'Blackfacing' that Fender (Silverface) Amp
It’s easy enough to ‘blueprint’ an old amp design - in this case ‘Blackface’, but there are some other ‘little’ things you should pay attention to. I start with the power supply and make sure the electrolytic filter caps are fresh, or new. I also prefer to use Sprague blue ATOMs here. 2x100uF @ 350V (before the standby switch), and for the 3x 20uF I use the Sprague blue ATOM 500V. I always check the 4 resistors in the ‘Doghouse’ as well - I’ve only found one of the 220k resistors bad when one of the large caps have blown up…. but, I religiously change the other resistors (between the 20uF caps) to fresh 2 watt, metal film (usually NTE flameproof) 1K and 4.7K resistors and mount them about ¼" of the ‘board’.
NOTE: I check ALL the electrolytic caps in an amp, cathode bypass, and bias board cap as well, with a ‘Capacitor Wizard’ for ESR (Equivalent Series Resistance) (URL: http://www.awiz.com/cwinfo.htm) This piece of test equipment WORKS, and I wouldn’t be without one! …I fixed 5! amps that were in the ‘dog pound’ the first day I got this! BUT, always remember to drain the electrolytics in ANY amp - that way YOU don’t get shocked, or killed, and it doesn’t damage this wonderful piece of test equipment.
The next thing I do is make sure ALL the tubes that are going to used with a particular amp are THE best. For this I check the tubes using a Hickok 539C, a Maximatcher (for matching power tubes), and a Geo.Kaye Small Signal Tube Checker, to test each triode of a preamp tube for noise, gain, output, and micorphonics (there’s NOTHING else like it out there, and unfortunately they’re not made any more…). The George Kaye tube checker was used to test almost 300 12AX7s for the Vacuum Tube Valley 12AX7 shoot-out in Issue 14. I’m ‘anal’ about tube quality, and ANY of my customers will tell you that….
Next I pay attention to what the tube plugs into - the socket. I retention the rectifier and power tube sockets, and clean ALL the sockets with compressed air, to blow out any foreign substances, and clean them with Caig DeoxIT D5.
NOTE: I also check the heater wiring at this point - yep, it’s important! Have you ever had an amp that hummed or buzzed, and everything ‘seemed’ correct? I’ve found early on that the heater wiring HAS TO BE ‘uniform’; one leg going to pin 7 on ALL the power tubes then on to pin 9 on ALL the preamp tubes. On the other leg, going to pin 2 of ALL the power tubes, and pins 4&5 on ALL the preamp tubes. THIS, I found, will help dramatically with hum and buzz in a Fender amp (since we’re talking about Fender amps here being ‘Blackfaced’)
The next area of the amp I concentrate on is the Tone Stack; this is very important to ‘shape’ the ‘Tonality’ of the (ANY) amp. I use to use decade resistor, and decade capacitor boxes to ‘tweak’ the tone stack for optimum ‘performance’. I found that WAY too ‘anal’ and just ‘ran with what sounded the best’ to me. I happen to like a .1uF, .022uF, and a Silver Mica 250pF for the tone stack combination - this, to me, is the quintessential tone stack for a BFSR - and what sounds THE best in my ’65 and ’66 SR….
I also prefer the Cloth Single Strand wire that Fender use to use…. You bend it - it stays, and you don’t get as much ‘cross-talk’ with the wiring as you do with the ‘70s ‘plastic’ wiring Fender used….. so, if I change any of the wire that’s what I use.
The coupling cap going into the Phase Inverter is quite important as well. I use a .001uF cap here instead of the later .01 - you can really tell the difference if you ‘push’ the amp….
Speaking of Caps - I prefer to replace ALL of the ‘Chocolate Drops’ with Sprague 715P Orange Drops. THAT brings me to another interesting area - the coupling and tone caps. Have you EVER wondered WHY certain amps sound a LOT better than other amps - and this with the same speaker, tubes, and settings??? I always wonder the same thing, until I read an article in VTV about ‘Signal Capacitor Polarity’. This was in Issue 11, and pointed out there is an Inner Foil, and an Outer Foil to all ‘non-polarized’ caps. I thought it was just ‘AudioPhile Snake Oil’ until I experimented with some caps and paid attention to their ‘orientation’. I have a webpage describing this: http://www.unclespot.com/sigcap.html
The last thing to having an amp sound it’s best is to clean it. Yes, dirt gets into potentiometers, tube sockets, and jacks - this will make pots ‘scratchy’, sockets arc, and jacks non’conductive. You’d be amazed at what a good cleaning will do!
Other than that I pay attention to how the BIAS is set; I use the Transformer Shunt method to BIAS. WARNING! If you do this wrong you can seriously damage your amp, and/or KILL YOURSELF! BIAS is like setting up a carburetor on an engine so it idles correctly, and when you go to pass another vehicle on the highway you have the correct ‘power band’ to do it. You can BIAS a bit on the ‘cold side’ to make your output tubes last a bit longer, but your tone might be ‘anemic’ and ‘thin’. If you set it on the ‘hot side’ you’ll break up earlier, your headroom will be a bit less, and your output tubes will NOT last as long….
One of THE biggest ingredients in your TONE 'chain' is speakers. If your speakers don't sound good, guess what? Yep, it doesn't matter how good the amp, or guitar sounds..... The speakers are what you HEAR - they deliver the signal and convert it into 'sonic waves'. This could be another page onto itself, but I just have to say "Do NOT scrimp on speakers! Buy the best you can afford. Your amp will sound it's optimal with good speakers."
This is just a brief overview of some of the things that I’ve done with Fender amps for a l-o-n-g time. It’s much more to me than a ‘job’ - it’s a passion, and the love of ‘TONE’ that drives me. It sure ain’t for the money!
Ron (Uncle Spot) Veil
Also visit my LINKs page: http://www.unclespot.com/USlinks.html
and AMP INFO page: http://www.unclespot.com/AmpINFO.html