Our Buyer’s guide to vintage Fender amps explains in detail how you can date your amp by looking at serial numbers, tube charts, transformer codes, speaker codes, Fender logo, etc. Lots of different speakers were used in the blackface and silverface era Fender amps. In a BF Vibrolux Reverbs you could have either Jensen, CTS or Oxford, the BF Super Reverbs had Jensen, CTS, Oxford. Step #1 – Find your Serial Number. Finding your serial number on your Fender should be very easy. They are almost always on either the top of the neck plate (the piece of metal on the back of the guitar near the neck), on the headstock (the top part of the guitar where the strings attach), or close to the body at the bottom of the neck. The serial number is b 065961 and it is American-made according to the silver plate at the back. DATING FENDER TUBE AMPS BY SERIAL NUMBER, PART 1 BY GREG GAGLIANO COPYRIGHT 1997, 20TH CENTURY GUITAR MAGAZINE. And: Your ultimate source for historical guitar amplifier information: THE AMP GUIDE. By Eric Barbour - Former Vacuum Tube Valley senior editor What the tubes do in most Fender tube amps. You can use this Fender serial number decoder to date a Fender guitar. The tool works for most Fender electric guitars including the Fender Stratocaster, Fender Telecaster, Fender bass guitars, Fender Squier models and many custom shop and reissue models (although some cannot be dated by serial number).

Why I started doing this
In 2002 I acquired a Princeton Reverb II. I became curious as to how many were made. Fender don't part with that kind of information*, so I put out a call for serial numbers on the website I developed for this amp's care and feeding, . Eventually, I thought, I'll get a rough idea what the highest and lowest s/ns were. Subtract one from the other and I'll have a rough-cut figure for how many were made. Oh, the naivite.
PRII owners were kind enough to start sending their serial numbers in. I was puzzled to see how some of them were separated by over 100,000. Could Fender make so many PRIIs, considering they were making the other 13 amp types in the range at the same time? Then Soren in Denmark started showing serial numbers on his excellent Super Champ website (which is no longer on the web) - some of those numbers fell in between some of 'my' PRII numbers. A little light Googling revealed serial numbers for a few other amps in the range - they seemed all mixed up together. Then the terrible truth dawned on me: they WERE all mixed up; Fender had decided to change their 35-year-old system of serial numbering so that, starting in 1982, every amp had a unique number. I would have to collect data for ALL the amp types, just to work out how many were made of mine. Then I became aware of the amazing work Greg Gagliano had been doing since the 1990s - the summary of his latest results are here - and that his research didn't take in the Rivera-era, or anything later. Then I read the challenge on page 245 of Teagle and Sprung's excellent book Fender Amps: the First 50 Years concerning dating the Rivera-era amps, and I decided to press on; maybe I could do, for this small range, what Greg has done for everything that came before.
* Fender have a right to keep that to themselves. However for this range of amps at least, I reckon it's not just a policy of withholding company-confidential information. I reckon they simply don't know. It's no criticism of Fender to suggest that they were too busy making great amps to keep records just so some amateur could use them nearly forty years later.
How I'm doing it
I run a couple of websites making the schematics for these amps easily accessible. As people download them, I'm hoping they'll respond to my request that they send me their amp's serial number for this project, and many do. For a while I also had automated searches running on eBay for these 14 amp types - whenever one appeared for sale I would contact the seller, asking for the serial number. 9 out of 10 did - many thanks to them for their trouble and good will. There are a handful of amp types for which I'm still running the searches because I don't have so much data for those (mainly in the solid-state range). In addition Greg Gagliano sent me the Rivera-era-relevant numbers from his huge research info, for which, along with his friendly encouragement over several years, I thank him. His info (rightly passed on to me without details of the amps' owners) still represents about a seventh of my database. I appreciate Jeff Lacio for contacting me (Dec 2015) with some more serial numbers and date codes, and for enlightening me regarding amps with a 'H' in their chassis stamp. I should also thank Pierre Boile in France for his original idea of keeping a log of PRII owners, way back in 2004.
As of Aug 2020 I've got info on nearly 2000 amps. Compared to my estimate of the total made, that's more than one in forty. It might not sound like much, but quite a lot can be deduced from such a sample. Advertisers and politicians make decisions based on smaller percentages!
Why I'm putting it on the web
I'm guessing amp-owners like to know when their amp was made, if it's old-ish. Certainly the hundreds of people who have helped me seemed keen to know. Meanwhile I've offered this info to Fender US, Fender UK, and a US magazine. Fender never replied, and the magazine showed polite disinterest. So, with my dreams of being A Published Author in shreds, I might as well make what I've got available to folks. It represents over fifteen years of time that could have been spent becoming a better guitarist, so if you quote it elsewhere, I'd appreciate a link and/or a name-check, either as 'Stratopastor' or under my real name.(C) copyright Andrew Waugh 2004-2020.

