I currently have several, older Fender fixed bias amps sitting in the work stable. All have had filter caps, dropping resistors, electrolytics and plate resistors changed. I'm getting ready to start bringing them up on the variac with a dummy load and running them thru the checks.
Bit of background- I have mainly worked with cathode bias hifi amps and so fixed bias is a bit of a thing to me. The amps will see, do varying degrees both studio and road use- so expected to be moved about a bit. Also not using NOS tubes just newer production "matched" stuff. I have bene working around tube amps for several years and am comfortable with the safety aspects so that is not concerning. However, I am a bit confused and at a crossroads when it comes to setting the output tube bias and the method I should take.
Originally I was going to settle for a pricey but easy to use bias probe like the Weber or Eurotubes version. But.. I can't seem to find any for sale online now- at least on the auction sites or even on Weber's main site?
I then thought it may be easier to solder in Dale 1% 1R 1/2w, but it would be a lot of soldering for multiple amps and I haven't been able to find any pictures of a completed output section. I also like idea of the 1/2w resistors adding /some/ additional measure of protection as a fuse. Always helpful!
I have a WES51 that gets up to 850 degrees but it doesn't seem to want to budge those board ground solders even with a wide screwdriver tip. I also don't particularly enjoy working around the output section with their thick gauge wire into those small octal pin holes. Everything is SO tight in there. I'm having a hard time seeing how I'd fit those little 1R buggers in there. Just clip the braid wire to ground and wrap the 1R around the braid? Other end to pin-simple as that? Does anyone have any pics just to give me a reference or a bit of confidence? I searched several of the big search engines but didn't really come up with anything.
The final method I saw was the OT shunt method.
I've read several of the previous threads here and I am not looking for perfection here in terms of matching the tubes. This is a guitar amp after all! I'd just like relatively decent life from the tubes and no redplating or runaway. I suppose back in the day before all this gear and methods were available the EARS, a multimeter and scope were all that were used. So I'm not trying to overthink or overwork myself over this.
It seems like there are several ways to skin this cat. But in terms of long term reliability I'm wondering if the harder/cathode resistor way would be more beneficial? I appreciate anyone's opinions or input on the issue. Thanks!
Topic: Fender amp biasing methods (Read 1531 times)