Home » Audio » Group Build » My idea...
My idea... [message #30002] |
Wed, 22 December 2004 13:11 ![Go to next message Go to next message](/forum/theme/AudioRoundTable/images/down.png) |
Damir
Messages: 1005 Registered: May 2009
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Illuminati (2nd Degree) |
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Build the linestage in little larger chasis (enough additional space for two SE OPTs and two tube sockets), with overdimenzioned PS (additional DC current say >120mA), with B+ about 300V. Choose OP for the 5687 a little higher (15-20mA, Ugk=4-6V, Uak=110-150V), CCS load. Then we can build line stage first, with amplification about tube mu, or 17. We can use it for (pre)amplification of low-signal sources (hundreds of mV) to "drive" power amplifier. But, our linestage can be a good "driver" for SE tube amp with CD player input - 2Vrms, say for EL34 in triode, or even 2A3/6B4G. Once "armed" with experience building line stage, additional work for SE output stage would be trivial :-).
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Re: My idea... [message #30011 is a reply to message #30006] |
Thu, 23 December 2004 08:41 ![Go to previous message Go to previous message](/forum/theme/AudioRoundTable/images/up.png) ![Go to next message Go to next message](/forum/theme/AudioRoundTable/images/down.png) |
Damir
Messages: 1005 Registered: May 2009
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Illuminati (2nd Degree) |
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Thank you for your confidence. It`s no problem - when we have a driver, SET power amp is just a few resistors, capacitors, OPTs, output tubes+sockets. But - if we use about 300V B+, then we have a few choices for the output tube. One of the simpler solutions would be EL34, triode connected. Pro`s - IDHT with "standard" 6,3V heater, easy to drive (say 16Vrms max, then our line-stage can "drive" it with 1Vrms input, +"reserve" 6dB with 2Vrms CD output). Bias is easy - just one resistor + capacitor (cathode bias). Con`s - With Uak about 280V, and Ugk =20...24V, and OPTs with Za=2,5k-5k, we can expect only about 2-3,5W output. Sensitive speakers is a must... Another candidate could be 2A3, "classic" OP (Uak=250V, Ugk=-45V, Ia=60mA, Za=2k5, Pout=3,5W). "Cool" DHT, but now we have some complications - we need 2,5V filament winding, filament hum balancing pot, and the most important - 2A3 "needs" 45Vp=90Vpp=32Vrms input AC voltage for max. power. Our 5687 linestage has A~17 and this is just enough, but with no "reserve" - it`s desirable to have at least 3dB more amplification, for "quiet" CDs. We can (almost) get it if we use similar ECC99 tube (mu=22). Well, I`d like to see some discusion (if anybody is interested) - what to do - separate linestage and power amp, or no. Then - which tube to use, topology, etc. I can post a schematics, calculate the component values, give descriptions and some building guidance, etc. Where to find the parts - I`d like to see a discussion, too.
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Line stage [message #30014 is a reply to message #30011] |
Thu, 23 December 2004 10:42 ![Go to previous message Go to previous message](/forum/theme/AudioRoundTable/images/up.png) ![Go to next message Go to next message](/forum/theme/AudioRoundTable/images/down.png) |
colinhester
Messages: 1349 Registered: May 2009 Location: NE Arkansas
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Illuminati (3rd Degree) |
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I vote for the line stage. The amps wpuld be next the next obvious progression. However, instead of using the 2A3 is there another, less well known, power tube we could use? I don't know, just something to be different......Colin
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Favorite output circuit [message #30019 is a reply to message #30012] |
Thu, 23 December 2004 14:39 ![Go to previous message Go to previous message](/forum/theme/AudioRoundTable/images/up.png) ![Go to next message Go to next message](/forum/theme/AudioRoundTable/images/down.png) |
Damir
Messages: 1005 Registered: May 2009
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Illuminati (2nd Degree) |
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![](http://damir.webizlog.com/VDV3070PP%20AMP.jpg)
Well, I didn`t try them all, of course. The last 5 years I listen to the music through my DIY monoblocks (PPP, 4xEL34 or 5881 sometimes, concertina phase splitter, Plitron/Amplimo toroidal OPTs, triode or UL, no NFB loop). I`m satisfied, only criticism can be low damping factor - little "boomines" through rear ported speakers, JBL4208. As you can see, I`m not an audiophile, I even listen "lo-fi" recorded music... I have "neverending" breadboarded 300B amp, tube rectification (CLC + LC for the driver), I constantly (but slowly) try different things. Right now it has a cascode 5687 driver...maybe I`d solder this mess together in the 2HE rack case one day... Two toroidal PTs, 2 Lundahl 3k OPTs, 4 chokes, Svetlana 300B tubes. Well, to answer your question directly - for the good, but simple enough amp I`ll vote for PP, good quality OPT, say "Plitron" 6k:5Ohms. Individual bias pots for the each output tube (say EL34, 6550, KT66, etc.). Split load (concertina) phase splitter with E182CC, ECC99 or 5687 tube. Power supply with another "Plitron" toroid, SS rectification, CLC+ LC for the driver(say, Lundahl chokes),B+ about 390V, good quality passive parts. About 25W in UL or half of that in triode. No NFB loop, AC heaters (good enough, IME). As you can see, 90% from the Vanderveen`s book, but it works well. (Hehe, Pltiron/Amplimo even has a similar kit - no affiliation:-)). That`s very subjective and YMMV, etc. To be continued... ![](http://www.audioroundtable.com/emoticons/smiley.gif) Merry Christmas to everyone!
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