The infamous Frank-en-Champ goes under the iron...again

[212Mavguy]

This amp started out with me as a low cost purchase from a friend in barely operating condition for very little cash around 8-10 years ago. I was very early in my tube lore learning, and I got to put this amp's chassis on a spare work bench at my amp tech friend's shop. There I learned what was wrong and smelled the solder fumes for the first time repairing it under my friend's guidance. First time I got to smell those since my childhood slot car hobby, which I participated to the level of rewinding my own motors for waaaaay more speed.

 

So since then it has slowly been repaired, repeatedly upgraded, and modded to what has been for the last few years... a very potent grab and go wolf in 70's silverface sheep's clothing. it is also pretty ugly inside because it's the first amp I ever rebuilt, it sounds great, nice parts in it. Too ugly for pics. It IS my first build.

 

In it's present it has a fiberglass turret board personally populated and installed in blackface style. Power supply caps are slightly higher value than stock. Both trannys have been replaced with more robust ones. particularly the output tranny, now larger than the power tranny, it's a 6-7 pound hifi unit mounted with t-nuts to the bottom corner of the cab, presently wired at 16 ohms. Stock was a walnut sized witto bitty baby chunk with 3.2 ohm output.

 

It uses a vintage, rated 8-16 ohm 25 watt, original cone University Diffusicone 8 inch speaker now, and oh so huge and sweet sounding instead of the lower quality construction and output rating Jensen with the torn cone and warped frame it came with.

 

Inside the guts, the latest surgery was in the tone cap section. The ones in there were at stock values, very top end and spendy they were, hifi weenie adored big fat bulky paper in oil thangs that were a tight fit to kludge in originally. For some reason when I did up the turret board originally I used a silver mica treble cap instead of the original Fender ceramic unit still sitting in the old factory waxed cardboard eyelet board relic. Mistakenly, I though that the silver mica would sound better.

 

The purpose of the present surgery was to get the amp to sound more opened up, at present it was too bottom and lower mid heavy, a bit sludgy and congested there, like many Fender circuits of the period. I learned from the Super Reverb Project that there is a cult of Fender circuit builder/hobbyists that found better sounding tone cap values than what Leo originally put in.

 

Before messing with tone caps it became apparent that other things affect that circuit's tone besides those. Previously, the power tube cathode bypass cap went from 25 microfarads at 25 volts stock to a more robust 50/100 for more robust, tighter bass, and improved reliability. So that fatter bottom and lower mid was the result.

 

The 500 ohm cathode bypass resistor, higher than stock 470, was yanked, a 680 ohm one went in, resulting in a more clarity, note definition, and slightly brighter tone as well as no more slightly redplating power tubes. This puts the bias for the power tube right where it needs to be with today's higher wall voltages than when the amps were originally designed...longer tube life for that rare NOS tube, a huge thang right there. I found out about that resistor value on a forum from a member who had an oscilloscope and knew how to use it. The value shown on historic Fender schematics of 470 ohms runs power tubes too hot and makes the tones too distorted when they need to be clean.

 

So now the power section is tuned satisfactorily, now to work further forward. Sonic improvement was happening. Next, and first thing on the current surgery was to yank the 250 picofarad Silver Mica treble cap and stick in the original vintage Fender one, the SM cap had a sound kinda like tearing cloth on the distortion tones, not Fender-sparkly enough.

 

The bass and mid caps were next, stock was .1 and .047. After several lengthy soldering and listening experiments with different values, hours later the ones that stayed were now .05 and .025. Next was the cap that coupled the second half of the preamp tube to the power tube, the value here shifts the entire amp tone towards brighter or darker, Stock was .022, I ended up with .01. All of the tone caps subbed in were Russian Military paper and oil units from earlier eBay purchases. Interesting was what sounded best was when those three caps were halved in value, but the ratios stayed the same between their values...And what worked there also depended on what was going on in the power section, the fattening up of the tone there from the beneficial increased power tube cathode bypass cap value may have helped necessitate the adjustments done in the preamp.

 

Tone inside an amp circuit is a juggling act. I originally wanted it to be bright enough with the treble set at noon, it ended up with the sweet spot on that knob being 9:00. Perfect, it worked out to be. Plenty of room now for opening up tones of darker sounding tubes and instruments. I played a nice Yairi acoustic with a K&K pickup in it, worked great after a bit af addition on the bass knob. Played a baritone scale guitar on stage it was great for that. I can scoop the mids or squeeze them on up louder with the tone pots enough to work with what ever gets plugged into it.

