I got yo big ol' Ultra Linear right here.

[Jackie Treehorn]

UL makes me cry. You guys all like way too clean a breakup. It's very bold by the time the volume is high enough to make up for the missing clipping.

I do have a question and with my level of understanding an answer may even make sense now: what must I do to remove the UL from a Major besides taping back the taps and the other obvious bits? (ieeieio; wire sockets like a plain old 100) The 1kV screen resistors are freaking tremendous, like a barrel full of monkeys.

The only thing sadder than UL is NOL if you feel me, yo.

Nah, you can get just as much breakup from UL, it'll just sound warmer and deeper, and probably at lower power depending on tube.

But, a ltp without fb sounds much better to me; you can dial it in for nicer distortion without the feedback tap. And we all know that power amp distortion in most cases is all phase inverter! So, ditching the global feedback for local may get you a nicer distortion amplifier, too.

[matt h]

And we all know that power amp distortion in most cases is all phase inverter! So, ditching the global feedback for local may get you a nicer distortion amplifier, too.

This... this this this!!!


Edit to respond to David Root: If you're going multiple tubes and not just trying to use onhand iron... get a real SE OT with a proper UL tap. I mean, if I were doing a ghetto-UL/pp iron for a parallel pair of 6L6GC's, I wouldn't dare do it using a tranny rated for any less than 40 "hammond" watts.

I don't remember Edcor being an option back when...

As for some pentodes in the pre? Yes!!! delightful .But it really depends on what it is you want out of the amp. I imagine something akin (not remotely identical) to a clubman topology would slaughter in a parallel SE UL build. I'd shoot for something like a triode gain stage (single non-paralleled triode) with a standardish 100k-150k Rp, switchable 1.5k/1uf or 2.7k/.6uuF for the first stage. A "set of decently lossy" tone controls of your choice. The clubman controls are neat, but even a Fender stack would work.

The choice then becomes- do you use the other triode for recovery? or the pentode? Merits to both here.

The key is then having a third stage to slam the power tubes. If you're using something like a 6L6GC (especially at 400ish V), you're going to need a decently large signal to drive them to full power (three to four times what your average SE el84 amp requires) Either a very warm biased triode stage for maximum swing (see p1 Extreme) OR use the pentode. It really depends on how much you love the sound of an overdriven pentode.

[David Root]

Thanx again matt h. I checked my stock, lots of 6L6GA and 6L6GC on hand, BUT the little Hammond 125 is an E (15W) which is too small.

I have a 270JX PT which is good for 150mA at about 350V or so.

I have two Edcor 100W PP OTs with UL taps, one is 1.7K primary, the other is 3.5K. The 1.7K might work OK and it's not currently in use either. They both weigh close to 10 lbs each so I'm sure they could handle it.

I also have a pair of Mullard EL37 I was going to put in my Corksniffer's '57 Twin, but it sounds so good with '60s Tung-Sol 5881s I haven't used them yet. The EL37s only need a whiff of signal to power up real well, so I might use them. I have several other PTs I could dig up to handle them if necessary.

With the 5879 and maybe the EL37s I would like to get some greasy down home GA-40 type tone. What do you think? V1A 12AX7 first stage, V1B recovery, V2 5879 in pentode mode, 2xEL37 and a big honkin' PP Edcor OT in ghetto UL?

[matt h]

Two part post (one for more general discussion, one more to david's followup)


The general comment: UL hookups in P/P amps offer one MONUMENTAL advantage that hasn't been discussed (directly). Namely, you know how people get a bit squeamish about using a dual-ganged PPIMV? generally because it starts to sound like crap by grossly throwing the GNFB circuit out of proportion?


Yeah- you can avoid that. Smooth sailing with a PPIMV. Gives you a tremendous amount of control.

For people who "love the 5f6a/jtm45" but "can't quite get along with an AC30".... Yeah, take those "Rockster"/Octal Rocket variants and give it a whirl. (though, uh, for the love of god people, please tweak your damn PI tail resistor for big bottle usage!)


For David-I sent you a PM because a number of my thoughts for what you're talking about aren't UL specific/related. If you've got a great PP OT kicking around with UL taps, I've got a challenge for you: forget about "ghetto-UL" and build a righteously DIFFERENT push/pull amp.

I will reiterate one thing from PM- I'm not sure *which* GA-40 circuit?

For the parts you've got on-hand, consider this (and this is entirely different from the PM I sent you).

Pentode input stage into a PARAPHRASE PI, dual ganged PPIMV, cathode biased UL output stage. The use of a non LTPI is important, because you need to make sure you really drive those power tubes HARD.

If by chance you happen to have a really really big choke (current handling), consider using a FWB recto (SS or tube/ss hybrid) with a choke input. It'll give you much higher voltage and a ton of current handling that typically gets sacrificed in cap-input recto/filter arrangements. It really depends on what you want from the amp, but it will mean that you can use the 150mA rating of your PT and still get mostly full power from a pair of 6L6GC's. Otherwise, by using just a FW setup, you're going to be asking a hair too much from the PT for a pair of 30W tubes. Now, if you use those 6L6GA's? that's much more in-line with the 150mA rating.

