Super Champ 1983 - Optimizing

[Bendyha]

Good job on the 33k snubbers, you could go higher, I've gone all the way to 100k on an EL84 amp to alter the way it clips when hitting the grids positive.

Aaah.. I don't think I want to go higher, my long time band partner has both a mesa boogie Studio 22 as well as the Caliber 50. These have 220k infront of the control grids. I've worked on them both, and have read Randall Smiths patent US4713624 which explains how it works, but I don't want to get to far away from that Fender thing. Also, when they realy hit their limits, the 6V6 can't sing in the same way as a EL84 with there aggresive mids and tight lows, and so can't take advantage of this compression effect. mesa uses an added supportive effect brought about by the high dropping resistor before the screens in conjunction with a larger elko.
6V6's sound at there best with thier warmer overdrive kept below thier farting wolf stage, and that is the balance I'm trying to achieve.

 

[Cleeve]

I once worked on an old Ampeg that used 6v6 tubes, I remember looking at the scope and noticing how no matter what I drove into it, and within reason no matter the level, the old thing converted the signal to rounded sine waves more or less.. I believe it used a cathode bias scheme.

Here is another writeup I'm sure you have seen dozens of times, but other readers may wish to see what can happen if the outputs of the cathodyne are taken care of by large snubbers coupling to the output pair, but no snubber is included on the input of the cathodyne.
http://www.valvewizard.co.uk/cathodyne.html
I wonder if sometimes the poor distortion character attributed to the 6V6 pair is due to artifacts generated by the overdriven cathodyne? Perhaps cathodyne driven EL84 pairs are in saturation and cutoff long before a cathodyne would be overdriven and go to hell, compared to the higher voltages the 6v6 can take on the grids before cutting off/saturating. On second thought, I'll edit this as I realize the tweed deluxe uses a cathodyne and is often thought to have quite the distinctive overdrive character, so um never mind?

 

[Bendyha]

Ya, I have both of Merlins books, and can only recomend them as being amongst the best, most understandable, no B.S. books on the subject of not only cathodyne's, but most everything else about guitar preamps, and power supplies.
Another of my amps is a 1972 GRO 100/2 Orange, and it manages to drive 4 X EL34's super cleanly upto frightenly high levels with a cathodyne. Pete Townshend's Hiwatt's, same thing.

 

[Bendyha]

The Preamp pots

I was just trying out some ideas I had for the tone stack, when I thought to measure up the resistances and tapers on the existing pots.

The Volume pot is the one that surprised me. It is stamped on its casing with the original Fender part number / 011540, and also with R, meaning round shaft, and 1378211, meaning it was made by CTS in the 11th week of 1982, so it is the original pot. It has a switch on the back for the channel selection, and a fixed resistance tap lug on the rear edge, which is connected through a 100p cap to the clockwise end lug. There are no marking denoting the resistance values that I could spot without pulling it apart. On the schematic it is rated at 1M. Measuring it though, I found it to have a resistance of 1580k ! This is way beyond any tolerance limit, and it was probably constructed as a 1M5. The half-way measurement was 1200/380k, so a 25% audio taper. The tap measures in at 1080/500k Ohm, so at 33%, and is physically located at 66% rotation.

So what effect would this higher rating have on the working of the amp? I guess it might give me a bit more maximum gain when turned right up. And maybe the function of the tone stack and the loading stress on the previous triode stage would change minimally. More of concern, is the effect that would occur at lower volume levels, with certain higher frequencies being more attenuated. For the relationship between R & C to be more like the design ratings, maybe I should change the 100p cap to 75p. But then again, raising the capacity here is a mod that is favoured by some people to beef up the low volume tone a bit. I will see what changes, if any, that I make with the tone stack before deciding what to do with it.

If anyone else has measured their Volume pot, I would be very interested to know what values you came up with. If you happen to have your amp open, it is a quick thing to check. To facilitate this one must plug a cable into the input jack to lift the wiper from being grounded, and unsolder the wire from the top lug where it joins at the wiper of the Treble pot, this removes the tone stack's effect on the measurements.

