Taking the Fender Champion 600 to the next level

Discussion in 'Glowing Bottle Tube Amp Forum' started by Wharfcreek, Sep 19, 2020.

  1. Wharfcreek

    Wharfcreek TDPRI Member

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    As someone who's captivated with small tube amps, I recently purchased a previously owned Fender 600, supposedly with some minor problems. After getting it home and plugging it in, I couldn't really find any specific issues. Seemed to play fine, just seemed a bit lame. At wide open volume I got a bit of grit out of it, but it clearly it's a candidate for some mods from stock!

    In this thread it's my plan to document my approach to changing this thing from its existing ho-hum stature to a respectable little screamer. As this is NOT a 'sky's the limit' project, I'm setting a few basic limits. First, the 'iron' in the amp will stay! No new Power or Output transformers to be used. This means sticking with a 4 ohm speaker. Second, no 'added' transformer for purposes of adding a tube rectifier! If found necessary for 'noise' reasons, a small choke might be added, but the SS power supply rectifier stays. Finally, its got to all work within the confines of the original chassis and cabinet.

    So, as I plan my attack on the amp itself, my first modification was to address the cabinet, as well as the 6" speaker. In that regard, I decided to shoe-horn in an 8" speaker, which took a bit of creativity. For starters, the original baffle board had to go. A trip to Home Depot produced a small piece of 3-ply 3/16" plywood for all of $4. A quick zip with a circular saw and I cut it to the roughly 10" X 6.5" dimensions that matched those OE baffle. I placed it into the cabinet and traced the opening area, then cut it out. I also marked the 4 mounting holes for drilling. Because the speaker mounting screws had to come from the front of the new baffle, I then glued a front frame using bands of paint stirring sticks. I then did some test fitting!

    This test fitting revealed the need to have to make a slight modification to the cabinet itself. Basically I had to cut out about 1/2" of the bottom of the cabinet at the inner front. This allowed me to drop the new speaker in about 1/2" lower than the current bottom of the cab. This provided the needed clearance at the top of the speaker to the amp chassis.

    As to the new baffle board, once all measured up, holes got drilled to mount it to the cabinet, as well as install the speaker mounting screws. Those were set into the baffle using some JB Weld. That will hold them firmly when tightening the nuts that hold in the speaker. I then painted it flat black.

    Now at the point of affixing the new grill cloth, then mounting the board into the cab, then mounting the speaker. Plan to do that tomorrow. Pictures to be provided then as well. I'll give it a quick test listen, then it will be on to the mods to the amp!!
     
    Last edited: Sep 20, 2020
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  2. Wharfcreek

    Wharfcreek TDPRI Member

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    Able to get some pics of the project this evening, so posting them now. Pic 1 shows the inner, lower edge of the amp cabinet being 'grooved' out. Pic 2 shows the 3/16" Plywood with the section cut out for the baffle. Pic 3 is the front of the completed baffle showing how the paint stirring sticks are used for 'framing' the outer edge. This is what permits the speaker screws to be recessed below this framing. Tomorrow when I find my staple gun and complete the installation of the grill cloth, the speakers screws will never been seen, nor will they leaving any protruding 'bumps' at their heads. You can also see how I've used the JB Weld to 'cement' the speaker screws in place. Pic 4 is the back of the baffle board. As it worked out. I used 1 1/2" screws for the speaker, and I probably should have used 3/4" screws. In the case of the upper right screw, when I did a 'test fit' this evening, I noted that about 1/4" of that upper right speaker screw needed to be cut off in order to give clearance for the power transformer behind it. So, while not pictured, that is now done. Pic 5 is a dry fit of the baffle board in the amp cabinet. Pic 6 (as they say in football) is with the speaker mounted to the baffle board. Pic 7 shows the new 'front', which will have the grill cloth by tomorrow evening. Pic 8 is of the back of the amp. This is 'pre' cutting of the upper right speaker screw, so that bit of interference is stopping the chassis from mounting flush to the cabinet. As I said, that's now corrected, just not done yet since I've yet to finish the grill cloth.

    I plan to play the amp a bit tomorrow once completed, and see if I hear any immediate difference between the old speaker and the new. I suspect I will to some degree, but I think the real issue is that as the mods are done to the amp itself, the bigger, better speaker will better be able to capitalize on those changes to produce some improved performance overall.

