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SET w/ Feedback Circuit Question???

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Posted on June 10, 2020 at 10:02:25
Posts: 13
Location: Northern Virginia
Joined: March 6, 2020
Hello... I recently purchased an old Magnavox 6V6 console amp that was said to be re-wired for SET. I wouldn't know if it was or not. It has the open-case 100-15k output transformers, but it still sounds pretty sweet on the metal tweeters in the bedroom with plenty of power. I see it has a feedback circuit recently added with NOS vintage pieces. I'm curious as to why the left-channel feedback goes to the input tube and right-channel feedback goes to the power tubes. Would it help to pull one and match it to the other? Input or output tube? Balance seems pretty close right now. Hard to tell perfection cause speakers are placed irregularly. Thanks for any insight... Roger

 

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RE: SET w/ Feedback Circuit Question???, posted on June 10, 2020 at 13:33:45
Ralph
Manufacturer

Posts: 3892
Location: Minnesota
Joined: April 24, 2002
It sounds like the two channels are not the same- so you might want to play them in mono and see which you like better. Then make the other channel work the same way.

 

RE: SET w/ Feedback Circuit Question???, posted on June 11, 2020 at 16:17:58
6bq5
Audiophile

Posts: 3234
Location: SF Bay
Joined: August 16, 2001
+1
Happy Listening

 

RE: SET w/ Feedback Circuit Question???, posted on June 21, 2020 at 08:45:05
Posts: 13
Location: Northern Virginia
Joined: March 6, 2020
Okay figured it out. After doing some mono listening it still seemed like the R channel was different or lacking. It had more detail but less fullness. Wasn't sure which way to go. So I dug a little deeper and found the feedback circuit I thought was going to the power tube, a 6V6, is just using pin6 for a solder point, which is actually absent or not used at the tube. They did it on some of the other tube sockets also. The feedback circuit does in fact go to both L&R input tubes, just the L channel went via a solder point on that power tube socket. There was also remnants of an old tube phone stage with a balance or gain pot and resistors to ground that was still wired to the input tubes and ground. However the input tube for phono was not present and it turns out this socket is also being used as a solder point. So I pulled that whole mess out of there and eliminated a bunch other wiring and solder points that seemed to be doing nothing but sucking photons and also rewired the inputs and feedback circuit with "decent" 18 solid replacing the old junk braid that was used..... and it sounds pretty damn good! Everything now seems balanced properly with "full" audio, excellent separation and detail, even with the 15k top on it. My Sunday morning FM jazz show couldn't sound better. The old classics sound better on this than they do on the big stereo, and all that new copper only has an hour on it. So thanks for mono tip, and all the non-tips that might have had me doing things I shouldn't have been doing. Happy listening!

 

Are you listening to the Christian McBride show?, posted on June 21, 2020 at 09:57:24
Lew
Audiophile

Posts: 10316
Location: Bethesda, Maryland
Joined: December 11, 2000
I get it on Real Jazz via SiriusXM. Was listening to a CD last night, Chick Corea with Christian McBride and a drummer. Some of the greatest jazz musicians alive.

 

RE: Are you listening to the Christian McBride show?, posted on June 21, 2020 at 12:17:14
Posts: 13
Location: Northern Virginia
Joined: March 6, 2020
Nope. Local analog FM WPFW Sunday morning show called G-Strings. Mostly acoustic jazz theme. Which leads into classic jazz vocal stuff like Nat and Jack and Frank and Nelson Riddle and the likes. Perfect production for this rig. I'm loving this old thing. Putting some volume on it now

 

G-strings..., posted on July 17, 2020 at 11:43:00
Lew
Audiophile

Posts: 10316
Location: Bethesda, Maryland
Joined: December 11, 2000
I'm in DC area too. Paul Bollenbach, is he still running that show? Great show.

 

RE: G-strings..., posted on July 21, 2020 at 02:50:52
Posts: 13
Location: Northern Virginia
Joined: March 6, 2020
Nope it's Tom Cole at the helm now. His young son does the weather forecast every hour. Almost too much love between them to bear. Very sweet and laid-back show.

 

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