New SE With Triode Mode KT120/150

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Cressy Snr
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#361 Re: New SE With Triode Mode KT120/150

Post by Cressy Snr »

OK.
Schematics corrected:
804 SEULDCC6SN7.jpg
807SEULPSUDCC6SN7.jpg
Something that interested me about the input driver stage is that it looks like a voltage amp, direct coupled to a cathodyne phase splitter with only the top output in use. I say that because the anode and cathode load resistors are the same on the driver. It looks like this front end could just as easily be used in a push-pull amp, if the HT was increased a bit.

Anyway, I'll take Nick's advice in future and just put up the circuits sans component values. It's a lot of messing about if you get a mistake somewhere.
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Nick
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#362 Re: New SE With Triode Mode KT120/150

Post by Nick »

direct coupled to a cathodyne phase splitter
Yep, I saw that as well. Maybe we should get a life :-)

I use a similar 6sn7 to 6sn7 circuit in the front of my 211 at the moment, though the two stages are not direct coupled and the second triode has a -300 supply in its tail.

What you have is not dissimilar to my favourite single ended interstage driver, except I used 5687, and the second valve anode load is the interstage primary. Then tweek with a cap on the cathode to extend the bass response of the interstage by the interaction of the L and the C
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#363 Re: New SE With Triode Mode KT120/150

Post by izzy wizzy »

There's a ton of amplifiers out there with SN7 SN7 ??? There must be a good reason for that maybe as is being discussed here.
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ed
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#364 Re: New SE With Triode Mode KT120/150

Post by ed »

I've just had one of those memory spark moments.....remember this little gem from 2008?
I built it for a friend and it started life as a Sun SV2A3 as the doner...had exactly the same front end as yours at the same op point as well...
srpp-2a3-top.jpg
It had a mains transformer that got well hot so I deduced it was 220v, and replaced it with a Hammond, but kept the Tamura outputs.....
the point of the post fwiw, I took out the front end and replaced it with 6SN7 SRPP which I thought sounded much better at the time....this led me on to investigating a proper load for the SRPP which I used in the 2A3 that I still use....

From an academic experts standpoint I'm not sure whether the direct coupled 6SN7s are a better bet, but I preferred the SRPP.
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#365 Re: New SE With Triode Mode KT120/150

Post by Paul Barker »

Steve, what about try moving 2k2 resistor upstream one node changing value to 1k2.. Might sound better
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#366 Re: New SE With Triode Mode KT120/150

Post by Cressy Snr »

Paul Barker wrote: Sun Feb 21, 2021 6:38 pm Steve, what about try moving 2k2 resistor upstream one node changing value to 1k2.. Might sound better
I’ll have a look at that tomorrow, see what happens. Cheers Paul
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#367 Re: New SE With Triode Mode KT120/150

Post by Nick »

Pauls post has got me thinking about the 1k on g2. That a low impedance point and current will flow, the g2 resistor is normally there as a current limiter in case of failure. I would have though 100R would have been more appropriate.
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#368 Re: New SE With Triode Mode KT120/150

Post by Cressy Snr »

ed wrote: Sun Feb 21, 2021 6:08 pm I've just had one of those memory spark moments.....remember this little gem from 2008?
I built it for a friend and it started life as a Sun SV2A3 as the doner...had exactly the same front end as yours at the same op point as well...

....From an academic experts standpoint I'm not sure whether the direct coupled 6SN7s are a better bet, but I preferred the SRPP.
There was some opinion way back in 2007 on DIYAudio, that the front end had insufficient HT to provide low distortion drive to the 2A3. THD figures of 5% coming off the driver, were being bandied around. SA may have been after distortion cancellation, but it also might be why you preferred the SRPP in that application.

For my part I thought that as the 807 in UL mode was dead easy to drive in comparison to a 2A3, the Sun Audio front end would work well in my amp, and so it seems to be.
Last edited by Cressy Snr on Sun Feb 21, 2021 7:34 pm, edited 2 times in total.
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#369 Re: New SE With Triode Mode KT120/150

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Nick wrote: Sun Feb 21, 2021 7:10 pm Pauls post has got me thinking about the 1k on g2. That a low impedance point and current will flow, the g2 resistor is normally there as a current limiter in case of failure. I would have though 100R would have been more appropriate.
I'll see if I can find some. I just wanted to equalise the G2 and the anode voltages, hence the 1K resistor in a crude attempt to drop the screen a couple of volts relative to the anode, but if that is undesirable I may have to revise my thinking.
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#370 Re: New SE With Triode Mode KT120/150

Post by Nick »

Remember that G2 looks like more like an anode than a grid and it's driven positive. If it's not driven by a low impedance distortion will be increased.

Also in terms of how easy G1 is to drive. It's not running as a pentode so there will be some miller between G1 and G2.
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#371 Re: New SE With Triode Mode KT120/150

Post by Nick »

If you want to drop the G2 voltage maybe a zener would be lower impedance.
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#372 Re: New SE With Triode Mode KT120/150

Post by Mike H »

pre65 wrote: Sun Feb 21, 2021 11:11 am For me Steve, I'd be happy for you to keep your posting style.

I like the type of threads that go into minute detail of how things are made. :D
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Keep on doing what you do it's OK. :D
 
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#373 Re: New SE With Triode Mode KT120/150

Post by Mike H »

Cressy Snr wrote: Sun Feb 21, 2021 3:02 pm Something that interested me about the input driver stage is that it looks like a voltage amp, direct coupled to a cathodyne phase splitter with only the top output in use.
That occurred to me too.
I say that because the anode and cathode load resistors are the same on the driver. It looks like this front end could just as easily be used in a push-pull amp, if the HT was increased a bit.
Yep - for this application tho, first thing I thought of was maybe bypass its cathode to ground - bit more gain, like.
 
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#374 Re: New SE With Triode Mode KT120/150

Post by Nick »

Or use a current source.
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#375 Re: New SE With Triode Mode KT120/150

Post by Cressy Snr »

Mike H wrote: Sun Feb 21, 2021 8:00 pm Yep - for this application tho, first thing I thought of was maybe bypass its cathode to ground - bit more gain, like.
I took out the bypasses on the driver as I had too much gain. :)
On the Sun SV-2A3 it was bypassed. Ultralinear 807s don’t need it. I found I had about 2 deg of volume control travel before I was blasting the windows out with everything bypassed.
Last edited by Cressy Snr on Sun Feb 21, 2021 9:23 pm, edited 1 time in total.
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