Stuff Like This is Never Complete or Totally Accurate
All these amps have serial numbers beginning F2, F3 or F4 followed by another 5 digits. It's sometimes said that F2 = 1982, F3=1983 etc. However Fender couldn't maintain that system for long, and there are no F5 or F6 amps. If you've got one of the 14 amp models in this range you can get a rough idea of its date-of-manufacture from these tables.
Please note this isn't official Fender information, nor is it anywhere near complete. It's just my data so far, and you may well find exceptions to it, in which case please let me know on NOSPAMstratopastor@hotmail.com (delete the capital letters). I never reveal names along with serial numbers, and I'm not making any money out of this.
For the batches labelled 'date codes needed', I haven't got any loudspeaker or transformer date codes, or (gold dust) the 4-digit inkstamp on the metal chassis, which is usually only visible when out of the wooden cab. However the dates for these batches are certain to be later than the batch shown immediately above, or earlier than the batch shown below. If you've got an amp in this category and can supply any of those codes as well as the serial number, I would luuuuurve to hear from you. The speaker codes are in the form 109xxxx or 67-xxxx; the transformer codes are 606-xxx.
Also, things got a little crazy during Fender's last few months in the Fullerton factory, and when the management buyout was complete (March 1985) they had some parts but no factory. According to Tom Wheeler's excellent book about the Stratocaster, it may be that they had no factory after December 1984! So (example) the last few hundred Super Champs seem to have date codes from 1984 but there's anecdotal evidence that they were assembled in nearby Brea, CA in 1986. One run of Princeton Reverb II serial numbers seems to stretch from 1984 to 1986 with just a few from 1987, yes 1987, when some 220V models were still being shipped to Sweden and the UK. So if you'd like a bit more detail on an amp in that category please get me the speaker date codes, not just the serial number.
There are a few other notes at the bottom of this page which you may find interesting.... you may not.Here's the date info!
Seasons of the year are for the northern hemisphere. I apologise for any parochial attitude this may convey.
Valve / Tube Amps
schematics, manuals, parts lists for these amps
Bassman 20 and Champ II
These 2 amp types shared the same metal chassis design. As explained (or assumed) elsewhere in this article, the chassis were given serial numbers before the amps were assembled. Upon arriving at Fullerton, any one of these chassis might be built as a Champ II or a Bassman 20, in a process which appears semi-random when tracked only by serial number. This means that these 2 amp types can only be treated together for dates or production quantities when, as in this study, the serial number is all we have to go on. (Fender did this chassis-sharing thing in earlier years, with the same implications for guessing quantities, as noted by Greg Gagliano.) I estimate about 5700 were made in total. While it's anyone's guess how many of those 5700 were Champ II and how many were Bassman 20, they seem to come up on eBay equally often. (There is a self-perpetuating internet myth that fewer than 500 Bassman 20s were made - I believe this is due to a misreading of the tables in back of Fender Amps: the First 50 Years by Teagle and Sprung. People keep on referring to this 'fewer than 500' thing, especially when they're trying to sell one as 'rare', but I'm still waiting for anyone to point back to the original 'fact' of the matter!) The last batch in this table also belongs in late 1983, judging by surrounding data for other amp types and the received wisdom that they were discontinued around that time.

from s/n F...	to s/n F...	date
200272	200500	spring 1982
201516	202972	late 1982
204702	205785	late 1982
206503	206604	late 1982
224142	224471	spring 1983
305807	306340	summer 1983
310741	311310	autumn 1983
313878	314245	autumn 1983
315766	316034	autumn 1983

Concert
All this amp's speaker configurations, and the head unit, included. Estimated total production is 12,500. If your amp's serial number falls into the last 3 batches then your best hope of dating it is if you've still got the original speaker. These 3 runs of serial numbers start in mid-1984, when production was fairly normal. Then comes the March 1985 management buyout, when the new owners were left with some parts but no factory! Then began a period in which amps were assembled from pre-existing wired-up chassis in a small ad hoc facility in Brea, CA. They bought in speakers, and probably cabs, on a last-minute basis due to cost and space considerations. This carried on until 1986.

