Dating fender tube amps by serial number part 1

Princeton and Princeton Reverb. Super and Super reverb. Vibrolux and Vibrolux Reverb. By Eric Barbour - Former Vacuum Tube Valley senior editor What the tubes do in most Fender tube amps: The first preamp tube or the first 2 tubes, in 2 channel amps provide the first gain of the guitar signal.

It usually drives the tone control "stack", depending on the model. A low noise, low microphony tube is recommended here. If the amp has reverb, there will usually be a 12AT7 to drive the reverb spring.

This is severe duty and will use up the tube's cathode quickly. This tube need not be low-noise or nonmicrophonic. Some early models used 12AX7s or s for this job, however we still recommend using a 12AT7 here. Reverb amps will also have an additional 12AX7 to reamplify the output from the spring.

Because this tube amplifies the signal from a reverb spring which is inherently microphonic , a really quiet tube is not really needed. However, it should be a 12AX7 with plenty of gain. Fender had tremolo or vibrato on some amps. Both terms mean the same thing--an oscillator makes a low-speed signal that varies the gain of the guitar signal.

If the amp has tremolo or vibrato, it will have at least one extra tube, usually a 12AX7. The last preamp tube before the power tubes is the "phase inverter", seen only in push-pull amps those having 2 or 4 output tubes.

It makes the "see-saw" drive voltages that properly drive the output tubes. It was usually a 12AT7, for the same reasons as the reverb driver above. Fender phase inverters in later amps used a very crude circuit which also provided some voltage gain. This tube need not be especially quiet, but its heater-cathode insulation must be very good.

If the heater shorts to a cathode in this tube, the amp will not work properly. Some earlier Fender models used a 12AX7 or 12AX7 for the phase inverter--recommend a good-quality tube for such amps 12AT7s will usually work as well. The power tubes in almost all Fender tube amps were either 6V6s or 6L6s.

They drive the output transformer, then the speakers. Small amps like the Champ had one power tube and no bias adjustment. Larger amps had two or four power tubes in push-pull, which work like a see-saw -- when one tube is decreasing in voltage, the other is increasing. Most push-pull Fender tube amps have a tube bias adjustment inside, which varies the idling current in the power tubes all at once.

Bias should be adjusted when tubes are replaced. Matched pairs are recommended to keep the amplifier balanced from side to side -- if you amp uses 4 or more output tubes, you can use groups of matched pairs, and you do not necessarily need to buy a matched quartet, sextet or octet.

So long as one tube from each pair is on one side of the transformer, and the other is on the other side, the amp will balance.

It is VERY dangerous to blindly plug different tubes into a guitar amp. If you have a later silver-face or blackface Deluxe amp, the plate voltage will be very high--plugging low-cost Russian or Chinese 6V6s into such an amp is risky. Note: Since this article was written Tung-Sol, Electro Harmonix and JJ Electronics have released 6V6 tubes suitable for high plate voltages making them a great option for these amps.

Many earlier Fender tube amps used rectifier tubes. These were almost always at the extreme left of the chassis, when looking at the rear of the amp. DO NOT blindly swap different rectifiers, some consume more heater power than others and might damage the amp. After , most Fender tube amps switched to solid-state rectifiers, until recent Custom Shop models reintroduced tube rectifiers.

Solid -state rectifiers do not wear out as tubes do, nor can they be replaced by the user. The solid-state diodes used in older Fender amps are rather primitive compared to modern devices--if you wish slightly better performance, suggest speaking to a service technician about replacing the diodes with modern fast-recovery epitaxial FRED diodes. Some early Fender 6L6 tube amps can use any of these types. Finally, meant a special high-quality tube in the past--it no longer means much today.

True NOS s are scarce and costly. If you really want to know the differences, we recommend you consult past issues of Vacuum Tube Valley magazine.

In all cases, if you are not certain which amplifier version you have, do not experiment! You might damage the amplifier and the tubes. See an experienced technician. Deluxe AA, AB blackface. B to B — Harvard 5F10 tweed. H to H — Musicmaster Bass CFA silverface. Princeton 5B2, 5C2, 5D2 tweed. Princeton 5E2 tweed. P to P — Princeton 5F2, 5F2-A tweed. Princeton 6G2, 6G2-A brown.

