Dating Fender Tube Amps By Serial Number, Part 2
by Greg Gagliano

Copyright 1997, 20th Century Guitar Magazine.

It's been about 6 months since Part 1 of this series was printed so I thought it would be a good time to give an update on the Fender amp research that I am doing along with Devin Riebe and Greg Huntington.  First I would like to thank everyone who responded to our request for data as outlined in the initial article that was printed in March 1997 issue of TCG.  Most notably, I'd like to thank Jeff Lacio for his contributions to our research.  Jeff is an amp tech who specializes in Fender amps, i.e. only Fender amps, and single handedly has submitted well over 250 very complete sets of data.  Despite the heroic efforts by Jeff and other readers, we still need more data, so please keep it coming.

In the meantime, we have discovered many fascinating factoids about Fender amps and we'll probably learn a lot more as our research continues.  Here are some examples of what we've found so far.

Early silver face amps:   The silverface amps appear to have been introduced as early as April 1967 (yes, April!) and by the Fall of 1967 the conversion from blackface to silverface cosmetics was completed.  The early silverface amps can be identified by the aluminum trim strip around the perimeter of the grill, the silver and blue grill, and black vertical lines silk-screened onto the front of the control panel.

The aluminum trim was retained through late 1969, though we speculate a few early 1970 amps may have had the grill trim as well.  If anybody has a 1970 amp with trim please let us know!  Two types of blue and silver grillcloth were used on the early silverface amps.  The first type (1967 - early 1968) had no silver metallic threads and the second is the more familiar cloth with the silver metallic threads and a much greater texture or thickness than the first type (mid-1968 onward).  The black vertical lines on the control panel were discontinued by May 1968 on most models, but we’ve seen a Bandmaster and Bassman from 1969 with them.

Interestingly, some silverface amps from early 1968 have 16 inch tilt back legs with serial numbers on one or both legs.  Tilt back legs with serial numbers were used only on the speaker cabinets of piggyback amps.  One of the legs on the cabinet would have the number while the other would simply be stamped with "Pat. Pend."  In 1967, CBS Fender discontinued the small cabinet design Bassman and Bandmaster an introduced new, larger cabs without legs.  Apparently, Fender had a surplus of 16 inch Bassman/Bandmaster tilt back legs with serial numbers on them.  Rather than waste them, they were used on combo amps such as the Twin Reverb and Pro Reverb.

Although the cosmetics changed, the circuits remained unaltered from the blackface circuits on these early silverface amps.  The date of the change from the blackface circuit to the CBS silverface circuit was dependent on the model, but most of the amps that were modified received the circuit change by mid-year of 1968.

Another interesting feature of the silverface amps is the change in chassis dates.  Many blackface amps were stamped with a date code on the inside of the chassis.  These read something like T020366 or F034267 where the "66" and "67" denote the year and the "03" and "42" denote week of the year.  This system was continued on the silverface amps, some of which have the stamp on the underside of the chassis (where you can see it easily) in addition to the stamp on the chassis interior.  This is very useful information in the absence of a tube chart or lack of a date code.

In the late 1970s and early 1980s, the chassis date stamp became more cryptic.  For example, a chassis stamp of 1831 must be read backward to reveal the date, in this case week 13 of 1981.  If you see a chassis stamp and you don't have any other dating info, please send it along with the serial number and model name to us, thanks!

Mistakes:  Errors happen and Fender was not immune to them.  Previously we discussed the "OA" date code stamped in dark green ink on January 1966 amps.  The code should have been "PA," but the production staff forgot to change the year on the stamper.  Well, I was contacted by one Chicago reader (I'm so embarrassed I forgot his name!) who has a February 1966 Deluxe Reverb stamped with "OB" in dark green ink (should be "PB").  This indicates that the production team didn't catch the error until early February 1966 at which time they switched from "O" to "P" and from dark green ink to black ink.  Again, if you have an amp with an OA or OB date code you have to look at the front and back panels to see if it says Fender Electric Instruments (in which case the "O" denotes 1965) or Fender Musical Instruments (the "O" is a mistake and the amp is a '66).