from s/n F...	to s/n F...	date
210325	210787	spring 1982
211716	214573	late 1982, early 1983 (hi Scott)
215250	215506	late 1982
222294	222479	early 1983
302752	303297	summer 1983
303525	0nly one s/n known	summer 1983
309939	310672	summer 1983
316046	317555	summer/ late 1983
326188	326476	late 1983
331187	332759	1984 mostly early
409435	410666	summer 1984 and 1986
415120	416316	mostly early 1985
419233	419404	spring 1985 to maybe 1987!

Deluxe Reverb II
Production total estimated at 3,500. If your amp's serial number falls into the last batch then your best hope of dating it is if you've still got the original speaker. This batch's run of serial numbers starts in mid-1984, when production was fairly normal. Then comes the March 1985 management buyout, when the new owners were left with some parts but no factory! Then began a period in which amps were assembled from pre-existing wired-up chassis in a small ad hoc facility in Brea, CA. They bought in speakers, and probably cabs on a last-minute basis due to cost and space considerations. This carried on until 1986..

from s/n F...	to s/n F...	date
200501	200550	spring 1982
205832	205847	date codes needed
208957	210279	summer / autumn 1982*
311346	312272	summer 83 / early 84
325838	325926	late 83 / early 84
329359	329629	84 to 85
410866	411122	autumn 1984
414906	414978	summer 1984 & 1986

* but with at least one amp from April 1983.... chassis stamps needed in order to be sure.
Princeton Reverb II
Production total estimated at 6,200. I am close to having serial numbers for 1 in 10 of them.
If your amp's serial number falls into the second-to last batch then your best hope of dating it is if you've still got the original speaker. This batch's run of serial numbers starts in mid-1984, when production was fairly normal. Then comes the March 1985 management buyout, when the new owners were left with some parts but no factory! Then began a period in which amps were assembled from pre-existing wired-up chassis in a small ad hoc facility in Brea, CA. They bought in speakers, and probably cabs on a last-minute basis due to cost and space considerations. This carried on until 1987 by which time there were only 220V models left. There are at least ten PRIIs in this batch with a 1987, week 7 speaker.

from s/n F...	to s/n F...	date
148501	148510	prototypes, only 2 known
203698	203900	spring 1982
205913	206350	autumn 1982
206681	207357	autumn 1982 but a few from early 1983
216501	217248	late 1982
219450	219979	late 1982
306737	306832	date codes needed
309585	309919	summer 1983
312295	313008	late 1983 -spring 1984
325025	325360	spring 1984
326181	(only one s/n found)	date codes needed
327432	328531	84 to 86
338204	(only one s/n found)	1984

Super Champ
Production total estimated at 11,500. If your amp's serial number falls into the last batch then your best hope of dating it is if you've still got the original speaker. This batch's run of serial numbers starts in mid-1984, when production was fairly normal. Then comes the March 1985 management buyout, when the new owners were left with some parts but no factory! Then began a period in which amps were assembled from pre-existing wired-up chassis in a small ad hoc facility in Brea, CA. They bought in speakers, and probably cabs on a last-minute basis due to cost and space considerations. This carried on until 1986.

from s/n F...	to s/n F...	date
200001	200241	spring 1982
200576	201478	spring 1982
202508	Only one s/n known)	summer 1982
202992	203666	summer and late 1982
208428	208932	late 1982
210920	211037	date codes needed
214772	(only one s/n known)	late 1982
215536	215878	summer to late 1982
217256	217799	summer to late 1982
221167	222274	early 1983
307284	308395	summer 1983
313043	313788	late 1983
319702	320535	autumn/late 1983
326486	326782	late 1983
327393	327422	date codes needed
400191	401119	spring 1984
411451	411913	summer 1984
414103	414894	summer 1984
416525	416840	85 and 86

Twin Reverb II
The head unit and the far more usual 2x12 are included here. Production total estimated at 7,000

from s/n F...	to s/n F...	date
214584	(only one s/n known)	possibly the prototype
215127	(only one s/n known)	date codes needed
220112	(only one s/n known)	date codes needed
225934	(only one s/n known)	date codes needed
226389	227083	summer 1983
300119	300646	spring 1983
302311	302587	early 1983
around 318700		seems to be a batch sharing numbers with solid-state Harvard Reverb IIs, which were made in another state...! assume some kind of numbering error...
318845	318905	summer 1983
320720	321188	late 83, early 1984
325959	326140	date codes needed
328556	329255	spring/summer 1984
400030	400052	date codes needed
404306	405517	spring 1984
407164	407655	late summer/autumn 1984
411246	411316	1986
413096	413757	1984 to 1986?

