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Help with Vibro Champ -67

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11/19/1999 6:30 PM

Help with Vibro Champ -67

I really never liked the sound in my VC. When I bought it, it was quite out of shape so I got it cheap. The speaker, cabinet and chassi was original but otherwise it was pretty mistreated. I thought that if I get it back to original specs it would sound nice. I changed the filter caps and substituted the caps to Orange drops and Silver Micas and checked the voltage. I also bought NOS tubes. After this the amp did sound better - but not good. So, I looked in Webers and Torres book. I did some mods (such as disconnecting the tone controls) but none of these changes did improve the sound. I think the amp sounds muddy, farty and without treble/presence. The last mod I did was to change the tone stack caps to .047 and .022 (from .1 and .047). That gave a somewhat better response, but not much.
I’m a bit lost here. I read several posts on how good this little amp is supposed to sound but I’m unable to get this amp to sing. I would be very thankful for any suggestions.

Bjorn

11/20/1999 7:13 AM
Bruce	IF you still have the original speaker, get a new one. If the baffle can be redone, make the speaker a 10". Also it's time to change the output transformer to a bigger SE piece of iron. Hammond 125D or E is good for these maller SE amps. Bruce

11/20/1999 9:17 AM

Bjorn:

You mentioned trying out some NOS tubes. Which ones did you try for V1? I've had great results with the EI 12AX7's (aka GT 7025) and the Sovtek 12AX7WXT+'s and 12AX7LPS's in my Fender amps. IMHO these tubes have a lot more character (read: distortion) than some of the cleaner sounding NOS 12AX7's (which are great further down the signal chain in a 2-6L6 amp). The EI's have been compared to vintage Mullards while the Sovteks have been compared to vintage Telefunkens (those being two of the "Holy Grail" NOS 12AX7 style tubes).

Steve Ahola

P.S. If you are really interested in tube amps for the long run you can't go wrong stockpiling good tubes, so I'd suggest that you track down some of the EI's- make sure that they aren't microphonic during whatever warranty period is offered. And be sure to test the Sovteks as well (look for a date code after 99 06 for the LPS's- they had some bad batches made in 1998). For a smoother, creamier sound the JJ/Tesla ECC83's are nice (aka GT ECC83, I believe). You can only use one of these tubes at a time in your VC but they are great tubes to have around...

P.S.S. To see how a speaker upgrade would sound, try plugging your amp into a ext cab (preferably 4 ohms but 8 ohms should work okay, too).

11/20/1999 1:25 PM

I recently completed an extensive comparison of various preamp tubes in my champ (I figured it was the best amp to do a comparison since it only has 1 preamp tube in the equation

). I'm going to post the results soon but based on my experiences, the clear winners were:

NOS tubes: RCA 12AX7A, GE 12AX7WA (both had a very balanced frequency response).
New tubes: Sovtek 12AX7LPS (scored as well as the NOS stuff).

In my experiments I also found that certain tubes worked better with certain guitars; the EI 12AX7's sounded ok with my LP, but sounded much nicer with a strat. A NOS Philips 12AX7A also worked better with a strat.

BTW - I agree with Bruce though; the first item to consider changing is the speaker. I've got a Mojo 8" in mine and it sounds much nicer than the stock speaker. However, it's got a pretty pronounced midrange so it can sound "honky" at times. I've heard nothing but good things about the WeberVST choices...

MJ

11/21/1999 8:14 PM

Steve,
I’ve tried several combinations of tubes and I don’t think that is the problem with this amp. The rectifier is a RCA 5Y3 GT, the power tube is a RCA JAN CRC 6V6. I’ve also tried several preamp tubes (mostly new) such as: Ruby, Tesla, Sovtec and an old Telefunken and a 7025.
Maybe the speaker is old and tired, but I’m reluctant to change it sonce like to keep the amp as original as possible. Maybe I put in a cap with a wrong value somewhere (not that there are so many)? I’ve read so much good about this little amp and I’m a bit sad that mine doesn’t sound that good at all.
Any way, my question was more: This muddiness and lack of treble/presence - Is this a common feature with the Camps? If not, this amp is probably not tweaked the right way. I really like the size of this amp (compared to my SR :-)

:-)

. I would like it to sound good too.

Something quite different:
I’m in a state of shock.
I’ve spent a lot of time and money to find the right Gibson guitar. I bought my dream guitar some years ago, a LP standard. After owning it a year I had to confess to myself (it was hard) that the LP was not IT, so I sold it and bought a Nighthawk (with two humbuckers) after trying several others, including a 335. I changed the small humbucker to a PAF and had the bridge PU rewind to a PAF. It sounded real good.
Somewhere along the way I also bought a Jap Stratocaster from 1981 (-62 RI, very cheap). I never cared much for the Fender since I never really liked them. Fender to me is (was) a mass produced thing and a Gibson a real instrument.
I spent the weekend in a studio with my band and brought the two guitars with me (you never know, maybe a Strat will come in handy somewhere). I ended up playing only on the Strat since everyone (band members, technicians and me) thought it had a killer tone. It did! Emotionally, I still have a problem with confessing that the Strat sounded better than the Gibson, but there it is – no doubt! I will probably carry both guitars to the next gig but only play the Strat.
I think the big difference this time was that I did not have to adjust the volume of the SR to the rest of the band (which also means using stomp boxes) but played the SR on volume 4-5 with no pedals in between. When a clean sound was needed I only adjusted the volume on the Strat. A truly remarkable difference.
A thought clings to my mind - how come I did not get this earlier?

Bjorn

11/22/1999 8:29 AM

Bjorn:

So how does your VC sound plugged into the speakers in your SR? I keep a double-ended 1/4" barrel jack around just for experiments like that. I see that you did try a lot of different preamp tubes... I think your amp may just need some tweaking (like a few different caps or resistors here and there).

As for the LP vs. strat thing... I hated strats for over 20 years and it's only been in the past 10 years that I've crossed over to "stratland". EC switched over to a strat in 1969 and Jeff Beck followed a few years after that, so there must be something to it! BTW your "cheap" 1981 MIJ strat is a real keeper! Many players like them better than the American ones Fender was making back then...

Steve Ahola

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