Crate Blue Voodoo Blown 1/4A fuses

[twilightofthedogs]

Hi all, just wondering if anyone could steer me in the right direction. I have come upon a Crate Blue Voodoo head that doesn't work. I opened it up and found that both the 250ma fuses mounted on the PCB were blown. Admittedly, I am not entirely sure what these guys do. Anyone have any particular area they might expect to be causing these fuses to blow? Highlighted schematic attached. THANKS!

[Leo_Gnardo]

They go to pins 2 of the multipin connectors - guessing on the other side of those connectors is the output tube board. Since one end of each of the fuses goes to ground, likely they're used as overcurrent fuses for the output tubes, one fuse in the cathode circuit of each 6L6. The MPC's are trouble in these amps, old as they are corrosion often prevents good contact. Possibly there's a fault in the bias supply or delivering that bias to the output tubes via the MPC's. OR someone ran the amp into too low or too high an impedance.

Hope you get your BV working: they may be "Crates" but are capable of being very good sounding amps.

[twilightofthedogs]

Thanks Leo. I just replaced those two fuses with 1/4A slow blow and it seems to be working now. I think the originals were fast acting. Is that what "normal" means on the schemo?

[Leo_Gnardo]

Thanks Leo. I just replaced those two fuses with 1/4A slow blow and it seems to be working now. I think the originals were fast acting. Is that what "normal" means on the schemo?

So far so good. I'd recommend "exercising" those multipin connectors though, pull that output tube board off, examine the pins & sockets, clean with solvent & caig D5 & solvent again then reassemble. There's little stick-brushes available at some groceries & drugstores, meant for cleaning between teeth, they're excellent for cleaning multipin sockets as well as tube sockets. Invest in a box of those probably $5, well worth it for your amps and teeth. A brief loss of bias because of poor connection in those MPC's could be enough to make fast/normal fuses pop.

[g1]

The common thing that would cause those fuses to blow would be power tube faults. So you could have a power tube (or both) that has an intermittent fault.
And yes, normal means fast blow there.

[mac dillard]

Check all the solder joints on the power tube sub board that are part of the bias circuit. Also check your bias voltage. If it is not on the schematic I can look it up. think it is around -45 volts.