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Someone mentioned about the new EH EF86 being really good and I have always wondered why someone doesnt make a dynaco st70 mod with the ef86 and a 12au7 or 12ax7 like Eico did? The best I have ever heard an el34 sound was in my Eico hf50s which use that Mullard circuit and I think if someone made a dynaco drop in board using that circuit with a few FB tweaks it would be a hell of a nice sounding mod.
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DynaGlow: Triode board is gone, Triode circuit remains as hard wired. Driver tubes are GEC EF86 and Brimar 13D5. Coupling caps are Russian teflon. The resolution and musicality of this amp if far greater than previous iterations with EL34'shttp://lonestarbottleheads.org/gallery/albums/072206/012.jpg
http://lonestarbottleheads.org/gallery/albums/072206/014.jpg
Sounds GREAT! Keep on keepin' on with the tricked out amps!
I've been running an EF86 Triode Electronics board the past 3-4 years. Sounds great!
Triode Electronics has made them for about 8-10 years now. It uses 2 ef 86s, each one direct coupled to one triode half of your choice of 6CG7, 12AU7 ECC99, E80CC etc, which works as a cathodyne phase splitter. Essentially identical to the Henry Klaus 7199 circuit, but with far better tubes and quality... and the board itself is a modern glass epoxy unit which alone is reason to do it. It sounds as good or better than the venerable Mullard 520. They introduced a new version that uses the godawful 6AU6 in place of the musical, neutral EF86.... but popular demand has put the EF86 board back into availability. And it does indeed make the Stereo 70 a great, great sounding amp. Installing Triode's bias mod which provides a seperate pot for EACH EL34 is fantastic too, and topping it off with the SDS power supply board that uses rapid charge cycle Panasonic caps in series/parallel, bypassed by Panasonic poly caps, completes the deal. I have heard MANY big $ amps that a Stereo 70 with the above Triode Electronic mods simply blows away, including 2 different Conrad Johnson EL34 amps. This EF86 board walks all over the 3 12AT7 board that was around for a few years.
I think your speaking of the vta board and that uses 12at7s when you use that with right output tubes its fantastic..I use 12bh7s in mine for the phase splitter and the 12at7 for the driver and I have a triode board laying around somewhere and I wasnt aware of it taking ef86s..That VTA board you speak of just smokes the curcio from A to Z but that doesnt take much. Now are you saying the current triode board runs an ef86?
mike
The board from Triode always ran EF86s; the change to 6AU6s was quite recent and not well recieved, so the EF86 board is now simultaneously available again. One curiosity from your post: I can't imagine the connection between the VTA INPUT board and "using the right output tubes" having some synergy--except possibly for the fact that great tubes like EL34 require less grid drive than 6L6GC, making it easier for the 12AT7s to throw signal down. I'm assuming you use 12AT7 as V1 for each channel voltage amplifier stage and then the 12BH7 is shared as the splitter.... I ran mine in much the same way before I put the triode EF86 board in. The VTA WAS a big improvement over the 7199 stock board, but really, the EF86 is just SUCH a musical, linear, non-microphonic, and low distortion tube that it's really the only way to fly. I had to futz around with a wide variety of 12AT7s in the VTA to get it right; Mullard CV4024s were nice, but the best turned out to be good old USA blackplate RCAs. The Triode board took the amp to a totally new level of transparency.
ARC
Thats it..The vta board has such good linear drive and I run 6l6gcs or even kt66s in my one st70 and being the board has such great drive and the 6L6s and kt66s take more drive,that circuit does it without breaking a sweat.THe el34s dont take anything to drive those.
The Triode Electronics board does indeed use 2 EF86's and 1 12AU7 or 1 12BH7 depending on which power tube configuration you choose. I've been running it in my ST-70 for a few years now and it sounds terrific. We've compared my modified ST-70 to more expensive production amps and it can hold it's own. A side benefit is the Triode Electronics board, with minor adjustments, allows you to experiment with a variety of power tubes in the ST-70.
The vta does that to..I have actually run kt88s in my st70 with great success but I usually run 6l6gc black plates which I cant find any el34 to compete with that sound of that tube..THe closest thing I have would be my telefunken el34s and even those arent like RCA black plates.
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