1973 SF Champ more clean headroom possible?

Muttlyboy

Gold Supporting Member
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3,094
Wattage is a measure of clean power. You can’t draw blood from a stone.
Not really the same situation.

Let's say that a correctly biased Champ with fresh filter caps and good tubes is capable of 4 watts clean.

Is the OP's amp putting out that 4 watts?

Also, that stock speaker is weak. The Jupiter speaker DOES get more volume out of whatever available watts the amp is putting out when compared to the stock speaker. It's a good "mod" if you're trying to get more volume out if a Champ.

Same deal with the 15 watt replacement OT that's available from a few vendors.

Same deal again with the 6L6.

8 clean watts out of a Champ is about as much as you can get. After that, you would need another amp.

Is it worth the trouble and expense to make the changes for an 8 watt Champ? Maybe, maybe not...

The OP's question was more like "can it be done?"
 

Tiny Montgomery

Silver Supporting Member
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10,294
Not really the same situation.

Let's say that a correctly biased Champ with fresh filter caps and good tubes is capable of 4 watts clean.

Is the OP's amp putting out that 4 watts?

Also, that stock speaker is weak. The Jupiter speaker DOES get more volume out of whatever available watts the amp is putting out when compared to the stock speaker. It's a good "mod" if you're trying to get more volume out if a Champ.

Same deal with the 15 watt replacement OT that's available from a few vendors.

Same deal again with the 6L6.

8 clean watts out of a Champ is about as much as you can get. After that, you would need another amp.

Is it worth the trouble and expense to make the changes for an 8 watt Champ? Maybe, maybe not...

The OP's question was more like "can it be done?"
A champ is nominally 6 watts, not 4 or 8. And you can’t just stick a 6L6 in one without significant modifications. A more efficient speaker can help a little, but a Champ is the last place to look for headroom. A speaker’s efficiency is its ability to deliver power that’s there in the first place.
 

bigben55

Member
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3,273
My amp tech is a great player who's gigged 5 nights a week for 30 years. His amp of hoice is a SF Champ that he modified to run a 6L6 and revoiced the tone stack. Runs it thru an efficient 12" speaker cab. Ive heard it, and it does sound great. Plenty of headroom, but I assume it's making more than 6 watts now, that might defeat the purpose for OP.
 

Geetarpicker

Member
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3,198
As mentioned in a prior post short of extensive and expensive amp mods, the biggest change will come from speaker upgrades. That said I’d skip the 8” speaker and go with an extension cabinet. An efficient 10” or 12” speaker is going to bury any 8” one. With the 4 ohm requirement of a Champ I’d suggest a x2 10” cabinet, perhaps with x2 8 ohm Eminence Ragin Cajuns wired in parallel. I can’t think of a more efficient speaker short of going to 12s. FYI a 10” can fit in a Champ size cabinet, like Rivera did with the Champ II and Suoer Champ but they moved the speaker cutout way off center to clear the chassis. Not sure if in a stock Champ you can simply enlarge the cutout an make a 10” fit or not. Still then you have the impedance issue and it might be hard to find a 4 ohm 10” speaker, which is why I suggest an extension cab with a pair of 8 ohm speakers.
 
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Muttlyboy

Gold Supporting Member
Messages
3,094
A champ is nominally 6 watts, not 4 or 8. And you can’t just stick a 6L6 in one without significant modifications. A more efficient speaker can help a little, but a Champ is the last place to look for headroom. A speaker’s efficiency is its ability to deliver power that’s there in the first place.
A late 70s Super Twin has six 6L6GC tubes, and I think was rated at 180 watts. They tend to be priced cheaper than most silverface amps. Ultra linear Twin Reverbs are also bargain priced.

Either of those amps should solve anyone's "headroom problems ".

I don't know that the OP is looking for quite that much headroom.

If someone wants to get "Some More" volume out of a Champ, I described a couple ways to move the amp in that direction. I believe that is what the original poster's question was.

You also might be surprised that a 6L6 tube will often bias-up in a good range with the Stock existing 470 ohm cathode resistor, as opposed to the 6V6 biased Super hot at 18 watts plate dissipation (again with the stock existing 470 ohm cathode resistor)

I made a fun project out of my old Champ for about $100 worth of parts including the new E caps, 2nd hand 10" speaker, 15watt OT, and a short bottle 6L6WGC/ 5881
 

tonedover

This Is Fine.
Gold Supporting Member
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7,742
nothing substantial without massively modifying the amp.

you are losing sparkle from compression as well.

get a different amp.
 

hank57

Silver Supporting Member
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9,644
At low clean volume I think a champ sounds very Fendery.

And I enjoy a Tweed Princeton with an efficient 10” quite a bit. ET10 gives more volume.

Not everyone can find a Tweed Princeton but people make them from kits and I’ve made one. Great amp: volume and tone controls only.

Blood from a stone…
 

gldtp99

Member
Messages
4,372
I don't know that anyone is trying to get a Champ to do something that it wasn't meant to do, or get a Champ to do the most that it reasonably can do.

Seriously ????

5 or 6 watts through a tiny speaker and ya'll want "More Clean Headroom" out of it ???