Solid State Amps
schematics, manuals, parts lists for these amps
Harvard Reverb II
Production total estimated at 3,500. The serial numbering of the HRII is a little flaky... some are mixed up with runs of other amps' numbers.

from s/n F...	to s/n F...	date
223380	223945	spring 1983
307022	307232	early 1983
318632	318813	summer 1983
319549	319549	summer 1983, only one s/n known
320515	320515	only one s/n known
322817	323491	late 1983
325405	325723	late 1983
329855	330531	spring 1984

London Reverb
All speaker configurations included. Production total estimated at 4,000

from s/n F...	to s/n F...	date
224503	(only one s/n known)	possibly the prototype
225982	(only one s/n known)	guess summer & autumn 1983
226031	226358	autumn 1983
304024	(only one s/n known)	guess summer & autumn 1983
305023	305716	summer & autumn 1983
321193	321349	autumn 1983
323751	323984	late 1983
329737	(only one s/n known)	early 1984
333141	333249	spring 1984
402651	403167	spring 1984
408648	408789	date codes needed
416354	(only one s/n known)	date codes needed

Montreux(mis-spelled on Fender schematics as Montreaux)
Production total estimated at 1,800

from s/n F...	to s/n F...	date
224558	225239	early 1983
309405	(only one s/n known)	date codes needed
321642	321967	autumn 1983
333589	(only one s/n known)	date codes needed
408861	409045	autumn 1984
417095	(only one s/n known)	assume later than autumn 1984

Showman
All speaker configurations included. Production total estimated at 2,000

from s/n F...	to s/n F...	date
225427	225851	date codes needed
308437	309266	summer 1983
324445	324539	autumn 1983
329780	(only one s/n known)
409073	(only one s/n known)	autumn 1984

Stage Lead and Studio Lead, made in USA
These 2 amps share the same chassis design (April 2016, thanks to Jim Thorpe for confirming this, as he owns one of each) so I have treated them in the same way as the pairing of the Bassman 20 and Champ II (see above). The Stage Lead and Studio Lead have turned up in roughly equal numbers in my survey, but it's a small sample so make of that what you will. I estimate the 2 amp types total 9,500. Thanks also to Ed C for a photo which shows these 2 amps also shared the same PCB, with a few component differences. The Stage Lead 212 had a wider cab to accommodate the two 12' speakers; the metal chassis had extra 'ears' to reach across the wider cab: the works inside the chassis were the same as the 1x12'. A completely different amp called 'Stage Lead' was made for Fender in Japan at the same time, with a different serial numbering system. They are not included in these figures and I am not tracking them.

from s/n F...	to s/n F...	date
218001	219270	early 1983
220379	220515	early 1983
300917	302131	spring/summer 1983 but one amp has components from 1984... ???
303370	(only one s/n known)	date codes needed
303774	303594	these 2 s/ns are for Stage Lead 212's - maybe the whole batch are this variant with 2x12' speakers
306383	306667	spring/summer 1983
318186	318598	summer/autumn 1983
319048	319069	autumn 1983
321515	321515	only one known
324061	324107	date codes needed
324650	324975	date codes needed
327123	327340	late 1983
330795	330906	spring 1984
333824	334214	spring 1984
401701	402265	date codes needed
403339	404153	spring 1984
407835	408600	summer 1984
412130	412470	late 1984
412914	412937	date codes needed

Yale Reverb
Production total estimated at 2,500

from s/n F...	to s/n F...	date
222534	223220	early 1983
304471	304704	summer 1983
318061	318137	summer 1983
319284	(only one s/n known)	summer 1983
320566	(only on s/n known)	date codes needed
322109	322402	late 1983
401186	401386	spring 1984
406951	(only one s/n known)	summer 1984
412792	(only one s/n known)	date codes needed