On the schematic, the Treble pot is rated at 250k. It measures 267k, set at half turn, it is 194/73 Ohm - so an audio taper of 27% . No surprises here. The Bass pot, also rated 250k, measures 290 Ohm, at half way - 224/66 Ohm - audio taper 25%, This resistance reading 16% higher than rated is still to be classified as good, and well within the 20% tolerance.

 

[Bendyha]

Correction

It's a shame the editing time for posts is so limited, as unfortunatly I have spotted a mistake in my post #34. Writing the post several days after swinging the soldering iron I made the mistake of refering to the lead gain poti as being 1M. It is of course 100k, and should remain so in the new stacked poti. After getting some playing in on the amp, I have decided that the 330k tail resistor I put on the new 470k poti half is much better if it is only 100k instead. So here is post #34 again as it should have been.

Adding a Variable Gain Control.
Going back to what I was saying in post #13 about the Lead Gain, and referring to the schematic drawings there, I've added a few more changes to my amp.
I thought it might be worthwhile to have the added flexibility of the Lead channel having a variable boost as well as the independent volume control. Not wanting to drill an extra hole for another potentiometer, or have something pocking inaccessibly out of the back, I decided that a "Dual Stacked Concentric Potentiometer" might be the answer. The problem is that there are not a lot of different ones on the market to choose from. There are 250k / 500k mixed ones, and 500k / 500k ones, both with audio tapers which are available from CTS that are used on Fender Jazz Basses. But I decided I wanted a 100k / 470k mix, with the 100k being an Audio taper to replace the Lead volume that is there without changing it's value, and the 470k being Linear because sitting on-top of a tail resistor it needs to be to function evenly. This proves to be no great problem, because it is quite simple to take a readily available CTS DSC potentiometer, and a separate 100k and 500k potentiometer, bend open the tags that hold them together, take out the resistive-track-conductor-board-discs, do the same to the stacked potentiometer, sliding the small internal C ring clip to one side that holds the two cans joined, swap over the discs, then close them up again. The hole in the middle of the 500k disc, (which realy does measure 470k), needed to be reamed out a little larger as it was a touch small.
I was not able to find a stacked knob pair to suit the amp, so I got a screw fastenable Fender style knob that I drilled through, truncated slightly, and added a small knob onto the protruding middle shaft. It will do till I find something better.
Referring to the photo's that show the Super Champ in both original state, and modified-
Wire #1 , coming from the switch on the back of the Volume control, is moved from the one end of the 1M resistor to the other . B to . A
A 47p cap is added parallel to the 1M resistor. The Ground wire #3 from . B to . E is removed, and the wire #2 from the reverb transformer is moved to Ground from . B to . E
Shielded wire #4 has it's core connected between . B and the wiper of the new 470k potentiometer, and the shield soldered to the back of it's casing, which is grounded through the chassis. A 100k resistor it also connected between the casing and the CCW tag.
The front potentiometer was rewired exactly as it was, except that I changed the ceramic cap to a polystyrene capacitor.
Now I can go from the gain set to 1 - Lead is just a bit more aggressive than the Clean channel, all the way to 10 - more preamp overdrive than I am likely to use, with plenty of available reverb to mix in.

 

[Bendyha]

The Input and First Stage

I had the amp open again to try-out some tone-stack ideas, which I will report on soon, when I decided to change the wire from the input jack to the grid of tube 1A for a shielded wire, and see if I could hear a difference by removing the "snubber cap" between the plate and cathode of this stage.
Looking at the schematic of the Super Champ, this cap is rated at 1200p, which is quite large, but in my amp, apparently original cap is only 500p, which would seem like a more normal value. Apart from this, I noticed that the schematic rated 33K input grid stopper, is actually a more normal 68K. Whether these discrepancies are peculiar to my amp, or an updated version that became the standard, I do not know. If anyone happens to have their amp open sometime, take a look at what you have in there, and let me know.

