Vintage HiFi Audio Forum
Audio Discussion => TUBES TUBES TUBES => Topic started by: Sir Thrift-a-Lot on March 08, 2014, 06:20:08 PM
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I found this at a local thrift for $35. The guy told me it had been there for about two months and was soon headed for the dumpster. I'm very glad to have rescued it.
All tubes are original S-Cs except the pre tubes which are RCAs. The previous owner changed them both at once and even bought a spare, which he was nice enough to leave in the cabinet. A NOS RCA tube is probably worth half of what I paid all by itself.
This will be my next project after I finish the RCA console pull. That one is a good learning experience, this one will hopefully be much easier. The layout is almost as clean as my Leak. I also have a Maggotbox SET waiting to be refurbed, but everything is packed so tight in there that I don't know if I will ever develop the soldering skills to work in such tight spaces.
The tuner is another stupid multiplex unit (which dates the console to early 60s IIRC). It will end up in the trash unless anyone here wants it. The cabinet is already at the curb, with the tweeters still in it because I drove a screw through one of them and wasn't sure they would be used anyway. The ALNICO woofer and full ranges will get used for sure. Maybe I'll do my first experiment with open baffle.
(http://i32.photobucket.com/albums/d11/markshan/GEDC0621_zpsd5c0c71c.jpg) (http://s32.photobucket.com/user/markshan/media/GEDC0621_zpsd5c0c71c.jpg.html)
(http://i32.photobucket.com/albums/d11/markshan/GEDC0624_zps451f203b.jpg) (http://s32.photobucket.com/user/markshan/media/GEDC0624_zps451f203b.jpg.html)
(http://i32.photobucket.com/albums/d11/markshan/GEDC0625_zpse00d3b66.jpg) (http://s32.photobucket.com/user/markshan/media/GEDC0625_zpse00d3b66.jpg.html)
(http://i32.photobucket.com/albums/d11/markshan/GEDC0626_zps5e9a489d.jpg) (http://s32.photobucket.com/user/markshan/media/GEDC0626_zps5e9a489d.jpg.html)
(http://i32.photobucket.com/albums/d11/markshan/GEDC0627_zps386a3ef9.jpg) (http://s32.photobucket.com/user/markshan/media/GEDC0627_zps386a3ef9.jpg.html)
(http://i32.photobucket.com/albums/d11/markshan/GEDC0628_zpsa61a6cbc.jpg) (http://s32.photobucket.com/user/markshan/media/GEDC0628_zpsa61a6cbc.jpg.html)
(http://i32.photobucket.com/albums/d11/markshan/GEDC0629_zps3a94da48.jpg) (http://s32.photobucket.com/user/markshan/media/GEDC0629_zps3a94da48.jpg.html)
(http://i32.photobucket.com/albums/d11/markshan/GEDC0630_zps83e43693.jpg) (http://s32.photobucket.com/user/markshan/media/GEDC0630_zps83e43693.jpg.html)
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Sweet, Mark. It looks like just a bit of dust to clean and it will sparkle.
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1960 vintage? Looks great Mark! Good score...
Pepe
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Congrats on the score!!
Hope your refurb goes better than my Pilot mono refurb. Blew up a brand new polar electrolytic today.
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Should be an easy recap. Cosmetically, I have much bigger plans than just making it sparkle. I want to get most of it covered and the front tubes caged so that I can keep it in the living area as a daily driver.
Does anyone know a good sheet metal guy?
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Congrats! Very nice looking amp! I can't see the number on the power tubes? They look like RCA black bases that have been rebranded.
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The output tubes are Stromberg-Carlson 7408 (same as 6V6). I figure this amp for about 15 clean watts per channel.
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Am I correct that the only cap I need to replace is the can cap? Everything else looks like either ceramic or mica. I have read that those don't need replaced unless there is a specific failure.
Could it be this easy?
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I'd replace the coupling caps too, same value, just, with films.
Great find! Sounds like you and I both have more tube projects in the works than we have time for! I'm sure you'll do it justice! Please keep us all posted!
You'd probably have to bias them a little hot to get 15W out of PP 6V6's. 10-12 is more realistic, depending on what Stromburg has them set to run and how far certain resistors have drifted. :)
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As far as sheet metal, what are you looking to have done? I know folks who do that sort of thing. That's the hold up on my SE Maggotbox amp. I'm waiting on the powder coat guy to do the chassis.
I'm also trying to get a cage / cover type thing built for the OT's on that amp. There's not enough room for proper bell ends or transformer covers. I have some DIY ideas I'd love to discuss with you, but, I'm far from a metal wiz.
