by Greg Gagliano

Copyright 2001, 20th Century Guitar Magazine

Yes, I know… it’s been exactly two years since the last installment in this series. Before we get into the amp info, let me give you an update on what’s been going on since I’ve been getting a lot of e-mail asking when the results of the research is going to be available.

First, we (Devin Riebe, Greg Huntington and myself) must collect enough information to be able to date amps by serial and determine production totals. "Enough" means an adequate amount of information to identify trends with reasonable certainty. Sadly, the majority of information we gather does not have any details about possible date of manufacture (pot dates, transformer dates, tube chart date codes, etc.) and without this important info, the research takes longer.

Second, we are very dependent on information sharing. Devin, Greg and I do collect data on our own, but the research goes much more quickly when we receive information from other sources, i.e. – other people. And it’s not always easy to collect data ourselves. Some stores and dealers at guitar shows are very happy to let use inspect their amps while others go ballistic and show us the door. Some collectors send information, others, upon first contact, run away to their secret underground amp lairs never to be heard from again. But we persevere through thick and thin.

This brings us to another topic which I will briefly mention. Many, many nice people from the United States, Canada, South America, Europe, Australia, New Zealand, and Japan have contributed information to our research and we are extremely grateful to all of you (and you know who you are dah’lings). I try my best to answer each and every e-mail that I receive that either requests information or that submits info for our research. Sometimes my answers are very short, but that’s usually because I have a lot of other e-mail to read and answer. It’s not because I’m trying to brush any one aside.

Occasionally, we have to deal with mean people who do not wish to contribute data as they feel our research is a one-way street. Honestly, I don’t understand why they the bother writing if they don’t want to contribute. Just don’t contact us, it’s that easy… sheesh. I find their rhetoric tiresome, but as the authors of the Ampeg book and I discovered during our Ampeg research, mean people are just part of the game. Ironically, it’s the mean people who most often ask to see our results – a one-way street, their way! Thankfully, the nice people far outnumber the mean people and I again want to thank all the nice people for their support and encouragement as well as for the information they provide.

Third, this is hard work. I could probably earn a Ph.D. from this project. Sometimes we need to take a break and taking a break means not making any progress. We don’t get paid for this and we all have day jobs. This is a hobby for us and a labor of love… or insanity, take your pick.

Lastly, during the course of our studies we’ve come across several complicating factors that have slowed things up. We’re are more frequently encountering "parts amps". As with vintage Fender guitars, Fender amps (which have lots of bolt-on parts) are being modified to make a less desirable amp (silverface) into s more desirable one (blackface). Most of this are really easy to spot, but we still have to weed through this "parts amps" to figure out what they are or aren’t (be careful out there!). As mentioned in previous installments in this series, the majority of Fender amps are serialized by model and/or chassis type. Many of these serialization schemes changed within a given model. Also, there is some duplication of serial numbers for a given model. I will go into the details of the serial number systems in the next article, but needless to say, it makes thing much more difficult for us.

If you would like to contribute information to our research you can do so by e-mail ( All the info is entered into our database anonymously and we don’t keep records of who sent what info.

Also please note, thanks to Mr. Gearhead (see below), we are no longer collecting data for any Fender tube amp made after 1984, except Reissue models (we still want info for those!). Solid state amps were, and still remain, excluded from our research. That means we don’t need info for models such as The Twin, Pro Jr., Blues Deluxe, Sedan deVille, etc. But we do want info for the ’59 Bassman, ’63 Vibroverb, ’65 Twin Reverb, ’65 Deluxe Reverb, ’63 Reverb Unit, Custom Vibrolux Reverb (not a true reissue, but what the heck… we dig it) and the newly released ’65 Super Reverb. Call us vintage snobs, but we gotta draw the line somewhere.

For those of you with "modern" Fender amps (tube or solid state made after 1989) or Fender reissue amps, you can go to FMIC’s "Mr. Gearhead" web site ( which now explains how to date these amps based on codes and serial numbers. We cracked the reissue amp code here first (kudos to us, see TCG Nov. 1997), but the Mr. Gearhead site is very convenient.

Now that we’re up to date, let me pass along some interesting tidbits of info that have surfaced in the last year or so.