Further Reading
Fender's Serial Numbering System for this range of Amps
Up to 1981, Fender's serial numbers were genuinely serial within one amp type. Thus, for a given amp (say, the 5E1 Tweed Champ) they started with a definite number, in this case C00001, and just kept adding '1' for each new Tweed Champ until the model was discontinued - in this case approximately C23000 nine years later (info from Greg Gagliano). So that's about, oooh, let's guess, 23,000 Tweed Champs. Easy. Some serial numbers were used more than once, on different amp types - example; A01600 could be a Bandmaster, a Bassman, a Champ, a Concert, or a Deluxe (info from Greg again). There was no possibility of confusion though, as the amps' names were clearly printed on the front panel....
For the Rivera-era, everything changed. One style of serial number was adhered to for all amp types, with each number used only once. If you sort my database by serial number, and then read it in that order, you can see they started with s/n F200001 ('F2' was meant to uniquely represent 1982). That was a Super Champ, as were many immediately following. F200272 is another amp type followed by several of the same, F200517 is a third amp type followed by more of that, F200576 starts a second run of Super Champs, and so on. As we follow the serial numbers upwards, more and more amp types appear; about 250 of those, about 500 of these, etc etc. This serialisation method means, in order to estimate how many were made of just one amp type, data must be collected for all 14 amp types (partly to eliminate which s/ns represent the amps one is not interested in), and guesstimates made for the size of each batch. The run of serial numbers seems to end with a bunch of 110V Concerts with s/ns a little over F419000. That 'top number' in my data used to be around 416,000 and it took seven years for anything higher to turn up, so I think it's safe to assume that anything YET higher out there must still be in the same ballpark. Some huge gaps are evident - the range totals about 70,000 amps, not 219,000 (which it would be if there were no gaps).
Fender's Manufacturing Process
Here follows some personal guesswork about how these amps were made.
It's decided (dealer re-stocking demand?) to build more of an amp type (say, Deluxe Reverb II). All the previous chassis for that amp type were built into amps the last time, so there are none left. Chassis are ordered from the metalwork supplier. They arrive, already serial-numbered*, and are put into the parts storage. They are pulled out of there onto the shop floor in no particular order or maybe even a rough accidental reverse order (last in = first out), built into amps, and shipped. Chassis are expensive and bulky, so no more chassis of that type are ordered until all are used up. Meanwhile the same thing is happening simultaneously with some of the other amp types. The result is a kind of stock rotation whereby the serial numbers definitely go up with elapsed time as you move from one batch to the next batch of the same amp type. But within a batch the numbers were used in semi-random order.
Fender evidently started in 1982 with the plan of making the first serial number digit represent the year of manufacture. That would have been easy if the completed amps were serialised just before shipping. But because the amps were serialised before assembly even began, the system would lose its meaning if a batch of chassis weren't all used by the end of their calendar year. And that happened. At the end of the first year. And the second. And the third. After which, they didn't even bother increasing the first digit; thus F4xxxxx covers 1984, 85, 86 and any stragglers from 1987. F3xxxxx could also mean 1984.
*this is also Greg G's assumption. It's not clear if the serial number were stamped onto the chassis by the metalwork supplier or by Fender, but I think it was the former. There's a lot of interesting anecdotal stuff on one of Greg G's earlier pages (though he points out there that the dating-tables have been superceded by his latest page)
The total number of amps
While the highest and lowest serial numbers in my database are 219,000 apart, there are vast banks of apparently unused numbers. My figures above suggest that, across the whole range, there were about 70,000 amps in total. This may conflict with figures you'll hear elsewhere - I am not trying to start an argument and I think any perceived differences lie in the sourcing a lot of Fender-badged amps from Japan, a whole different range, serialised very differently, in the same period. When you consider that the vast majority of the US range were made in three years ('82, '83 and '84) my figures suggest the factories averaging over 50 hand-assembled amps per working day, which is not to be sniffed at. Meanwhile, if you know different - especially if you worked at Fender during the relevant period - I'd be pleased to hear from you. Email NOSPAMstratopastor@hotmail.com (delete the capital letters).
Here is Paul Rivera talking about his time at Fender...he has been running his own fine amp firm for a couple of decades. Mr.Rivera has kindly responded to a couple of my emails during my project, and I really appreciate the way he was happy to discuss a period from which he stopped profiting many years earlier.