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I'd replace the coupling caps too, same value, just, with films.
You'd probably have to bias them a little hot to get 15W out of PP 6V6's.
Which ones are the coupling caps?
I don't know how to bias something. I'm just replacing parts. If it needs any fine tuning when I'm done, I'll have to have one of the experts here (such as yourself) help me or send it to Anders.
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I'm also trying to get a cage / cover type thing built for the OT's on that amp. There's not enough room for proper bell ends or transformer covers. I have some DIY ideas I'd love to discuss with you, but, I'm far from a metal wiz.
When I was Googling for info on the amp, I saw one treatment that I liked but felt could be improved upon.
(http://i32.photobucket.com/albums/d11/markshan/PICT1559_zpsc77d1d60.jpg) (http://s32.photobucket.com/user/markshan/media/PICT1559_zpsc77d1d60.jpg.html)
(http://i32.photobucket.com/albums/d11/markshan/PICT1560_zpsdb16e5ef.jpg) (http://s32.photobucket.com/user/markshan/media/PICT1560_zpsdb16e5ef.jpg.html)
(http://i32.photobucket.com/albums/d11/markshan/PICT1561_zpsc7adb2a9.jpg) (http://s32.photobucket.com/user/markshan/media/PICT1561_zpsc7adb2a9.jpg.html)
I like the way this covers up the entire back end in one swoop. The wooden side caps would be easy enough to make. I would make mine out of a nicer wood and coat with polyurethane rather than painting. What I don't like is the gaps between the metal plates. My idea is rather than making two separate metal plates then a black wooden back, I would round the angles at the top and use one piece of metal which would be heavy enough to mount jacks onto but thin and flexible enough to bend at at couple soft 90 degree elbows. I think this would look amazing and make final assembly fairly easy.
So I would need someone who could cut me a sheet to my measurements, drill vent holes at the top and cutouts for the jacks on the back. Plus the holes for the mounting screws. I would also want a sheet for the bottom cover.
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I am far from an expert on this crap.
Let me talk to a friend from the automotive fabrication world. Those guys love building stuff out of sheet metal. Sorry for the short reply but I'm pressed for time this morning.
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Nice find man. I just scored a Magnavox myself, but it looks too nice to dissect. I hate that I like these things.
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Well, the turntable was already gone before I got to it. Plus, presumably someone at the thrift put a huge gouge on the top. So even if I liked the furniture (which I didn't), it would have been a lot of effort to get it back up to speed.
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Yes Sir that would make it easier for me. I'll get some pictures up when I get out to the garage.
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Cool. Start your own thread so people can give you advice on how to proceed.
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Looks like a fun project, congrats on your pickup!
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Thanks Rev! Wish me luck.
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Well, as you can tell by the dates on these posts, I tend to let projects sit around for a while. I finally got around to recapping this amp. I played it for about 15 minutes and it sounded good. It was actually bass heavy, which I didn't expect. On my phone EQ I lowered 120Hz and boosted 4k to make it sound good.
I was cruising along, listening and taking pictures when suddenly, like someone flipped a switch, the music was replaced by a loud buzzing sound. I took a quick glance at the tubes to make sure none of them looked like they were stressed (and they didn't) then I quickly shut it down.
You guys have a lot of knowledge, what should I look for as a culprit?
BTW, don't be too hard on me for how I ciphered those caps in there. Remember I am remedial and this is the farthest I've gotten with a console pull. Thanks.
(http://i32.photobucket.com/albums/d11/markshan/GEDC1587_zps7snktug9.jpg) (http://s32.photobucket.com/user/markshan/media/GEDC1587_zps7snktug9.jpg.html)
(http://i32.photobucket.com/albums/d11/markshan/GEDC1591_zpstwv1ilos.jpg) (http://s32.photobucket.com/user/markshan/media/GEDC1591_zpstwv1ilos.jpg.html)
(http://i32.photobucket.com/albums/d11/markshan/GEDC1593_zpsknvqsf5y.jpg) (http://s32.photobucket.com/user/markshan/media/GEDC1593_zpsknvqsf5y.jpg.html)
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How is the input from your phone grounded?? A bad input ground will cause a hell of a buzz. I don't see any wire going into the input ground lug hole, just your left/right channel wires.
Did you replace the coupling caps (small orange looking ones on the bread board that also has all the small resistors)?
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I did not replace the coupling caps. I thought they were Micas and didn't need to be replaced. If it will bring significant improvement I can.
