Concert Amp Question

Dave Hopping · Post by **Dave Hopping** » 23 Dec 2011 8:53 am

I have a nice old (datecode KL) brown Fender Concert that's much louder on the normal channel than on the vibrato channel.The normal channel was a bit louder when I got it in 1967(!) but it's more pronounced now.The amp had a "cap job" 7-8 years ago and has a replacement grill with reissue Jensen P10R's.Tubes are old but seem OK.I've only gigged this amp once since the caps were replaced.
I've heard that 2 channel blackface Fender amps had this sort of volume disparity,but is it typical of brownfaces? If it isn't,is there a fix?
Not that it helps identify an amp's internal glitches,but here's a pic anyway.

Tim Marcus · Post by **Tim Marcus** » 23 Dec 2011 10:06 am

this amp has a very different circuit than a blackface style fender. On a BF Fender amp, vibrato is typically applied to the output of channel 2, which does cause a certain amount of gain loss - especially the optocoupled type you see in Twins and Deluxes etx.

Your amp is kind of a different animal - the Vibrato is applied within the second channel, before the last gain stage where the two channels meet up at the phase inverter. Its actually a fairly sophisticated vibrato circuit - I bet it sounds fantastic!

You may want to have a tech check the values and voltages in the second channel, something may have drifted which is causing a gain reduction.

Beautiful amp! You have taken very good care of it

Larry Robinson · Post by **Larry Robinson** » 23 Dec 2011 10:43 am

I believe input 2 is attenuated 6db which accounts for th different levels.

Bill Terry · Post by **Bill Terry** » 23 Dec 2011 2:22 pm

Tubes are old but seem OK.

I'd swap some tubes just to see if the problem persists.

Tony Prior · Post by **Tony Prior** » 23 Dec 2011 9:01 pm

Dave, as you noted there is a slight gain difference between the two channels but to understand why one channel is down even more requires putting it on the bench. The obvious answer is YES it can be brought back to where it should be.

That is a fine amp you have !

T

Dave Hopping · Post by **Dave Hopping** » 24 Dec 2011 1:47 pm

Thanks,guys! It'll be going to the amp doctor after the 1st.Just one little story about this Concert-I had a pretty nice BF Concert,but I'd had a big preference for the brownfaces,and lucked into this one in the spring of '67 for $75.00.Sometime shortly after I got it the band learned "For What It's Worth" and the first time we played it out was at a dorm exchange at the U. of Arizona-outside.I got to play the 12th/7th fret harmonics on my '63 Gent thru this very amp-cranked up with the vibrato full on and dead slow.Heavenly!

Thanks again. And Merry Christmas!

DH

Bill Terry · Post by **Bill Terry** » 25 Dec 2011 12:30 pm

I had a brown face 1962 Super, the 2-10 version of this amp I think. It sounded great and the tremolo on these amps is way cool. I traded it off for a '69 drip edge Deluxe Reverb and a pile of cash.

Unfortunately, my house burned with the DR in it, so now I've got nada, but I'm almost glad I sold it or it would have surely been a casualty too. It lives in NY now.