61 01 21 CG preamp repair

[Hydrolastic]

Hello Guys, The 60 CG sounds great it has range, a lot of bass. Is nearly silent on startup. No hum. If you turn the volume up hallway and put your ear to the speaker you can hear a very faint static like sound.(On tape position with Bluetooth adapter) get a foot away you can't hear it. So its an excellent performer. The pre amp has issues. Intermittent magic eye. No FM on FM only or MPX AM is silent also, Silent like no static or any sound. When I wanted to take the mpx out of line there are similar but not matching plugs on the MPX i would like to fix. I have a spare mpx that has the male and female plugs needed. Record player needs work also so I can't test that part I reported last Christmas that my repair guy his shop burned down! So I resorted to one of the guys listed in the antique radio site. Picked one of the advertisements to send my continental to him its been two months now he has not even looked at it to give an estimate on it. The Continental is in restoration mode but the CG I dont want it out of commission that long. So I just want to ask you guys if there is a "go to" guy out there to have this preamp repaired? I am in Seattle so I can ship it anywhere. Hydro

[TC Chris]

One solution is some DIY sleuthing to figure out why you have no AM or FM. One thing you already know is that it's not the audio amplifying tubes--you have audio. It must be something earlier

I don't have the schematic for your unit but I do have it for my '56mono model and I wonder if the same design philosophy carried through--they often do. In that case, some tubes are shared on AM and FM, like the IF amplifier. Sounds like it may be one of the shared tubes if both AM and FM are silent. Loss of IF would probably explain the loss of eye tube function too.

Testing tubes requires a tube tester. But sometimes it's not the tube, it's the sockets. It's always a good idea to at least wiggle (gently) the tubes in their sockets to make sure the pins are making good contact If you're more ambitious, pull each tube and clean the pins and sockets with DeOxit or a similar contact cleaner.

Or it could be the loss of your B+ high voltage, perhaps by reason of a burned-up resistor feeding the plates of the tubes. On your unit, is the power supply for the preamp/tuner located on that chassis, or on a power amp chassis? Do you have a voltmeter the check voltages on the tube sockets? The schematic will tell you what they should be. When you have no sound, I'd start with the plates. Carefully. This is high voltage!

Chris Campbell

[Hydrolastic]

Thank you Chris, Absolutely I would love to be able to repair it myself I will give your suggestions a go. I have no interest in getting shocked I will take every precaution.

[William]

Hydro, do you have a schematic? What are the chassis numbers on the amps and tuner?

Bill

[Hydrolastic]

Hello William, The tuner/preamp is the 61-01-21 and the amps are AMP 82-01-00. I plan on getting the schematics from Steves in pdf form then have them printed up at fedex. Hydro

[William]

Hydro, please check your email. I sent you something that might help.

Bill

[electra225]

Hydro, there must be two dozen members on this forum who would be imminently qualified to talk you thru the repair on you CG. They are big and overbuilt, but not really all that hard to work on. If you can read a schematic and have basic electronics repair skills, you shouldn't have any problems getting a successful repair with us helping you.

I addition to what Chris mentioned, I would suggest you check the antenna on both AM and FM. They are fairly "breakdownable" and can be easily damaged. When you have the back off, all you have for an FM antenna is the twin lead from the back to the tuner. AM has a loopstick of varying effectiveness. A short piece of hookup wire and a test lead will get you enough antenna to see if the eye tube moves and if the radio talks. Check all the tube elements to make sure you have B+. Does the eye tube light? If the eye tube doen't move and you hear no radio, then you need to trouble shoot and find the culprit. The function switch is always suspect. The speaker switch is spared blame since the audio works. You may have two problems, a dead radio and a dead eye tube. Whatever you do, don't go on AudioKarma and let those guys convince you to throw parts at it. You need to establish directed tests and get to the core of the problem rather than guessing and tossing parts. The 6BA6 IF amps are the most common place AM and FM are connected. I'd swap both 6BA6's just because. After you get the schematic, you can make deeper tests. I have that schematic, both on my hard drive and on a hard copy if worse comes to worse and that would help you. Good luck, Hydro.

[Hi-Fi-Mogul]

Hello William, The tuner/preamp is the 61-01-21 and the amps are AMP 82-01-00. I plan on getting the schematics from Steves in pdf form then have them printed up at fedex. Hydro

Is the Sams's number 510-11 from 1960 ?

I have it in a pdf, if you send me your email address.