There are wires to the ground, but they may be somewhat precarious. I'm going to wire up another adapter and see if that helps.
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BTW, what is the function of a coupling cap? I'm weak on basic theory but should probably know this stuff.
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I replace coupling caps just for good measure in all tube amp restorations. My guess is many times they are still good, but do it just as an insurance policy.
Check out this AudioKarma link: http://www.audiokarma.org/forums/showthread.php?t=443915 (http://www.audiokarma.org/forums/showthread.php?t=443915)
What do coupling capacitors do in an a tube receiver or tube integrated amp?
Coupling caps are wired in series between the signal tube anode (plate) and power tube grids and are some of the most important capacitors in an amp because they can affect the sound quality the most of any small value capacitors in a tube amp. Typically, coupling caps are non-polar (doesn't matter which lead is soldered where) and are replaced with high quality paper in oil (PIO) or metalized polypropylene capacitors. Capacitors are widely used in electronic circuits for blocking direct current while allowing alternating current to pass. Coupling caps wired in series block DC voltage and allow AC voltage to pass through to the power tube control grid.
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So, if I'm gathering correctly, you MUST replace power supply caps or risk catastrophic failure. Coupling caps can have a drastic effect on the sound but aren't likely to take out anything with them in they bite the bullet. So, the PS caps should be done before powering the amp, but the coupling caps can be done at your convenience. Would this be a correct statement? Thanks again for sharing all of your knowledge.
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Congrats Stal thats some clean good looking tubage you have there.
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Hey Mark,
I think both power supply and coupling caps are important. Which is more important?..........don't get me started lying. I do both on all original tube amps from the 1960s and earlier.
Regards,
Scott
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....don't get me started lying.
I don't get it. All I was asking is if a coupling cap failure will damage associated components. I understand about sound quality and know that can be controversial, but that isn't the question I was asking.
You know so very much more than me and have been exceedingly generous. I wouldn't deliberately put you in a bad spot.
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Okay, I resoldered the inputs and had two sessions each over an hour tonight with no issues. Seems it was as simple as dropping a ground at the input. The first session I had with my phone, then later I put in my Pas3 pre. It turns out that the bass heavy voicing is my stupid phone, not the amp. They must do it that way for the earbud crowd. It also turns out that 80s Sony CD player into Pas3 into SC 6V6 into B&Ws is a very pleasant combination.
I do, however, need some engineering help with one issue. The SC console was an entirely passive pre, so the inputs are quite hot. It was literally a 1/4" turn of the volume control to get from silent to a comfortable listening level, then another 1/4" to get to "blow your face off".
What, if anything, should I do to get this amp to a more standard input level? TIA.
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The simplest fix is to use some RCA line level attenuators like these:
http://www.amazon.com/gp/product/B0006N41B0?psc=1&redirect=true&ref_=oh_aui_search_detailpage (http://www.amazon.com/gp/product/B0006N41B0?psc=1&redirect=true&ref_=oh_aui_search_detailpage)
If that link doesn't work, Google "Harrison Labs 12 dB RCA Line Level Attenuator Pair".
What are the driver tubes in the amp (e.g. the small signal tubes)? If they are a 12AX7, trying a lower gain substitute might do the trick. You can read about that here: http://www.thetubestore.com/Gain-Factor (http://www.thetubestore.com/Gain-Factor)
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....don't get me started lying.
I don't get it. All I was asking is if a coupling cap failure will damage associated components. I understand about sound quality and know that can be controversial, but that isn't the question I was asking.
You know so very much more than me and have been exceedingly generous. I wouldn't deliberately put you in a bad spot.
No ill intent assumed on my part. Just didn't want to act like I knew the correct answer to your question. Do know an amp will a bad coupling cap can cause the power tube downstream of the coupling cap to red plate. That can cause the power tube to fail, which might also take out the output transformer it is connected to.
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Thanks for all of your help, Scott.
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So, today I broke out my Leak Stereo 20 to try with the PAS 3. Turns out it's not the input of the SC that is hot, but the output on the Dynaco. It was just as hot into the Leak as into the SC. It also turns out that after changing four caps, I think I actually like the sound of this console pull better than the Leak. I might be crazy, but in this setting it sounded better to me. Much more experimenting to be done.
Oh, and the in line attenuators did bring the gain to a more reasonable level, but they also gave an unacceptable coloration to the tone. Maybe these ones are just junk (I don't remember where I got them) or maybe they alter something besides just the level.