There are some silverface Twin Reverbs from circa 1970 and Vibro Champs from circa 1973 without an "A" prefix in the serial number (I hate when that happens). Several Twin Reverbs from late 1971 (specifically October) have been observed with master volume chassis holes, but with conventional faceplates. This would indicate that FMI was already thinking about the change to the master volume circuit in Fall 1971 and probably even earlier.

Regarding model numbers, the model number for the Super Six Reverb is CFA7106 and the model number for the Quad Reverb is CFA7104. It appears that the last digit refers to the number of speakers. Since these model numbers are for the master volume models which shared the same chassis and circuit as the master volume Twin Reverb, I have to wonder if the model number for the master volume Twin (2x12) would be CFA7102 and the Vibrosonic Reverb (1x15) would be CFA7101. I haven’t yet found the model numbers for these amps with the ultralinear circuit. The "D" suffix in the model numbers for the Dual Showman Reverb (TFL5000D) and Bandmaster Reverb (TFL5005D) denotes an amp for Domestic sale. Those with an "X" suffix, such as TFL5005X, were for eXport sale.

And speaking of export amps, I have several reports from Sweden that Fender export models from that country do not have the usual multitap power transformer with selector switch on the back of the chassis. Rather they are hardwired for 220V to meet the Swedish equivalent of U.L. approval. Another interesting tidbit is that Fender amps may have been distributed in Sweden by Hagstrom.

One frequently asked question I receive is "What is the difference between the AA763 and AB763 circuit for a Super Reverb (or Twin Reverb or Deluxe Reverb)?" For those without access to schematics, here are the differences:
Tone Cap
.033 uf cap
.047 uf cap
4.7M resistor
3.3M resistor
56K resistor
100K resistor
Phase Inverter
27K/100K resistors
22K/82K resistors
Grid stoppers
1.5K resistor

The most important difference is the addition of the grid stoppers (safety first!). The only major difference in tone between the two circuits would be attributable to the different tone caps (.033 vs. .047). The .033 cap would yield slightly more midrange, but I don’t think it would be very noticeable.

For some models like the blackface Concert, there was no change in phase-inverter resistor values, and no changes in tone stack cap values (fascinating!). And for other models, the tone stack did not change from .033 to .047 uf, but rather from .033 to .022 uf. The Bandmasters also saw no change in tone stack cap values between the AA763 and AB763 circuits. The "universal" changes do seem to be the oscillator circuit, cathode resistor change from 56K to 100K, and the addition of the 1500-ohm grid stopper resistors.

Did you know that early blackface amps (1963) do not have white silk screening around the bright switches? It’s not certain when Fender added the white rectangle around the bright switches, but they are there by early 1964. Whether this was added before the end of 1963 is not known (yet). This feature would have been phased-in at slightly different times for the different amps as faceplates were ordered and used in somewhat different amounts and at somewhat different rates for each model.

Some general information about cabinet construction: solid pine, finger-joined cabinet construction from 1946 to circa 1972. An interesting feature on the tweed-style cabinets is the use of a dowel reinforcement in the top on either side of chassis. You can’t see the dowels unless the tweed covering is removed, but this reinforcement prevented the wood from splitting due to the weight of the chassis.

Baffle boards were made of plywood from 1946 to 1962. Particle board (some call it MDF – medium density fiberboard) baffles debuted in 1963 and were used through the early 1980s. The baffle board was removable on amps made from 1948 to about 1972 and glued-in thereafter.

From circa 1972 to the early 1980s, the cabinets were no longer made from solid pine boards, but cheaper laminated, multi-piece pine boards. Each side of the cabinet was made from several pieces about three or four inches wide, glued side-to-side, to make up a plank the depth of the cabinet. These laminated cabs were not finger joined, but rabbet joined. The baffle board on these rabbet joined cabinets was mortised into the sides and bottom (i.e. – not removable) to hold the whole thing together. That’s why these post-1972 cabinets have the grill cloth stretched across a frame that is attached by a velcro-like system to the baffle. CBS almost certainly went to this construction method to save money, though at the expense of overall quality.

And with Fender, there are always exceptions to the rule. I have received reports of some pre-CBS blackface amps with one or more sides made from a multi-piece board. As well, I have received reports of some particle board bottoms used in master volume-era silverface amps.