    Just a quick word about all this speaker change-out: For what it's worth, I'll note that the Ted Weber speaker I'm using was chosen for 3 reasons; 1) It's a known good speaker for these smaller amps, 2) I had one here from past projects, and 3) It's a 4 ohm speaker, so it will work properly with the existing output transformer. Note that it is a 'round' speaker! In truth, I've not 'tested' the PI at the rated load of this 'stock' output transformer. At some point I will. But, schematic says '4 ohms' for the speaker, so I'm taking that at face value. But, were this an 8 ohm output, I had an 8 ohm 'pin-cushion' Alnico speaker that could have been installed on the new baffle board WITHOUT having to make the recess cut into the front of the cabinet. So, if anyone has an old pin cushion 4 ohm 8" speaker they might want to use in a project like this, I suggest that you consider 'fitting' it all BEFORE you go digging into the cabinet wood. You may find that part unnecessary.

    OK.....that's it for now. Onward............ Tom D.
     

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  3. Aldus Bunbury

    Aldus Bunbury TDPRI Member

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    This is one of my favorite amps. I’ve only made three upgrades:

    1) Upgraded the stock AX7 tube—marginal improvement (to my ears)

    2) Upgraded the speaker to an Eminence (same size)—noticeable improvement

    3) Replaced that weird original grill cloth with some actual grill cloth—probably the best thing I did.

    Then again, I wasn’t looking for more gain. I just wanted it to sound like a better version of itself, if that makes sense.

    For me, it’s the perfect practice amp. If there were a way to eliminate the hum, I’d consider it for a lot of the recording I do.
     
  4. Wharfcreek

    Wharfcreek TDPRI Member

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    Aldus, your comment is well-noted! And, in the end, I think that 'making it a better version of itself' is really all that I'm after as well. Honestly, as that's a 'value judgement', most any change to it that anyone makes for their own idea of improvement is really just that..... making it better......to them! Honestly, I wrestled a bit with doing any of this, for the simple reason that in some ways I felt as if I was trying to make it into something that it wasn't designed to be. But, in the end, I decided that people have been 'modding' amps for decades now, from Fenders to Marshalls, and they do so in order to achieve their own objectives. As you said, it's really all about the 'For me...' aspect of it. But, in keeping with your comments, I will do my first evaluation as related to the noise floor of the amp. And, if I find it's humming too much, I may start by doing the choke modification. If you don't mind, maybe you could tell me more about the hum you're experiencing so that I can compare your description to the performance of my amp? A few questions: Does it (yours) hum with the volume turned all the way down and with nothing plugged in? Does it hum with the volume turned down and the guitar cord plugged in? Does it hum with nothing plugged in and if you turn the volume up....a little, half, full? And, finally, will it hum if you pull the 12AX7 out and turn it on? It's the answers to these questions that indicated if the hum is 'input' related, which can be a function of design, or a problem, or perhaps something other, like problems in the power supply filtering. If the amp hums with no cord plugged in and with the 12AX7 out...then you've got a problem in the power supply section that might indicated that your particular amp might need servicing in the form of filter capacitor replacement. Anyway, I know that what I'm doing is NOT for everyone. It's really just an exercise in what 'can' be done vs what 'might' be done but as yet is not. In the end, I may hate it, though I doubt it. I'll make these changes in small steps, and hopefully approach this in such a way that I personally will consider each completed step to be an improvement. My goal is to make the amp 'sing', which means I will need a bit more gain out of it, as well as moving more air. If I can get some nice harmonic feedback out of it I'll be delighted. If not.....oh well.... I will have tried! Tom D.
     
  5. tweedman2001

    tweedman2001 Tele-Afflicted

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  6. Wharfcreek

    Wharfcreek TDPRI Member

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    Tweedman, Just for the record, I made a list of over 15 possible parts to address in this amp, either removal & jumpering, replacing with different values, or just plain deleting. All this was based on what it would take to modify this amps stock circuit to that of 'almost' being a 5F1. That said, I just tested the amp with just this speaker mod completed (incl the new baffle board, new grill cloth, and obviously the new 8" Weber Alnico speaker! To my surprize, the thing sounds great now 'as-is'! Im tempted to do nothing more to it. I did an A-B-C comparison with 2 5F1 'replica' amps I have here, and I was amazed by the fact that the replica amps both sounded darker, and had no more apparent gain than the stock 600 with just this speaker mod.

