Hello fellow guitar tone aficionados! If you know me, then you know that I am a total Fender amp geek; my desert island amp is a blackface Super Reverb, and the blackface Bassman, Pro Reverb, Vibrolux Reverb, and Deluxe Reverb probably round-out my top-5 list. Yep, I'm crazy about vintage Fender amps, and, like most folks, I feel the blackface era amps are among the finest amps ever, period. The tweed Fender amps (and browns, too) tend to not have as much solid bottom as I need, and the latter silverface amps just sound a little too sterile and clinical. There are a couple of notable exceptions, see here: Drip Edge Fender Amps , and 1967 Silverface Deluxe Reverb; but for let's assume we are NOT talking about the few rare 1967 drip-edge silverface amps that actually still sport blackface circuitry inside. Right here and now I want to point out the one single most important mod for "blackfacing" a silverface Fender Amp. Ready, let's go!
First I must credit the source of my photos, another fine blog on this same subject from Blueglow.de. If you want to do the work yourself, there is a very good walk-through there. However, the scope of this blog is simply to make you aware of the importance of the mod. WARNING: if you are not well-versed in tube-amp repair, thoroughly educate yourself before sticking your hands in a tube-amp chassis, there IS available current inside to KILL you! Nuff said, that's why I'm going to recommend you take your amp to a qualified tech to do this mod. Here's what you request:
Remove my "balance" pot and give me blackface bias specs, pretty please.
In the silverface era Fender changed the bias supply from a level to a balance control. The balance control allows the tech to match the tubes, but not set the bias level which is very much something that determines tone! I generally change the bias supply to blackface specs because we generally use matched tubes these days!
Here are examples of the bias balance pot in different silverface amps and eras:
Now, this last thought: Like I said, I snagged my pics from Blueglow.de, and he recommends actually KEEPING the bias balance pot but ADDING a bias adjustment pot for sorta a best of both worlds arrangement where you CAN set bias for the desired tone but can ALSO use unbalanced output tubes. I'd be a little wary of using output tubes that are too terribly unbalanced as I'd be concerned they are of poor quality and/or one is worn out and on its last legs, but if you are a cheapskate always looking t save a few bucks on output tubes, it might be wort at least considering, so check out Blueglow.de and also https://robrobinette.com/Silverface_Amp_Mods.htm