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Vintage threads from the first ten years

Guytron GT-100

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12/15/1997 11:02 PM

Guytron GT-100

I tried this idea with a 6V6 single ended driving a phase inverter and a pair of EL34's. The Champ-like output is only around 8 volts, Where the phase inverter wanted to see 12-20 volts. So I added a gain stage after the Champ output transformer! I too found that the whole thing sounded better if the Champ was driving a real speaker. I also discovered that a better sounding speaker translated to better sound to the second output section. The Guytron idea of using a pair of EL84's is wise because the output from the first [15 watt] transformer is perfect to drive the phase inverter to the second output section. I'll be interested in hearing the Guytron.
Matt I.

12/17/1997 1:44 AM
Steve A.	Matt: >>>I too found that the whole thing sounded better if the Champ was driving a real speaker.<<< For an authentic speaker load, could you just remove the cone and run the output into the voice coil and magnet? I was wondering if anyone has tried this. Steve Ahola

12/17/1997 8:01 PM

Steve:
I know this sounds like a teaser because I can't remember the brand name, but before I got seriously into amp building someone showed me a little box with a couple of tubes and a small speaker without a cone [just the magnet and voice coil] for a load. I never listened to it. If you just rip the cone off of a speaker, then the voice coil won't stay aligned, so there are some customizing issues related to that idea. But geeze, it seems like it really could work? How about having a pair of EL84's sharing the same output transformer as the larger output tubes [or having seperate primary windings for each output set. Isn't Mesa Boogie already doing this?] thus driving a good sounding load. Turning up the "master volume" would add in the larger output section. OK, I'm out of obsessive ideas for now!
Matt I.

12/19/1997 6:45 AM

Unless the cones mass, or inertia, is allowed to oppose the force generated by the electromagnetic signal in the voice coil, and allowed to act as a motor or generator creating a back-EMF as it returns from extension to rest position, it will not present the highly interactive load that a speaker really is.

You can't just cut away the cone, insulate the loose voice coil former by glueing in place, and expect this 8-ohm fixed inductor to behave like a speaker producing zero sound. Even with a built-up "equivalent network" of resistors & capacitors it will not present the same complex interactive load to the amplifier. There are some power soak loads that are built in a similar fashion, such as a groove tubes unit, that try to accomplish this but do not produce the superior quality of sound you can obtain by audio coupling, or miking, an actual functioning speaker.

12/22/1997 11:51 AM

Doc,
Thanks for spelling that out so clearly. "Geeze, it seems like it should work" was my sarcasm coming out. The combination of output tube saturation, output transformer, and real speaker load is complex and highly sensitive to changes in dynamics, pitch, attack, timbre, etc. I sometimes compare tube amp saturation [and near saturation] to a piano string in that it is very difficult to mimmick because its so rich and complex. Samples of piano strings rarely satisfy a true pianist. Just capturing a piano onto tape is a challenging proposition. I make this rather lengthy point for those people weighing the pro's and con's of a "flexible" style amp against a "vintage' style amp. The "flexible " amp usually has a great screaming lead sound with the master volume turned low to medium [still plenty loud]. Switch to the clean sound and dime the master volume and what do you get? Exile on Main Street? Disrieli Gears? Live at Leeds? No. Add your Tube Screamer and still no. Why? Because the pedal only sounds great if your output section already sounds great. If you want the more subtle overdriven sounds with the option of different volumes, Maybe its time to start collecting two or three small to medium size tube amps? Often the same ones used to record those sounds in the first place. And now that I've expressed my opinions laced with tech ammo, I'm sure I'll get some other opinions back at me!
Respectfully,
Matt I.

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