1960 Magnavox Concert Grand model 1ST800F rehabilitation

[electra225]

I'm sorry, Doug. I didn't know the amp schematic wasn't there. I checked on my computer and it's not there, either. I need to see what Sams it is in, then check my external hard drive to see if it is there. I'll get it posted. Thanks for letting me know.....

Later........I found the amp schematic for the 82-series amplifiers. Somehow it got separated from the manual I posted. I found it in a file called "service manual", which I think is of my own doing. In 2014, probably. I will post this information, but it will be a few pages down from the rest of it. Maybe I can move it, I'll have to check on that. But, for the time being, and if I can post it, we'll have what we need.

I downloaded it. It is on page 5, Amps and Tuners. Thanks again for the head's up....

[stbasil]

I was looking at the service manual that you uploaded, and wondering why the 15" bass speakers are spec'd with different magnet weights, 50 oz for channel 1, 35 oz for channel 2. You would think that they should be identical. Is it really built that way?

[TC Chris]

Bass frequencies are essentially non-directional so symmetry is not important. I recall some discussion about the magnet variation and one thought was that this was a way of covering a range of bass frequencies--each speaker having a slightly different response. Or perhaps the different cabinet configurations at each end required speakers with different free-air response in order to sund the same in place.

Chris Campbell

[electra225]

The Concert Grand really has 15" speakers with different size weights. If the purpose was to enhance bass, it missed the mark. By a mile. Their bass components are bizarre. The thing should damage drywall, but it doesn;t. I've said this before, but maybe before your time that my wife calls the Concert Grand "the three hundred pound clock radio". That might give you a hint at its performance........

[Doug]

You need to hook up a set of good known aux speakers to determine if it's the speakers or Amp.
I couldn't get that download to open
Doug

[electra225]

You won't be able to open a download file on this forum. You need to download it to your computer, then open it that way.

Now that I have the Fisher speakers ready to use, it might be a good idea to use them for woofers and see how that sounds....

[Doug]

If it is the Amp I would suspect c209d 20mfd.its the filter for all the cathode 6v6

[TC Chris]

Just remember the Magnavox theory that they engineered their products as units, so they would sound the way the company wanted. Individual parts of it might not have flat response, but if they complemented each other properly, the audio output would sound as intended.

The competing theory was proposed for stereo components. Each individual component should have flat response so you could mix and match. You could hook up any 8-ohm speakers, or any turntable and phono cartridge, or any tuner, and everything would sound just fine. Then careful listeners discovered subtle differences in sound resulting from things like impedance mismatches, cable capacitance, speaker impedance variation with frequency, etc. But still, the idea is that any amp ill work with any speaker.

But back to Magnavox, keep in mind that if they found that the upstream components had nonlinearities that they could correct via choice of speakers to compensate, then substituting a "flat" response speaker [there really are none] might not sound good.

Chris Campbell

[electra225]

As I have pointed out, ad nauseum, Magnavox missed the mark with their bi-amp instruments. They just did. I still think there is a component, a "something" that can be changed to correct their anemic bass condition so prevalant in the bi-amps. God knows they used enough componentry. If GE used all the parts that is in a Concert Grand, they could have built several stereos that sound better than the CG does, all things considered.....

[electra225]

I finally got caught up enough around here to get on this project. I have the changer and tuner/power supply/MPX assemblies out. My challenge with the changer is that the upper bearing of the motor is really stiff. If I don't run it for a month or so, the motor won't start without removing the platter and giving the motor shaft a twist to get the motor started. I need to completely remove the motor from the changer, take it completely apart, clean it WELL, put it back together, then pray I get the fan and turret back in their right spots, and that I have not bent the fan. I've read where taking the motor apart may be a fool's errand, but, in this case, I don't see a way around it. Then I need to figure out why the tuning eye doesn't deflect, just sits there. I need to check resistors R342 a 15K, R345 a 470K and the likely reason for no deflection, R206 a 1.5 MEG, and R208 a 2.2 MEG. There is also a .1uf cap that I need to check and maybe change, even if it has already been changed. Then I need to test all the tubes in the tuner and MPX.

[William]

As I am reading your post and looking at the photos a question popped onto my head, is the CG tuner and the Imperial tuner the same?

Bill

[electra225]

The tuners are essentially the same. The CG uses 12ax7 audio tunes vs. 6eu7. Then there's the remote control components. They both have 11 tubes.

[William]

Thanks, Greg, and would be nice if the Imperial would have used the 12AX7. How many times total in a CG?

Happy Birthday!

Bill

[electra225]

There are three 12AX7's in the tuner. One for audio amp, one for phono amp, one for cathode follower. I think then there are two in each amp. One for audio amp, one for phase inverter.

I measured the 470K resistor in the eye tube circuit, from pin 2 to pin 4 of the 6E5 eye tube. It measured over 3 megohms. The socket on the eye tube is designed to be serviced without being destroyed. If you notice the slots in the tube socket, you put a thin screwdriver in that slot and pry the socket up. Once you get it started, you can use a thin blade to pull the socket out of the base. It starts coming hard, then pops out all at once. I got the 470K ohm resistor changed and checked the other three, which checked just fine. The tubes all checked good. I have the tuner ready to go back into the cabinet. Next up will be the phono motor.

[electra225]

I have the tuner, power supply and MPX all back into the cabinet. It may just be my ears today, but I could swear I actually heard some bass responce today in my old CG. I replaced the cathode follower 12AX7, but that wouldn't affect the bass response any. The good news is that the eye tube now works like it should. The dial is off somewhat, but that seems to be a feature of Magnavox tuners. Some frequencies it seems pretty close, others it's way off. I have the changer rigged up so I can get the motor out and get it cleaned.

[William]

Progress is being made and I wish you all the best with the Collaro changer. They still scare me.

Bill

[electra225]

This particular Collaro changer has the remote control components to deal with, so it has a few more goodies than others have. My goal here is to remove the motor with a minimum of drama. Then I'll decide what I need to do otherwise. It works fine. I'm sure I can fix that, though.....

[electra225]

The motor on this particular changer is different from the other Collaro motors I have worked with. The "shift" mechanism is built as part of the motor housing. There is a plate on the bottom end of the motor that comes off so the rotor will drop out of the motor. I had to remove the cycle drive tire, the turret and fan (gentle as she goes there boys!). Not really any drama so far. The next stab I take at this project will involve removing the plate on the bottom of the motor, then find out if I can get the rotor out. The upper bearing is really sticky. Let's keep a good thought......

[William]

Good luck, Mr. Greg, but I know you can do it.

Bill

[electra225]

I'm really paranoid when I have a Collaro changer on the bench. So much can go wrong and I'm not experienced enough to both figure out what went wrong and then how to fix it. I'll need all the good thoughts I can muster...