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In Reply to: RE: Worst ever FleaBay sale ever posted by h00hbt on December 20, 2015 at 12:13:46
I know a few OTL amps use these, but it's designed to be a VOLTAGE REG tube!
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Because of its low Rp, low mu, and high Gm, the 6AS7 and its family of triodes are well suited both for use in a voltage regulator circuit and as an OTL output tube. Because historically it was mostly used in VR circuits does not mean that it is not also excellent as an OTL output tube. (Of course, 6336, 6C33C, 7241, etc, are even better.) However, I would not pay big money for those tubes on eBay.
These are used in headphone amps, and Chatham is one of the best. They are not used in place of 6SN7s obviously.
Are you using them as followers? They're not very linear when used in the typical common cathode configuration.
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Buy Chinese. Bury freedom.
in a number of OTL headphone amp designs. Commonly a 12AU7, 6SN7 or similar is used as the voltage gain tube and the 6AS7 is used as a cathode follower. Pete Millett's Wheatfield HA2 used that basic topology, as does the Bottlehead Crack - they actually specify the 6080 as an output tube but 6AS7 is an alternative.
I really like cathode follower topology, but not the the large coupling caps needed ahead of 32 ohm phones. That's why I haven't built an amp like this for myself, despite having a decent stash of NOS 6AS7s. I've been looking for economical low-power transformers for this use for some time, but no luck. It just isn't a common application. I think it's a real shame none of the commercial suppliers of headphone amps have taken this approach. Buying in more volume could reduce the cost of the transformers significantly.
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Buy Chinese. Bury freedom.
Yeah, the big cap is a problem for low impedance phones. I think some people are looking at using D-Link polypro caps for those - I'm guessing that's what is used in the Millett Apex Teton headphone amp, although that is more designed for 300 ohm phones than 32 ohm phones.
Is this the military cousin to the 6AS7? Craziest, toughest tube, I've ever seen. A guy put two into this stereo DIY guitar amp, years ago. Heavyweight monster.He like the tone.
8^)
Edits: 12/21/15 12/21/15
Yep, those are used in some headphone amps.
Those old Red Bank tubes are over the top...would love to find a stash of those. Too bad they never got asked for big damper diodes...LOL
cheers,
Douglas
Friend, I would not hurt thee for the world...but thou art standing where I am about to shoot.
Edits: 12/23/15
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