Difference between Twin reverb and Vibrolux?

[guitarhvac]

I was wondering if you guys could tell me what is responsible for the major difference in the sound of the vibrolux vs. the twin reverb.
I have a twin and to me it sounds horrible next to a vibrolux.  Maybe it's just my preference, but the vibrolux has so much natural compression and sustain!!  My twin has none and just sounds too............not good for lack of better explanation.  Anyways, I wanna make my twin sound as close to a vibrolux as possible.  Any help is much appreciated!!
Thanks a lot!!!

[HotBluePlates]

Vibrolux or Vibrolux Reverb? Silverface, blackface or ??? for each amp?

Knowing nothing else, think about the schematic and/or the amps in front of you.

Twin: 12" speakers, 100w, feedback loop of 820 and 100 ohm resistors.
Vibrolux: 10" speakers, 50w, feedback loop of 820 and 100 ohm resistors.

The different-size speakers can be a different sound on their own, but the lower-power amp might also get turned up more than the higher-power amp, probably causing more speaker break-up. You might be hearing a bit more distortion in the smaller amp all around.

The feedback loop also looks-same, but isn't. Both use the same resistors, going to the same places, but each amp has a different amount of power (we are assuming blackface Twin Reverb vs silverface Vibrolux Reverb here). So what? I'm glad you asked...

Because each amp has the same 4 ohm speaker load but outputs different power, there is a different amount of voltage present at the OT secondary, assuming each amp is turned up to maximum clean power. The point here is that for something like a similar volume-knob setting, there is a each amp outputs a different amount of power.

Power = Voltage²/Resistance, so Power*Resistance = Voltage². Take the square-root to find the voltage present at the speaker terminals.
SqRt (100w * 4 ohms) = 20v
SqRt (50w * 4 ohms) = 14.14v

After being reduced by the 820/100 feedback voltage divider, the Twin has 2.17v of feedback, while the Vibrolux has 1.54v of feedback. That's not a big difference (in volts or dB), but probably enough to help the Twin have a cleaner, more authoritative sound.

[plexi50]

The Twin Reverb has a 460VDC power tube plate 340-0-340 PT

The Vibrolux has a 410 VDC power tube plate using a 325-0-325 PT

For starters you would need to change the PT out for a lower B+ to get the lower preamp & power tube voltages

Your twin does not have a rectifier tube so your plate VDC may still be a bit higher using rectifier diodes

Is your Twin Reverb vintage or a reissue?

[jjasilli]

Difference between Twin reverb and Vibrolux?  about 20 lbs.   


http://www.ampwares.com/fender.asp  : SF Twin Reverb:  Weight: 69 lbs.  SF Vibrolux: Weight: 50 lbs.

[guitarhvac]

My twin reverb is a silverface early 70's!
Thanks for the help!

[P Batty]

Assuming the bias is set correctly,  I'd change the 820Ω NFB resistor to about 3300Ω, and disconnect the tremolo. You could replace the 10kΩ midrange pot with a 50kΩ pot. If that doesn't open it up you could rebuild the PS and replace the PT and OT- not really a cost effective option.   You can get a Twin Reverb to sing, but only at ear-splitting volumes.  It isn't  a 135w Twin Reverb, is it? You'll never get that to sound like the Vibrolux, sell it to someone who wants a high-powered clean amp and buy a Vibrolux (or perhaps a Pro Reverb.)   

[DummyLoad]

turn your twin into a vibroverb? 

http://www.el34world.com/charts/Schematics/files/fender/vibroverb_ab763_schem.pdf