1967 Magnavox Imperial

[Moto_TJ]

I have finally started working on the Imperial. Last night I worked on the Tuner/Preamp section as everything was working, but I knew that the caps were showing their age. I had noticed that there was a service sticker in the record changer cabinet, but that could have been who sold it or a minor repair. Boy, was I in for a surprise when I flipped over the chassis. This imperial has had some serious work done to it in the past. It looks like every transistor had been removed and reinstalled as had most of the electrolytic capacitors. I don't know what issue they were trying to track down, but whomever worked on this, must not have had a lot of experience with a soldering iron and circuit boards. There were traces missing with leads stretched to make the next contact point. Lots of dwell time and or a soldering iron that was too cold. After seeing all of that I was surprised that it had been working.

I replaced all of the Electrolytic capacitors, only 2 of the original caps were truly dead, most were about double their original capacitance values. Cleaned the dirty controls, the volume pot had barely worked before hand.

I reinstalled the chassis last night and everything is still working and sounding better than before!

I also ordered the caps for the Amp, remote chassis, and the crossovers this morning. I have yet to test the tape deck, debating if I even want to attempt it as I have heard this model can be finicky.

I will attach some pictures and also include the link to the Google Photos album for this project that I will update as I work on the unit.

Picture Album: https://photos.app.goo.gl/EVJAs61HDzarWFe49

[electra225]

Boy, somebody's been gomming around in there pretty good. That looks like something I might have done. You cleaned it up well. Nice work.

[hermitcrab]

I still think the solid state maggie's are some of the easiest sets to work on...of course not counting on finding someone else's shoddy work before you get in there

[Moto_TJ]

I've found repairs in the Tube equipment that I've worked on, and it was usually a capacitor or resistor that had been replaced, and the work always looked pretty good. I wonder if they had a new tech and was training him on this.

I didn't like working on Solid State equipment due to a Zenith Z906 that destroys output transistors. I gave up on it, I checked every component, replaced every capacitor, transistor, and diode on the amp board, cleaned everything, and couldn't find the culprit. The cabinet makes a nice storage table though...

The Astrosonic 30 turned out well, as did the Pioneer SX750 receiver and Kenwood KR7600 receiver that I repaired. As long as the previous tech's repairs continue to hold, and the amp doesn't have any nasty surprises, this Imperial should finish well.

Being a '67 the tuner board has been changed over to Silicon transistors, but the preamp board and the amp are still germanium (except for the silicon rectifier diodes).

The Z906 that gave me all the problems was all Silicon transistors and it sounded good when it worked, but it never worked very long.

[electra225]

I'm pretty ignorant about solid state components. The germanium transistors look like top hats, don't they? I'm assuming you checked the Zenith for a broken trace somewhere.

[William]

It looks like someone took a blow torch to it in a couple of spots. Nice job TJ, and it sounds good too.

Bill

[hermitcrab]

I have toyed with the Idea of changing out the germanium output transistors to silicon and re-biasing , you can still get the replacement ECG 121's but they are not cheap like 30-40 bucks each...but so far my amplifier plays great and as the old adage says... if it ain't broke. ..also a word of advise ... check the bias 2 watt resistors... I had a few that were cracked from the heat cycles, and they get super hot while it is running...

[TC Chris]

I have toyed with the Idea of changing out the germanium output transistors to silicon and re-biasing , you can still get the replacement ECG 121's but they are not cheap like 30-40 bucks each...but so far my amplifier plays great and as the old adage says... if it ain't broke. ..also a word of advise ... check the bias 2 watt resistors... I had a few that were cracked from the heat cycles, and they get super hot while it is running...

Better to replace with a higher wattage rating for better heat dissipation?

Chris Campbell

[hermitcrab]

They could even be 3 watter's , not really sure , but mine were the 270 ohm that had cracks in them ... when the system is running you can't even put a finger on them for a second ... since I had no 2 or 3 watt 270's , i did find a couple 5 watters in my junk bin...just mounted them to the heatsink and ran wires up to them... so far so good...

[Moto_TJ]

Bad news, and going for a long shot on this one. I recapped the amp and the crossover, but the treble still didn't sound right, it has had weak sounding treble since I got it, attributed it to them amp and or crossover. I put my ear down to the speakers and noticed there was nothing coming from the horns. I took the back panels off of the speaker boxes and tested all 4 horns, and all 4 horns are showing open on the ohm meter. Anyone here have a working quad set of horns for a '67/'68 Imperial? They are the 8 ohm, 600 cycle horns, most Magnavox horns are 16 ohm, 1000 cycle.