 

[Wally]

Hello, Bendyha. Since Ihad a Princeton REv II on the bench this morning and noticed and 'oddity' in that input stage resistor, I thought I would open up one of my super Champs and take note of what was going on in the area that concerns you.
Fwiw, the schematics seem to have 'conflicts. The schematic that I have had on hand for years shows that input resistor as a 68K. The schematic at Schematic Heaven for the Super Champ shows a 33K....and that is what my 1983 SC has there....in conflict with the schematic I have but in agreement with the Sch. Heaven schematic. The Prin REv II schematic shows a 68K, but the one I had open this morning carried a 33K. IT seems that there was a 'change' during production..both in practice and schematics????
The snubber there in my '83 SC is a .0012 mfd cap...1200pfd....also.

 

[Bendyha]

The schematic that I have had on hand for years shows that input resistor as a 68K.........
IT seems that there was a 'change' during production..both in practice and schematics????
The snubber there in my '83 SC is a .0012 mfd cap...1200pfd....also.

Thanks Wally, thats interesting, I hadn't noticed that there are two different schematics before now. I will hopefully be able to find one like yours, then go over it with a fine toothcomb to see if any other differences are to be spotted. When the change took place would be interesting to know, and which is the first and which is the updated version.
You have got a 1n2 snubber! (just to help confuse) I imagine there would be quite a difference in sound if you removed it, probably be too bright for you.

 

[Wally]

Bendyha, the schematic that I have had for over 20 years doesn't have a date on it. The Schematic Heaven schematic does have a date.....hard to read it but it looks like 3 ** 82. So....no help for comparisons of dates there. I'll let you know what my '84 has in it.

 

[Bendyha]

Wally, I finaly found a version of the schematic that I presume you have. It is available at;
http://www.thevintagesound.com/ffg/schem/champ_super_schem.gif

Other than the different input resistor 68k vs 33k, and the first snubber 500p vs 1200p which you had mentioned, the bias setting resistor is 12k vs 15k, resulting in the bias being given as -32V vs -33V.

Just to complete the list of other info available here are a few links;

The other schematic version is available all over the place, a good copy can be found at;
http://ampwares.com/schematics/SuperChampSch.pdf

and the layout at;
https://web.archive.org/web/20101010014531/http://superchamp.dk/papers/Super%20Champ%20Wiring%20Diagram.jpg

a copy of the owners manual here;
http://www.prowessamplifiers.com/schematics/manuals/Super_Champ-Fender_Super_Champ_Owners_Manual.html

and the parts list at;
https://web.archive.org/web/20101010004643/http://superchamp.dk/papers/Super%20Champ%20parts%20list.jpg

 

[Wally]

Yessir, Bendyha...that is the schematic that I have had for more than 20 years. I don't even remember where I got it. And...now that I look through a couple of books, I realize that I have also had the schematic that shows the 33K input resistor. It is in the Aspen Pittman books.
I had these two SC's set-up for me by a good tech before I ever started working on amps....he left town and there was no one else to work o n my amps...so I started studying a bit. They both sound so good that I have had no reason to 'question' anything about them... but...you have spurred my curiosity to some extent. Thanks for the links.
I am going to think that the schematic with the blank date box was the first one....with the 68K resistor. I now regret not having taking close notes on the other SC's that I have had through here. I have only seen one 1982 model...and I bet it fits that 'blank date' schematic with the 68K resistor. What year is the one you have that is carrying the 68K? 1982??? My 1983 with the 33K/1200fpd arrangement is serial number F3267**.

 

[Bendyha]

Well Wally, your F3267** is from late 1983 and has a 33K with a 1200p.
My S.C. (despite thread heading) F2035** has the purple ink stamp 2803, read backwards that gives you the 30th week of 1982 (first week of august) . I have 68K with 500p.
Strangly, niether of our amps coincides with either of the scematics, and my amp has that 2700p cap there in place of the 1000p on the schem, joining lead boost to reverb transformer, which is not on either. Unfortunatly I'm not sure which bias set resistor was in there, but I would guess it was the 15k, as I think I would have noticed if it was different from my schematic. I replaced it with a trimmer.

The dated schematic is 3/19(?)/82, the 11th week. It also has in the box marked REV an A. I think it is safe to assume this Revision A is the later of the two schematics.

Well, maybe someday more people with bother to take a look and report back, then we could start to build up a picture of the evolutuion.

