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ehedwr

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Everything posted by ehedwr

  1. If you stick with the rectifier tube just make sure you don't use that Standby switch. Leave it switched on, you don't need it. Your amp will thank you for it. My BC30 is running a pair of EL34's with a solid state rectifier. The voltage did go up so I replaced the 250 ohm 25 watt cathode resistor with a 330 ohm alternative to lower the plate current.
  2. Like others have done I snipped C3, C5 and C6. At first I liked it but later realised something was missing, you lose treble but you lose dimension too. I fitted a triple pole mini toggle switch and wired the capacitors through the switch so I can switch em back into circuit whenever I need. It's like a bright switch. I also replaced R3, R8, R15 and R21 with 1K/1 watt resistors. The GZ34 rectifier is now gone and replaced with a solid state recifier, this however has raised the plate voltage to 450 VDC. I wanted to fit EL34's so I replaced R45 and R46 with 1K/5 watt resistors, popped in a pair of EL34's and it worked fine however with 60mA of cathode current at zero signal I replaced the shared cathode resistor R44 with a 330 ohm 25 watt alternative which is now mounted if front of the fan for better cooling. Cathode current is now 50mA per tube and this amp is running like a dream. The fizz I had with the 6L6 tubes is gone, now I have creamy overdrives and gorgeous cleans. I use a THD hotplate attenuator so channel 1 cranked up gives the best overdrive tone of all. This amp is superb now. I might yet fit another input jack socket and maybe look into building a tremelo circuit and effects loop. But they are considerations for the future and not exactly easy mods to perform.
  3. The standby switch is not needed in this amp. Why? It has a tube rectifier which has to warm up itself before it will allow voltage through to the plates on the rest of the tubes. By the time that happens the rest of the valves are sufficiently warmed up and ready for action. If you have a solid state rectifier fitted like me, use the standby switch. When I do go back to a tube rectifier I'll be fitting some current limiting resistors to the plates to slow down the inrush.
  4. Many older amps didn't need a standby switch because the tube rectifier takes time to warm up and allow voltage through anyway. One thing I'm looking into at the moment is fitting limiting resistors to the rectifier plates which will reduce inrush. Check out the tube data for the GZ34. http://www.mif.pg.gda.pl/homepages/frank/sheets/035/5/5AR4.pdf Most amps don't have limiting resistors and manage fine. Something is very wrong with the design of this amp this amp. I'm wondering if it's the choke not holding back the current flow enough.
  5. I know what is causing the main fuse to blow. It's a design flaw. The rectifier tube pulls too much current on startup and arcs inside causing the main fuse to blow. I've had it happen enough times. Best start procedure from cold is to switch on the standby switch first, then the main on/off switch. The rectifier will allow voltage through more gradually this way and the other tubes wont get full voltage for at least thiry seconds anyway. Other than that replace the rectifier tube with a solid state rectifier designed to fit straight into the octal base. It will bump up the voltage slighlty but will work fine. My rectifier tubes are now very dodgy because of this, they work but the slightest current increase can make them arc and blow the fuse. If you want to stick with a GZ34 rectifier get a new one and it should be better.
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