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Old 14th January 2017, 12:43 PM   #1
Gluca is offline Gluca  Italy
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Default Ask the dust ... an amp with the mighty 801A

Just finished a few days ago. Schematics is not 100% accurate as I am driving the 801A from the lower anode and I have a 12V zener at the 801A virtual cathode and the voltage divider at the power supplies may be a bit different. But you got the idea. The good thing here is that I can swap in different noval drivers as I can switch from 6.3V to 12.6 filament voltage making the amp pretty flexible.

Super happy with the sound and measurements look great too. Well, but I love the 801A ... my favorite tube.
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File Type: jpg ASK_THE_DUST_801.jpg (388.0 KB, 248 views)
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File Type: jpg IMG_0685.jpg (959.3 KB, 233 views)
File Type: jpg bandwidth.jpg (462.1 KB, 226 views)
File Type: jpg sq_1khz.jpg (401.1 KB, 206 views)
File Type: jpg noise_db.jpg (623.2 KB, 83 views)
File Type: jpg 2KHZ_THD.jpg (506.7 KB, 60 views)
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Old 14th January 2017, 01:53 PM   #2
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hi, very very nice amp! ( Also very nice tube)

My 801SE ( white ceramic base, gaphite plate)has 2c22 choke loaded as drivers.
My OPT are the same, they are much better than Tango 14K.

BR
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Old 14th January 2017, 01:58 PM   #3
Gluca is offline Gluca  Italy
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Quote:
Originally Posted by Triodenklaus View Post
hi, very very nice amp! ( Also very nice tube)

My 801SE ( white ceramic base, gaphite plate)has 2c22 choke loaded as drivers.
My OPT are the same, they are much better than Tango 14K.

BR
Yup, LL2735B has a flat bandwidth and it really sounds good. Great job Lundahl. I would have preferred a 45mA gap to drive the 801A deep into A2 biasing at lower voltage and higher anode current
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Old 15th January 2017, 11:59 AM   #4
45 is offline 45  Italy
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Try 6E5P (triode wired).
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Old 15th January 2017, 01:42 PM   #5
45 is offline 45  Italy
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Quote:
Originally Posted by Gluca View Post
Yup, LL2735B has a flat bandwidth and it really sounds good. Great job Lundahl. I would have preferred a 45mA gap to drive the 801A deep into A2 biasing at lower voltage and higher anode current
If you can accept approx. 3.7W @30Hz and the full 5W "only" down to 35Hz instead of 5W @30Hz then you can use 35 mA anode current. At frequency higher than 35Hz is not going to change anything.
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Old 15th January 2017, 02:01 PM   #6
Gluca is offline Gluca  Italy
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To be honest I am not worried about the 801A life and output transformer saturation and max power is really not a limit (as I have very high efficiency speakers) but a transformed sized to swallow 45mA DC would open a different opportunity. I am really curious to try the 801A well into A2 as I never did in all these years.
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Old 15th January 2017, 09:30 PM   #7
45 is offline 45  Italy
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Quote:
Originally Posted by Gluca View Post
To be honest I am not worried about the 801A life and output transformer saturation and max power is really not a limit (as I have very high efficiency speakers) but a transformed sized to swallow 45mA DC would open a different opportunity. I am really curious to try the 801A well into A2 as I never did in all these years.
Buying the same OT gapped for 45 mA (which is possible if you order it) might be a good idea only if the actual speaker load is some 5-6 ohm max because inductance would go down to 60H and to use efficiently A2 as high as possible plate load is not a good rule of thumb. I think 10-12K max is a better option with 45 mA anode current. The A2 region is more linear where anode current is high and lower load impedance brings you there but of course there has to be a balance with what happens to the other end. Otherwise something like 600V/30-35 mA with effective 17K would get the same or even better plate efficiency. The latter set-up in fact can generate up to about 6-7W (and even up to 8W at the on-set of clipping at around 5% THD).
Anyway high impedance OT's are always a bit compromised and limited respect to lower impendance equivalents regardless of the effort, design and budget. With these tubes a PSE is very likely to bring better results in practice.

Last edited by 45; 15th January 2017 at 09:40 PM.
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