 

[knopflerfan]

Bendyha - nice work and mods.

 

[Wally]

Bendyha, I just pulled my 1984 SC's chassis.....same set up as the 1983....33K input resistor, 1200pfd snubber. The serial number on it is F4145xx.
Fwiw, I do not think that one can date these amps to the week of the year from the serial number. These numbers on the amps from 1977 through the early '80's are like the guitar serial numbers from '77 on. That is, the letter denotes the decade and the first digit indicates the year in that decade. Ex: S7xxxxx is 1977 for both guitars and amp. IN the '80's, the guitars are dated with 'E', but amps use 'F' for that decade. So, my F4145xx is from 1984.....week unknown. IN the '90's, guitars used 'N'....and the amps were given a date code system that reverted back to the old.....1952-Mar, 1967....system of two letters...one for the year and one for the month. ...plus a serial number for specific ID of that chassis---not a dating serial number, though. Ex: my 1996 custom shop Pro Sonic has an 'LOxxxxxx' number...indicating that it was built in Lake Oswego, OR. The date code is HG, IIRC....August of 1996....on a small silver and black tag in the cabinet.
Before 1977, the serial numbers on amps meant nothing.....that is, there was no code in that serial number that would indicate the year. Three fellows...Greg Gagliano, Greg Huntington---RIP, and Dave Riebe gathered a mass of data from vintage amps and collated the info that enabled them to build serial number charts for the pre-1977 amps. All of the serial number charts that are found in various places on the web are derived from that work....copied one might say. There were originally 5 articles that were published in 20th Century Guitar about 15 years ago. Here is a link to t he article that lays out those serial number charts and also makes note of the 1977 and later Fender serial numbers that actually carry the date code in the Letter and the first digit.

http://www.ggjaguar.com/fendamp5.htm

IF you google/serach 'Greg Gagliano Bibliography', you will get to a list of his published works and find those original five articles..."Dating Fender Amps"...plus a 6th article that was put out just in the last few years. IN those articles one will find invaluable information on vintage Fender amps....particulars, oddities, exceptions...whatever. That info was drawn from many thousands of vintage Fender amps over a long period of time....a lot of hard work using information sent to them from techs and vintage amp owners. Great reading....and necessary for anyone who wants to delve into vintage Fenders amps, imho.

 

[Bendyha]

Dating your Super Champ

...and necessary for anyone who wants to delve into vintage Fenders amps, imho.

I'd rate it as an indebted duty to participate for anyone who has ever wanted to know about dating amps to send in any information they can obtain, especially those who work on amplifiers.

Fwiw, I do not think that one can date these amps to the week of the year from the serial number.

True, but we can now take an educated guess as to which year and quarter it was made from that number, and if you look at the date stamp on the amp, there you have the week of production.

In the last instalment of Greg Gagliano excellent research - DATING FENDER AMPS BY SERIAL NUMBER, PART VI , he does for the first time, give some information on the amps built during the so-called Rivera-Era, although not much. Towards the end of the document he writes;

"Thanks to everyone who sent information about their amp(s). Many thanks to Andrew Waugh for his help with the 1982-84 tube amps. Andrew works in parallel with this research, but is specializing in the Rivera era blackface amps. As with the late ’70s serialization patterns, the early 1980s amps are a tough nut to crack and his task is even more daunting because the solid state amps also get thrown into the mix."

