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SE 6L6 power amp, 12AT7 driver (design by Suncalc)
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Author:  mwhouston [ 08 Feb 2017, 20:15 ]
Post subject:  Re: SE 6L6 power amp, 12AT7 driver (design by Suncalc)

The 5881 didn't last long. Ugly looking valve and no real advantage in sound. Back to the prettier 6L6GCs. Currently flipped back to the T3 Class D monoblocks but feel I like Silver Supreme better.

Author:  mwhouston [ 16 Feb 2017, 20:57 ]
Post subject:  Re: SE 6L6 power amp, 12AT7 driver (design by Suncalc)

Suncalc, what would be the advantage and disadvantage of removing the bypass cap Ck from the 12AT7? In some of the designs in the pass you have suggested to leave Ck off on the driver. I realise there will be a little less gain.

I do understand it increases output impedance but I don't see that an issue here.

Author:  Suncalc [ 16 Feb 2017, 21:05 ]
Post subject:  Re: SE 6L6 power amp, 12AT7 driver (design by Suncalc)

mwhouston wrote:
Suncalc, what would be the advantage and disadvantage of removing the bypass cap Ck from the 12AT7?
As you noted, gain goes down by ≈4dB. With a gain of 21v/v you should still have no problems driving the amp to full power.

The real difference will be in tone. I imagine that the amp sounds pretty warm and full right now. By "unbypassing" the driver cathode, the 2nd harmonic in the driver will drop substantially. This will likely make the amp sound much more neutral. Personally, I wouldn't do it as I really like that full sound. But some prefer a more neutral power amp.

It's really in the ear of the beholder.

Author:  mwhouston [ 16 Feb 2017, 21:11 ]
Post subject:  Re: SE 6L6 power amp, 12AT7 driver (design by Suncalc)

Suncalc wrote:
mwhouston wrote:
Suncalc, what would be the advantage and disadvantage of removing the bypass cap Ck from the 12AT7?
As you noted, gain goes down by ≈4dB. With a gain of 21v/v you should still have no problems driving the amp to full power.

The real difference will be in tone. I imagine that the amp sounds pretty warm and full right now. By "unbypassing" the driver cathode, the 2nd harmonic in the driver will drop substantially. This will likely make the amp sound much more neutral. Personally, I wouldn't do it as I really like that full sound. But some prefer a more neutral power amp.

It's really in the ear of the beholder.


Thanks mate. Or you could install the "mood switch". Switch Ck in or out. Also because the driver stage is a 4SU I can drop any 12A*7 in as driver. Correct? But I'm really liking how it sound now and the driver is Psvanes best "T".

Author:  mwhouston [ 17 Feb 2017, 06:59 ]
Post subject:  Re: SE 6L6 power amp, 12AT7 driver (design by Suncalc)

Matt, what are the benifits of ultra-linear and how would you say it effects both performance and the sound? Interesting to hear you say that removing Ck from the driver tube will drop the amount of 2nd harmonic. I'm interested to hear about the effects of UL.

Author:  mwhouston [ 19 Feb 2017, 19:48 ]
Post subject:  Re: SE 6L6 power amp, 12AT7 driver (design by Suncalc)

What are the benifits of ultra-linear and how would you say it effects both performance and the sound? Interesting to hear that removing Ck from the driver tube will drop the amount of 2nd harmonic. I'm also interested to hear about the effects of UL.

Any comments.

Author:  Geek [ 19 Feb 2017, 20:05 ]
Post subject:  Re: SE 6L6 power amp, 12AT7 driver (design by Suncalc)

IME, the sonic difference between triode, pentode and UL (my test bed is switch selectable for all three) is highly dependent on the speakers and associated X-over (if any).

Cheers!

Author:  mwhouston [ 24 Feb 2017, 00:59 ]
Post subject:  Re: SE 6L6 power amp, 12AT7 driver (design by Suncalc)

Attachment:
P2243590 (800x600).jpg
Attachment:
P2243589 (800x600).jpg
This was the original 6L6 tube amp in a wine gift box. From this I built the far more improved model in the stained wine box. Listening to it now and love it.
 
I had another crack at the original but with 12AU7 and JJ blue glass KT88s. Sounds excellent and dead quiet but I'm not happy with the PS. So tomorrow, once more, I'll alter the PS to the one I know works. It can us the tranni box or the second one (Silver Supreme). I have some black metal 6L6s which I'll drop in. For now here are some images with the KT88s

Author:  mwhouston [ 25 Feb 2017, 06:23 ]
Post subject:  Re: SE 6L6 power amp, 12AT7 driver (design by Suncalc)

Got the PS sorted by using the external tranni box I made for the Second amp. With KT88s in stalled HT=320V with 300V to the 12AU7. Biasing to the KT88 is 23V and with the Rk - 470ohms each tubes pulls nearly 50mA. Sounds good but I need a big listen to really get a handle on it. a 12AU7 and KT88s have to sound different. Having the external tranni box means I can have a number of amps sharing the filament and HT voltages. That allows me to amp roll with a saving of about $100 for each amp.

Author:  mwhouston [ 25 Feb 2017, 06:25 ]
Post subject:  Re: SE 6L6 power amp, 12AT7 driver (design by Suncalc)

mwhouston wrote:
Got the PS sorted by using the external tranni box I made for the Second amp. With KT88s in stalled HT=320V with 300V to the 12AU7. Biasing to the KT88 is 23V and with the Rk - 470ohms each tubes pulls nearly 50mA. Sounds good but I need a big listen to really get a handle on it. A 12AU7 and KT88s have to sound different. Having the external tranni box means I can have a number of amps sharing the filament and HT voltages. That allows me to amp roll with a saving of about $100 for each amp.

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