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Mini-amp for Output Tube Distortion
Mini-amp for Output Tube Distortion
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Old 6th December 2018, 07:00 PM   #61
Gnobuddy is offline Gnobuddy  Canada
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Quote:
Originally Posted by Printer2 View Post
...making it a functional music box
<snip>
...Two good university stations...I mainly listen to them digitally.
Why not restore the lovely wooden cabinet, install a Bluetooth receiver, class D power amp, and matching power supply and speaker inside, and remove the original chassis for your guitar-amp projects? You could add a Raspberry Pi 3 and USB sound-card if you also want to listen to digital music / radio streams.

It's the best of both worlds in some ways. You get to enjoy the lovely vintage aesthetics, and at the same time, the thing is actually useful and people will actually listen to it.

I know there is the impulse to preserve it as a museum piece, but it probably won't get much actual use that way.


-Gnobuddy
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Old 7th December 2018, 02:41 AM   #62
Printer2 is offline Printer2  Canada
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I will have it to produce music, in what form I don't know yet.
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Old 7th December 2018, 03:57 PM   #63
Tubelab_com is offline Tubelab_com  United States
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In order to come up with a set of speakers with an acceptable level of WAF, and fit into her decor, I came up with a solution. It was partially her idea when we were wandering through a flea market and she said something like, "all the speakers you make are ugly, why can't you make some that look like that".....as she points to an old console radio. Suddenly the light bulb lit up, and I said OK and bought said old radio.

Upon dragging it back home I set out to find a matching radio. Having one 1941 vintage Zenith radio was easy, now what are my chances of finding another one that looks similar? The odds were slim, but a quick look at Ebay turned up an IDENTICAL radio in "working condition" a few miles from my house.

I make the arrangements and meet the seller at his house. As I walk in the radio is indeed playing music and has a nice pair of 6V6G's tubes inside. I buy the second radio.

I carefully removed the original field coil speakers, the wavemagnets (rotating antennas) and the front board that the speakers are mounted on, package everything and store it for possible radio reassembly in the future. I cut some new front boards with new grill cloth and mount a 15 inch Hawthorne Silver Iris coaxial driver on each board and install them in the radios. The crossovers are mounted to the back of the radios.

!0 years and two moves totaling 1100 miles later they are still rocking. With 96 dB efficiency, and 150 watts power handling, I mean ROCKING!
Attached Images
File Type: jpg One_radio.jpg (285.0 KB, 72 views)
File Type: jpg Radio_back.jpg (252.1 KB, 72 views)
File Type: jpg Radio_Speakers.jpg (283.3 KB, 67 views)
File Type: jpg Radios_dark.jpg (346.4 KB, 68 views)
File Type: jpg P2330984_x.jpg (563.1 KB, 66 views)
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Old 7th December 2018, 06:35 PM   #64
Printer2 is offline Printer2  Canada
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Those are nice. I would love to find another like I have. I do have another console radio of the same size but it does not quite match the other one in style. Maybe I will have to make my own.
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Old 7th December 2018, 07:22 PM   #65
Gnobuddy is offline Gnobuddy  Canada
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Originally Posted by Printer2 View Post
Those are nice.
I second the motion.

Our TV is flanked by a pair of Alesis studio monitors. They're nowhere near as pretty as 1940's electronics furniture, but my wife puts up with them because she knows the sound quality really matters to me.


-Gnobuddy
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Old 9th December 2018, 06:29 PM   #66
Printer2 is offline Printer2  Canada
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I couldn't help it. Another $20 console radio although this one is a little rough. Do I need another low wattage single ended project? I have enough transformers. The PT seems rather large for the 6AQ5, OT is average. Seen these speakers before, might even have another one somewhere. For a quick project. the speaker had a covering on it and the cone looks like new.


Click the image to open in full size.
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Old 10th December 2018, 12:16 AM   #67
Gnobuddy is offline Gnobuddy  Canada
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Here's an update on my 6JW8 mini-amp schematic. It's beginning to look more like a real amp schematic.

I still have tweaking to do. Bass doesn't overdrive gracefully now, as there is some audible blocking distortion. I don't yet know exactly which part of the circuit it's coming from.


-Gnobuddy
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File Type: png 6JW8_SE_Mini_Amp_schematic_v_005_2018-12-09.png (32.4 KB, 37 views)
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Old 10th December 2018, 03:57 AM   #68
Printer2 is offline Printer2  Canada
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From my untrained eye I would say R? might be the culprit.
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Old 10th December 2018, 05:55 AM   #69
Gnobuddy is offline Gnobuddy  Canada
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Originally Posted by Printer2 View Post
From my untrained eye I would say R? might be the culprit.
Yeah, that must be it.

An annoying thing about Kicad - it doesn't keep track of resistor names you've already used (R1, R2, etc), so you have to do it by hand. Every new resistor you place is named "R?".

-Gnobuddy
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Old 10th December 2018, 02:58 PM   #70
Kay Pirinha is offline Kay Pirinha  Germany
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Grid leak biasing an output valve won't work, I'd say.
Best regards!


Edit: My advice would be: Omit C4, make sure that the voltage rating of C5, C6, C7 is sufficient, get a 22nF cap between the treble pot's wiper and R3/R12, change R3 to 1M, and check R1 for correctly biasing the final valve.
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Last edited by Kay Pirinha; 10th December 2018 at 03:08 PM.
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