Marantz 10b advise needed...please

JBryan

New Member
Hello,

Long-time lurker here... I recently picked up a Marantz 10b locally and have a question for the experts. First, when I spoke with the gentleman who was selling the tuner, he said that it hadn't been powered up in 20 years so I asked that he not switch it on. Unfortunately, another interested party insisted that I was working an angle and plugged it in just to see if the tubes lit up.

The good news is that I was able to get the tuner for a very reasonable price. The bad news is that although the tuner works, one channel's gain is much lower than the other. The left channel occasionally "crackles" and seems to come and go between frequencies. It also seems to come back to full gain just as I turn the unit off and fades away (with a crackle or two). I did check the gain pots and switched the tubes and interconnects - to no avail.

Although the worst was already done, I did bring up the 10b with a variac using the 'Soft-Start' method to avoid any additional damage. Aside from the low-gain in the left channel and the dial bulb being out, the tuner seems to function well.

Could the problem be limited to a bad cap or is this a symptom of something deeper? If it is the cap, is replacement the only option? Do you have any other suggestions and advise in regard to maintenance - all tips and tricks will be appreciated. Also, I am not going to attempt any repairs and would prefer to have this serviced by an experienced tech in the Baltimore/DC area - any suggestions?

Thank you in advance for your help, Bryan
 
Welcome Bryan!

The 10b is an excellent tuner, and the scope is cool as well (if its still working). The first thing I would do to this tuner is grab some de-oxit and clean all the controls and switches, and then pull each tube individially and clean the tube sockets. I had a problem with my scott that had a distorted quiet channel that turned out to be a dirty tube socket. Simply spray a little de-oxit in the socket, insert the tube, and work the tube around in its socket. I have also used small pipe cleaners, but they don't quite work as well. Do not work on a circular motion, mostly up and down.

If the cleaning does not yield any better results, I would find a tube tester and test all the vaccum tubes. These can usually be found on ebay or at electronic surplus places. THere is probably a bad tube in the MPX section or sound output.

If the tubes are all good, there is most likely a bad cap or two in the signal path that are in need of replacement. Since this is a 40+ year old unit, it would be better to replace all of them while the unit is apart. Afterwards you'll need to have the tuner aligned, but the results will be amazing...

As for tuner service, I would check out Radio-X. THey have a link here at the bottom of the page. From what I understand he does excellent work and has very reasonable rates. Good luck with your marantz. I love the look of the older gear.
 
I'd bet money that the problem is indeed the contact of tubes in their sockets. I've rescued three old tuners lately (Sherwood, Radio Craftsmen, and h/k) fundamentally by resocketing the tubes.
 
Well, I spent last night cleaning and Deoxit'ing all the tube pins and sockets and took the opportunity to give the rest of the chassis a good cleaning. It looks good - but the problem is still there. I know very little about these things but I played with the tuner a bit more and discovered that when I move the tuning wheel the volume increases on the left channel an then fades back to @20 dB below the right channel. I then flipped the tuner to mono and the channel came back - maybe even exceeding the other channel's volume (!?). When I listen to the left channel only it seems lean - more so than just low volume. And occasionally, the channel cracks and the volume increases dramatically (maybe not to the same level as the right channel though).

Another symptom I noticed was that on the 'OUTPUT' display, the trace indicates almost all output was coming from the right channel (near horizontal) but when I move the tuning wheel, the trace moves midway between vertical and horizontal but moves back to horizontal within a few seconds.

Does anyone have any ideas of what the problem is and what I can do about it? Also, does the 10b have a lighted face panel and if so, I how do I get behind the faceplate to change the bulb?

Thanks again for all your help! Bryan
 
sounds as though an AF amp tube is going bad, or perhaps a capacitor in the signal path. Either case is going to requie that you disassemble the tuner, test all the tubes and start tracing the audio signal back to where it originates.

Tuners are really not something you want to mess with if your a beginner. This is best left to someone with some knoledge on tuner repair
 
Where are you located? The 10B does not need alignment and in fact will be damaged if someone tries. On the other hand it does go trough tubes. You could have many things wrong with it but this is not a unit that should have the caps all changed out. It needs to go to one of the few 10B experts who have familiarity with the 10B.

thanks,
Ron-c
 
One item not mentioned so far is that the 10B utilizes three "optocouplers" to implement muting and stereo/mono switching. These things are notorious for going intermittent or outright bad. They use an NE2 neon lamp optically coupled to CdS photocells. Both the NE2s and photo cells can be the culprit. I have a 10B where all three were intermittent. The symptoms were similar to yours. The proper solution is to replace them with new mfg. These show up on epay and other places frequently. It's also possible to rebuild them but since they're potted assemblies you'll have some work ahead of you if you choose this route. Generally 10Bs aren't much fun to work on due to crowding and complexity.
 
So, you thought you were going to clean it, and off you go, right?

Nope, you now have an Icon of audio history, which, along with the Fisher FM-1000 vies for Best Tuner of All Time, Tube Category.

You have a responsibility to our hobby to take care of one of these historically important "Holy Grail" pieces.

Or, you could just let it run for a while. Old tube stuff sometimes takes some burnin' to come back to snuff after it's sat around...

ps: and Raccoon dem Woogers!
 
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