I love my Champ....but...

[BobbyFudge]

I've found a sweet spot on mine just past 8 but it gets so farty bass wise.I just put in a NOS Brimar and am loving it but I feel I'm not getting the full potential of the amp.

Any tips?
Thanks!

[Reeek]

What speaker is in it now? What preamp tube are you running?

[John Phillips]

Tweed, BF or SF?

Farty bass is normal on later BF and all SF Champs. Partly it's the speaker, but partly it's because the stock bias is way too hot... WAY too hot. So much so that the waveform clips at the forward end first, which actually reduces the clean headroom and makes the distortion mushy and farty. (As well as wearing out the tube more quickly.) They were made like this, for some reason.

To fix it, you need to replace the cathode resistor with a higher value - typically either 820 ohms or 1Kohm, in place of the stock 470 ohms - and raise the voltage rating of the cathode bypass cap to 50V. It's also a good idea to fit a screen resistor (470-ohm).

If you do that you will get tighter, more even overdrive and more clean headroom, and longer tube life.

It may be a good idea to replace the filter caps too if they haven't been done - the BF/SF ones use a multi-cap can which is more of a pain to replace than the Tweed type with three separate caps (and usually lasts a lot longer too, but even at that will most likely be getting near the end of its life, especially on a BF or earlier SF).

[Trout]

You can get a lot less fartyness by upgrading the OT and speaker also. The BF/SF OT's are very limited.

Using a JJ 6V6S could help the bias situation as then can handle a lot more current and voltage than most NOS 6V6's without getting muddy.

Im running a JJ 6V6s at 391V on plate, 386V on the Screen, The bias resistor is 500ohm giving me 23.9 on the cathode and the tube is very happy there. No excessive heat and huge bass response, But, Its not the stock OT.

I also changed the slope resistor to 68K instead of 100K, and Put a .022 in instead of the .047 which brought up some of the low mids and upper bass notes a couple db.
Now it is very smooth and not flappy at all, But I will admit it is much louder than the average champ.
Any decent 12" speaker hovering around 99db will work well, I personally like the Jensen Neo 1st choice, C12N second choice. I am thinking weber most likely has a great choice also, The 12A125 Might be a great one.



Trout

[BobbyFudge]

Thanks everyone.It's a 76 SF with original speaker,and the pre is a Fender ....I will definitly do the upgrades when money permits.What I love about my champ is that it is just an honest great sounding amp.My VT40 is a monster that I love also, but is just too freaking loud for practice.

One more thing...what do you think it should cost to upgrade the cathode resistor,fit a screen resistor and replace the caps?I want to keep it as stock as possible.

[philbarnes]

I would think speaker. My Kalamazoo Model 1 (very similar circuit to tweed champ with a simple treble roll off tone control) has the same issue with the Weber 12A125 in it, but not with the Weber Silver Bell in an external cab. And go see Mike at KCA NOS tubes to get set up. Right tubes = huge difference. I am putting a Mercury Magnetics Champ OT in, we will see what that does. If you can't have a Kalamazoo I am sure you can rescue that Champ! (save it, kidding my friends.....)

[epluribus]

OMG, more Kalamazoo content! They're multiplying. :eek:

I just stuck a Weber Alnico 10S, speaker in/out jacks, and a set of JJ's in one of my Kzoo IIs. I suspect we're looking at very different bias settings than the Champ, esp the SF, so the results of those mods will likely be different from the Fender, but FWIW...

Stock, Kzoo's are very cool amps, esp with a Strat plugged in, lots of compression, tailor-made Strat voice, and thick tweedy drive, but they get very attack-ratty near the ten-spot. The JJ's smoothed that out a ton. The speaker, much less susceptible to breakup than the Kzoo's, tamed the amp even more and made a significant improvement in frequency response, better lo-mids and more balanced highs. A far more civil amp, but maybe too civil. I miss the feisty I'm-fixin'-ta-bust-outa-my-box character and the stout compression. To me, that hot and squishy drive is such a Tweed thing that I miss it.

BTW, I ran the speaker-out to a Deluxe Reverb II with a Weber 12F150 in it. Amazing--where did all that tone come from? Doesn't sound Champ-y anymore, more like a miniature Tweed DR, but way cool.

Anyhoo, the point is, I managed to make the amp much more usable, but perhaps at a bit too much cost to its Champ-tone. Thank heaven I have a second one that's basically showroom inside and out. Just food for thought as you make your design choices.

--Ray

ps: I'm still tinkerin'.

[trisonic]

John Phillips' tips on fartiness reduction (also known to Jimmy Somma, who actually worked on my BF VC) do work!

Completely changed the amp, I use it nearly every day now (Somma also put in a reversible, switchable tone stack bypass so that I can get BF or Tweed).

Best, Pete.

[Clearspider]

To fix it, you need to replace the cathode resistor with a higher value - typically either 820 ohms or 1Kohm, in place of the stock 470 ohms - and raise the voltage rating of the cathode bypass cap to 50V. It's also a good idea to fit a screen resistor (470-ohm).
Can these be done to a Deluxe Reverb to reduce the "fartiness" and front-end clipping?

[mr coffee]

champy is single ended and cathode biased
DR's are push/pull with adjustable fixed bias

the DR's can be tweaked but a better than stock speaker helps alot also

[Jeff Flowerday]

I'd recommend a weber 8F125 speaker replacement.

[epluribus]

Can these be done to a Deluxe Reverb to reduce the "fartiness" and front-end clipping?

There's been some excellent discussion on this in the last several months...

http://www.thegearpage.net/board/showthread.php?t=187541

http://www.thegearpage.net/board/showthread.php?t=216455

http://www.thegearpage.net/board/showthread.php?t=216061

http://www.thegearpage.net/board/showthread.php?t=196272

Caveat emptor, however. I went through all this regarding my DR II, and finally came to the conclusion that beyond a few mods, I was really getting into trying to turn this into a different amp. Funny thing was, I found tons of stuff in the amp that I liked as is. JJ's and the Weber made it a hugely playable amp while retaining all the Deluxe character.

BTW, my Deluxe patch on my CyberTwin doesn't fart out at all...y'know I actually miss that? :NUTS

--Ray

[epluribus]

I'd recommend a weber 8F125 speaker replacement.

Glad you mentioned this Jeff. A tight modern 10" almost sounds too stout and tight for a Champ, to my way of thinking. Champs oughta rattle a little bit.

--Ray

[edward]

My Champ had definite flatulence at volume. Stank badly IMHO ...but I loved the tone so long as vol stayed under 7 or so. The first and arguably most significant step is a speaker swap. I put in a Weber Signature 8 (AlNiCo 8") and it is a different animal altogether! Turned it into a real tone machine, and smooth up to 10. Prob can get even better once you do said mods after this point. BTW, the Weber will set you back, what, $30 bucks? You'd be hard pressed to get any other good-sounding mod for that price!

Edward