Fender Twin II Loud Hum

[dpm309]

I am working on a Fender Twin II that has developed a very loud hum.  The owner said that he was not happy with the tone of this amp and had it re-tubed and some of the caps and resistors replaced.  The amp worked fine when he brought it over but as I powered it up today to test, all I get is a loud hum even with all of the controls turned down, and with the reverb and footswitch unplugged.  I pulled the chassis (these things weigh a ton) and will start looking at the filter caps etc.  Does anyone have a layout of this amp?  All I can find is the schematic and the layout of the footswitch.  I looked at Doug's schematics and the Fender website with no luck.

Thanks,

Dan

[dpm309]

The hum problem was related to a problem with the foot switch shorting out.  Now that thats fixed, has anyone done any modifications to a Twin II to improve the tone?  I did notice that the original filter caps are still in the amp but they appear to be working properly.  Being that this amp is over 30 years old, a re-cap is probably in order.  I have read various reviews on this amp and a lot of them said it doesn't sound as good as the original Twin, blackface or silverface.  I believe this amp was developed by Rivera to compete with the Mesa Boogies before he left Fender.  IMHO, the gain/overdrive channel on this amp sucks.  The clean channel sounds good but you have to dial in the sweet spot for that particular guitar.  Change guitars, you need to re-tweak.  Anyway, I would appreciate any suggestions on how to improve the tone.

Thanks,

Dan

[John]

Dpm, I am worthless at tone suggestions, but I did find 2 things that may or may not help you; links are below.

http://www.schematicsunlimited.com/download.php?manu=fender&file=fender-twin-rev-ii.pdf
I haven't downloaded it, so don't know if the layout is included or not. I have downloaded a few other things from there with no problems.

http://support.fender.com/schematics/guitar_amplifiers/Twin-Amp_schematic.pdf
That includes a layout, but is not labeled as "II" so probably is no help. But hey, it's free! :)

[dpm309]

John, thanks for the links.  The second one is for a Fender Pro/Concert Reverb. Actually owned one of these before I started building amps.  Liked the ones I built better, so I traded it for a Yamaha powered mixer.  I am going to see if the owner wants the filter caps changed since they are very old.  Don't know if this will help the tone but it might eliminate the slight distortion that I am still hearing.  Someone did change out the coupling caps to Orange drops recently but I don't think this helped improve the tone.

Dan

[sluckey]

The Concert II circuit looks like the Twin II but it only has 2 output tubes. I found a schematic with layout. Take a look and see if this can help...

http://www.stratopastor.org.uk/strato/amps/twoseriesfenders/concertschematicwiringdiagram.pdf

[dpm309]

Slukey,

Thanks, this will work just fine.   Same schematic except for number of output tubes.

Dan

[dpm309]

Just finished changing all of the filter caps and this did eliminate the intermodulation distortion that I was hearing.  Have not been able to find anything about tone mods for this amp.  I ran across a couple of references to a "Rivera modified" Twin II but they did not explain what they did.  There was even a You Tube clip of someone playing the modded Twin II but it sounded just like this one without any tone mods.  Anyway, time to ship this back to the owner and suggest that if he still doesn't like the sound, he should sell this since it could be somewhat of collector's item due to the limited number of these made.

Dan