ASK SKIP
REGARDING USED BLACKFACE AMPS... � Skip Simmons
Hello Skip,
Regarding Used Blackface amps: Sometimes we see them for sale, but they are robbed and gutted of the components that make them so desirable. So a couple of questions: A) Besides transformers, are there any specific caps and resistors to look for? For example, I always look for the dark blue caps, but those may not have been factory on“ Champs.” B) Do you recommend any resources that would illustrate“ factory Blackface boards”? I can ' t read schematics so I look for colors and shapes like a first grader. It works for me... Cheers, Billy
It is true that many blackface amps have received less than sympathetic repairs and modifications. When the DIY tube amp craze started heating up, complete“ re-capping” and capacitor“ upgrades” were promoted by many authorities as essential for good reliable performance while many, many modifications were touted as“ improvements” over the original circuits. When I started back in the eighties, old amps tended to have either minimal,“ quickie” repairs by radio / tv techs or were completely untouched. Now I often see old amps( especially Fenders) with lots of capacitors and other components that have been recently replaced.
Now to your question. I would say that original coupling and tone caps are the most important. Notice I didn’ t say filter caps or other electrolytics. I don’ t believe that competent replacement of these caps significantly harms the tone of a vintage Fender amp. The darkblue“ molded” caps are one of the bestsounding coupling caps ever made and have the added advantage of excellent reliability. Many vintage caps are prone to“ leaking” DC voltage which causes bias problems and a muffled tone. The blue caps seem almost immune to this problem, which is another great reason to leave them in a vintage Fender. The smaller disc capacitors also rarely fail, and the common practice of replacing them with silver mica caps changes the tone of the amp quite a bit.
Resistors are very important as well, especially those in the signal path. Since they rarely fail and are easy to check, there is no reason for mass replacement, but I remember having a customer bring in a beautiful‘ 62 Concert with every( yes, every) capacitor and resistor in the entire amp replaced with Radio Shack parts. What a shame. One exception here would be plate-load resistors. Original carbon types can cause crackling, hissing, and other noises, so replacement on“ gig-ready” amps is common.
One more issue that is lurking behind your question is very important and concerns quality of workmanship. Poor soldering is one of most common problems I see, and if your amp is full of cold solder joints they will eventually cause noise and other intermittent problems.
Since it is good to be skeptical, some of you may wonder how I have come to my conclusions. Actually, they aren’ t really my conclusions, they are the product of servicing a lot of amps for a lot of people. The bottom line is that many, many of my customer’ s favorite Fenders have nearly all of their original coupling caps and resistors, and a look at the vintage amp market will show that original amps are generally more expensive and better investments.
You can find great pictures of original blackface part boards on the Internet and in books. I believe the Dave Hunter and Aspen Pitman books show quite a few, and I am sure there are other books and resources as well. This makes it fairly easy to learn what to look for, but I would encourage everyone with a real interest in vintage amps to learn a bit about schematics. Start with the tweed Champ schematic; except for special effects like reverb and tremolo, every single tube amp ever made uses the same basic building blocks of preamp, output stage, and power supply.
34 Nov � Dec 2016 CollectibleGuitar. com