Start with an amp that isn't a toy to begin with
 

AndreasG

Member
Messages
2,196
Like others suggested a speaker swap is easy and cheap. Jupiter and WGS makes some 8“ speakers that sound double the amp. And then a Champ is a beautiful amp for home playing. Don‘t expect to put it against drums and other instuments unless miked, but you will not hear it in that situation.
 

Guitartim

Member
Messages
892
As mentioned in a prior post short of extensive and expensive amp mods, the biggest change will come from speaker upgrades. That said I’d skip the 8” speaker and go with an extension cabinet. An efficient 10” or 12” speaker is going to bury any 8” one. With the 4 ohm requirement of a Champ I’d suggest a x2 10” cabinet, perhaps with x2 8 ohm Eminence Ragin Cajuns wired in parallel. I can’t think of a more efficient speaker short of going to 12s. FYI a 10” can fit in a Champ size cabinet, like Rivera did with the Champ II and Suoer Champ but they moved the speaker cutout way off center to clear the chassis. Not sure if in a stock Champ you can simply enlarge the cutout an make a 10” fit or not. Still then you have the impedance issue and it might be hard to find a 4 ohm 10” speaker, which is why I suggest an extension cab with a pair of 8 ohm speakers.

I connect my '70 Vibro Champ to a 2x10 ext. spkr and it sounds killer. The cab is a '60's Epi/Gibson with 2 CTS AlNico speakers. Also, the Vibro Champ was serviced to make sure all of its innards n tubes were in top condition.

Let the Champ be the 5 watt amp it was designed to be. If more clean headroom and volume is desired in a small package, there are plenty of rigs (Princeton/Princeton Reverb/etc) to fit that bill.
 

Tiny Montgomery

Silver Supporting Member
Messages
10,294
At low clean volume I think a champ sounds very Fendery.

And I enjoy a Tweed Princeton with an efficient 10” quite a bit. ET10 gives more volume.

Not everyone can find a Tweed Princeton but people make them from kits and I’ve made one. Great amp: volume and tone controls only.

Blood from a stone…
Not really. A tweed Princeton has exactly as much power as a tweed Princeton, which is more than a Champ and less than a Deluxe. It’s relative. Pretty much every amp has some degree of clean headroom. That’s basically what wattage is.

It’s just a matter of how loud the clean sound is. With a Champ, not very. There’s only so much headroom you can get out of a champ before it’s not a champ anymore.

But the clean volume available is more than adequate for playing at home alone or recording, provided it’s working right. It’s just a matter of using the right tool for the job.
 

Geetarpicker

Member
Messages
3,198
Many years ago I gigged with a plexi Marshall Superlead 100 fully dimed, but I attenuated down to either 6 or 12 watts and miced it via the PA for room coverage. That said I always ran two 4x12s w/efficient G12H speakers stacked pointed right where I stood on stage. Point is IF you don’t have much power, you can make up some of it with efficient speakers…to a point.
 

scelerat

Silver Supporting Member
Messages
3,395
Use a more efficient speaker. A champ through a pair of EVM12Ls can be quite loud (and clean). At 6W you're always going to be hitting a headroom issue trying to compete with a loud dummer, but a more efficient speaker is definitely the easiest way to go.
 

Muttlyboy

Gold Supporting Member
Messages
3,094
Seriously ????

5 or 6 watts through a tiny speaker and ya'll want "More Clean Headroom" out of it ???

Start with an amp that isn't a toy to begin with
Okay Whatever...

Pour some gas on the the Champ and set it on fire. I'll have to get over it.
 

amstrtatnut

Member
Messages
14,385
I used to buy tubes from groove tubes and they were graded from break up early to not so much break up. I think you can buy tubes that will tighten up the sound but, if the speaker is farty, then ya gotta get a better one.
 

Khromo

Silver Supporting Member
Messages
1,456
Two tricks have helped me get a little more clean headroom and usable overall volume out of the silverface Champ.

Replacing the baffle with a replacement cut for a 10" speaker is the surest way to get some decent results. The Weber 12F125 bumps the Champ up out of practice/recording amp territory. It is still a little snotty, especially as you turn up the volume, but you will get more headroom.

Putting a clean boost in front of the amp can help. I use an always-on compressor with a small boost, and together with a lower volume setting on the amp it seems to get a little more out of the little 5 watt engine.
 

alberto2000

Member
Messages
15
Thanks all for your help. Some answers to your questions:

- Electrolytics have been updated 4 years back
- Jazzmaster has Antiquity II pickups and standard orange drop capacitors, 1M pot
- Speaker is Weber Signature Series

Updates:

- Swapped tubes to TAD 12AX7 preamp, 5V4GA / GZ31 rectifier, TAD 6L6GC power
- Placed 100pF ceramic capacitor in between volume lugs 1 & 2

The amp sounds beautiful now playing at volume 3 to 4 has a beautiful clean and sparkly sound and going through the -20db attenuator (Two Notes Torpedo Captor) I can play in my apartment!

I measured the dissipation:

pC = 36.7 V / 1000 ohm = 0.0367 mA
pV = 370 V
pD = 370 x 0.0367 = 13.579 W

Does that look right to you?

Thanks so much all of you!
 

TDLP

Member
Messages
302
Speaker swap for a more efficient speaker will give you a few more dBs

Aside from that, Fryette Powerstation + External Cabinet
 




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