| Author | Message | ||
| hammondd
New Username: hammondd Post Number: 5 Registered: 12-2003 |
I recently bought an F-2B preamp on Ebay and have a few questions; hopefully this will get to Mica, but I'm interested in anyone's input, of course-- Any way to tell the age of the unit? Its serial number is: 903267. The face design is the same as what's currently posted on the Alembic site, so I assume it's not too many years old. Is there a preferred brand of tubes to use? The ones in the unit are unmarked and the previous owner didn't know. Is there a way to get a manual for it? I'd like to understand more about the dB differences between the two inputs on each channel. Can you describe how the Main input on the rear is used? I thought there was a way to use both channels at the same time, but when I plug into the "M," only channel B operates. Is this a problem, or something I'm not doing right? Both channels work fine, independently. I own 2 Alember basses, an Essence and an Epic, by the way. Life if Good! Mike | ||
| peter_jonas
Junior Username: peter_jonas Post Number: 38 Registered: 11-2002 |
Hi Michael, Well done buying an F2-B. They are a lovely preamp. Age is not a factor with these, as the circuit itself has not changed since its first release in the early seventies. Well, early sixties really, as this circuit is virtually (for most intents and purposes totally) identical to that used in the preamp section of a Fender Dual Showman. Today you can still buy early exapmles of the F2-B in perfectly good working order. Cosmetically the unit has changed somewhat, and that is all for the better. In my opinion today's heavy gauge steel enclosure is much superior in all respects to the ones used earlier. I am not quite sure of the year they changed over to this new look, someone else could perhaps help me out here. The circuit itself is simple, not much can go wrong with it. However, you do want to make sure your tubes are in good shape. As far as brands of tubes go, you'll probably hear many different opinions. Most have merits, some more, some less. Here is mine: The tube these preamps use is a 12AX7 (in fact the F2-B uses two of them). It is also called 7025 in millitary circles or ECC83 in Europe. Today, there are not many places that make these (or any) tubes. China, Russia and some eastern European countries like Yugoslavia and Slovakia still make tubes. I have not had too much luck with Chinese tubes, but the Russian Sovtek brand and and the Yugoslavian EI brand are largely reliable. Go get two brand new Sovtek tubes, put them in and listen. These tubes do not cost too much (about $10 to $15 each), but they are reliable and sound very decent. In fact, Alembic fits the Sovteks to the F1-X and F2-B preamps as standard. This should be your starting point. In my opinion, in a bass amp application (the F2-Bs are also often used as gitar or electro-mechanical keyboard preamps, which is a somewhat different matter), they will be at least 90% as good as anything else, and anything else (like a NOS Telefunken ECC803S) might cost you $250 to $300 a pop. You can find plenty of used and New Old Stock (NOS) tubes on ebay. I personally would not buy used ones, unless I knew and trusted the seller. Some brands to look for are Sylvania, RCA or GE from the USA, Mullard from the UK, Amperex from Holland, Valvo, Siemens and Telefunken from Germany, Tesla from Slovakia or Tungsram from Hungary. It is generally agreed that the best ever mass produced 12AX7/ECC83 tube is the "Smooth Plate" Telefunken ECC83. These are no longer made, but you can find NOS tubes on ebay, and they may set you back about $120 a piece, or a perhaps less with a bit of luck. I have got a pair of these in my F2-B, and they do sound nice. But again, so did the Sovteks. The difference is marginal, and I don't know if I could identify them with any degree of certainty in a blind A/B test. Other than the Telefunkens you might like to try an RCA or GE tube, they would cost you about $40 each. I have a soft spot for NOS Tungsram ECC83s, I think these are a very good, rather underrated tube, and you may get these for about $20-$25 each. One that I have not tired yet, but would like to, is a Tesla ECC803s. These are produced today, and apparently are an exact copy of their Telefunken namesake. The ECC803S is a long life, high gain, low noise version of the ECC83, and they are distinguished from their regular brothers (amongst other things) by their gold plated pins. As you can see, you could go on forever spending lots of money buying and trying out vast numbers of tubes chasing that elusive "PERFECT SOUND". On the other hand, you could stick those Sovteks or Tungsrams in, and just keep playing. I think you'll be happy. Keep in mind that your sound is the product of many, many variables in you signal chain. If you are not happy with your sound, chances are it's not your preamp that needs changing. The most important thing is the source of the sound: your instrument. With an Alembic you got a very good start. In my opinion, if you find a bass that you like more than you do your present bass(es) it will be another Alembic. In any case, I got a bit carried away here, but I hope I have given you some info on tubes you find useful. Ultimately let your ears be the judge. As far as the front input jacks are concerned, the one on the left is the higher sensitivity. Through this, your signal goes directly to the grid of the tube (or to that of one of the two triodes in it). The jack on the right goes through a voltage divider first, so only half the signal gets to the grid of the tube. The sensitivity of this input is half of that of the other one, or it is 6dB down from the left one. This one is more for active basses, as its low input imedance (136 kilo-ohms as opposed to the 1 Mega-ohms for the left input) does not really suit passive pick ups well. If you connect a signal to both input jacks (of the same channel) then they will be mixed at equal proportions at the higher sensitivity, and (if I am not mistaken) the lower input impedance. The overall gain of the preamp is about 120 for the more sensitive, and about 60 for the other input. So, if you think in terms of output voltage required to drive your power amp, which would be somewhere around 1.5 volts RMS, then your input sensitivity works out to about 12 milli volts (mV) on the left input and about 25 mV on the right input (within one channel). The jack on the back marked "M" should not be an input. This is a mono output normally, but it might have been rewired by the previous owner to be an input to one of the channels. I cannot comment on this any further without seeing the inside of your preamp. Happy playing, Peter Jonas | ||
| hammondd
New Username: hammondd Post Number: 7 Registered: 12-2003 |
Thanks, Peter. I put in a pair of Sovtek NOS tubes and it sounds just fine. |
