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6N3/6N6 headphone amp using PCB.
6N3/6N6 headphone amp using PCB.
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Old 11th June 2021, 06:13 PM   #231
Ryssen is offline Ryssen  Sweden
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dl3it keep us updated,interessting to se how it goes.
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Old 12th June 2021, 12:41 PM   #232
NickKUK is online now NickKUK  United Kingdom
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Quote:
Originally Posted by Ryssen View Post
It´s working now.no I am under 5W/tube.
But now I am beginning to understand the importance of using matched tubes....
Or complicate the biasing etc for individual tube support (assuming a close curve for like models). Current, balance, etc all end up needing adjusting.
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Old 12th June 2021, 02:09 PM   #233
rongon is offline rongon  United States
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Location: Across the river from Rip's big old tree...
6N3/6N6 headphone amp using PCB.
It depends how critical the application. For an ECC89 or 6N6P running at high heat like this into a heavy load like headphones, yes, you want the WCF to work in push-pull, which means you want to be able to adjust the WCF so that each half is delivering half the signal drive.

I was just playing with Koda's original 6N3P-version PCB circuit, thinking I might make a line stage out of it, to drive 10k ohms impedance loads.

Using a 250VDC B+, with a 6N3P as the totem-pole input tube and a 6922/6DJ8 as the CF-with-active-load output, and using four different models for each of the tubes (to deliberately unbalance them), I'm getting great looking results -- but only if the Rk of the top 6N3P triode (V1) is bypassed (or you use an LED to bias it).

Once this is done, and with 13dB NFB, the model predicts 0.02% THD at 1V rms into 10k ohms (1kHz). If I use identical models for the two each of 6N3P and 6922, I get 0.007% THD, which is too good to be true, for sure.

This totem-pole > CF w/ active load circuit looks noticeably better into 10k ohms than a standard common-cathode DC-coupled to cathode follower with resistor loads, and with similar level of NFB.

The operating points are:

6N3P
Vp = 125V (125.55V with the unbalance)
Vk = 2V
Ip = 4.3mA
Rk = green LED on top triode V1, 470R for bottom triode V2

6922/6DJ8
Vp = 125V
Vk = 3.2V
Ip = 8.25mA
Rk = 390R

The 6N3P is running at about 525mW plate dissipation.
The 6922 is running at about 1W plate dissipation (pretty hot, but not maxxed out).

The max Vp for 6DJ8 is 130V, so I think the above would be OK, as long as you don't mind running 6DJ8 tubes near their maximum ratings. I'd use 6N23P as the active-loaded CF if I needed to buy new tubes.

--

Last edited by rongon; 12th June 2021 at 02:13 PM.
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Old 12th June 2021, 03:52 PM   #234
rongon is offline rongon  United States
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6N3/6N6 headphone amp using PCB.
This is the circuit diagram (attached)

Quote:
The 6N3P is running at about 525mW plate dissipation.
The 6922 is running at about 1W plate dissipation (pretty hot, but not maxxed out).
That's plate dissipation for each triode
--
Attached Images
File Type: png kodabmx pcb 6N3-6922 linestage +250V_00.png (19.1 KB, 136 views)

Last edited by rongon; 12th June 2021 at 03:55 PM.
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Old 13th June 2021, 08:30 AM   #235
dl3it is offline dl3it  Germany
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I finished the layout. Some minor changes were applied to the schematics, mainly for ground/return current control.
Let's see, what the board house will deliver
Attached Images
File Type: jpg theCarefulApproach_3D_comp.jpg (120.7 KB, 120 views)
File Type: jpg theCarefulApproach_3D_top.jpg (122.0 KB, 120 views)
File Type: jpg theCarefulApproach_3D_bottom.jpg (94.2 KB, 116 views)
File Type: jpg theCarefullApproch_layout.jpg (915.4 KB, 111 views)
Attached Files
File Type: pdf theCarefulApproach_final.pdf (89.7 KB, 18 views)
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Old 13th June 2021, 09:39 AM   #236
knauf1919 is offline knauf1919  Europe
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Put more vias.
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Old 23rd June 2021, 06:51 PM   #237
dl3it is offline dl3it  Germany
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to keep you updated...
components soldered, first trying on... everything as expected so far. I did not apply any voltage as I need to build a test fixture first. That's something for the weekend
Attached Images
File Type: jpg tca001.jpg (71.5 KB, 44 views)
File Type: jpg tca002.jpg (62.7 KB, 43 views)
File Type: jpg tca003.jpg (69.3 KB, 31 views)
File Type: jpg tca004.jpg (75.4 KB, 32 views)
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Old 23rd June 2021, 07:17 PM   #238
Ryssen is offline Ryssen  Sweden
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Looking fine..
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Old 24th June 2021, 10:46 AM   #239
NickKUK is online now NickKUK  United Kingdom
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What you could do is make the PCB with the sockets reversed - so the sockets are mounted on the top and the rest of the components are mounted below. That way the tubes don't heat the caps.
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Old 24th June 2021, 12:36 PM   #240
kodabmx is offline kodabmx  Canada
Spreading triode love.
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6N3/6N6 headphone amp using PCB.
Looking good!
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I offer circuit boards, kits, and complete systems for DIY vacuum tube audio.
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