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Wright Mono 8 Schematic & Operating Points
Wright Mono 8 Schematic & Operating Points
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Old 15th October 2017, 04:16 AM   #51
audiowize is offline audiowize  United States
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By not drawing that connection, R13 and C6 appear to have no use. (Not that there's a ton of purpose to it anyway)
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Old 15th October 2017, 05:08 AM   #52
jdrouin is offline jdrouin  United States
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OK, thanks. And I should really be writing "Draft" at the top of these until all the errors are worked out, lest someone think the schemo posted above is final.
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Old 15th October 2017, 06:36 AM   #53
jazbo8 is offline jazbo8
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Wright Mono 8 Schematic & Operating Points
You can use the call-outs or you can show the actual connection on the schematic as Ketje did in his drawing, either way, you make it clear that back-bias is used.
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Old 7th November 2017, 04:33 PM   #54
jdrouin is offline jdrouin  United States
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Had a chance to get back to this. Here is the revised (beta 02) 6EM7-300B schematic with call-outs.
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File Type: jpg mono-8-6EM7-schematic-beta-02.jpg (689.7 KB, 85 views)
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Old 21st May 2018, 08:07 PM   #55
jdrouin is offline jdrouin  United States
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Looking over all of the images I have, the Mono 8's use two-prong power chords, like in vintage equipment, and do not seem to have a ground point per se. I've not even been able to locate a chassis ground point, though it might be there but not visible in the images I have. The HV center tap is connected to the power supply negative rail, which is also connected to the ground tab on the RCA signal input socket.

Do you think it's OK to run it this way, or should I add a chassis ground point for safety? Not sure if it would induce a ground loop buzz or change the operating perameters of the circuit.

Would the neutral connection act as power ground?

Signal ground would exit through the interconnect shield and go to ground via my line preamp, which is properly grounded with a three-conductor power cord and star point.

Last edited by jdrouin; 21st May 2018 at 08:12 PM.
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Old 21st May 2018, 08:14 PM   #56
rayma is offline rayma  United States
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Quote:
Originally Posted by jdrouin View Post
Would the neutral connection act as power ground?
No, that's very dangerous.
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Old 22nd May 2018, 08:58 PM   #57
jdrouin is offline jdrouin  United States
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Thanks. I ended up adding a ground point near the third conductor lug, so it's a ground bus configuration. If the ground channel down the power cord creates a ground loop hum, I can just put a two-prong adapter on the end. That way it would still have chassis grounding, and it would all go out the interconnect to the linestage, and to the wall from there.

I had breadboarded this amp in a stereo build, using a 5U4GB rectifier and 6SN7 input tubes, but with the resistor values for the 6EM7 build I had pictures from.

Now I've assembled one of two mono blocks for a final build with all the proper tubes (5Y3GT, 6SN7, 300B), with changes in those resistors to reflect what's in the 6SN7 version that I have pictures for (basically Rk1 goes from 3.1K to 3.9K and R15 from 27K to 75K). I am also using the Magnequest TFA-204 output transformer, which has a max DC current of 60mA.

Initially the voltages were a little north of where they needed to be to keep the 300B Rk below 45V/60mA. Eventually I added a 390 ohm resistor after the 5Y3 to bring everything down. 300B Vk is now at 42.2V and about 56mA.

I will try to get the other one built by tomorrow so I can conduct a listening test. This is basically a 2A3 amp with a 300B stuck in it.
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Old 25th May 2018, 05:42 PM   #58
jdrouin is offline jdrouin  United States
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Here are some pics of the build. It sounds really lovely. Much better than I thought it would at such low voltages.


This has been a labor of love for the past couple years. The first tube amps I ever heard, in 2001, were a pair of Wright Mono 8's, customized by George for my friend, using the Magnequest/Peerless TFA-204 output transformers (instead of the stock FS-030). Those amps changed my life, so I've been on a search for lost time to regain that sound. I've breadboarded a number of circuits along the way, and am *very* please with this one.



I'll keep fiddling with the operating points to try and voice it with a higher 2nd order harmonics profile for that "euphonic" sound. I'd appreciate any tips on how to do that.


Thanks for looking/participating.
Attached Images
File Type: jpg IMG_1049.jpg (714.0 KB, 30 views)
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File Type: jpg IMG_1063.jpg (743.8 KB, 11 views)
File Type: jpg IMG_1005.jpg (922.2 KB, 15 views)
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Old 25th May 2018, 08:55 PM   #59
jdrouin is offline jdrouin  United States
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Not sure how well a phone video will sound, mais voilą:





This one was taken from down in the image:


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