Quick Champ question

Jeremy Palmer · May 10th, 2008, 06:25 PM

Well my new silverface Champ is awesome except for one problem: when I turn the volume up to nine or ten and really dig in to a single note, the sound drops out for about three quarters of a second, then comes back kinda slowly in a fizzy fashion. There was also a slightly weird smell coming from the back

. I did a search on a similar question and someone suggested changing the power tube. Is this also what I need to do? I am new to tube amps and would really appreciate any input on this issue. Thank you.

eugenedunn · May 10th, 2008, 07:34 PM

Rather than a tube, that sounds more like one of your electrolytic capacitors is going to fry soon. Better get those replaced if that gal hasn't been recapped in the last 15 years or so.

Those electrolytics have acid inside that do have a distinct acrid smell....

If a major cap goes, it could blow other major components along with it.

DrewB · May 10th, 2008, 07:50 PM

The cap is a real good possibility, as is the bias resistor drifting way out-of-spec. My buddy's '66 Vibro Champ did the same thing. The bias resistor had drifted badly and the electrolytics were leaking DC.

eugenedunn · May 10th, 2008, 08:11 PM

It's one of those things about old tube amps, is that once you get them, you have to figure that if they haven't had a recap or major service in a decade or so, you should consider spending another 150 bucks to have them brought up to date, have a 3-prong plug installed.

If they have old stock tubes in there, like old RCA's or GE's, Sylvanias, etc.... those tubes might last you a long time, but if they've been replaced with some of the commonly available modern tubes, you might expect to replace them soon because they just don't have the same longevity as many older tubes.

Well, with all that being said, the SF Champ is a fabulous amp. I highly recommend putting in a lower gain tube in the V1 position. Replace the stock 12AX7 with a 12AY7 is a really cool thing to do. It will give you a lot more usable clean headroom and still allow some good overdrive when you have the amp dimed.

My Champ is the most fun to play out of all my amps.... please check out my gallery if you wanna see some of the speaker mods I've done, etc...

JohnnyCrash · May 10th, 2008, 10:45 PM

If you have a multimeter you can measure that bias resistor DrewB mentioned pretty easily... you'd have to pull the amp chassis out of the cab, and be carefull not to touch anything else while measuring - caps hold a charge.

I'd recommend new filter caps and cathode bypass caps if it hasn't been serviced in a while, like eugenedunn said - you don't want to blow one of them with continued use.

Take her to a shop for a tune up...

lewis · May 10th, 2008, 10:56 PM

Get it serviced properly and that amp will be around forever and sound like a million $$$ the whole time.

Dennis68 · May 10th, 2008, 11:52 PM

Quote:

Originally Posted by lewis

Get it serviced properly and that amp will be around forever and sound like a million $$$ the whole time.

+1. Sound advice! (pun included).

bradpdx · May 11th, 2008, 02:24 AM

Old Champ checklist:

1. The 3 section filter cap - REPLACE
2. The 1watt 470 ohm cathode resistor - REPLACE WITH 2 TO 5 WATT
3. All smaller electrolyic caps - REPLACE
4. Install 3-prong grounded power cord
5. Check the B+ to see if it is too high - over 400VDC. Consider dropping resistors to lower the voltage to around 350VDC

The first 4 are must-dos, while 5 is your choice. Many BF/SF Champs run 6V6s at dangerously hot levels, and this is not good for the tube or the tone.

May 10th, 2008, 06:25 PM	#1 (permalink)
Jeremy Palmer TDPRI Member Join Date: Sep 2007 Location: Princeton, MN Age: 30 Posts: 29	Quick Champ question Well my new silverface Champ is awesome except for one problem: when I turn the volume up to nine or ten and really dig in to a single note, the sound drops out for about three quarters of a second, then comes back kinda slowly in a fizzy fashion. There was also a slightly weird smell coming from the back . I did a search on a similar question and someone suggested changing the power tube. Is this also what I need to do? I am new to tube amps and would really appreciate any input on this issue. Thank you.

May 10th, 2008, 07:50 PM	#3 (permalink)
DrewB Tele-Afflicted Join Date: Feb 2005 Location: Independence, MO Posts: 1,108	The cap is a real good possibility, as is the bias resistor drifting way out-of-spec. My buddy's '66 Vibro Champ did the same thing. The bias resistor had drifted badly and the electrolytics were leaking DC. __________________ There is no substitute for Sound Pressure Level

May 10th, 2008, 10:56 PM	#6 (permalink)
lewis Tele-Afflicted Join Date: Mar 2003 Location: Colorado Posts: 1,922 28 Photos	Get it serviced properly and that amp will be around forever and sound like a million $$$ the whole time. __________________ "I'm a maestro, I'm a maestro," Taj Mahal, 8/20/05.

May 11th, 2008, 02:24 AM	#8 (permalink)
bradpdx Tele-Holic Join Date: Jul 2006 Location: Portland, OR Age: 50 Posts: 908 1 Photos	Old Champ checklist: 1. The 3 section filter cap - REPLACE 2. The 1watt 470 ohm cathode resistor - REPLACE WITH 2 TO 5 WATT 3. All smaller electrolyic caps - REPLACE 4. Install 3-prong grounded power cord 5. Check the B+ to see if it is too high - over 400VDC. Consider dropping resistors to lower the voltage to around 350VDC The first 4 are must-dos, while 5 is your choice. Many BF/SF Champs run 6V6s at dangerously hot levels, and this is not good for the tube or the tone. __________________ ---------- Tech Geek and Sensitive Artiste String bender ordinare!

May 10th, 2008, 07:34 PM	#2 (permalink)
eugenedunn Tele-Holic Join Date: Dec 2006 Location: Sacramento, CA Age: 55 Posts: 839 37 Photos	Rather than a tube, that sounds more like one of your electrolytic capacitors is going to fry soon. Better get those replaced if that gal hasn't been recapped in the last 15 years or so. Those electrolytics have acid inside that do have a distinct acrid smell.... If a major cap goes, it could blow other major components along with it.

May 10th, 2008, 08:11 PM	#4 (permalink)
eugenedunn Tele-Holic Join Date: Dec 2006 Location: Sacramento, CA Age: 55 Posts: 839 37 Photos	It's one of those things about old tube amps, is that once you get them, you have to figure that if they haven't had a recap or major service in a decade or so, you should consider spending another 150 bucks to have them brought up to date, have a 3-prong plug installed. If they have old stock tubes in there, like old RCA's or GE's, Sylvanias, etc.... those tubes might last you a long time, but if they've been replaced with some of the commonly available modern tubes, you might expect to replace them soon because they just don't have the same longevity as many older tubes. Well, with all that being said, the SF Champ is a fabulous amp. I highly recommend putting in a lower gain tube in the V1 position. Replace the stock 12AX7 with a 12AY7 is a really cool thing to do. It will give you a lot more usable clean headroom and still allow some good overdrive when you have the amp dimed. My Champ is the most fun to play out of all my amps.... please check out my gallery if you wanna see some of the speaker mods I've done, etc...

May 10th, 2008, 10:45 PM	#5 (permalink)
JohnnyCrash Poster Extraordinaire Join Date: Mar 2005 Location: Lost Angeles and Orange County Posts: 7,128	If you have a multimeter you can measure that bias resistor DrewB mentioned pretty easily... you'd have to pull the amp chassis out of the cab, and be carefull not to touch anything else while measuring - caps hold a charge. I'd recommend new filter caps and cathode bypass caps if it hasn't been serviced in a while, like eugenedunn said - you don't want to blow one of them with continued use. Take her to a shop for a tune up...