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I need help ASAP; Thanks in advance!

7/19/2000 12:09 AM
mitchell	I need help ASAP; Thanks in advance! Greetings all. I'm working on a new homebrew amp and I just finished wiring up the power supply and the output section. The PS is a Hammond 270FX; I'm getting 314V on each secondary tap with my 121V line voltage. A 5AR4 is used for rectification and this feeds a pi-filter (20uf-8H choke-20uf) with the second cap feeding my OT (a Magnequest with UL taps). When testing I'm using an 8-ohm load. The problem is: If I turn on the amp with no power tubes (Philips 6V6GT's) installed everything seems peachy, with around 420V at the first and second filter caps and the same on the plate and screen grid tube pins, which are feed by the UL taps via 470-ohm 2-watt resistors. If I install the 6V6's the voltage at the first filter cap drops to 330V and I'm reading 71V across my 330-ohm cathode bias resistor (currently unbypassed). This is around 215 milliamps through the two tubes, way too high obviously. What could the problem be? Thanks in advance for whatever help you might give. Morris

7/19/2000 12:09 AM

mitchell

I need help ASAP; Thanks in advance!

Greetings all. I'm working on a new homebrew amp and I just finished wiring up the power supply and the output section. The PS is a Hammond 270FX; I'm getting 314V on each secondary tap with my 121V line voltage. A 5AR4 is used for rectification and this feeds a pi-filter (20uf-8H choke-20uf) with the second cap feeding my OT (a Magnequest with UL taps). When testing I'm using an 8-ohm load. The problem is:

If I turn on the amp with no power tubes (Philips 6V6GT's) installed everything seems peachy, with around 420V at the first and second filter caps and the same on the plate and screen grid tube pins, which are feed by the UL taps via 470-ohm 2-watt resistors. If I install the 6V6's the voltage at the first filter cap drops to 330V and I'm reading 71V across my 330-ohm cathode bias resistor (currently unbypassed). This is around 215 milliamps through the two tubes, way too high obviously. What could the problem be? Thanks in advance for whatever help you might give.

Morris

Replies:

Les Do you have the grid resistors inst... -- 7/19/2000 12:25 AM