And speaking of back panels... the back panel of our reader's Deluxe Reverb states "Division of Colombia Records Division" instead of "Division of Columbia Records Division."  Note the spelling of Columbia has an "o" instead of a "u"!!  At first this typographical error appears to have been short lived and confined to February 1966 since it hasn't been reported for any amps made in January or March 1966.  However, just before this article went to print, I found a late 1965 Deluxe Reverb with Columbia misspelled.  If you have an amp with this typographical error, please let us know and I'll report the results in Part 3 of this series!

And don't think that pre-CBS Fender was immune to mistakes... they weren't!  I have seen two narrow panel tweed Deluxes from late 1957 with a misprint on the tube chart.  Instead of showing the model number as "5E3" the tube chart was printed with "5F6."  The 5F6 was the two input 4x10 Bassman, yet the tube chart is a Deluxe tube chart.  Plausible reasons for this mistake making it into production:  1) Leo Fender, being frugal, may have use these erroneous tube charts just to save money, 2) the error wasn't noticed until a few dozen Deluxes were made, 3) there were no other tube charts available and Fender had no choice but to use the ones with the error until a new batch could be printed.

Another example of a mistake from the pre-CBS days is a brown '62 Concert amp that was mistakenly fitted with the circuit board from a blonde Twin/Showman!  Oops!

Hole to Nowhere:  Some of you may have noticed that the very early brown tolex amps from 1960 have a hole (sometimes plugged) on the back of the chassis labeled "Pulse Adjust."  We have yet to find an amp with a potentiometer mounted there and no schematics that we have found to date show a "pulse adjust" pot.  We speculate that Leo may have envisioned (and maybe even prototyped) a simple signal-injecting circuit whereby he planned to inject a pulse into the amp and adjust a control to optimize the amp's response to that pulse.  This could have been a high frequency pulse and the amp's response could have been adjusted to yield the best high frequency reproduction just short of allowing a high frequency parasitic oscillation.

Or... it could have involved injecting a high level pulse and the control was adjusted to optimize the amp's response to obtain the best (balanced) sine wave with minimum crossover.  Or... it could have involved injecting a "square wave" and the control was adjusted to obtain the best non-ringing, non-sagging waveform.  Or... it could simply have been a bias adjustment.  Despite all the theory and conjecture, Fender clearly deemed the Pulse Adjust control to be unnecessary.

First, Last and Transitional:  During our research, we do find some amps that are especially interesting because they are one of the first, one of the last, or a transitional example of a particular model made.  For instance, we found a very early Quadreverb (s/n A38053).  This model was introduced in 1972 and this particular amp had transformers and speakers dated from late 1971, though it was probably assembled in the very early part of 1972.

The Tremolux (AB763) and Reverb Unit (6G15) were both discontinued in 1966.  In fact, Greg Huntington has a Fender catalog dated September 16, 1966 and it does not list the Tremolux.  The latest Tremolux that we have in the database (s/n A07779) hails from September 1966 and has a production number of 71.  We also have two others from this same production batch with September 1966 tube chart dates so it looks like this was the last month of production for the venerable Tremolux.  The latest Reverb Unit that we have seen (s/n R10651) is from May 1966 with a production number of 46.  However, we aren't sure at this point if May is the last month of production for the tube reverb unit.  If you have a later example, please let us know!

An example of a transitional amp is the first batch of blackface Dual Showmans (AA763).  These are very rare and are prized more by collectors than players.  The blackface Dual Showman circuit was introduced in September 1963.  The amps were covered in smooth blond tolex and had tan/gold grill cloth.  The very first batches of these amps (Prod. #2 for sure, but likely Prod. #1 as well) from September and October 1963 used a quad of 7355 power tubes instead of 6L6GCs as the blonde Dual Showman (6G14-A) and most blackface Dual Showman (AB763).  This amp uses a completely unique output transformer (Part # 125A18A) not found on any other amp though there is speculation and some evidence that a few of the very earliest Twin Reverbs used 7355s since, like the Dual Showman, it was an 80 watt, 4 power tube amp with a 4 ohm output transformer.  In addition, the 1963 catalog specifically shows 7355 power tubes for the Twin, Showman and.... the Bassman and possibly the Concert!

