While I'm awaiting the proper time to get after my Jayphat experiments (when fewer are around to disturb), I thought I'd post about the my last amp acquisition. My good friend, Craig Watts, somehow gets his hands on some remarkable vintage amplifiers (I'll explain my relationship with Craig when I get back to my education posts). We were talking one day about one of his two '65 Super Reverbs and he was asking if I would take a look see and determine why it sounds like a race car when it was flipped off standby. I told him that it was most likely out of my realm of expertise, but I'd look it over. I did and it was beyond my scope of experience, so he took it to a real tech--who fixed it. While we were at our discussions, though, he mentioned a little Sear 5XL amp that he said I could have if I wanted to mess with trying to fix its noise. He took the amp in a trade with his motocross motorcycle. The trader said that the amp worked fine. NOT! He found out real soon that amp emitted nothing musical at all--just a loud a%$ huuummm. Since he didn't want to mess with it, I reluctantly accepted the gift.
Research told me that the amp was one of those power transformerless amplifiers that can basically shock the pee-waddily-doo out of you because the chassis has the potential to become hot with live AC. Since us harp players instrument of choice involves placing a microphone in very close proximity to our lips with the cord plugged into an amplifier, then one that has a zap tendency could pose a problem. Seems that as long as internal components are up to snuff, then the problem is non-existent, but capacitor failure can be a hair raising experience.
I gave the little dude a new home and went about ordering the tube compliments, resistors and necessary capacitors with the intention of a complete re-work. The tubes were those found, back in the day, in radios that were designed to work without power transformers. The power tube was a 50c5, preamp 12au6 and the rectifier 35w4 and that was that. The amp has an output transformer and a filament transformer.
The Sears 5XL was also available in a solid state model, but the tube model is very similar to the Silvertone 1430 and the old Silvertone/Sears amps in a guitar case models. This one sports a 6" alnico speaker of unknown variety, but looks to be original. I found a website with very specific modification details of a 1430 at: www.clarkhuckaby.com/AmpMods/Silvertn.htm It sheds a great deal of light on these types of amplifiers.
It seems that the main safety issue involves adding an isolation transformer to keep the chassis isolated from the power supply. My research led me to decide upon an outboard/standalone isolation transformer that I found on eBay for $20. It is pictured above and is a Hammond 171C and I can simply plug any amp I wish to into it. It may make more sense to install one in the amp itself, but since I ran across this one, I figured I could put it to use. It can be used to plug in amps that are in the process of being worked upon and provide for a safer situation there. Also, I have no intention of replacing the 2 prong plug on this amp because what I've found is that doing so with these amps is a sticky trick. The Hammond will intervene between the amp and my lips--I think.
Reworking the amp was cheap and didn't take long and it all worked. It makes a great little practice amp for the homestead. I'm pretty sure that it puts out a couple of watts of power at the most and has been tolerated around here when I crank it up. It saturates with distortion early on the volume knob and reaches its volume peak at about 1/2 wide open. After that it just distorts more and get a little murky. So, I can sit with my Ipod stuck in one ear, crank up the 5XL and get away with a little amplified practice (for awhile). Anyway--