New Twin UL build. Tube types. OT specs.

[soma_hero]

I want to build a Twin Reverb and want to experiment with Ultralinear output section. Ultimately I want to have a platform for fooling around with tube types and output configurations.

I hope to try KT66, KT88, alongside 6L6. Here's what I think is my starting point. The Fender replacement OT for the 100W Twin is 2K. From what I can gather, the UL Twin OT is 2.5K. So a quad of 6L6 can run in tetrode or UL from 2 to 2.5K.

KT66 from my interpretation of the datasheets and literature like 3.5 to 4K in tetrode and 4K in UL. KT88 in tetrode at 4.5K and UL 4K to 4.5K.

Since I started this wanting to build a Twin Reverb I think I need to stick to what works for the 6L6 and try and accommodate the other tube types. Hammond 1650T is 1.9K/120W. Looks good for both tetrode and UL. Will running KT66/KT88 at this lower impedance dramatically vary their sound from what they're generally voiced for? Edcor CXPP100-MS-2.5K is 2.5K/100W. They also have 4.2K/100W. These both have 40% taps. Do you suppose running 6L6 at 4.2K would take away some of the Fender feel?

And about power ratings. I'm not really interested in getting max power output so I'm not going to be running 600V plate voltages on the KT types. Probably stick around 450-500V as per the fender schems. Would I be in danger of ruining a 100W OT with a quad of KT66 or a pair of KT88?

Lastly, more philosophical than technical. With this project I want to make a loud, clean amp. I do not need to kill myself with the volume, I'm not trying to make the loudest amp I can here. Just want to play with output designs and such. This amp weight wise will probably be a bear. An ultralinear OT that size, the hammond is 14 lbs. A PT with that kind of voltage and heater current will also be huge. And I wanted to put it in a 2x12 combo. Does it seem more practical to just stick with 6L6 so I don't need any extra current, loose some weight in the PT, and pick up an UL Edcor that's lighter than the hammond, though only 100W?

Thanks all for any advice,
Michael

[soma_hero]

Read a clip by Michael Zaite saying he could never get 6L6s to sound good in ultralinear. He also talks about the negative feedback generated and how Fender adding extra negative feedback causing a sterile sound.

So maybe I'll grab something around 3.5k for max flexibility.

EDIT: Actually I could just go with a 2k ultralinear OT and mismatch the speaker load to double it when I want to use KT66 or KT88s. Will this work the same way with ultralinear configuration?

[Cliff Schecht]

What sounds good for hi-fi will not necessarily sound good for guitar. Ultralinear operation is meant to even out the frequency response of the output section and consequently in doing so also reduces gain and distortion in that section. Part of "the sound" of the guitar amplifier is that it is one of the few "linear amplifiers" that actually encourages distortion, although in relatively controllable manner.

I would think that a lot of "the sound" would be lost using ultra-linear operation. The reason even a clean tube amp sounds sweeter than a linear amp is because there is still some harmonic distortion still going on in the pre and power amp. Typically what you get in the best sounding guitar amps is a fairly strong second harmonic (harmonically related to the octave, pleasing to the ear) and maybe the slightest amount of third order distortion to add some huevos. These are the two harmonics that dominate the response of a distorted guitar amp, along with the fundamental; higher order harmonics are relatively small compared to these two. An ultralinear configuration is going to take away a lot of the great power amp harmonic distortion and leave you with a bland sounding power amp (where the *magic* happens IMO). I'll bet you'd get about the same sound with a transistor output section and could save some money on the expensive OT.

I think you need to consider what you really want out of this amp. Do you want something that is a platform for modifying/testing or do you want an amplifier to play. If the former then weight is probably a secondary issue but if the second, I would stick with what is known to work and go for the lighter weight option you mentioned. A test platform would allow you to tweak the sound to your liking but this avenue can also be a waste of time and money; you may eventually end up just converting the entire thing back into a Twin.

[soma_hero]

Yeah thats what i've read about harmonic response. I'ma give it a go anyway. Won't be for months till I get around to it but I'll report back with my findings..

[M Fowler]

Mike Zaite did use ultralinear taps in his Route 66 which is a good amp.

[fperron_kt88]

Marshall Major is ultra-linear. Sounds quite good cranked (what? can't here ya??? Louder please!!!). Think AC/DC For Those About to Rock.

Mine has a PPIMV and the sound of the amp is very similar when dialed down a fair bit... So the pre is compressing and distorting things more than anything else, I take it. It gets a good buzz. Nothing like the 1959's mid-crunch, but again, sounds good for guitar.

[muchxs]

I can't imagine why anyone would want to clone an ultralinear Twin. Real ones are cheap right now, say $400 for a beat up one in a private sale. $300 on the low end on eBay. You can't buy the parts for that.

[soma_hero]

Yeah, this is more of an experimental platform. The Twin is the basic design with option for ultra linear operation. Switchable extra gain stages, etc....