Preamp questions

[jimipage]

Still haven't built a 'Wreck yet, but the time is coming soon. In studying the schematic I have two questions:

1) the 2nd 12ax7 uses only one triode; could the two triodes be paralleled?

2) if only three triodes are necessary to the design, would using a triple-triode, such as a 6C10, be OK?

thanks!

[jaysg]

I don't keep up with it well, but one of the Komets takes that unused section and uses it as a cathode follower on V2. Paralleling it would be a good experiment. In the case of the el-84 amps, it could be used like the Vox Normal channel which has no tone controls except the post-PI Cut.

As to the triple triodes, the layouts are conceived around the 12a_7 footprint. It's compact....so either build a meticulous clone first, or just play around with it and see where it takes you.

[jimipage]

Thanks for the reply.
I've been toying with the idea of maybe even attempting a small 'Wreck using three tubes -- one 6C10 and two 6GW8's.
If anybody else has any input on this or anything pertaining to my first post, please feel free to share your thoughts and opinions.

[sliberty]

If you build a "full sized Wreck, built it as specified. The amp is amazing - you need to experience it for yourself. Don't miss out by taking a detour so early in the trip.

If you decide to build something smaller, there are certainly lots of options. My MiniWreck is a straight Express preamp with a single ended power stage and a simplified power supply. The Derailment (not sure if that is the correct name) uses different tubes to reduce the tube count. I think it uses an ECL86 which combines the 3rd preamp tube stage with the power tube stage. And other options are out there too.

I can tell you from my own experience that a small TW can be similar, but it won't be a TW. Don't get me wrong, I love my MiniWreck, and others have enjoyed it too. But the shere oomph of an Express is not there with such low output power. I consider it a different animal with similar voicing.

[jimipage]

thanks for the advice, Steve. I definitely do want a "full-size" 'Wreck, and I'll more than likely go with Ceriatone rather than source everything scratch myself. The 6C10/6GW8 idea has been on my mind since I have most of the components to do so -- just none of the bravery!
Still gonna build that z-28, too, but I've been sidetracked by tow other projects that seem to be constantly in the "refining" stage. Is it just me or does everybody else still wanna tinker even after an amp is built and done?

[dehughes]

Oh yes. I tinker. Tons. That's half the fun. Getting the amp built is just for the sake of putting your mind at ease as to whether or not you can actually create the thing. Once it has been built, then that tension has passed, so you can tinker away without wondering if the "finished" product will turn on and work.

[doctord02]

Just a word of caution on triple triodes... there is a good reason you dont see many (if any) triple triode tubes in audio amplifier schematics. I hear on good authority that they are very noisy and succeptable to microphonics...

[jimipage]

At the beginning of this thread I asked:

1) the 2nd 12ax7 uses only one triode; could the two triodes be paralleled?

Having thought about it a little more, I'm now curious as to whether the first 12ax7 could be paralled and the second stage of the amp moved to the second 12ax7, and of course, have the third stage move over to the other half of the second 12ax7? Does that make sense? Anybody tried this?
I'm really wanting to build an Express soon, but the thought of leaving a triode unused kinda drives me crazy!
thanks!

[Matt72]

I'm in the middle of an Express build myself and have been curious about trying to parallel V2 also. But as was mentioned already, I'm going to build it stock first just so I can hear what all the fuss is...then mod away! Or maybe not!

I do like the sound of a 12ax7 paralleled like that. Not quiet as much gain as one side only, but the quality of the sound is just fatter and a hair smoother. Twice the current! So I'll definitely try that out.

I also usually prefer 12AT7s over the AX's. So I'll probably try that. Again, it smooths out the sound and the highs a little, drawing more current than the AX's.

I've been getting into using different kinds of preamp tubes lately and it turns out the 12AX7s are my least favorite! Too bad most amps use those nowadays. But some of the octal guys, or the pentodes (EF86, or 5879) sound incredible! They put the raspy old 12AX7 to shame IMHO.

[Fischerman]

FWIW, if having an extra triode bugs you, you could put a cathode follower between the first stage and the tone stack and make everything else pretty much stock. A guy on this forum tried it and said he couldn't hear any difference.

That guy said he also tried a cathode follower at the end of the preamp, a la Komet, and it did make a difference but he preferred the tone without it.

[Bickster]

I think that there may be a reason why Ken didn't use that last triode. Yes, it seems wasteful but for whatever reason it is unused. Very cool that you have a built in opportunity to experiment.

[Matt72]

Just build an amp that only uses the other side and after you've burned up half in your TW, pop em in your other amp!

[d95err]

I saw a TW design somewhere on this forum which used the spare triode as an alternatively voiced third gain stage. There was a switch to select which one to use. The alternative stage had some attenuation before it, a different coupling cap and a bigger cathode resistor IIRC. Sort of an evolution of the Fast/Gradual switch on some TW derivatives.

[Matt72]

Whoa, now there's an idea!

[Zippy]

See the thread on "Split Plate Load Resistor Switching".