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Small SE tube amplifier using 12B4A and ECC802S
http://diyaudioprojects.com/Forum/viewtopic.php?f=9&t=1358
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Author:  Bennybuis [ 16 Jan 2010, 22:21 ]
Post subject:  Re: Small SE tube amplifier using 12B4A and ECC802S

Thanks Azazello,

I will try that, but maybe my power transformer cannot handle the extra load, I have 275 Volts B+ idle, now under load I have got 205 volts, if I increase the load more, my B+ will drop under 170 volts I am afraid. I have no ccs, cause the LM317 eats too much current on it's own and B+ drops to 120 volts, I tried. Next amp I will build I will use better transformers.

Author:  Bennybuis [ 17 Jan 2010, 00:49 ]
Post subject:  Re: Small SE tube amplifier using 12B4A and ECC802S

Hi everybody,

well, I changed the cathode resistor to 605 ohm and I have now 32 ma cathode current at 190 Volt B+. Good enough for me.

Author:  Bennybuis [ 17 Jan 2010, 07:21 ]
Post subject:  Re: Small SE tube amplifier using 12B4A and ECC802S

Hallo everybody,

here is the final schematic, also from the PSU. I replaced the 2nd filter cap with a 220 uF and added a 0,01 poly cap. That reduced the rest of the ripple to virtually nothing, even with sensitive headphones. I use the amp as a headphone amp, because it sounds so nice. It definitely sounds much better than my headphone amp kit, and this one is a real tube amp. This is defenitely worth building, if you have stuff laying around and are bored, build this little amp. I build mine over the weekend and perfected it over one week. You can start with a pretty perfect version and maybe make it even better. Here are the final schematics from the amp and PSU. Have fun.


Now, this setup works for me, I have now 32 mA current on the cathode and still 193 Volts of B+. If you have a better transformer, you may have to juggle the cathode resistor to not fry your tubes. Mine is now good enough, I wanna start something new. This one was a total success.

Thanks to all my friends, by name Bruce and Magnus and Nikola for their help and suggestion. Thanks guys.

Author:  azazello [ 17 Jan 2010, 10:14 ]
Post subject:  Re: Small SE tube amplifier using 12B4A and ECC802S

Hi, BEN!
195 v are small for SRPP ECC83 for linear mode. You have for good sound 2 ways:
1. Use only 1 triode section of ECC83 or
2. Use ECC88 /PCC88/ in SRPP with resistors 220 ohm in cathodes.

Author:  Bennybuis [ 17 Jan 2010, 11:02 ]
Post subject:  Re: Small SE tube amplifier using 12B4A and ECC802S

Hi everybody,

well Nikola, this amplifier is as good as it gets, the following will have a better power supply and ccs and a LM317, very important, that really helps thge sound always, did you ever try? I will send you a couple.

Author:  moonbird [ 24 Jan 2010, 19:28 ]
Post subject:  Re: Small SE tube amplifier using 12B4A and ECC802S

Ben--

This amp looks way cool. Thanks for the PM message about it. I have many of the parts. thx again!!

Author:  moonbird [ 24 Jan 2010, 19:39 ]
Post subject:  Re: Small SE tube amplifier using 12B4A and ECC802S

Soundbrigade wrote:
If it was the trannies I sent you, I can send you more.

Hello - I would like to start looking for parts to build this amp. If you are the source for these trannies, please tell me about them and how I can obtain them. thank you!

Author:  Soundbrigade [ 25 Jan 2010, 03:09 ]
Post subject:  Re: Small SE tube amplifier using 12B4A and ECC802S

The trannies are simple 100V line transformers. I have no other info than this given on Conrad.de website: http://www.conrad.de/goto.php?artikel=516104.
I got a package of transformers from a friend in Sweden and it is from this package I have sent
The transformer is a special one mainly used for distributing sound into wharehoses and factories on a 100V signal. As the OP-signal is pure AC, the transformers contain no airgap and can only be used in low wattage amplifiers.
Guess you can grab this one almost everywhere.

Author:  moonbird [ 25 Jan 2010, 12:45 ]
Post subject:  Re: Small SE tube amplifier using 12B4A and ECC802S

Thanks for the info on the OT. What load impedence is used for the 12B4 at Ben's this operating point? thx again.

Author:  Bennybuis [ 26 Jan 2010, 11:38 ]
Post subject:  Re: Small SE tube amplifier using 12B4A and ECC802S

Hallo everybody, hallo Moonbird,

sorry for not following the thread, but I have been busy with my KT88 amp, now finished and rocking.

I know nothing about the specs of those opts, just that I got really lucky with them in combination with the 12B4A's. That little amp turned out to be a real audiophile amplifier and I didn't plan on doing that, it was supposed to be my wifes TV amp, not very loud, but easy and ever lasting, but upon listening to it I found out what I really created (with the help of Nikola and Bruce). If you wanbna build this amp, ask Magnus about the specs or where to get those. I got one more set, but those are for Nikola, sorry. Anyway this amplifier is defin itely woth building, mine is running day and night ni my living room, it is now my main amplifier. Have fun.

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