In 2002, Andrew Waugh started his Unofficial Princeton Reverb II page http://www.stratopastor.org.uk/strato/amps/prii/PRII_hub.html, and has since then devoted a lot of time and effort into compiling and sharing information related to this amplifier. Asking owners of PRII's to send him their amps serial numbers, he hoped to establish a data base that would allow him to know how many were made, and when. In Denmark, Soren Thomassen started doing something similar with the Super Champ. It soon came apparent to Andrew that to consolidate the growing dossier, the single amp approach was insufficient, as the one set of serial numbers were not only shared out individually across the whole line of 14 different amplifiers, but mixed together into many smaller blocks of consecutive numbers that related to the system of "one-model-at-a-time" production runs, in the manner that Fender seems always to have built, fulfilling the demands of sales-orders. This system differs from what Fender had been using prior to 1981 whereby each model had its own unique set of serial numbers.
For this reason, the "Unofficial Princeton Reverb II page" started to gather information on all 14 Rivera Era amplifiers. Soren Thomassen shared all the information he had gathered on this period of production, as did Greg Gagliano, who is still in contact with Andrew. Contact was made to many ebay sellers, with most being willing to pass-on the details of their amps. Emails have been exchanged on several occasions with Paul Rivera and other fender workers of this period.
As of Jan 2015 he has information on over 1500 amps. Compared to the estimated number of amps made during this period, that's better than one in fifty, which might not sound like much, but quite a lot can be deduced from such a sample, even though the information is incomplete, and can therefore never totally accurate.
Many owners of amps have answered his call to send in their amps details. I hope anyone who reads this will also do so if they have not already ! Send as many of the following details as possible to ; stratopastor(at)hotmail(dot)com
The serial number; this is stamped into the chassis on the back of the amp and is readily readable.
The transformer numbers; the power and output transformers both have two sets of numbers stamped into their top side, one will be the six digit Fender part number, the other one is the relevant manufacturers stamp EIA606 - *** The first part of this tells us that the transformer was made by Schumacher, the *** numbers tell us the year and week of manufacture. 144 = 44th week 1981, 217= 17 week 1982, etc.
The speaker code; this will normally be printed on the frame of the speaker such as 109**** or 67-**** the number printed on the cone is not relevant.
The date stamp; This takes the form of a four digit number stamped in blue/purple ink onto the chassis. This number is in many cases only visible if the chassis is removed from the cabinet, as it is often printed onto the one side of the amp, along with other numbers. On my amp, it is just visible as a reflection, purple on black, right below the serial number - see photo below. My amp has the date stamp 2803. The key to understanding it, is to reverse the numbers 3082, and this gives you the week number and the year, the 30th week of 1982.
It is the serial number, and the date number together that are perhaps of the most interest. The speaker and transformer numbers give us "not made before" dates, but can also help to group production runs together.

I've exchanged a few emails with Andrew, and I recently asked him if I may copy some of his work relating to the Super Champ into my thread here. He kindly agreed, writing back;

I never publish owners' names or contact details
I'm not using this info for commercial purposes
There are no 'magic' production batches, so the date of your amp will not affect its value
Don't ask me how much your amp is worth, I really don't know.

"......one more thing - please quote me as saying that Greg Gagliano is the man, and what I'm doing is small compared to his work. "

That maybe so, but I believe he is being overly modest, and I am most indebted for the great work he has, and still is, doing.
To read the complete research done by Andrew, visit his informative website. Unofficial Princeton Reverb II page.
Here is my summing up of what Andrew has worked out, specifically in regard to the Super Champ, just one of the 14 amps in production at the time.

Super Champ - Production total is estimated at 11,500. At the hight of production the factory was averaging over 50 hand-assembled amps per working day.

This isn't official Fender information, nor is it anywhere near complete, and you may well find exceptions.
All the amps built during this period have a serial numbers beginning F2, F3 or F4 followed by another 5 digits. Fender evidently started with the plan of making the first serial number digit represent the year of manufacture. F2 = 1982, F3=1983 etc. but this doesn't hold true, although the chassis maker/numberer may have used this system, F3 amps were made in 1983 and 84, and an F4 amps could be either 1984, 85, 86 or even 1987. There are no F5 or F6 amps.
The first amp of this so called Rivera-era to use this system F200001 was a Super Champ.

