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Yay for tubes!

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Steve Conner

Tue Dec 04 2007, 10:13AM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

Hi all,

I've been building tube amps for years (longer than I've been making Tesla coils!) and I have a fair idea of what I want now.

The clean channel on my new creation is just the standard circuit you'd find in a Fender or Marshall, except that I used an anode follower to mix the dry signal with the reverb return. It has plenty of output to overdrive the power amp if needed.

The dirty channel is just the same standard circuit again, but with an EF86 pentode stage stuck on where the guitar input used to be, and a gain control and some bass cut (controlled by the Fatness switch). It uses a separate tube, so this can be replaced with a 12AT7 or 12AU7 without affecting the tone of the clean channel.

The P.I. and power amp are just the standard Fender/Marshall circuit again. Now, the main effect of a 12AT7 in the P.I. is to decrease the negative feedback around the power amp, compared to a 12AX7. So if you prefer a 12AX7 in the PI, this means you like the sound of negative feedback! Ditto for EL34s vs 6L6s, as EL34s increase the loop gain too.

Finn: An amp with 833s would put out nearer 1300W than 300, and would have more iron in it than a blacksmith's anvil :P I'm planning to use three pairs of 6550s or KT88s, running off about 700V. The chassis needs to be suitable for the road... there's not much need for 300W of bass guitar in my apartment! :P I'm thinking of modding an existing 19" rack housing like I did with my first amp.

Two of the Sovtek 6550s in the pic below are bad, but I've since found another two tubes that are a reasonable match. I also got a big 500VA toroidal mains transformer from an old medical isolation unit. The output and interstage transformers were found on Ebay.

1196763215 30 FT35302 Imgp0918 Amp Small

ShawnLG

Tue Dec 04 2007, 11:43PM

Registered Member #286 Joined: Mon Mar 06 2006, 04:52AM
Location:
Posts: 399

I have been pondering on building a tube amp for my guitar, but finding tubes and having little experiance with tubes makes this project not easy.

On the other hand, distortion technology is now moving to DSP.

Hazmatt_(The Underdog)

Wed Dec 05 2007, 12:24AM

Registered Member #135 Joined: Sat Feb 11 2006, 12:06AM
Location: Anywhere is fine
Posts: 1735

Actually Shawn, DSP and effects have been around for a couple of decades, its not something that is just happening now. Line 6 provides a stand-alone USB unit called the Guitar Port, and its been around for a few years now, so you might want to check that out if you're interested in DSP.

On the other hand once you start playing will all of the processor toys some of us realize that it's not what we thought it was and go back to basics. Some people are really good with the programming and can get fantastic things to come out, but non-sophisticates like myslef have troubles with all of the options and go back to something more basic in favor of guitar, boost, and amp.

Steve Conner

Wed Dec 05 2007, 10:17AM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

Well, I've heard people get some really good tones from the likes of the Line 6 Pod or the Amplitube modelling software. The original DSP effects units from 10 years ago were awful, but it gets better by the day, now everything has 24-bit converters and huge amounts of cheap CPU power. But I get enough DSP in my day job, thanks.

ShawnLG: Building a tube amp is easier than you'd believe. Probably the hardest part to find is an output transformer.

EDY19

Wed Dec 05 2007, 11:28PM

Registered Member #105 Joined: Thu Feb 09 2006, 08:54PM
Location:
Posts: 408

I'm just starting to build a tube based plasma tweeter using EL519, ECL82, and EF86- Its my first audio tube project, so we'll see how it goes! I'm still debating on the rectifier though- anyone have strong preferences for rectifier tubes or Solid State?

Steve Conner

Thu Dec 06 2007, 09:39AM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

Solid state, rectifier tubes are just a waste of power and space these days. :P Unless you manage to get a mercury rectifier tube, and you like the cool blue glow!

Marko

Thu Dec 06 2007, 01:55PM

Registered Member #89 Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145

Why do then audiophiles all go for tube rectifiers? I don't see any particular advantage, except for kewl factor (all tubes, no silicon).

Steve Conner

Thu Dec 06 2007, 03:15PM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

Same reason as they believe that painting the edges of CDs green improves the sound, I guess.

Tom540

Thu Dec 06 2007, 04:46PM

Banned on 3/17/2009.
Registered Member #487 Joined: Sun Jul 09 2006, 01:22AM
Location:
Posts: 617

I think they just want all tubes.

In my opinion I think hybrid designs are much cooler. Like a boost converter for the power supplies then powering tubes or something. Straight tubes makes things bulky, heavy and hot. Might even sound better.

It's like the difference between restoring an old car with all original parts or adding new stuff to it.

While original is always cool, it isn't always practical or as high performance and when it comes to audiophiles i would think performance was the goal. Of course I think most audiophiles are insane. lol

Dr. Drone

Thu Dec 06 2007, 05:07PM

Registered Member #290 Joined: Mon Mar 06 2006, 08:24PM
Location:
Posts: 1673

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