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Can someone explain Ultra Linear operation in guitar amps?

Sol

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Oct 26, 2001
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A number of 1960s Vox amps have the prefix UL. Jimmy Page was known to use these amps. I myself have what I'm told is a UL operating amp. I associate Ultra Linear with Hi Fi, but know it is close to Cathode Bias in certain aspects.

Could someone help us understand this unusual breed of guitar amps please?
 

thejaf

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Without going technical, it's powerful and clean. Good for bass and the 1960s clean pop sounds that were popular at the time I suppose. I'm sure it had its purpose in the studio, where Page worked his wizardry with using weird and cheap stuff that was at hand.
 

Sol

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TM1

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All the Vox “UL” Series were made by Triumph Electronics for JMI. Sadly that series was a flop.. Vox gave a local Petrol station up the road a bunch of used & loaner stock amps to fill in a hole where an underground tank had been. This was around 1968/69... so there’s a big load of old Vox amps buried in that place.
I’ve worked on about 20+ Vox UL Series amps over the years. They’re pretty rare number one & number two they didn’t build that many for starters, especially compared to AC30’s which they built around 4,000 of those between 1959 to 1968 when JMI sold the company to Royston(I believe..)
 

Sol

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So, what were Vox thinking? The amps were a flop, despite being used by household famous names, but it wasn't enough to convince guitarists to buy them..
 

TM1

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Ultra Linear is used in HiFi for getting more clean headroom along with more power before clipping. Back in the late Sixties Fender use to use UL output transformers in Twin Reverbs. They though everyone wanted more clean sounds and Leo was trying to do away with that “nasty distortion”. They never quiet got that we wanted more distortion, mainly cause Leo was consulting with Country & Western guitar players....
 

Andrew Andrade

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I believe that for Vox Amps it means Ultra Linear. This is what is said on the Vox Showroom site and it is what my amp tech confirmed to me some time ago. However, my amp tech said it only applied to the larger Vox Seven and Four series amps such as the 760 and 7120 or the 460 and the 4120. Don Butler is right the JMI engineers were going for a loud clean signal. You definitely have this clean signal with the Vox 7120.
 

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Wally

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Ultra Linear is used in HiFi for getting more clean headroom along with more power before clipping. Back in the late Sixties Fender use to use UL output transformers in Twin Reverbs. They though everyone wanted more clean sounds and Leo was trying to do away with that “nasty distortion”. They never quiet got that we wanted more distortion, mainly cause Leo was consulting with Country & Western guitar players....
Fender’s ultralinear amps were introduced in 1977 in all of the 6L6 amps except for the Vibrolux Reverb, which is the only 6L6 Fender amp not to get the Master volume thing, either.
There are other guitar amps that utilize UL output transformers..,notably the Dr. Z Carmen Ghia and the Rte. 66. Dr. z came from the Hammond organ world and carried that use of UL outputs from the Hammonds into some of his amps. The first Carmen Ghia Amal’s were built directly out of the AO35 reverb amp from Hammond organs.
 

Wilko

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Fender’s ultralinear amps were introduced in 1977 in all of the 6L6 amps except for the Vibrolux Reverb, which is the only 6L6 Fender amp not to get the Master volume thing, either.

While not the master volume, the Vibroliux Reverb did get the U/L and a "pull for boost" type thing that sucked. I had mine removed.
 

Wally

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While not the master volume, the Vibroliux Reverb did get the U/L and a "pull for boost" type thing that sucked. I had mine removed.
No....the Vibrolux Reverb never got the UL treatment. The VR was the only Fender 6L6 tube amp that did not get UL output. The only change to the amp in the 70s was the push/pull boost...as with the DR. The DR and the VRnever got the MV, either. The Vr remained a 4o watt amp. You can do a search for this if you would care to....here is a 1978...40 watts.
Here is a 1980 when they went back to BF cosmetics...you can see the ’4’ of the 40 watts.
 

Wally

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This lack of changes along with the lower voltages that the VR runs compared to the other 6L6 Fender Reverb amps makes the VR my favorite of the BF/SF reverb amps....bar none. I had a 1976 VR that ran almost the same exact voltages as shown on the first BF schematic when biased to 60% of mpd.....411VDC on the plates compared to the scheme’s 410VDC. Hey, that is lower than the Deluxe Reverbs ran! Wonderful amps, imho.
 

Wilko

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I do like them a lot. I was playing more smaller places and so I let it go in favor of my Deluxe Reverb. Got rid of the 135 UL twin reverb and my actual favorite-- Black Face Pro Reverb! isn't that basically the same amp as Vibrolux Reverb in a 2x12 configuration?
 

Wally

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Wilko, the Pro Reverb runs higher voltages than does the VR, ime. The Pro Reverb is a Bandmaster Reverb in combo form.
The VR is an amp alone, imho and Ime.
 
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markgreco57

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Ultra Linear amps in guitars are cool and different. I've been playing guitar for a long time, and I've noticed these amps sound more apparent and can handle loud sounds well. That's great for when you want your guitar to sound clean and robust, even if you're playing loudly.

Like the 1960s Vox ones you mentioned, these amps have a unique sound. They're unlike regular guitar amps, usually warmer and softer. That's probably why famous guitarists like Jimmy Page liked them. They give you a sound that's both clear and powerful.

I learned much about how these amps work and their unique sound from a website: https://faqaudio.com/. They explain things in a way that's easy to understand, especially about the technical stuff behind ultra-linear amps.
 
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ADP

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I absolutely love my 1980 "McDumble" 135w Ultra Linear Fender Twin Reverb. The JBL D120f speakers. The glorious vintage 6L6 tubes. It was made for export and features a voltage switch, too!
 
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