Fender Amp Date Serial Number To Text

What about the Rack-Mounts?
The 1983 amp catalogue includes the RGP-1 preamp and RPW-1 power amp, a matching pair of rack-mount units. For a couple of years I expected to 'find' examples of these out in the field. After drawing a blank, I began to believe that these were never made, the catalogue photos being space models and the spec sheets being a way of gauging interest from the dealerships. Finally, in 2010 I discovered this interview. In the first two and half minutes Paul Rivera confirms, yes, the Fender rack-mount units were never sold. I was wrong, however, to think that the photos in the catalog were dummies with LEDs lashed up behind the front panels.... in November 2013 I was very kindly contacted by Robert W who worked in the Hoopeston factory during the Rivera years. He had the only RPW-1 in the world - the prototype - and had recently, generously, passed it on to Paul Rivera. Mr. R already had the matching RGP-1 and gave Robert a new Rivera amp in exchange...
The Fender Rivera-Era; an abbreviated time-line
(sources include my own database, books by Teagle & Sprung and Tom Wheeler, FDP discussion threads, YouTube, and personal email; thanks everyone)
1980
Fender introduce the 30, 75 and 140 amps, all designed by Fender's Ed Jahns, all in imitation of Mesa's range of channel-switching, built-in-overdrive amps. These 3 amps are often erroneously described as belonging to the Rivera-era range of Fenders, possibly due to the design of some circuit elements and the fact that Ed Jahns carried on to be a key player in the design of the Rivera-era amps.
1981
In January Paul Rivera is hired by Fender as Marketing Director. In May he scopes out their next range of guitar amps. The Super Champ was one of his own designs - the rest are designed by the Fender team in fulfilment of Rivera's specifications.
1982
The tube amps are launched in the Spring.
1983
Early in the year, the solid-state amps are introduced; they are all made at the CBS-owned Gulbransen organ factory in Hoopeston, Illinois. Sourcing of Fender Blue Label speakers is shifted from Pyle to Eminence. Assembly and wiring of some tube amp chassis is moved to Fender's factory in Mexico; these get chassis stamps beginning with 'M'. Some of those 'M' chassis are sent to Fullerton to be fitted into cabs, some to Hoopeston (those gain an extra 'H' stamp). At the end of the year the Champ II and Bassman 20 are dropped from the range.
1984
Fender/CBS let Paul Rivera go in October as a political move in anticipation of the buyout. He then presumably sets about developing the fine firm which bears his name today. Late in the year the Gulbransen/CBS factory is sold off (= no more of the range's solid-state amps).
1985
CBS sell Fender to the Fender management team in March. The workforce is down from 700 to 275 (reported LA times, 6 years later, June 6 1991 in an article about the move to Scottsdale) The Fullerton factory is not included in the sale. The new Fender uses a small facility in nearby Brea (1130 Columbia St) to continue assembly of the remaining inventory of amp parts, buying cabs and speakers just-in-time when needed to make Concerts, Deluxe Reverb IIs, Princeton Reverb IIs and Super Champs using chassis wired up in 1984. This goes on through 1986 and even into 1987, with the last amps being sold into Canada and Europe.
1987
Fender buy Sunn and move in with them in Lake Oswego, Oregon. Maybe a few Rivera-era amps were assembled there; no evidence of that so far. The entirely new, PCB-based 'red knob' range of Fender amps is launched. As with the 30, 75 and 140, Paul Rivera was not involved with the red knob series. By 1991 there were 115 people still working for Fender in Brea, of whom around 40 moved to Arizona, the rest taking redundancy.
Suggestions and Corrections welcome! (but please don't ask me how much an amp is worth. I might make a very rough guess for the UK market because I live here. For other countries, unknown factors like rarity and relative income levels mean I.just.do.not.know.)
Email me onNOSPAMstratopastor@hotmail.com (delete the capital letters).
(c) copyright Andrew Waugh 2013-2020
more... Pro Advice • Ask Amp Man • Gear • How-Tos • DIY • Amp DIY • Fender • Amps • Speakers • Tube Combo • September 2013

Whether it’s a vintage amp or a recent model such as this Fender Pro Reverb, hum can have several causes. Possible culprits include the preamp tubes, the power tubes, the hum balance resistors, and the power supply caps.

Hi Jeff,

I was just reading some of your responses about Jonny Lang’s Deluxe Reverb amps. Thanks for your input.

I have a 1965 Deluxe Reverb and am trying to figure out if it has a Utah or some other kind of speaker. I was thinking of trying a Celestion Gold 50, but I usually only play in my bedroom, and I don't want to increase the amp’s volume. I’d rather decrease it. Any speaker ideas on that front?

