms. Either way, replacing that failed R, you're on the right track. "Could" fit the amp with a larger wattage R, less likely to fail in the future.
down technical blind alleys . . .
Re: B52 AT100 Class A failure
Sorry about that, it measures zero ohms (like touching my probes together). I'm sure that's it.
Owner/luthier of Flintrock Guitar Shop, Flint, MI.
Owner of Hawkins Effects Pedals
Owner of Hawkins Effects Pedals
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JazzGuitarGimp
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Re: B52 AT100 Class A failure
Do you have your meter set to the lowest ohms scale? What is the resistance of the resistor supposed to be?flintrock wrote:Sorry about that, it measures zero ohms (like touching my probes together). I'm sure that's it.
Lou Rossi Designs
Printed Circuit Design & Layout,
and Schematic Capture
Printed Circuit Design & Layout,
and Schematic Capture
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Stevem
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Re: B52 AT100 Class A failure
If that AT 100 in the model name is in regards to rms, or even peak wattage than that 15 watt resistor never had a chance!!
I would up it to a 25 watter, or a 20 watt type in its own aluminum heat sink that bolts to the chassis.
I would up it to a 25 watter, or a 20 watt type in its own aluminum heat sink that bolts to the chassis.
When I die, I want to go like my Grandfather did, peacefully in his sleep.
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
Re: B52 AT100 Class A failure
Dang I just replaced with the same 15 watter. I will do that if it happpens again.
Owner/luthier of Flintrock Guitar Shop, Flint, MI.
Owner of Hawkins Effects Pedals
Owner of Hawkins Effects Pedals
Re: B52 AT100 Class A failure
Found a blown rectifier diode just after the standby switch. Goinf to replace both of those and we should be up and running.
Owner/luthier of Flintrock Guitar Shop, Flint, MI.
Owner of Hawkins Effects Pedals
Owner of Hawkins Effects Pedals
Re: B52 AT100 Class A failure
Gut shot or schematic?
From the on-line manual, I have a difficult time believing that it is actually supposed to operate in Class A - more likely that it is cathode biased.
http://www.b-52stealthseries.com/at100.html
I'd check all the diodes. If one has failed, it's cheap insurance to replace them all.
From the on-line manual, I have a difficult time believing that it is actually supposed to operate in Class A - more likely that it is cathode biased.
http://www.b-52stealthseries.com/at100.html
I'd check all the diodes. If one has failed, it's cheap insurance to replace them all.
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Stevem
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Re: B52 AT100 Class A failure
Was it a 1n4007, or a 1n4004 diode?
When I die, I want to go like my Grandfather did, peacefully in his sleep.
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
Re: B52 AT100 Class A failure
In "Tube AB" and "Solid-State" -modes the circuit is fixed bias. In "Tube A" -mode the circuit converts to cathode bias. I don't bother to calculate if it's cathode biased class A or class-AB. But given poor efficiency of A I'm almost certain it's just generic AB still. ...But don't take my word for it.
Schematics? No reason to post schematics when Google search finds them in a heartbeat.
Schematics? No reason to post schematics when Google search finds them in a heartbeat.
Re: B52 AT100 Class A failure
It was a IN 4007 that was blown. Part of the class A circuit. Its up and running again. Easy fix.
Owner/luthier of Flintrock Guitar Shop, Flint, MI.
Owner of Hawkins Effects Pedals
Owner of Hawkins Effects Pedals
B52
Mine stopped working in distortion mode, then 2 days later stopped working all together. I can see 2-470 ohm -2watt resistors that are both burnt. They are next to the power tubes. The other 2 are fine. Strange that the distortion channel stopped working over that though. Must be 2 different problems.