[Hydrolastic]

Hello guys thank you, I guess its on and WE are going to fix this CG. I will be asking a lot of questions. I need to get a work area set up. I should set up a new thread probably in the Magnavox section. Also I have a ton of projects going on with the plumbing in the house, My wife working from home, A 8 month old puppy in the house. I also am getting a race engine together and my teams suspension to put in on the MG. It will happen though. Hydro

[Hydrolastic]

Hello Hi fi. IDK what the Sams file number is as I don know how to look up the file numbers it kind of confusing really as I have kind of just hoped I got it right with Steves, Its been ok so far and worked out up to this point.

[electra225]

I moved this thread to the Magnavox board. I left a link on Components so you could find it. We'll be thrilled to help you get your CG going. Please don't start another thread on this project. It will be easier to follow if you continue the discussion on this thread.

[William]

Hydro, please check your emails as I sent you a link for that schematic. It should give you everything you need to rebuild your Concert Grand.

Bill

[Motorola minion]

If the CG is anything like my (bought from customer) 58 RCA Orthophonic SHF-1, it is just as easy as a simple radio, just lots more parts changes on 3 modular chassis.

Get ready for all the drudge checking those 60 year old parts. You cannot get shocked testing resistors in-circuit, power off. Do this and get a good meter like a Fluke 27 or 77. Replacing resistors alone WILL solve several of your issues, Mag used some wide-tolerance carbon resistors like RCA did.

[electra225]

I typically replace the wide tolerance (i.e. out-of-tolerance) resistors with 1% metal oxide resistors. I'm wondering if replacing the old drifty factory resistors with precision new ones causes performance problems. On one hand, why specify a value if anything will work, on the other hand, it was built at the factory with "close enough" resistors. Which is right?

Dave, my experience with the CG I babysit with is that there are lots of parts in one. A coffee can full. The upside is that the circuits are fairly straightforward and simple, with lots of room to work. Working room gets a touch tighter in the tuner, partially due to it's greater complexity, partially due to the remote control hardware. Still fairly uncrowded compared to a TV chassis and some radio chassis, such as the big Stromberg-Carlson 1121 I have. The remote control system can be a pain to troubleshoot and get working properly. I've never messed with mine, partly due to the expensive 22.5 volt battery the remote needs and partly due to lack of interest in getting it going. I'd say that if someone possesses a modicum of electronic repair capability, stays out of circuits he may get into trouble, i.e. the FM discriminator, and makes notes and diagrams of his work, most anybody can get a CG going safely and successfully. They are marvelous, over-built instruments that are truly works of art. Equipped with remote control and an MPX chassis, there are six chassis, six rectifiers, three power cords, 44 tubes.

[TC Chris]

I typically replace the wide tolerance (i.e. out-of-tolerance) resistors with 1% metal oxide resistors. I'm wondering if replacing the old drifty factory resistors with precision new ones causes performance problems. On one hand, why specify a value if anything will work, on the other hand, it was built at the factory with "close enough" resistors. Which is right?

/quote]

If you've got a 20% resistor that's at 18%, it only takes a little drift to affect the circuit's function. But by then, it was the buyer's problem, if they even noticed. Performance can downgrade a lot before some people notice. My theory is that the resistor's specified value is the engineering design for best performance. Go with that. Don't settle for good-enough or the kind of creeping decline that we don't notice because it happens so gradually.

Chris Campbell

[Motorola minion]

44 tubes!
I was deluded that my Motorola was high in tube count but the CG is double my "smaller room heater" 24-tube '63 SK112 that is warming the 3rd floor office right now using 6V6s, 12AX7s, 6AU6, 3DG4 (15 watts on that rectifier) .

[Motorola minion]

A friend of mine has high standards, so when I traded him my Dynaco Stereo 70 (PP EL34), he replaced the entire preamp circuit board with a souped-up aftermarket and parts for using 12AX7 instead of the 7199s like the original.

That aftermarket solution would never fly in a hand-built Magnavox, their design is uniquely simple and easy to troubleshoot like RCA, and even resistor upgrades always count. The .001-.47 uf capacitors being on point value-wise, compared with +/- 20% paper/wax they were fitted with, is really what makes these more expensive-designed consoles sound better than new, IMHO.

[electra225]

The CG has 44 tubes, the Stereo Theater 36, the Imperial 26, Symphony 17 and the two little ones have 15 each. I appreciate the comments about exact-value components.

[William]

Greg, if you turn them all on at once you could heat the shop in the winter.

Bill

[Motorola minion]

Greg, if you turn them all on at once you could heat the shop in the winter.

Bill

You sometimes need heat in AZ, right?