Blackfacing a 135W ultralinear Twin Reverb?

[Leo_Gnardo]

This amp is designed as essentially a full wave bridge with a center tap connected to the series caps after the rectifiers- it shouldn't sag much if at all. I've done it on similar designs and not had trouble. If a given amp uses series caps without the transformer center tap present, yes, it will sag like crazy. jamie

Hmm, yes, quite rightly so! Those big Fenders do have a FWB don't they - for amps that don't have that, try my big resistor.

[Chuck H]

Yup... But a nod to LG on the idea of a simple series resistor. BUT... Make it a Pi filter! Decouple, then a resistor, then decouple again. The resulting circuit, with a hanging cap to ground, a resistor and then another hanging cap sort of looks like the Pi symbol. That's how it got it's name. But it's remarkably effective at reducing voltage and sag at the same time. I'm sure there is some math to determine exact benefits. But the dual caps reload faster than the time constant of the circuit, basically. So you get a voltage drop, a reduction in ripple AND acceptable sag in many cases.

[Leo_Gnardo]

Yup... But a nod to LG on the idea of a simple series resistor. BUT... Make it a Pi filter! Decouple, then a resistor, then decouple again. The resulting circuit, with a hanging cap to ground, a resistor and then another hanging cap sort of looks like the Pi symbol. That's how it got it's name. But it's remarkably effective at reducing voltage and sag at the same time. I'm sure there is some math to determine exact benefits. But the dual caps reload faster than the time constant of the circuit, basically. So you get a voltage drop, a reduction in ripple AND acceptable sag in many cases.

Thanks Chuck and true'nuff. I considered going pi filter but liked the compression a lot so left it thataway. Customer is looking for a Duane Allman type response from what's essentially a 50W Marshall with double the power. Considering we're hearing compression on all those recordings I figured let the amp squash a bit. These Traynors were originally fitted with EL34 - this one still has original Mullard pre tubes that amplify not rattle & squeek as some do - but no way any modern EL34 will put up with 550V. Just for fun I tried a pair for a little while & found screen grids lighting up past my comfort zone, even at the reduced SG voltage. Super saggin' power too with the EL34's, so KT88's the choice.

OK now back to the 135W Fender, already in progress.

[wizard333]

blackfacing everything on it besides the ultralinear sounds awesome

That. Nothing says you have to push it into overdrive. So go for it. It won't be *exactly* blackface because you aren't messing with the UL taps and screens, but so what.

Also, when working properly (i.e. crappy old electrolytics replaced, adjustable bias added and set correctly, messy lead dress cleaned up) those amps sound REALLY GOOD already, in spite of all the internet nonsense you read to the contrary by people who've never played through one or at least one that was in proper working order. Yes, they stay cleaner longer. Are you pushing a blackface twin into breakup? Really? I don't know any club that wouldn't get you removed from. If you need that kind of volume nowadays, you are mic'd and through a PA. Most people use a clean amp and pedals. They are excellent amps for that, along with Pedal Steel, Keyboards, etc.

[zoranrataj2000]

Like Bob p write.
Ultralinear Fenders are King of Clean.Keep it that way.
I just do not understand, why should for example mod Marshall amp to get Fender? Buy what you like.
It is cheaper to buy BF Fender then convert it. My UL SF Pro reverb is fine, but is lack for more warm tone. And this can be easy to correct and not expensive.