THD Univalve on the Atlanta Craigslist. $625 or trade for "AN ACOUSTIC GUITAR OF THE SAME VALUE OR A BASS AND BASS AMP."

All caps, though. Shouty.

I've only known one guy to play a THD, and it was actually a VHT so I don't know anybody that played a THD. So I have nothing to offer. Except one thing. The only amp I'm somewhat aware of that is a "plug in whatever you want and it's biased cool" amp is the YBA-200, which is a dog. What's the mechanism by which they make it so you can put in whatever you want? If it's cathode bias, that may or may not be cool. But if it's fixed bias (aka manually adjustable bias) then I might think about steering clear. Not to get all snobby, but is it all tube or is it using solid-state whatnot to make it so you don't have to adjust the bias? If it's using a solid-state mechanism, I'd go for the "adjust it yourself" kinda bias.

From what I know of you, you're the kinda guy who could handle buying a bias probe and setting the bias yourself, rather than letting primitive computer circuitry handle it for you.

Etc.

BadComrade wrote:I think I'd be playing at about 1 watt most of the time at home, so...

Then I would get the Univalve... Single-ened guiter amps sound wonderful.

I am not a fan of these amps. I just don't like the way the sound. They do look pretty rad though...

if you can save your bones and spend a little more money, I recommend the REEVES amps with the London Power Scale feature. It's like an attenuator that won't cook your tubes. These amps are essentially little Hiwatts that can get "that sound" without killing small mammals. THD Univalves in comparison (IMO) sound chintzy, even if they cost less.

Wait, it'll take EL84's as well? That's starting to sound really bad. Aside from the sockets being a different size and having a different number of pins, EL84's will be destroyed pretty quickly by much more than 400V on the plates. And at the same time, EL34's don't sound super great until you get at least a good 450V, or 550V for that matter.

FWIW, any amp that will take 6550's will also take EL34 or 6L6GC, and any amp with separate bias adjustment for each output tube will take mismatched tube types. And you can hook a hotplate up to whatever amp you want. So really, other than the automatic bias adjustment thing (which I'd steer clear of unless it's cathode biased) it doesn't actually have an advantage over other amps except that it's marketed as such.

You would like my amp design. It'll do what the THD does in terms of handling combinations of almost any output tube types (6V6, 7591, 6L6, 5881, EL34, 6550), and it has a single-ended 1W output built right in. No hotplate necessary. If you don't mind waiting a couple years and paying like $3K, I'll make you one.

Okay, I'll give my super-double-secret idea away... take any amp you want, and right before the phase invertor, add a 12AT7 tube driving a Fender reverb transformer. There ya go. Single-ended cathode-biased 1W speaker output.

scott wrote:You would like my amp design. It'll do what the THD does in terms of handling combinations of almost any output tube types (6V6, 7591, 6L6, 5881, EL34, 6550)...

7591 has a different pin-out than those else mentioned... did you mean 7581?

Naw, I did mean 7591. The plate and screen are the same, so it's only the control grid and cathode/beam-forming-plate/suppressor pins that have to be routed to a switch to select 7591 vs any of those other tubes. I think the 7591 is one of the best tubes ever, and wanted to make sure my amp design could handle them. The tubes I expect to use the most are a pair of either 6V6 or 7591, and a pair of EL34.

And I'm still debating using a 7199 for the 1W output, to get the whole pentode thing going on there.

Aha, there ya go. Selectable higher or lower plate voltage. The voltages aren't bad. The high is similar to what you'd find in a typical Fender or Marshall. The low is a little lower than what I'm used to for EL84's or 6V6's, and way lower than what you'd want to use for any of the other octal tubes. But it's definitely a safe voltage for 6V6 or EL84's.

Got a schematic for it? I'm curious to see how many computer chips, if any, are in there, and how the auto-biasing works in general. And also I'm curious how they deal with the issue of impedance matching through the OT, if you can operate different tube types at different voltages. I wanna see if they designed it to perform ideally with one specific combination of voltage and tube type, or to be set up for more of an average performance across all types. It's one of the things I've been researching for my amp.

Is there a local dealer who's got one in stock that you can go mess around with?

THD Hot Plate on Atlanta's Craigslist for $225.