My other option would be to buy 4 regular 1000 cycle horns and take out the 4.7 ohm resistor that is in line with the horns. See attached diagram.

[William]

I'm sorry to hear of your bad luck TJ. I hate surprises like that. I think I may have a couple of horns but they are not from that generation. I'll check the next time I go the the barn and let you know.

Bill

[TC Chris]

Is it possible to take the driver portion of the horn apart? It's possible, maybe even likely, that the open wire is not in the voice coil, but at one end of it. I burned up a cone tweeter on a KLH Model 17 speaker and was able to repair the burned wire, just before it joined the VC. The coil itslef provide a bit of heat sink maybe. Worth a try....

Chris Campbell

[hermitcrab]

Sorry to hear that... check out www.partsexpress.com ... , they are pretty reasonable , I buy my speakers from them,... looks like they carry the replacement coils but they are on backorder https://www.parts-express.com/GRS-RDIA1 ... rn-280-051
Elton

[Moto_TJ]

So, I got 2 sets of standard 1000 cycle Magnavox horns off of eBay, installed them and everything seems to be working great! I had already slightly modified the crossover using 15uf caps as it originally called for 16uf caps which are not made anymore. The slightly smaller cap, along with the rest of the crossover design, should be about right for the 1000 cycle horns.

I got the record changer working, and the original cartridge is still in good shape! I will order a new needle for it.

The tape deck, well, it kinda works... I don't know if I want to put any time into the tape deck as I will be installing Bluetooth, and the tape deck probably isn't worth my time to restore.

The remotes are not working, but that is probably due to the hack job that was done to the remote chassis by the same tech that did all of the other scary work to everything.

[William]

Congrats on getting it up and running, TJ. Will you try to get the remotes working?

Bill

[electra225]

TJ, I think I have a spare remote control setup in my stash, which is currently in storage. I have the amp, mic and even a remote. I got the extra setup with my Stereo Theater. Open reel tape is the best music medium ever created. I heard one time who built those tape decks for Magnavox, but that escapes me this morning.

[hermitcrab]

I tested the mic that is suppose to rec'd the signal from the remote on my set... it reads open... but I was told on another forum they are not a standard mic and can't be tested like one...? so that is as far as I went on mine I believe they are suppose to operate in the 22 - 26 mhz range? I wished they worked as it would be cool to show them off in action... but it plays great so not concerned about it...

[hermitcrab]

TJ, I think I have a spare remote control setup in my stash, which is currently in storage. I have the amp, mic and even a remote. I got the extra setup with my Stereo Theater. Open reel tape is the best music medium ever created. I heard one time who built those tape decks for Magnavox, but that escapes me this morning.

I solved the tape speed problem on mine so it plays a tape recorded from any other machine... I was at the last MARC meet and picked up a small autotransformer ... when I say small it weighs around 5 pounds ... I mounted it to a bracket in the back of the set with the control sticking out the back... and I can independently fine tune the 120 volt input to the deck to correct the motor playback speed... it is like operating it on a variac ...the decks are panosonics ...

[electra225]

Got it! Panasonic it is. Thank you.

[Moto_TJ]

It's been a while since I did an update on the imperial, I think I have repaired as far as I am going to go. This past weekend I worked on troubleshooting why FM was weak at picking up stations. My earlier discovery of all the work that had been done on it in the past and the pulling of all the transistors by the previous tech gave me a good idea that there was a transistor issue.

I had guessed that this unit had been hit by lightning in the past, the previous owner, who was the second owner after his uncle, stated that his uncle had it connected to an outside antenna. Knowing this, I started with the first FM RF transistor, which turned out to be the winner. It looks like whoever worked on it, did not have the correct replacement transistor and installed a transistor that did not have enough gain.

I have a Zenith parts chassis, and the first FM RF transistor on that unit had the same original part number as the Magnavox, I pulled that transistor, installed it, and the FM really woke up on the imperial. I did a quick, by ear, peak of the FM cans, and all is good!

The only thing I am not going to do is restore the tape deck, at least not now, when I sell it, and the buyer wants to use it, I will fix it for a price, otherwise, it isn't worth my time for what I will get out of the unit.

I hope to finish putting everything together this weekend, and hope to get pictures and videos of it running soon!