 

The best surprise was when my friend plugged his harp in, we were both floored at both how loud and how sweet it sounded. The same things that helped the guitar to sound better also worked for harmonica through a bullet mic..

 

Because an earlier procedure had reduced the signal loss to ground through the tone pots and caps to a quarter of original, the tone caps have about a quarter of their original effect on the amp's tone, but what is available from the treble and bass knobs is now just barely enough. The amp also acts like it has about four times the gain of stock now, it breaks up starting at 9:00 on the volume knob and easily gets to unlimited sustain at above noon settings. And for what small wattage and physical size it is is, it gets ungodly, hugely sounding loud now, a baby bubba balls breaker, this one is now.

 

The present result took lots of thinking and tinkering and playing hours to attain, but was worth it. Then I started to play it on stage recently, through a 16 ohm 2/12 with Altec 417 and JBL MI-12, could only turn up the volume knob to less than 10:00 when playing out with a full band and drummer...with a single 6v6 power tube. I don't do clips, but take my word for it, a simple circuit with only three tubes can yield some pretty astounding results in both volume and tonal qualities. Going as a grab and go combo the amp is loud enough to keep up with that same band at 11:00. When you change the guitar, you hear the guitar, when you change the pickup, you hear that, the amp is very expressive of what goes into it. The clarity, complexity, and balance on the clean as well as dirty tones are well within full on uber-spendy boutique amp territory now. When I took the rig to a couple of open mic/jams for the on stage portion of the experiment, the results were beyond expectations, some real "wow" moments happened while playing through that amp.

 

Am I done? Naaah, While staring at the circuit layout I found the place to break the circuit and stick in a serial fx loop, then I can use a tube loop buffer and go after Dumble territory...The amp will do unlimited sustain like few do as well at volume knob settings above noon, but too loud for gigs when doing that. The tube loop buffer allows cranked amp tones at lower volumes besides being the place for time based effects to be inserted within the tone chain. But that's for later...

 

Lastly, I went for the earlier, tweed-ish "Big Fender" amp tone via tube rolling. The amp was now opened up enough on the upper mids and top end to run it with the treble knob less than noon and still sound great. So since there was tonal room for darker preamp tubes now...I wanted to try a couple of types that were not optimum in the earlier preamp too dark sounding back then. The 12ax7 socket has a raised rim to mount the tube shield on, to clear that height I used a 9 pin socket saver as a spacer, then stuck an adapter in the socket saver, and socketed a Tung Sol 6sl7w series, it has plates like their later 12ax7 in it, a bit too full sounding in the earlier preamp configuration, grabbed a GE labeled RCA 5691 6sl7 military and ran it as well, each tube for a full half hour, musically simply amazing, more note separation in chords, more distinct clarity overall, yet huge in the mids and bottom. To gain more clean headroom and girth, next was a power tube upgrade. The Allen power tranny upgrade earlier installed has excess capacity available. When run as a combo it gets very loud now and there is enough pressure from that speaker close by the tubes to rattle them into microphonics, the massive 6sl7 preamp tube/adapter stack socketed in there now was now pretty much immune from the microphonic thang being both more massive and the military spec tube choices.

 

So a 5932 Sylvania subbed in for the 6v6, more oomph from that type of early 6l6 compared to 6v6,. they are built for rough military environments. Very nice sounding, one variant of that tube type has two sets of guts mounted side by side inside to help with shock/impact resistance in battlefield conditions, rated for around 20 watts in a pair compared to 6v6's 14 watts and modern 6l6gc's 30 watts. Compared to vintage Tung Sol 5881, the Sylvania 5932's of either construction type have every bit as much tonal detail, with the tS's having more mid focus and the Syl's having more mid scoop, both types work greeeeeeeeeeeeeeat here. Stock 5y3 rec tube supplies more than enough current to run a 6l6. Louder and brighter can be had by running a 5v4 or 5ar4 rec tube but louder and brighter are not necessary anymore. Don't stick a 6l6 or mod to run an el34 in a vintage Champ without upgrading the stock power tranny first. It'll fry eventually, right when you are in the middle of a good time.