Princeton AA blackface. Princeton AA silverface. Princeton Reverb AA blackface. Princeton Reverb AA, B silverface. Pro 5A5, 5B5, 5C5, 5D5 tweed. Pro 5G5, 6G5, 6G5-A brown. Pro AA, AB blackface. Pro Reverb AA blackface. Quad Reverb CFA silverface. Reverb Unit 6G15 brown, blonde, blackface. R to R — Showman 6G14, 6GA blonde. Showman AA, AB blackface. Showman AB silverface. Super incl. Dual Professional tweed. Super 5E4, 5F4 tweed. Super 5G4, 6G4, 6G4-A brown. Tremolux 5E9, 5E9-A tweed.

Tremolux AA, AB blackface. Twin 5F8, 5F8-A tweed. Twin 6G8, 6G8-A blonde. Vibrasonic 5G13, 6G13, 6GA brown. Vibro Champ AA blackface. Vibro Champ AA silverface.

Either the factory worker was asleep at the wheel that day or there was a new hire that was still learning how to assemble amplifier circuit boards. I tend to believe that the latter idea has some merit since Fender practically doubled its size after the CBS takeover. Bigger facilities meant more workers with little or no experience.

So, I have compiled a list of speakers used in Fender amps and took some photos of some of them as well. The list, presented below, is based on our actual observations, but is not comprehensive. JBL D-series speakers can generally handle upwards of 60 watts each. A pair of JBL DFs in a Twin Reverb are only seeing about watts each no sweat , but remember that no speaker likes to see square waveforms.

So, driving the Twin with any amount of distortion lowers the power handling capacity of the speaker, which makes any speaker more susceptible to damage… even a high-wattage type like the JBL. Jensen: Jensen was the prevalent stock speaker in Fender amps from through about As the story goes, Leo Fender wanted Jensen to make some changes to speakers and either the speaker couldn't price constraints? That's when ol' Leo switched over to Oxford as the standard speaker though Jensens were still used from time to time.

Just conjecture, but the lack of orders from Fender from - 65 must have hurt Jensen's pocketbook so they hit up the new owners of Fender CBS for some business. These Jensens wear brown and gold Fender by Jensen label and were put into Fender amps beginning in late through about mid Some amp geeks don't like the way these Fender label Jensens sound, but let your ears be your guide.

I think they sound just spiffy. I have included them here because I get a lot of questions about them. They are were often sold as replacements for blown speakers which is probably one reason why the ended up in more than a few Fenders.

The Vibranto LI series speakers had a lifetime warranty and it seems that Jensen went out of the musical instrument speaker business just in time to avoid the claims. All speakers can and will fail eventually just like the hard disk on your computer … remember that. Jensen speaker models denote their approximate power handling capacity and magnet type. The actual power ratings have been published in several books so I'll discuss them in general terms here.

The R, S, and T suffixes denote a low power rating… good for Princetons and Champs, but the R is barely able to handle the power of a Deluxe.

The Q and P suffixes denote a medium power rating. These are especially good for multi-speaker amps up to watts since multiple speakers divide the amp's total output power between them.

Note that it does not appear that Fender used the "P" rated speakers very often. The N and LL suffixes denote a high power rating, with "high power" being a relative term. The P12N, on a good day, can handle 20 watts. It's no wonder that watt Twins easily shredded a pair of them.

Note that Fender did not use the "L" rated speakers but Ampeg and Leslie did. Oxford: Oxford speakers codes work in a similar fashion, but it is the letter that denotes power handling. The higher the letter, the higher the power rating. It is important to note that these are peak power ratings, not RMS power. The RMS rating is more realistic and is usually about half of the peak rating so use that as a rough guide.

The "J" rated speakers are usually found on watt Princetons. The "K" rated speakers are found in reverb and non-reverb Deluxes and in multi-speaker amps up to watts such as the Tremolux and Concert. Champ 25 SE. Concert II. Concert ' Dual Professional. Dual Showman. Fender Fender Head. Hot Rod Deluxe. Hot Rod Deville.

Princeton Reverb. Princeton Reverb II. Pro Junior. Prosonic Combo. Prosonic Head. Rumble Bass. Studio Bass. Super Reverb.