Tube recitifer simulation resistors

[demonstratedspatulas]

I've read that if you use a resistor in series with the negative output of the bridge rectifier, you can basically simulate tube rectifier sag without the expense of an actual tube rectifier.

The ripple current is 1.5 * the dc current so to calculate wattage we have (assuming 400 mA for a 100 watt amp):

(1.5 * 0.4) ^2 * 150 = 54 watts, if I want to simulate a 5U4GB.

I can get, say, 2x 40 watt wire wound resistors and bolt them to the chassis, but dissipating 50 watts through a resistor in my amp seems a bit ridiculous. It also seems like it would damage the powder coating of the chassis at that point.

Has anyone ever tried to simulate a 5U4 on a 100 watt amp?

My other idea was to just try lower resistances, maybe 50 or 25 ohms. Would I still hear the sag? I've only built amps with silicone rectifiers before and I've been curious about this but certainly don't want to bother with a real tube rectifier.

[Bergheim]

I bolted a 100 ohm 50 watt chassis mount resistor to my amp. At full blast I get 40-50 volts of b+ sag, and it rarely gets any hot. This is on a 50 watt amp. I'd say the same resistor wattage rating as the output of the amp itself is a pretty good rule of thumb.

Check this link out: https://www.google.com/url?sa=t&source= ... 6285896747

[demonstratedspatulas]

I bolted a 100 ohm 50 watt chassis mount resistor to my amp. At full blast I get 40-50 volts of b+ sag, and it rarely gets any hot. This is on a 50 watt amp. I'd say the same resistor wattage rating as the output of the amp itself is a pretty good rule of thumb.

Check this link out: https://www.google.com/url?sa=t&source= ... 6285896747

Nice! It's warm to the touch perhaps but not hot?

Is your chassis powder coated?

How do you like the sound by the way?

Gonna dive into that pdf, thanks for sharing that!

[Bergheim]

Warm but not hot. My chassis is bare steel but I guess powder coated is fine too. Don't forget thermal paste! Tonewise, sag is all about the feel/compression, and naturally it only shows when overdriving the power stage. My next ordrer to mouser is gonna include a 50 and 75 ohm resistors as 100 is a tiny bit on the saggy side for my taste.

[Stevem]

You can use a tube with this set up if you care to.

[Roe]

the weber wz34 seems to use 60R, but the actual resistance of a gz34 will vary somewhat - its not constant. In some amps (e.g. aC30) where the current draw is relative stable this is not big issue

[thetragichero]

the fender excelsior used 270r 7w resistors spliced in between the cathodes of the two rectifier diodes in the bridge and meeting at the first filter cap (wimpy non-center-tapped power transformer so bridge rectifier instead of full wave)
makes the amp spongey enough that a common mod is to jumper them with either a wire or dpst switch

[demonstratedspatulas]

I've decided to try 25 and 50 ohms, that way I'm only running them at 9 at 18 watts respectively. Going to use 25 watt wire wound resistors.

Thank you everyone!