To try to ascertained the method used in the manufacture of the amps from the gathered information, it might be safe to assume that shortly before each model went into a production run, a set number of the previously ordered chassis were delivered from the supplier - possibly already stamped with a serial number, and briefly stored before being either randomly selected, or possibly taken in a vague reverse order (last in = first out), to be built into amps, and shipped. Probably before all the supplied chassis were used up, production would shift to another model, the chassis for these would have been delivered carrying a serial number that was a continuation from the previous models delivery. Any remaining unused chassis from a particular model would then wait until that model went into production again, the following delivery of later production and serial number chassis would then be ordered. This results in the serial numbers from one batch of chassis to the next batch of the same amp type definitely going up in time, but within a batch the numbers were used in semi-random order, and sometimes in two separate amplifier model production runs, such as the Champ II and Bassman 20 that used the same chassis. Some chassis batches are of over a thousand each, as were some of the production runs of one model of amp, so given any 2 amps from such a chassis batch, or production run, and the serial number won't tell you which amp is older. Only the four digit ink-stamp can tell you this.
As the production of amplifiers progressed, there was an expansion in the number of different models being built that where becoming part of the same serial number progression. This mixing of the models is what makes it necessary to gather information on Fenders complete U.S. production of amplifiers for this period, in order to correlate the individual amplifiers.

 

[Bendyha]

Dating your Super Champ - part 2

In the table below, we have the information that's been gathered so far.
The photo shows my amps serial number, and just visable below it, the date stamp 2803.
For the batches labelled "date codes needed", we have no loudspeaker or transformer date codes, or the 4-digit ink-stamp date code. However the dates for these batches are certain to be after the batch shown immediately above, or before the batch shown below.
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, and possibly 1987.
The first batch has serial numbers spreading an interval of 240, but was very likely 250, the second batch the spread of known numbers is 902, possibly 925 were made. With many of the other batches it is not yet possible to hazard a guess; more information is needed. So please.. SEND YOUR AMPS DETAILS TO STRATOPASTOR

 

[Wally]

BE4ndyha, the F serial nubmers were used before 1982....they were a continuation of the A = six digit numbers that were begun in 1977.
I recently worked on a 1981 Vibrolux REverb that had an F1---1981--- number.
I will take a look at my chassis stamp date codes....and add my info to that listing that is being complied....but....I don't see as much need for that study as there was for the Gagliano/Huntington/Reibe work that was published in 20th Century Guitar. Since 1977, FEnder amps are datable, ime, whether through the serial number or through the two letter date codes that began in 1990. Actually, except for some 'oddities' I still date pre-1977 Fenders the old fashioned way......just as Gagliano/Huntington/REibe did....with manufacturer codes and tube chart codes.....excepting those April, 1967 through 1976 amps which had no tube chart codes, right?
What oddities, you ask? There is a BF Pro REverb around here that has a tube chart code of OPA. That is a good one, eh? The G/H/R work caught that snafu, too.. A worker at Fender forgot to roll the date code stamp forward in the beginning of 1966. The P was added to the "OA"...because the amp was built in January of 1966...not in January of 1965.

Solid state Fenders???? I don't care when they were made. Don't play 'em, don't listen to 'em, don't work on 'em much, either. But, I have one here that has the black and silver code label....AI.....A = 1990......I = September, I think.....and the component codes match that.

 

[Wally]

Fwiw, all of the Rivera-era amps....Champ II, SC, PRII, DRII, Concert and TRII's....I have run across that had original speakers all had date codes that corresponded with the serial number dating scheme...tranny codes, etc, all checked out. I just have never had any reason to question the validity of the F_xxxxx serial number scheme on these amps. And...imho, there is no concern...but I admire hard work. And...there are always exceptions to any rule, ime.

 

[Bendyha]

Your quite right Wally, but the dates are not realy the point. I've just finished reading Tom Wheelers' - The soul of tone, and I have dozens of other books about tube amps, and the fact is that everyone seems to know less about this period of Fenders history than any other. Why? Because nobody up to now has bothered to research it. The most interesting revelations gleaned this collecting of information, include how many of each of the models were built, how did the factory opperate, what was the date and order of the introduction of each of the models, and the discontinuation? Have the advertised rack models ever been produced and sold? Were any ChampIIs' every made after late 1983. How many Bassman 20's exist?
There is a lot to learn, and yes it is of interest, although many people take the knowledge for granted that gets printed in books and repeated in Forums, but behind the simple facts lies hard work from dedicated researchers who can only help us all by being helped by others.

 

[Bendyha]

A New Output Transformer.

