Blackfacing for fun rather than practicality...

[RyanVee]

Hey everyone, been nosing around the forum for a few days and thought I'd come join in.

I got a 78-79 or so UL Pro Reverb from a friend of mine and decided I wanted to BF mod it. I didn't know at first that you can't really do that to the UL's, and then got in touch with an amp tech who will help me with rewiring the transformer and PI circuit and then proceed with doing the BF mod. While I'm in there I'll also change it to the older bias design and eventually new WGS speakers will be installed.

I gigged with the amp as-is last night and it actually did really well. I'm looking forward to doing the work and bringing it a full level up...

I'll likely also remove the push/pull master volume.

I hope to do some building of my own in the near future. It's hard to find chassis' and things in my area and I refuse to pay the exorbitant prices I see on eBay....

Glad to meet ya'll.
Ryan

[Firestorm]

Just so you know what you're getting into, black facing a UL Fender is non-trivial. You'll need a choke and pretty extensive rework to the power supply. You might consider leaving the UL alone and just modding the PI and the feedback circuit.

[Reeltarded]

Howdeee!

Can't you just tie back the UL taps and then reboard it with BF stuff? Extensive, but not expensive.

I hate UL!

[RyanVee]

---Can't you just tie back the UL taps and then reboard it with BF stuff? Extensive, but not expensive.----

Yes. That's what we're doing. Taking out the taps and moving the plate voltage to B+ rather than the taps. Moving a few wires, removing a few thing like the MV and it's associated crap...

I don't hate UL. I think it worked despite it's "taking away" of something that a lot of people liked. As I said - I played with it last night and it wasn't the worst ever, and still better than my Peavey Bandit 112 which does a decent job.

Also, and there has to be some that agree I'm not rich. I have plenty of solder and time, but not much money. So while this IS a big undertaking, it's also fun for me and it's essentially free other than the BF kit. The other parts I need are coming from my dad "up north" from his stockpile.

[Reeltarded]

UL is like the fence between my guitar and freedom...

FREEDOM!!! -zzzzzzt!- ouch...

[Firestorm]

Taking out the taps and moving the plate voltage to B+ rather than the taps. Moving a few wires, removing a few thing like the MV and it's associated crap...

The plates are already tied to B+1; the question is, where are you going to connect the screens? You'll need an additional node in the power supply, a choke if you want it to sound BF, and you may want to do away with the resistive voltage stabilizer Fender added when they took out the choke. Yeah, that MV and its pull-boost circuit could stand to go. You may also want to remove the .01 cap bypassing the NFB series resistor.

[RyanVee]

Taking out the taps and moving the plate voltage to B+ rather than the taps. Moving a few wires, removing a few thing like the MV and it's associated crap...

The plates are already tied to B+1; the question is, where are you going to connect the screens? You'll need an additional node in the power supply, a choke if you want it to sound BF, and you may want to do away with the resistive voltage stabilizer Fender added when they took out the choke. Yeah, that MV and its pull-boost circuit could stand to go. You may also want to remove the .01 cap bypassing the NFB series resistor.

Yeah, I'll ask you to excuse my uneducated answers. The changes I'm making are understandable when explained but still a bit out of my knowledge so I have a hard time explaining as I am still learning. There may be things I'm doing that I don't even know of yet as I'm essentially working for myself as a satellite for the amp guy that is helping me out. I'll get there, though!

[chief mushroom cloud]

Miles...the Selmer Zodiac is UL

[Reeltarded]

Yes, and I once dated a girl with a beautiful singing voice. Most of the other ones had huge boobs.

haha

[M Fowler]

Keep the UL taps and add 6550 power tubes and change bias 220k/220k to 150k/150k be different.

[chief mushroom cloud]

dump the NFB!

[rdjones]

Another minor mod to UL you can try before making major circuit revisions is to increase the value of the screen resistors.
1.5k to 2.5k will soften the sound a bit.
Remove the cap across the feedback resistor.

Also note that the "pull boost" is a very low parts count function.
It's only the switch and a 1K insertion resistor, as long as the switch is not pulled there's no change to the stock sound or signal path.
Same with the master, no real need to physically remove it, just turn it to 10.

rd

[cbass]

dump the NFB!

yes thats what I was gonna say.Try it before you undo the UL taps

[RyanVee]

I think that what we're looking at doing requires the taps to be moved because he said there's a chance of the coil taps arcing because of the power we plan to pull. Raising voltage somewhere.

I do have the volume dimed when I use it. We had a long gig last night and I had the MV at 10 and the channel vol (vibrato channel, preamp tube removed from V1) at about 4. For drive/gain I used a simple boss SD-1 just because that's what i had, and for solos paired with with my tubescreamer. It was "ok." I did get some compliments last night, even up against our other guitar player with a humbucker equipped G&L Strat playing into an Analog Outfitters Sergeant with a Dr Z cab! (which sounded amazing!)

[jjman]

Unless the OP tubes are clipping, I wonder how much the "UL sound" differs from traditional. I guess more speaker signal is created before clipping with the UL since the screens are also driving the primary.

Adding a choke probably means drilling. I would try big(ger) screen resistors 1st as mentioned. With the MV at 10 and volume at 4 you may not be reaching output clipping.

I wonder if there are any before and after recordings of a UL conversion.