Scored New Donor Amp - Fender 75

[Darkbluemurder]

Has anyone tried to convert this into a D-style amp? This amp was built in the late 70s and from the tube compliment should have everything to be turned into a Hybrid Rev A ODS (5 preamp tubes, one tube reverb and loop already (!), 4 extra control spaces). The only thing which is different from a "normal" Fender amp is that the 75's OT is wired ultralinear. I have never heard an ultralinear amp but read that it makes the power amp cleaner. My feeling is that this should not hurt the D-style tone. Otherwise I still could take off the ultralinear taps.

Any input would be greatly appreciated.
Cheers Stephan

[groovtubin]

Has anyone tried to convert this into a D-style amp? This amp was built in the late 70s and from the tube compliment should have everything to be turned into a Hybrid Rev A ODS (5 preamp tubes, one tube reverb and loop already (!), 4 extra control spaces). The only thing which is different from a "normal" Fender amp is that the 75's OT is wired ultralinear. I have never heard an ultralinear amp but read that it makes the power amp cleaner. My feeling is that this should not hurt the D-style tone. Otherwise I still could take off the ultralinear taps.

Any input would be greatly appreciated.
Cheers Stephan

FWIW, it`s FLAT OUT THE BEST AMP i`ve ever converted, LEAVE THE UL TAPS ON!! I went HRM, ABSOLUTELY STUNNING!! The 500 B+ and the UL taps are just amazing, man ya can`t go wrong....................

[Bob-I]

I used UL mode on my peavey transplant. Sounds GREAT. Dogears doesn't like UL but I'm sold.

[dogears]

I had Andy Fuchs replace the UL Fender 75 tranny in my convert with one of his sweet 50 watt massive regular outputs...... The amp sounds amazing!!

Jim, how do you know the amp would not sound even better with a regular OT?? Never know unless you try!

I used UL mode on my peavey transplant. Sounds GREAT. Dogears doesn't like UL but I'm sold.

[groovtubin]

I had Andy Fuchs replace the UL Fender 75 tranny in my convert with one of his sweet 50 watt massive regular outputs...... The amp sounds amazing!!

Jim, how do you know the amp would not sound even better with a regular OT?? Never know unless you try!

I used UL mode on my peavey transplant. Sounds GREAT. Dogears doesn't like UL but I'm sold.

cuz the amp sucked w/o the taps, hook up taps, WOW, course i`ve learned what YOU and glasman know since then

[dogears]

I'm talkin' about a regular OT. Not the Fender 75 unit which is optimized for the UL taps. I'll buzz you later.....

I had Andy Fuchs replace the UL Fender 75 tranny in my convert with one of his sweet 50 watt massive regular outputs...... The amp sounds amazing!!

Jim, how do you know the amp would not sound even better with a regular OT?? Never know unless you try!

I used UL mode on my peavey transplant. Sounds GREAT. Dogears doesn't like UL but I'm sold.

cuz the amp sucked w/o the taps, hook up taps, WOW, course i`ve learned what YOU and glasman know since then

[Darkbluemurder]

That certainly sounds encouraging. I will keep the original tranny UL wired for starters. I can still change to a different tranny in case I don't like the sound.

[skyboltone]

I had Andy Fuchs replace the UL Fender 75 tranny in my convert with one of his sweet 50 watt massive regular outputs...... The amp sounds amazing!!

Jim, how do you know the amp would not sound even better with a regular OT?? Never know unless you try!

I used UL mode on my peavey transplant. Sounds GREAT. Dogears doesn't like UL but I'm sold.

cuz the amp sucked w/o the taps, hook up taps, WOW, course i`ve learned what YOU and glasman know since then

Apples and Oranges Groove. UL changes the optimum load impedence of the P/P pair from the standard to something a good deal higher. I was going to make mine switchable from fixed to UL screen connection but found that I would also have to switch the OT plate taps at the same time to operate the KT-66s at the same place on the curve.

Dan

[jaysg]

The conventional wisdom on the UL Fenders is to remove the feedback, leave the UL taps alone, and then give it a listen. For a Dumble, you'd lose the Presence control if you did that. Are you running both UL and NFB?

[Darkbluemurder]

I'm not running anything yet - still waiting for that amp to be shipped. It was an Ebay purchase.

[groovtubin]

I had Andy Fuchs replace the UL Fender 75 tranny in my convert with one of his sweet 50 watt massive regular outputs...... The amp sounds amazing!!

Jim, how do you know the amp would not sound even better with a regular OT?? Never know unless you try!

cuz the amp sucked w/o the taps, hook up taps, WOW, course i`ve learned what YOU and glasman know since then

Apples and Oranges Groove. UL changes the optimum load impedence of the P/P pair from the standard to something a good deal higher. I was going to make mine switchable from fixed to UL screen connection but found that I would also have to switch the OT plate taps at the same time to operate the KT-66s at the same place on the curve.

Dan

Dan the amp was a tad TOO bright, the UL taps really made it sound great, lik emost here i`ve learned a GREAT deal @ these circuits, and continue to, i`m a serious Eric Johnson FREAK, smooth and glassy is what i go for w/MUNDO gain, right now i have that sound..and dang its good to be alive to enjoy it! lol!

[Darkbluemurder]

Amp arrived yesterday. It's in good working condition although one of the power tubes was smashed during the transport. The pilot light did not work. Both easy to replace. Anything else seems to be fine although I hear some crackling and hiss - could be the carbon comps. No problem there since they will be replaced by RN 65 in the new build.

It seems that I could use the 2 optocouplers for the clean/lead switching.

I will definitely have to add more stages to the power supply and to rearrange the tube stages to get this in line. I don't know what Fender had in mind to hook 3 preamp tubes to the same power supply node. I will also have to ditch all the switches that are now in there - except for the treble boost switch none is really useful.

I plan to build a non-HRM amp. I will use the bright switch (currently 120pf). I will convert the treble boost to a treble shift, the mid boost to preamp boost and the bass boost to a deep switch. Maybe I replace the volume pot with a push-pull so I could have a Rock-Jazz switch as well.

Does anybody have a source of a better readable schematic of the 75? I find the CBS schematic hard to follow.

I will let you know how she turns out!

Cheers Stephan