    So, I actually do plan to do the tone-stack removal mod. But, I can see myself putting it back in too!

    Ive run into one more small glitch with this speaker mod: While its done and working perfectly, the frame of the alnico magnet prevents the output tube from being pulled or changed without removing the chassis and sliding it outward some. Not a big deal to me, but maybe a deal-breaker to others.

    Anyway, progress being made!!
     

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  7. Wharfcreek

    Wharfcreek TDPRI Member

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    Tweedman, Just for the record, I made a list of over 15 possible parts to address in this amp, either removal & jumpering, replacing with different values, or just plain deleting. All this was based on what it would take to modify this amps stock circuit to that of 'almost' being a 5F1. That said, I just tested the amp with just this speaker mod completed (incl the new baffle board, new grill cloth, and obviously the new 8" Weber Alnico speaker! To my surprize, the thing sounds great now 'as-is'! Im tempted to do nothing more to it. I did an A-B-C comparison with 2 5F1 'replica' amps I have here, and I was amazed by the fact that the replica amps both sounded darker, and had no more apparent gain than the stock 600 with just this speaker mod.

    So, I actually do plan to do the tone-stack removal mod. But, I can see myself putting it back in too!

    Ive run into one more small glitch with this speaker mod: While its done and working perfectly, the frame of the alnico magnet prevents the output tube from being pulled or changed without removing the chassis and sliding it outward some. Not a big deal to me, but maybe a deal-breaker to others.

    Anyway, progress being made!!
     
  8. Wharfcreek

    Wharfcreek TDPRI Member

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    trying to upload a pic of the space between the speaker magnet frame and the 6V6 tube. Its fine for normal use, but just has that limitation if wanting to seap tubes around quickly. Might also be a problem if a much taller tube were attempted for use. Remedy may result in removal of pc board, complete rebuild, and relocation of octal socket.
     

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  9. BCblues55

    BCblues55 Tele-Meister Gold Supporter

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    I did two great mods you might want to consider. I put a 250k pot on R19 so I could “dial out” the fixed tone stack. At “0” it’s stock, and at “10”, the tone stack is removed so it’s very much like a 5f1. I like being able to dial in the amount of grit I want.

    I also had the negative feedback (R7) on a switch. With it disengaged, it’s a wild amp, but with it engaged it was too tame. I’ve ordered a 50k pot which I hope will let me dial in just the right amount of grit. And I also hope it helps tame the hum (which mine has as well).

    Nice amp to play with!
     
  10. MikeBee

    MikeBee TDPRI Member

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    Thanks for the pics and info. I will be installing a 8" Jenson mod soon. The groove is a great idea I may use, not sure at this point. It is all torn apart now, I was really enjoying it up to that point.
     
  11. dlaroe

    dlaroe Tele-Meister

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    I've recently been working on mine playing with some stuff from the 5f2a but went back to how I had it. Both preamp bypass caps on a two pole pull switch and a big pot in series with R19 to dial out the tone stack, replacing the volume control.

    I had previously done 22k nfb, old tubes, grill cloth. I didn't like the Jensen Mod 6 and went back to the stock speaker.

    One thing I do love is a bass cutting small cap parallel with the low input series 68k resistor; great for humbuckers. I like it so much I put my 5E3's normal channel coupling cap back to stock and did the same mod to it. Great for jumpering the 5E3's channels.
     
  12. Wharfcreek

    Wharfcreek TDPRI Member

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    The groove was pretty easy. I have an 'electric' Whiz-wheel....and aside from a very minor touch to the front, I was able to cut the groove with pretty much no problems. The 'touch' was my fault..... I just got in too much of a hurry. But, I'd say that if you do the 'groove' thing, you're going to need to do the replacement baffle as well. And, of course, that will lead to the need for some more grill cloth. So, plan ahead. I'll be interested to know if the Jensen speaker works well for you.

    As to those mods you did, I like those ideas. I thought about a switchable feedback using a small mini-toggle inside the amp. Hadn't thought about a 'dial in / dial out' tone stack mod....but that's a great idea. I may try that as well. Did you put the pot on the front, back, inside?
     
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  13. AxemanVR

    AxemanVR Tele-Afflicted Ad Free Member

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    Last edited: Sep 20, 2020
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