Hiwatt DR504 clone build - burning power circuit resistor

[eahudimac]

Hi. I just completed a DR504 clone. Upon powering up with no tubes installed, the 220K resistor on the power circuit filter cap instantly burns up. The only components between it and the power transformer are the rectifier diodes. The wiring diagram is attached. One thing that is different are adjustable bias pots for each tube and test points. Any idea what might be causing this?

[martin manning]

Is the value correct, 220k ohms?

[eahudimac]

Yes, I checked the resistor prior to sautering in. It was very close to 220k ohms.

[sluckey]

Can you verify the band colors on that resistor and the other one soldered to the other cap? My monitor thinks the colors 'may' be red, red, brown, silver.

[pompeiisneaks]

agreed, that third band should be yellow, not brown, if it's brown, its 220 ohm and that would burn up fast at that voltage.

~Phil

[eahudimac]

Yep, it's brown - 220R. Thanks for noticing that! Will have to order the 220Ks.

[sluckey]

I highly recommend using a two or three watt metal oxide resistor for both of those 220K bleeders. For sure, don't use 1/2W carbon comps.

[JD0x0]

I highly recommend using a two or three watt metal oxide resistor for both of those 220K bleeders. For sure, don't use 1/2W carbon comps.

This. Carbon Comps are probably the worst choice for power applications. They drift, they crack, they absorb water, they're generally not very reliable. There's no advantage using them there, even if you believe in the 'Toan Mojo' of CC's you don't get it using them as bleeder resistors. Plate resistors will be effective if you want that 'resistor distortion' Also worth noting that I believe Hiwatts often used carbon film, not carbon comp.