 

it's truly astounding sounding now. Glad to have gotten it such a long time ago and what a mostly rewarding long strange trip it's been to get it where it now is. There is no way to anticipate what it sounds like from looks, it does very much sound like a real American build Fender Champ wishes it could when used as a combo, used as a head driving a cab it becomes a full on sweet sounding monster, not so much of a one trick pony practice amp. But...it only has three tubes in it, it does make a GREAT practice amp built to be left on for hours at a time as a compact combo or running through bigger cabs.

 

Boutique amps for boutique guitars!

[yoslate]

What a post! What a project! Would so love to hear, too, rather than just read.... Used to know a guy who had a beaten up old Datsun 510 sedan. Total beater. The only hint was it sat about four inches low on a set of Minilites, wrapped in Pirelli P-10's. Under the intentionally crappy, primer and rust coach work: A fully blueprinted, fuel injected 240Z engine; Bilstein tuned suspension; oversized disc brakes at all four corners; and on and on. Sounds as though you have the amp version. Love it!

[212Mavguy]

Thanks!

 

As a follow up adventure I went down to a jam in a club 50 miles from home last night. Took the rig in, at this venue they don't mic the amps. I got to put that thing at it's absolute sweet spot, 1 to 2:00 on the volume dial. It was just perfect, did anything I wanted to, I was really relaxed and the music just gushed out. Got some nice compliments on it.

 

When the amp is behaving exactly like the sounds your head wants at the time it is easier to play well!

 

It is true that a post like this thread's starter ought to have pics and video. I had the camera at the bar last night but got up on stage playing and forgot to find an operator, Ooooops!!

 

Finding an old silverface Fender Champ is not necessarily cheap anymore, but the 60's yielded a treasure trove of not so sacred amp platforms with wonderful tones in their bones. I pretty much have what I want now, but I do lust for an early Sano to hot rod. If someone handed me another 70's Fender Champ to re-do I'd so be all over it!

 

There is a future project on the bench right now, I don't know whether it runs or not...a friend's recently acquired silverface master volume early 70's Fender Bassman 100 head. If the amp's iron turns out to still be good that will be a very fun ride to raaaaawwwwwk when I get done. I'll use my cell phone camera to take some pics.

 

Much more satisfying to catch a fish in a high altitude wilderness lake using a personally built rod and home crafted tackle. You tweak what you are using to catch that fish. Same thing for playing on stage through a personally built, repaired or tweaked amp.

 

Retail therapy is pretty damn awesome in the personal satisfaction department, but home grown tone beats store bought tone eventually. It just takes time, toilet seat reading, and a bit of persistent madness...as well as the willingness to spend some of that throw away Chinese style modeling amp money to buy a couple of books to learn from what to do, a few inexpensive tools, a well lit workplace, and the willingness to burn a few fingertips at first. There is a road map to get to a good amp place here. There are a lot of silverface champs out there, likely some of you have one. They are not sacred, it's OK to drill holes in the chassis on one of those...or a vintage cheese amp.

 

And finally, if your home grown amp performs reliably over time like a spendy boutique amp does, then it must be boutique..... too.

 

Boutique guitars for boutique amps!

Boutique amps for boutique guitars!

[Gitfiddler]

Very cool posts.

 

Every time I read one of Mavguy's amp adventure threads, I smile from ear to ear the whole time...and I read them slowly to savor all of the delicious amp-delights.

 

If you are ever in the SF Bay Area, give me a shout. I have a few 'baby cheese-amp-fire-breathers' that you would enjoy.

[gpuma]

Thanks for sharing! This is really fun to read

[212Mavguy]

Thanks for the compliments. I did and do enjoy writing. I had a blast composing the original post, almost as much fun as the ongoing occasional adventures with playing my guitar harem out through that amp.

[sfceric64]

I bet that Franken Champ rocks....I love the older pre-amp tubes. I have a National (Valco) that uses a 6SL7 to push a pair of 6v6's wired in parallel and a 5a3 that uses a pair of 6sc7's to push the 6v6's....Really great full cleans w/ both amps or they can be driven w/ Buckers/pedals to get classic overdriven tones. My DRRI is sometimes neglected, but not forgotten completely.

I'm not a big mod guy but I do all the work myself when there is a problem. It was a lot of fun learning to DIY my gear and rewarding. Great story you wrote, I could feel the excitement in your words. A picture or two would be great to tie the story together! Thanks for posting your experience.