Have you ever noticed how your reissue BF just doesn't have that old tone you really wanted. It sounds great but its just missing that little thing that makes that amp sound "THAT" way....
When dealing with Fender Amps for that issue any amps it is good to mind a couple of things:
1) Tone coupling caps foils should point up stream of signal flow. This means in most instances the foil goes to the high DC voltage side or from where the signal is coming from in the circuit, closer to the input. In a fender Black/silver face amp only the .01uf leading into the PI will be reversed facing from the other coupling caps. This is the 3rd from the left looking at the amp in standard Layout Diagram orientation.
2) Tone caps. If you have an older amp that doesn't have the old blue molded Coupling caps a change will make a big difference. I have bags of Moulded blue caps that I re lead regularly but for new builds for some pro's I have settled on the Zoso Blue caps. $'s for donuts they sound the best and almost in distinguishable from the originals. You need to break them in. Why the manufacture doesn't do this burn in I don't know but you will notice over a 10hr playing period that the get warmer , more open and will make your BF sound right
3) Heater circuit phase.. Taking notice of your heater circuit wiring is very important to make a very quiet amp with less chance for tone sucking interference. If you look at the diagram it is unimportant which leg starts out as phase A or B but keeping them lined up as in the diagram is. If your tubes are in and you heater wires are connected to the Power Transformer you will be unable to verify continuity with a tester so remove these obstacles. This will keep heater noise to the smallest possible sans going to DC heaters. The subsequent induced AC noise should cancel not add with this configuration. Note that the wires are still run as twisted pairs above the tubes.
4) Tubes: There is a place for Mojo and there is a place to just forget about it.. These are my observations and the confirmed observations of 2 of the best Amp techs I have ever seen. These are sort of the secrets for setting these amps up and this is the first time I have ever talked about it in a forum. I don't htink these other guys have either.. At least I have not seen.... so
For your First preamp tubes NOS RCA Grey plates 12AX7A's are the way to go if you never use the normal channel don't waist money on it .. Throw a EH 12ax7a in there...
Reverb Driver should be an RCA 12AT7 (Mill version RCA 6679 is the same thing maybe better). This tube is being driven like a power tube . Most every other tube will take a dump short term being driven that hard. This will last. They are not that expensive. If you put one in you will not change it for a very long time.
Reverb Recovery you can use any good tube. if you have a monophonic RCA 12AX7A go for it but a an EH, Ei, Groove tube all work here..
Phase inverter: GE12AX7 Grey... Most musical you will find. Makes a big difference.. For your tweeds the best thing you could ever do to the amp is to put a NOS Long Plate Black RCA 12AX7 as your PI Just magic
Vibrato tube: The cheapest most micro phonic piece of crap you have makes absolutely no difference.
power tubes.... I have a stash of older STR tubes Plenty of GE , Phillips and RCA 6l6's For 6v6 I happen to have a bunch of old Tungsols branded as IBM and older RCA Black plates but I put EH and the new New sensor Tungsols in most new builds. They are cheep and very musical.
Don't believe the rectifier nonsense in the GZ34 world.. Just get one that is on spec.. 5y3's are easy to come buy NOS cheep so buy them, 5u4's buy the eh don't spend big coin..
5) WIre and boards...if your amp has that shitty stranded wire from the early 70's swap it out! these amps have boards that look waxy too. Definatley lift all components off the board. They used some really crappy material that tends to take in moisture and develops a capacitance. . You can see voltage on many of these boards. even if you don't they sound like crap. Yes the boards sound horrible. The worst of them are found by using your DMM. Put the black lead to your ground point at the PT and with the red probe read the voltage around the eyelets with the power supply plate resistors. If you see any voltage on the board near the eyelet you should most definitely make sure no components are laying on the board... Better yet swap out the main board or sell the amp and get one without the problem... These older amps have had usually seen mods and Ahab and the blow torch have most likely had their way with the main board. Take out the crews holding the board to the chassis and slide the backer board out.. Blow out with air under the board in the chassis. Wipe down the backer board with deoxit and clean it good .. Scrub it with steel wool even. make sure if you do this that you wipe it very clean with a cloth so as not to leave any metal hairs on it. There is usually big time oxidation on these and the cleaning removes it and any stray partials that give your amp those ghost crackles and fizzes. Many of you mechanically/ vibration based problems are here
6) Tube sockets. Tighten them with a sharp pick. Loose tube pins cause a lot of havoc and can lead to arcing and ghost notes. use deoxit on them.