You're at the point where you have the possibility to run a PP *actual* class-A amp.

The biggest "problem" is that your OT is "hugely oversized"- this doesn't have to be a problem. Just remember to run a "mismatch" on the secondary to get the Zpri in the right ballpark. You won't get OT saturation, or anything close to it. That... isn't a bad thing. Just know it's not an option. (unlike, say, a supro thunderbolt)

[LeftyStrat]

I forgot to add the link to the RK article:

http://www.ampbooks.com/home/amp-techno ... tralinear/

[Reeltarded]

Either way now. I am right. Jerome! Bring me my mirror.

[Teleguy61]

Me thinks ol' Suz is a spambot.

Was your first clue that she was selling shoes or that she was-gasp-a girl on TAG?

[LeftyStrat]

She probably had stinky feet.

[TUBEDUDE]

The best sounding twin reverb I ever heard was UL. The key was trashing the feedback and cathode bias portion, returning to straight fixed bias. Besides the reverb sounds best delivered to the other input to the phase inverter. It sounds good even at lower volume but is certainly overkill for small gigs, but the owner does mainly big stage and outdoor gigs. Sorry Reel, I guess we don't all share the same tonal ideals, I just can't believe you wouldn't love the tone also. How do you feel about the new UL Tone King amps?

[matt h]

The best sounding twin reverb I ever heard was UL. The key was trashing the feedback and cathode bias portion, returning to straight fixed bias. Besides the reverb sounds best delivered to the other input to the phase inverter. It sounds good even at lower volume but is certainly overkill for small gigs, but the owner does mainly big stage and outdoor gigs. Sorry Reel, I guess we don't all share the same tonal ideals, I just can't believe you wouldn't love the tone also. How do you feel about the new UL Tone King amps?

A heavily modified twin reverb (pre-UL) is my favorite low-volume practice amp through an 8ohm 15" speaker... haha blackfaced, a pair of 6L6's, and a PPIMV taking it down a few pegs. If you feed that into an attenuator knocking it down just a bit more, set the volume to 3.5ish (use the eric johnson settings, actually), the MV to about 5, the attenuator a bit... and throw a RAT w/ LED mod in front of it, it sounds like a cranked marshall stack (the open back 15" gives a bit more low end than your average twin's 12s, effectivelyish emulating a quadbox-at-cranked-volume sound at friendlier volumes). Weirdest thing ever to have the borked NFB ratio work to your advantage, but, there ya go and Bob happens to be my uncle.

[TUBEDUDE]

Matt, I've never been a big fan of diode clippers. Nothing wrong with the iconic cranked Marshall tone though. How does the amp sound without it? The thing I like about amps without output feedback is they have chime and a dynamic quality of the upper mids and treble, even at low volumes. I enjoy the tone and dynamic response of these amps without any effects.
I think feedback that travels around a transformer to the PI has too much phase shift , skewing and destroying the harmonic structure. This extracts the liveliness and excitement from the signal that spins my crank, so I try to do without it when possible. If needed for stability, or to shape response of a stage, local feedback has a less deleterious effect. I've found some output stages however that resisted my best efforts to make them unconditionally stable without some feedback .

[Reeltarded]

Majors don't have the squatting under your fingers thing that the Marshall 50s and 100s do at all. No bounce. That is a drag. It's all about the freakin UL. These are the Genelex designed amps I am talking about, not the so called "Pig" early model. These amps were made only to be efficient and very efffing loud, not to sound like the other amps.

That makes me cry. It has made me laugh before too. I have not always used them for good. You should see what a pair does WFO though a split 4x12. Ugly.

[TUBEDUDE]

After the JMP series, every amp Marshall made was varying degrees of colder and less responsive (just one peckerheads opinion).

[Reeltarded]

These are all from the early JMP period. One design 67-74 when they ran them out of stock. Rip your face off with the real tubes. Another problem.

I wish I could pad these things down to 34s and clip the UL completely. Needs a proper pi too. I am busy and lazy. Bound for glory, for sure. hehe

[matt h]

Tubedude, the amp sounds great without the rat, and using different vtmb settings. (the ones I yanked from eric johnsons's fenders are absolutely idea for running a fuzz-of-sorts). I can't say I love the pedal in front of the other amps or with other settings. I almost never run the twin with 12's anymore, and almost never with a quad of 6l6's. The pair of 6L6's with the 15's really have something special. Very SRV "lenny" sounding.

What you describe about the chime I largely associate with pentodes in a way that beam forming and kinkless tetrodes don't always have. I'm sure a lot of that corresponds with historical association in guitar amps of NFB though. I'd wager a lot of what you're responding to is due to the lower drive requirements-- be it naturally (by tube type) and then compounded by associated factors (like nfb application). I've recently been reading up on EL37's, and the original designer apparently said they "only need a whiff of signal to be driven to full power." The high gm carried into EL34s... el84s also ain't so shabby. Surprise surprise, the chime kings, eh?