The standard layout for the Super Champ, is to have the two speaker wires coming straight out of the amps back panel, with no speaker jack connection. To change this over to having a jack in the speaker out position, is a simple mod that doesn't need explaining, enabling the amp to then be played through an external cab. The output transformer in the S.C. only has a single, non-tapped secondary winding, suitable for an 8 Ohm load. If one wants to have more flexibility than this, then the only option is to replace it. The specifications of the transformer have remained unchanged since it was first used in the AA964 Princeton

Output Transformer - 022913, (125A10B) Made by Schumacher, Paper-wound
Core - EI57, 57 X 47.5mm, 48 laminates, 17.5mm thick,
Mounting holes - 2 13/16", 71mm
Height - 2", 49mm
Width - 2 5/16", 59mm
Depth - 2", 49mm
Weight - 15 OZ, 425g.
Power Rating - 15/18W. (with limited frequency response)
Impedance - Primary - 8500 Ohm, Secondary - 8 Ohm.

Some available drop-in replacements with an additional secondary would be
Magnetic Components Inc. - "Classic Tone 40-18045" - 8.5K primary, 4 & 8 Ohm secondary.
Hammond 1760E - 8K primary, 4, 8 & 16 Ohm secondary.
Mercury Magnetics - typical lack of information, unstated primary & dimensions, 4,8 & 16 Ohm secondary.
Then of course, one could decide to opt for an "Upgrade"

So what would be an Upgrade? One could say something that makes it stop sounding like a Super Champ, reacting & compressing like a Super Champ, or even being a Super Champ.
Being as it is, essentially a Princeton reverb with boost, an Upgrade from a Super Champ is called a Deluxe. The standard output transformer of the Deluxe; 125A1A, is not only a bit larger, but has a primary inductance of 6K6 instead of 8K5. Then their are Upgrades of the 125A1A that are bigger still, and have additional secondary outputs.
So what would be the changes brought about by swapping over to a transformer like this be?
One could expect to have an increased dynamic head room of clean tone, a fuller, warmer tone of added volume, and less compression when driven hard. Having a greater mass also means it is likely to run cooler. Plus the possibility of running different speaker cabinets. One could then even try running the amp with 6L6 at 6k6 / 400V.
Super Champ / Super Deluxe?
Let's give it a try!
I opted for the Classic Tone 40-18087. Deluxe Upgrade, 6K6 primary, 4, 8 & 16 Ohm secondary. It is a whole lot larger than the original transformer, with mounting holes .3" wider (8mm.) meaning one does have to drill a new hole, but it does fit without any problems.
The wiring-up of the primary is simply straight replacement, the secondary offers a few options.
Removing the back-plate lug for the original speaker wire, replacing it and the unwanted line-out jack with two stereo Cliff style switching jacks, I now have the option of running two cabs. Having my wonderful EV10 8 Ohm speaker in the amp, that will be running off the first jack, and for the second jack, I built a matching cab with a 8 Ohm 12" Alnico Fane AXA-12. - Smooth & dark and loud.
Although quite impressed when I first tried it out, even though the Fane still needs quiet a bit of playing-in, I decided to try-out the new set-up using a pair of moderately biased JJ-6V6S, and I must admit that these tubes seem to prefer the lower impedance output transformer, and I am now very impressed by the amp. It does sound quite different than before, even without the extension cab plugged in it sounds a lot bigger, and I would have to say better, and I currently doubt I will change it back. With the extension plugged in, I get gigging volume & power.

Trying to find information on how to wire-up the output jacks correctly, so that the impedance is automatically correct regardless of whether the extension cab is plugged in or not, is rather difficult. Also the added option of a 4 or 16 Ohm solitary extension, and whether the two speakers are better in a series or parallel configuration?
I opted for parallel 8 Ohm speakers running off the 4 Ohm tap, with the added choice of either a single 4 or 8 Ohm output, for just the internal speaker, or my 4 Ohm 4 X 12" cab. The wiring diagram for the two options is below.
One must use insulated jacks that don't take their earth reference from the chassis. With the parallel cabs wired this way, it is necessary to invert the polarity of one of the two speakers so that they run in phase with each other.