I’m often asked if the marking on the inside of the cabinets are date codes. Sometimes date codes are ink stamped on the inside of the cabinet (mainly blackface and silverface amps including the piggyback speaker cabs), but those handwritten numbers you see in wax pencil or lumber crayon are actually matching marks. As a worker would through a run of cabinets and fit baffles to each one, he would mark the cab and baffle so they could be "married up" again after the baffle was grilled. The cabs were probably numbered sequentially within the production run. The number did not have any relationship to a particular employee though Sam Hutton is known to have marked the cabinets he assembled (usually in yellow lumber crayon) with an "S" superimposed over an "H" which looks like a $ with two strikes instead of one.

We’ve received some interesting reports about some oddball amps. The first was a 1960 brown Super Amp. The latest date code on it indicated 30th week of 1960 and the circuit and layout were neither 6G4 nor 6G4-A. This must have been one of those "Leo messed with it" amps that Forrest White speaks of in his book. This circuit is unique and transitional - part 6G4 in places, part 6G4-A in places, part "unique experimentation" in places.

An October 1963 Deluxe Reverb was reported with transformers (all Schumacher) all dated to mid-1963, except the reverb drive transformer which dated to December 62! The tube chart indicated the AA763 circuit, but there were some very strange original resistor values inside. Specifically, the reverb drive tube's cathode bias resistor was a 1K, 1-watt, instead of the normal 2.2K, ½-watt. The tail resistor in the phase inverter was 6.8K, the plate load resistors in the phase inverter were 47K and 56K instead of the normal (for AA763) 100K. The bias feed resistors were 68K instead of the normal 220K, and there was a disc ceramic cap on the board connected between the phase inverter plates. The ceramic cap is more commonly found on brown and blonde amps to prevent parasitic oscillation.

Some amp techs have observed examples of blonde and blackface amps with power transformers without center-tapped filament windings. These amps are usually the ones that have "hum" problems if they don’t have 100-filament resistors added. Somewhere along the line Fender went to a center-tapped filament winding and no 100-ohm filament resistors. These amps could be modified simply by lifting the center tap, and installing the 100-ohm resistors in the usual place on the power lamp socket. If a filament in a tube shorts (happens most often in power tubes) it is a lot cheaper to replace a 10-cent resistor or two, than an $100 power transformer.

Fender’s sudden transition from cloth wire to thick PVC wire (in pastel greens, white & yellows) is well documented by anyone who has ever pulled a chassis. Sometime in late 1968, the cloth covered wire went away. However, several amps from the late ‘60s (non-reverb Princeton, Vibrolux Reverb, Bandmaster Reverb, and possibly a Deluxe Reverb) with oddball wire have been reported. The Princeton Amp was an early-mid 1969 model entirely wired (factory original & stock) with thinwall, 22awg irradiated PVC (IPVC) wiring. IPVC wiring is usually found in electronics like computers, not lo-fi amps. Keep your eyes peeled for wire with very thin, cream to yellow insulation. It’s likely IPVC.

Scanning a few internet discussion pages, I’ve noticed quite a bit of misinformation going around regarding Fender tube amps mainly from people who haven’t studied the available published literature on Fender amps, i.e. – they haven’t been reading these articles in TCG. The good thing is that the misinformation is often corrected by someone who is knowledgeable. One of the most common topics that falls into this category is early silverface amps. Here’s a very quick summary that may be helpful: the earliest silverface amps were made in 1967 not 1968, not all "drip edge" silverface amps are from 1968 or 1969 (they could be from 1967), not all "black line" drip edge silverface amps have the blackface circuit except for Vibrolux Reverbs, Deluxe Reverbs, Princetons, Princeton Reverbs, Champs, Vibro Champs, and Broncos.

I’ll leave you with a bit of juicy info, namely, some preliminary production estimates for several random amp models. This info will be further refined and presented in a future article (and y’all can hardly wait, I know).

Bassman (blonde) – 12,000 units

Princeton Reverb (blackface) – 19,000 units

Tremolux (blackface) – 8,000 units

Vibrolux Reverb (blackface) – 10,000 units

Vibroverb (reissue) – 6,000 units

Special thanks to amp tech guru and fellow Jersey Boy, Mark Norwine at Carlson Amplification Inc., and Gregg "Portaflex" Hopkins at Vintage Amp Restoration for contributing interesting and fun facts to this series.

About the author: Fender amp guy, Greg Gagliano, can be contacted by e-mail at

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