Though we don't know why 7355s were used, perhaps Leo got a good deal from RCA on a boatload of these tubes so he tried them out in the Dual Showman and Twin Reverb.  So why did he switch back to 6L6GCs?  Probably because the 7355s aren't rated to operate at the higher voltages that the Dual Showman and Twin Reverb could dish out.  They are a smaller tube, similar to a 5881/6L6GB and hence can get hotter than a tube with a larger envelope.  By all accounts from two owners of Dual Showman with 7355s, they don't produce as much power as a Twin Reverb or Dual Showman with 6L6GCs, though the tone is apparently acceptable.  These days 7355s aren't too easy to find either.  Hence, these are reasons why players don't care about these rarebirds very much and have converted some of them to use 6L6GCs.  Debauchery!

Dating by Serial Number:  Here's the part everyone has been waiting for.  Yes, we are confident that we have cracked the date codes on the reissue amps!  We have some transformer date code information to support this, too.  There are two letters stamped on the tube chart on the line that says "Production."  The first letter denotes the year and the second letter denotes the month just like on the amps made in the '50s and '60s.  However, the reissue codes are as follows:

A = 1990    A = January
B = 1991    B = February
C = 1992    C = March
D = 1993    D = April
E = 1994     E = May
F = 1995     F = June
G = 1996    G = July
H = 1997    H = August
                    I = September
                    J = October
                   K = November
                   L = December

For example, reissue Bassman (s/n AA05559) with the Production Code EJ would have a production date of October 1994.

Unfortunately, for the older amps, we still are not at the point where we can give any kind of definitive dating scheme.  To satisfy your thirst for knowledge, here's another sample from the database that shows that we are on the right track, but that we desperately need more data sets:

A20599     Princeton Reverb     1968
A20979     Princeton Reverb
A21270     Princeton Reverb
A22267     Princeton Reverb
A23034     Princeton Reverb     1969
A23435     Princeton Reverb     1969
A24546     Princeton Reverb
A24588     Princeton Reverb     1969
A24824     Princeton Reverb
A24868     Princeton Reverb     1969
A25009     Princeton Reverb
A25261     Princeton Reverb     1969
A25946     Princeton Reverb
A26279     Princeton Reverb
A26512     Princeton Reverb
A26767     Princeton Reverb
A29800     Princeton Reverb
A30417     Princeton Reverb     1974
A31069     Princeton Reverb     1974
A32113     Princeton Reverb
A33977     Princeton Reverb
A34057     Princeton Reverb
A34476     Princeton Reverb
A34618     Princeton Reverb     1976

As you can see, we do get quite a bit of data without any date code info which create "holes" in the database.  This is problematic, but lately folks are feeling more comfortable finding the transformer date codes and sending them to us with the serial number/model name for their silverface amps.

Reminder:  We are still in need of information about any and all Fender tube amps.  Everything is confidential, we don't make record of who owns what amp in the database.  What we need is the following information (note item 1 and 2 are essential):

1) Serial Number
2) Model name
2) Model number on the tube chart
3) Date code letters on the tube chart
4) Speaker codes and model (if speaker is original)
5) Transformer codes (if the amp doesn't have date codes on the tube chart)
6) Cosmetic features (flat/raised logo, tweed/tolex, blackface/silverface, rough/
   smooth blond tolex, white/skirted knobs, TV-front/wide-panel, etc.)

So please send your amp data to the author by e-mail to  Thanks for your support and stay tuned for Part 3 of this series!

The author and his partners would like to thank those people who have sent us Fender amp information (and you know who you are dahlings).   Also thanks to the many dealers at the various guitar shows that we visit for allowing us to make notes about the amps at their booths.