I also have one of the newer Fender Pro Reverb amps with an effects loop and a silverface Twin Reverb with a volume control. Both amps produce very loud hum whether or not a guitar is plugged in. Could this just be bad caps? Or is there some other possible cause you can point me to?

Thanks, Jeff. Keep up the good work!

Steve Goldner San Diego

Hi Steve,

Thanks for your questions. Let’s start with the Deluxe Reverb.

Figuring out which manufacturer’s speaker is in your amp shouldn’t pose a problem unless it’s some aftermarket mystery speaker with no markings. Most factory speakers in Fender amplifiers have what is known as an EIA code that specifies their manufacturer. You should be able to find a number stamped somewhere on the speaker’s frame. The format may look like this:

220 637

Here the number 220 designates the speaker as a Jensen, and 637 indicates a production date of the 37th week of 1956 or 1966.

Fender has used only a handful of different speaker types over the years. Here’s a list of brands along with their EIA codes. (I’ve also included a few others brands you might encounter as aftermarket installations.) This should help you identify your speaker.

• Jensen 220
• Utah 328
• Oxford 465
• JBL 73
• CTS 137
• Altec Lansing 391
• Electro-Voice 649
• Pyle 1098
• Weber VST 1279

Fender Amp Date Serial Number

You also mentioned that you’re looking for a speaker option that decreases the overall volume of your amp. You need a speaker with a lower audio output, so you should consider the spec known as SPL, or sound pressure level (sometimes called sensitivity). The SPL rating specifies how loud a speaker is at a distance of one meter when driven by one watt. The higher the number, the louder the speaker.

Fender Serial Number Lookup

I don’t know what speaker is in your amp, and even if I did, its specs might not be available. That’s probably a moot point, though—experience tells me that most original speakers in amps of that age are substantially fatigued and generally sound very weak.

You mention the Celestion Gold 50. It's a great-sounding speaker, but with a sensitivity rating of 100 dB, it’s relatively efficient and would probably be pretty loud in that amp.

Let’s take a look at a couple speakers from Warehouse Guitar Speakers (wgs4.com) so I can better explain this. Their G12C/S speaker is listed as 99.79 dB, while their G12C is listed at 96.10 dB. The G12C is more than three dB lower, which equates to approximately half the loudness of the C/S. If you want the least volume from your amp, search for a speaker in the style you like with the lowest SPL rating.

Another option you might consider: Eminence (eminence.com) makes a speaker called the FDM, which stands for “flux density modulation.” (Yeah, it sounds a little Back to the Future.) It comes in both American- and British-voiced versions and has a very unique feature: a large knob on the rear of the speaker that allows you to adjust the strength of the speaker’s magnetic field, effectively changing its sensitivity. It might be worth checking out.

Let’s move on to your Pro Reverb and Twin Reverb amps with hum issues. There are quite a few potential causes of this symptom, and it’s impossible to diagnose your amps without having them on the bench. I’ll list a few possible causes, but be aware that the cause of the hum in one amp isn’t necessarily the cause in another one. You have to troubleshoot each one individually.

• If the hum level varies with the volume control settings, check the preamp tubes by substituting replacements one at a time and listening for whether this changes the symptom. Some types of preamp tubes hum more than others in some amps. Also, if the amp has a hum (or hum balance) control on the rear panel, try adjusting that to minimize the hum.
• If the hum is independent of volume settings, install a new set of matched output tubes. Mismatched output tubes can create hum in the output stage, and the more mismatched they are, the greater the hum. (Remember, if you need to install a new set of output tubes, they should be properly biased.)
• If the problem is not tube-related, the electronics need to be examined. This should be done by a qualified tech familiar with tube amps. If the amplifier has hum balance resistors (as opposed to a center tap on the filament winding), the tech should verify that they aren’t burnt. Also, if the amp has a hum or hum balance control, make sure it hasn’t been damaged.
• The next thing to check is the integrity of the power supply caps. Bad or weak caps here can definitely cause hum.
• One more thing (and an often overlooked one): the capacitors in the bias supply. A noisy bias supply causes output stage hum.

I hope these tips help get your Fenders into phenomenal form!

Fender Bassman Serial Number Lookup

Warning: All tube amplifiers contain lethal voltages. The most dangerous voltages are stored in electrolytic capacitors, even after the amp has been unplugged from the wall. Before you touch anything inside the amp chassis, it’s imperative that these capacitors are discharged. If you are unsure of this procedure, consult your local amp tech.