SkyFi Audio's Preservative Restorations of the Marantz 7 Tube Preamp and 8B Tube Amp

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SkyFi Audio is a small startup business specializing in the purchase, reconditioning, and reselling of select high end audio equipment. We only buy equipment that we admire and are passionate about. No mid-fi, no gimmicks, and no junk.
Each piece of equipment is cosmetically restored and fully tested in our well-equipped lab by an engineer with 30+ years of experience in the HiFi world. If it does not meet or exceed the original manufactures specifications, it will not be sold. We are very selective about the equipment we purchase, focusing on mostly analog, high-build quality, American, and European built units.
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[@crooner2007]

Looks like you adopted the Hayseed Hamfest filter capacitor approach from my ultimate Marantz 7 restoration on Audiokarma. Good choice!

[@NickP333]

crooner2007 I saw that thread. Phenomenal job! The Khozmo attenuator with the remote was a great idea to add. 🎶🔊😁

[@SkyFiAudio]

Hi there - yes we DID! Thank you very much for that. SkyFi Audio's Lead In House Technician, Ben Hase, performed all the work seen in this informative video.

[@kstlfido]

Nice video and glad you did a conservative restoration. I gather your tech checked the .01uf 400V caps right at the tube sockets on the 7. Of all the 7's I've worked on, those are PIO and are always bad. Also Marantz used Allen Bradley for the carbon composition resistors, the best CC resistors at that time. They can be identified by their shiny surface.

[@SkyFiAudio]

Thank you Kent!

[@dilbyjones]

One day I'll visit this amazing place! 🍋

[@phillipchance6992]

Cool video. There may be additional reasons for retaining the carbon resistors on the output tubes. It is my understanding that with a tube short, they heat up and pop apart, acting like a surrogate fuse, thereby blocking the passage of abherrant current elsewere that might damage other components (e.g. the output transformer). I had this to happen on several occasions with Model 9s, and had replaced them with wire wound resistors (thinking this was a good thing to do). I did see the light, and later had a technician in Portland, replace them with new carbon resistors.

[@thevintageaudiolife]

Thank you for sharing this video. For the last past few years i've been working on my clone Marantz 7c. I'm utilizing the same circuit, with the exception of the RIAA circuit, i used components to match closer to the RIAA curves. I used DC for all the heater tubes, polyprop caps, separate power supply and military super low noise (film) resistors. I also etched my own circuit board. Anyways, i've been using this preamp now for 3 years and im telling you, amazing sound, i know there are other better phono pre-amps out there, but Marantz sounds truly amazing with my turntables. I can only imagine what the sound of the Marantz you have at your shop. I'll post a video sometime and talk about it. Thanks for your information!!

[@carlfuggiasco7495]

That was Fantastic!!!!!

[@fabieneldridge3414]

Looks like new ! Beautiful and bet sounds even better !

[@SkyFiAudio]

It does!

[@user-go9yz1gk7k]

Gigantic resistors!!!

[@danknox9986]

Well done.

[@RealHIFIHelp]

Very interesting design.

[@toneyisaiah3556]

Now that's something you can learn.

[@seraphin_creates]

Nice amps! But even nicer explanation of some of the considerations for originality that went into the restoration. The term sometimes being misused for heavy modifications to some modern idea of aesthetics.

[@melockavich9596]

The old caps have a good sound to them do not change

[@SkyFiAudio]

Totally agreed. We do *not* go through and replace everything as part of our process. We only replace what truly needs to be replaced to preserve the original intended sound.

[@mangist]

Sure, if they're still in spec, which they often are not. Can result in muddy sound or even risk damaging the tubes.

[@70smarantz61]

Very informative video. Nice pieces. I bet these are in marvelous condition technically now these are restore. Who is the guy that restored them? He did a great job!

[@SkyFiAudio]

Thank you very much! You can tell from Ben's video that this was truly a labor of love. Ben is our in-house lead technician and led the restoration from start to finish. We are very luck to have him!

[@danielkrug2575]

Would you please share the part number to the NTC thermistor used?

[@MikeFreda]

Can I get some information on that inrush current Thermistor you installed? Thank you

[@vinylclassicalfans1739]

Hi.Do you have the selenium rectifier for Marantz 7 preamp?

[@jpensado1]

❤

[@vivianvaldi7871]

Oxydation of exposed metallic parts (whether on engineering side or 50 years later on the restoration side) is not accounted in sonic results. I don't know if there is any study on this, but the general knowledge tells us it will mostly affect the restitution of highs. That is given we know higher frequencies current will run on the outside of any usual round wire. Gold plated component for the all circuitry would be a solution : so yet, one can imagine why no manufacturer has gone into this.

[@kstlfido]

For microwave frequencies, sure.

[@jimcatanzaro7808]

Hard up for work ?

[@toneyisaiah3556]

What to do and not to do when it comes to restoration.

[@moodyga40]

all the bumblebee caps black beauties will cause problems in theses amps any 40 year old 50 year old caps should go

[@stephengreene9380]

The bumblebees are notorious for going bad (electrically and physically). When I refurbed my own Marantz 7, I found one bumblebee cap with a crack in its body running its entire length. Needless to say I replaced all the caps on the top phenolic board. The tone controls also have a bunch of bumblebees but they would be an absolute nightmare to replace. You'd have to remove the controls from the chassis to get to all of them. I, too, left those alone and simply run the tone controls flat.

[@kstlfido]

Some late 'bumblebee' caps are indeed early 160P Di-film and will likely be as good as new. You can't tell by appearance. You NEED TO CHECK FOR INSULATION RESISTANCE before shotgunning all the components! I'm finishing up on a 7 restoration and all the large signal caps checked out fine (Di-Film). No need to replace. The small .01/400V had cracked and had failed (PIO).

[@jimcatanzaro7808]

Russian tubes are junk