Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: hesamadman on May 25, 2015, 11:00:51 am

Title: Did a resistor swap
Post by: hesamadman on May 25, 2015, 11:00:51 am
After battling a noise with my 30 watt for sometime, I decided to do a resistor swap in the whole amp (well preamp anyway). I originally used metal oxide resistors from parts express. Seems like a good idea right? Metal oxide supposedly pretty quiet components. However I began to question these guys due to the cost. Just under a nickle each (wholesale). Also parts express is known for speaker building components and not so much amp. It was a long shot but I decided to order some metal film resistors from Doug. Changing all my plate resistors. Cathode. And all in between.  Don't ask me why, but the amp was soooo much quieter. Turning the gain at noon you would have had an audibly annoying hum with master set at 2.......well the reduction this made was tremendous. Pretty excited about it.
Title: Re: Did a resistor swap
Post by: eleventeen on May 25, 2015, 01:39:31 pm
Dramatic, huh? It's really the preamp plate resistors that will make the most difference.


I was not aware that you could buy "metal oxide" resistors; I knew you could buy metal oxide varistors and oddball kinds of things. I only knew that for the plain old resistors scattered around an amp, "metal film" resistors were the ones to get. Good to know.
Title: Re: Did a resistor swap
Post by: hesamadman on May 25, 2015, 03:05:43 pm
Metal oxide film rather
Title: Re: Did a resistor swap
Post by: hesamadman on May 25, 2015, 03:06:20 pm
My guess was gonna be plate resistors being the biggest affect
Title: Re: Did a resistor swap
Post by: MakerDP on May 25, 2015, 07:35:55 pm
Quote from: eleventeen on May 25, 2015, 01:39:31 pm
I was not aware that you could buy "metal oxide" resistors; I knew you could buy metal oxide varistors and oddball kinds of things. I only knew that for the plain old resistors scattered around an amp, "metal film" resistors were the ones to get. Good to know.

https://www.tubesandmore.com/products/resistors (https://www.tubesandmore.com/products/resistors)

Metal Oxide resistors are usually used for the 1 to 3 watt range in the power supply or flame-proof screen resistors.

Carbon Comp or Metal Film everywhere else... I prefer metal film too.
Title: Re: Did a resistor swap
Post by: Willabe on May 25, 2015, 11:08:02 pm
Quote from: MakerDP on May 25, 2015, 07:35:55 pm
Metal Oxide resistors are usually used for the 1 to 3 watt range in the power supply or flame-proof screen resistors.

Yes, metal oxide (MO), to my understanding, for higher wattage than metal film (MF).

I think out of the different types of R's being made that MF is the quietest, with MO being the next quietest. Carbon comp. (CCR) being the nosiest.

It doesn't make sense to me that MO R's were a hiss noise source? But maybe they were 'cheap' badly made MO R's?


                        Brad     :think1:         
Title: Re: Did a resistor swap
Post by: hesamadman on May 26, 2015, 05:59:27 am
Well most certainly cheap. That's why I used them. Ha.