[Killercrush]

So would you think that the 7318 is a good candidate ? My pair have D-Getter, 1959 date codes and are build like little tanks, the glass is very thick.

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Originally Posted by Zanth Best 12au7's...tough but NotoriousBIG_PJ and I went through everything the world had to offer a coupla summers ago. We determined that the CBS/Hytron 7730 though ridiculously rare...is only "okay" compared to the CBS/Hytron 7318. The 7318 is pretty well the best tube I have ever come across save for the Bendix Redbanks. This tube is powerful, neutral, detailed, airy etc etc. Sadly they are impossible to find. They used to be pretty cheap before the current craze, then folks went mad over Teles etc. and the 7318s were dumped for a bit, now they can't be found at all. Do a search over at Audio Asylum, there are some phenomenal threads on the 12au7. The RCA Cleartops are nice and I was using them before I went with the CBS Hytrons. The 7318 ssell for about $200/tube now when they can be found, and that was a bit ago too...

 

[dsavitsk]

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Originally Posted by Killercrush /img/forum/go_quote.gif So would you think that the 7318 is a good candidate ? My pair have D-Getter, 1959 date codes and are build like little tanks, the glass is very thick.

Good candidate for what? Looking around a little more, it does seem that this must be a datasheet typo, and that you can sub these in for 12AU7s. So, for that you are fine.

My objection, though, is that there is nothing magical about a 12AU7 or any variants thereof -- even the premium ones. A lot of these tubes, 6SN7, 6DJ8, 12AU7, are used in commercial gear because people know them and they have always been used. This has driven up the prices on these to where the good examples cost a mint. But, there are many many tubes that are just as good or better for audio. For instance, you can pick up a 6688 for about $5 that has lower output impedance, lower distortion, a better distortion spectrum, and that in general sounds better than any 12au7 version. Now, if you are a commercial manufacturer and you want to have a successful amplifier, then you seem to have to stick to the classics, but in DIY you have other options and it is a waste of money to keep spending tons on rare run of the mill tubes.

Anyhow, the series of articles starting with this one might be worth a read: http://www.nutshellhifi.com/triode1.html

I don't think thick glass or getter shape has much to do with sound.

 

[looser101]

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Originally Posted by dsavitsk /img/forum/go_quote.gif For transformers, I think the Hammond 119DA is a gem and really inexpensive.

I hate to disagree. IMO it gives you fake soundstage and sucks out the mids. Heard the same thing with my Aikido and a Mapletree.

Anybody want to buy a pair?

~Renato

 

[jbloudg20]

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Originally Posted by looser101 /img/forum/go_quote.gif I hate to disagree. IMO it gives you fake soundstage and sucks out the mids. Heard the same thing with my Aikido and a Mapletree. Anybody want to buy a pair? ~Renato

I'll take em off your hands.

 

[jbloudg20]

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Originally Posted by headphonejunkie /img/forum/go_quote.gif I was wondering what is the soha/VanTotl in your sig. Did I miss something with the SOHA?

No i split up my individual amps with a slash.

 

[headphonejunkie]

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Originally Posted by jbloudg20 /img/forum/go_quote.gif No i split up my individual amps with a slash.

Oh. I was hoping there was some new hybrid design to try.

 

[J-Pak]

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Originally Posted by dsavitsk /img/forum/go_quote.gif For tubes, I think I'd use a 6C45, but be aware that they can be difficult to work with as they will oscillate if you look at them funny and get edgy if you run them too hard -- about 15mA and 1.8V bias (via a red LED) seems about right. Otherwise, maybe a 6H30 or 6N6p. Triode strapped 6688's and 7788's have become my tubes du jour, but the 6688 is just on the edge of having enough power here and the 7788 is even more of a beast to work with than the 6C45 -- the 7788 can also get a little spendy (~$30 to $40 per tube). For transformers, I think the Hammond 119DA is a gem and really inexpensive. Otherwise, Sowter makes a similar transformer for about 5x the cost, or you could get Electra-Print to custom make something ... I'd just use the Hammonds. For CCS, try this design: It gets the Walt Jung seal of approval: http://www.diyaudio.com/forums/showt...95#post1258495 Finally, for parafeed caps, choose your favorite. Maybe a Sonicap gen 1? Oh, and one of the best things about parafeed is that the power supply is much less important than in other designs as the CCS isolates it. So, just put together a CLCRC or CRCRC sufficient to get the ripple down, and you'll be good. No need for fancy rectifier tubes or expensive PS caps. I'd put this against a Melos (modded or not) any day -- in fact I have. My Melos has been keeping my closet shelf company for years now -d

Thanks for the info David. How would the same amp fair as a preamp?

I was googling for impressions on the Espressivo and saw that Gary Dahl uses his in a ridiculously nice speaker setup.

Like you said at the very least I'd like this to outperform the Melos.

And Jay mentioned the HP-2, I was actually planning on using it with the L3000, which are a bit more sensitive than the HP-2.

I don't have any technical knowledge of this stuff, so I had Jay helping me out here, thanks again to both of you.

 

[Roam]

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Originally Posted by ericj /img/forum/go_quote.gif Why two 12au7's? They have enough gain that running two triodes in series would be way too much gain, and with a solid-state output, there's no reason to parallel the triodes.

Depends on the topology of the solid state output stage. The typical MOSFET buffer used in audio has a high gate capacitance, to prevent frequency roll-offs and overcome the non-linearities, a low-impedance high-current output is required from the tube stage.

 

[dsavitsk]

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Originally Posted by J-Pak /img/forum/go_quote.gif Thanks for the info David.

It's Douglas

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How would the same amp fair as a preamp?

It could do quite well, but how well will depend on the components you choose and the quality of the build. The transformers that Gary used are really nice, but also really expensive. The Hammonds are clearly not going to come close to those. But, if you only want to use this as a preamp, then you might pick up a pair of Magnequest B7's or Lundahl LL1674's. For headphone amp use, you'll need something that can handle more power and that have a lower output Z. As I say, I think the Hammonds are pretty good here.

The thing to keep in mind is that the Hammonds are 600:8 transformers. If you use them with a 32 ohm load, then the reflected Z is about 2400 Ohms, which is why you need a tube with a low rp (~1200 ohms or less). They have been reported to work well with 300 ohm phones (which reflects as about 20K), but as you push the load higher you will start to lose bass (I'm told they are flat to 20Hz even with a 300R load.) So, my guess is that you should load the secondary with a 300R to 500R resistor to use them in a preamp config.

OTOH, if you use the autoformers, then it should work great as a preamp -- with the limit being the autoformers' quality.

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And Jay mentioned the HP-2, I was actually planning on using it with the L3000, which are a bit more sensitive than the HP-2.

The L3000's are 48 ohm? All to the good as this eases your tube requirements a bit. You want the primary Z to be 2x the tube's rp. As I said, with 32 ohm phones, you need the rp to be 1200 or lower. With 48 phm phones, rp can be as high as 1800 ohms which means that one side of a 6dj8 is fine, and a 6H30 is better.

As to competing with the Melos -- the Melos circuit is really pretty nice, but it has some inherent limitations, not the least of which is that in use as a preamp there are 3 or 4 coupling caps in the signal path as well as several power supply caps which tend to be low quality electrolytics, and which are also directly in the signal path. Even modded, you would need to spend a ton to bring these up to high quality. The less-pressivo has 1 cap in the signal path, and this is the parafeed cap -- the PS caps are not. It is also small enough, and the rest of the amp is minimal enough, that you can go crazy quality wise.

-d