UL taps for guitar amps!

[tedmich]

Billy Zoom of X (also an EE I believe) states that OT UL taps just give better pick dynamics and are essential additions to the custom amp he built and has used for decades...opinions?

Having always avoided distortion minimizing HiFi things, I am ignorant on how UL taps are employed: can these be added as an +/- switched option to test or does circuit tolopology have to change too much to have them switched in and out?

[defaced]

I'm also interested in this. I'm doing a 4xKT-88 built and want to experiment with UL taps, switchable or static.

[loudthud]

In a 4x6550 bass amp I built, I always liked the UL taps switched out. The power was slightly lower in UL probably because I used 1.5K screen resistors. That amp has NFB and a resonance control. The control didn't work as well in UL mode. A long time ago I built a 2x6V6 amp with UL taps and no NFB. It worked well but I had different expectations back then. Most of the time I hear about UL guitar amps, they have no NFB. The exception is the Sunn Model T (70's vintage).

[kleptocracy]

I was thinking about this too, actually, because I'm building a 4x6550 guitar amp based on the Sunn Model T, but was wondering if I should make the UL switchable or even variable on a pot. How does switching them in and out seem to change the sound and feel of the amp?

[tedmich]

to quote Mr. Zoom in a recent article in Guitar Player he talks about his personal amp.


Q So how has your amp managed to be so indestructible throughout the years?
A It’s not something I can put into a simple sentence that non-engineers would understand. I design things so that none of the components are highly stressed. Everything can handle two or three times what they’re getting. It’s real stable, and it’s pretty much the opposite of what everybody thinks they want. It has an ultra-linear output section, for example, which I read on the Internet is not suitable for guitar because it doesn’t want to distort. That’s complete B.S.—a linear output just makes the amp sound louder, and you get better speaker damping.

(so I remembered wrong, speaker dampening not pick dynamics...)

Fender made UL 135w amps, discussed here:http://www.tdpri.com/forum/amp-centr...near-amps.html

some describe a switch for a SE power amp:
"If your transformer has ultralinear taps you can use a 3 way switch to go from triode to UL to pentode mode. I put a switch like this in the guitar amp that ate the previously mentioned KT88's. 38 Watts in pentode, 30 Watts in UL and 18 watts in triode mode with about 400 volts B+."
but it makes LOUD transients which can't be good for tubes or speakers IMO.

[kleptocracy]

The guitar amp handbook ... - Google Book Search

Here's a Dr. Z interview in Dave Hunter's book: "I found I could get a nice distortion with these ultra-linear amps, but also a nice articulation" He also talks about why the 70s UL Twins seem to sound kind of tight.

[pontiacpete]

Doesn't the fender bassman 135 have a UL OT? Has anyone ever built one of these? I'm thinking of doing something like this amp and was wondering about this design and where to get a UL tapped output xfmr.??
pete

[anson]

This website is on the audio-phile end of the spectrum, but is very informative of what UL is all about:

ultra-linear


hope it helps.
Anson

[Robert M. Martinelli]

Billy Zoom of X (also an EE I believe) states that OT UL taps just give better pick dynamics and are essential additions to the custom amp he built and has used for decades...opinions?

Well,
my Vox UL ( Ultra Linear ) 4120 ( 4x KT88 ), the "bass" version of the 7120, has been used by Paul Mc Cartney; Jimmy Page used it on some of the most famous Zep recordings, but, when it was issued ( 1966 ), it failed to catch immediately the attention and respect of players, because, as stated by Petersen-Denney in "The Vox Story" in the chapter dedicated to the UL series "Although loud and reliable, they had a bland and unremarkable sound".

( I can only be happy about it, because this makes it a very rare amp and a collector's dream nowadays )

Anyway....
Excessive fidelity in guitar amps can result in an overly flat and dull sound.

The world's most famous guitar and bass amps are well known for being everything but linear, as we know, an AC30, a Bluesbreaker or a '59 Bassman color and alter the sound in many ways, so I can imagine the poor reaction the UL amps faced when launched in such a market and facing such "strong" opponents.

I think Mr. Zoom's statement to have no "absolute" value, I' d rather say that he "considers" UL to be an "essential" ( to use his words ) addition to achieve HIS sound, furthermore, I do not agree with his statement about the improvements on picking dynamics, which have more to do with other factors ( PS filtering, fixed vs. cathode bias, speaker's efficiency, and so on ) IMHO. The main reason the UL configuration's been developed is fidelity-related.

IMHO the usefulness of an UL amp lies in the fact that, being SO linear and faithful, it has a "natural inclination" to give maximum effectiveness and audibility to external effects.

Just my .002 cents.

Cheers

Bob

[Steve Conner]

I'd be worried about arcing the OPT when switching UL taps in or out. If the screens briefly come disconnected as the switch contacts move, the tubes will turn off quickly, which could generate a big inductive kickback. You probably want make-before-break switches.

I recently restored an old Crown UL stereo amp, and I love it for hi-fi. But I think for guitar you actually want less speaker damping and more distortion! The AC30, since it has pentodes with no NFB, is about the least damped and most non-linear power stage you can get, and everyone loves them. If you wanted a linear power amp with tight damping, you could just use solid-state, and save weight and money.

The 4120 probably sounded bland because it didn't have a master volume, and it was so powerful, players never got a chance to crank it and get the power amp distorting. Nowadays we'd just stick a Tube Screamer in front of it and go to town.

[Robert M. Martinelli]

The AC30, since it has pentodes with no NFB, is about the least damped and most non-linear power stage you can get, and everyone loves them. If you wanted a linear power amp with tight damping, you could just use solid-state, and save weight and money.

The 4120 probably sounded bland because it didn't have a master volume, and it was so powerful, players never got a chance to crank it and get the power amp distorting. Nowadays we'd just stick a Tube Screamer in front of it and go to town.

Hi Steve!
Glad to hear that, more or less, we have the same opinion on this subject, and....you're right about the 4120, the damn thing is so loud that when rehearsing with my group I nearly got killed by the other band members when I tried to turn the volume knob past "1"

( I've reverted to my '64 AC30 TB since then )

Cheers

Bob