Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: blues man on November 30, 2014, 11:45:50 am

Title: 10kl & 50kl trim pots
Post by: blues man on November 30, 2014, 11:45:50 am

Does anybody know what the watt rating is on the 10 & 50kl trim pots Doug sells? I would assume they are probably 1/2 watt.

Title: Re: 10kl & 50kl trim pots
Post by: HotBluePlates on November 30, 2014, 01:06:30 pm

Most likely, they are about 1/3w or less.

It shouldn't matter much, because there is very little current through the pots. It would matter if the trimmer was used to divide couple-hundred volts, but dissipation is probably under 1/6w in a typical bias circuit dividing up 40-50vdc.

Title: Re: 10kl & 50kl trim pots
Post by: blues man on November 30, 2014, 01:45:59 pm

Thanks for the reply. I was thinking of experimenting with the 10kl on the preamp with the cathode bypass cap for tweeking.

Title: Re: 10kl & 50kl trim pots
Post by: HotBluePlates on November 30, 2014, 05:58:41 pm

They should work fine for that, as far as power rating goes.

One formula for power is Voltage²/Resistance. A typical Fender gain stage will only have 1.5-2.2vdc across the cathode resistor.

2.2v²/470Ω = 1/10th watt. Even less for higher resistances.

You don't want to dial the cathode resistor to 0v, so put a 470-820Ω resistor in series with the pot to set a minimum resistance.