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magnavox Imperial Stereo restoration

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Darrelltarte

Member
hi everyone! I'm in the middle of restoring a 1961 or 1962 magnavox stereo. It worked whenever I bought it, but it always distorted after about 30 minutes of playing. Of course, I knew something was wrong, so I took it apart a few weeks ago to take a look & replace parts if necessary, & it is necessary. The rectifier tube has a small piece of metal in it, & it hasn't been serviced at all. Every thing is all original, & I'm surprised (& glad) that it still works. Of course, I'll be recapping, getting new tubes, & anything else it needs. The numbers are: amplifier, 9304-20
Tuner, 7909-10
Multiplex 70-2-00
I've been working on console stereos for a while now, but this is my 2nd vacuum tube stereo. I've learned quite a bit since I bought it, but I still have a few questions. On the tuner chassis, there is a few square looking things that appear to adjust something using an Allen wrench. What do these do? Also, the rectifier tube is red plating. How would I fix this? Thank you in advance everyone! Ps. It also has a hum knob on the amp, I never did anything to it, but when ever it was playing it never had any hum, just the distortion. The image is from the tuner chassis
 

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Those square things with the "allen key adjusters" are your IF(intermediate frequency) coils for the tuner. DO NOT TOUCH them or you'll screw up the tuner, period!

Rectifier redplating? replace the CAN CAPS, and all wax, and electrolytics internally and replace the rectifier tube.

The Hum knob is to adjust the AC voltage balance in the tube heaters so each side is balanced against the other, and nulls out the hum. Don't mess with it unless you have hum, and the instructions.
 
Those square things are called IF tuning cans and should never be touched unless you want to do a complete alignment which requires a scope, a frequency generator, and a knowledge of how to align it all. Probably not needed so don't mess with that part of it.

If it is indeed the rectifier tube that is red plating, and you say it has metal piece rolling around inside, the tube should be replaced but not because of the piece of metal in it, but because you don't know how long it has been red plating and/or abused. The red plating is usually an indicator of a shorted power filter capacitor. So replace the filter capacitor and all coupling capacitors and the rectifier tube and you should be good to go.

The 9304 series amplifier is one of the more desired amps that people are keeping their eyes out for so you have a good amp there.

EDIT: I was typing the same time Larry had posted. He basically said the same thing I just did.
 
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danrclem said:
Anytime a rectifier red plates then it's toast?
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Not necessarily! I have several that red plated but I caught them in time. They still test over 80% so they are still good. I am still using one that red plated at one time as I am typing this but since the OP doesn't know how long that one has been red plating or abused, then yes, it should be replaced.

A long period of red plating will cause the tube to get very gassy and will even melt the glass. :yikes:
 
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I bought it for 30 bucks c: not a bad price (I hope) c: & I'm glad I found it so I can repair it & get it back into working order. & I thought it was the can caps, I just wasn't sure. But yeh the only thing I did was fix the changer, carefully inspect the wiring, & the tubes & dusted off everything. & what should I replace those can type caps with? Some of them are 450 v & I think one on the multiplex is 250. & also found an extra needle in the back, so the changer is taken care of. The changer runs, but it has a unique plug so I can't test how it sounds till I get it back together. Thank you for clearing that up c: I have a lot of people wanting to see it after its finished :)
 
Well, everything was covered in dust inside, so I figured it's been doing that for a while. The Pilot lights have also burned out, all except the one for the fm meter.
 
But i do have one thing that is worrying me. It looks like a small output transformer, but it looks like something was spilled on the transformer, but I could be wrong I'll post a pic of what I'm talking about
 

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Thanks for the explanation cademan.

You bought that for a good price Darrelltarte. It's probably a small Imperial model. Pictures please.
 
We want to see the amp! :beerchug:

Of course I will never let any tube red plate for any long periods of time, but I am the type that has caused them to red plate on purpose just to see what happens. I don't waste tubes and I did this in my earlier youth but now I have rectifier and output tubes up the ying-yang which I will probably never use. lol
 
Darrelltarte said:
But i do have one thing that is worrying me. It looks like a small output transformer, but it looks like something was spilled on the transformer, but I could be wrong I'll post a pic of what I'm talking about
Click to expand...

That's just a choke coil for smoothing out ripple current. It is associated with the rectifier tube and main power filter capacitor so if it looks melted, it could be bad but you would have to measure it just to be sure. It looks ok to me from the top side.
 
Darrelltarte said:
But i do have one thing that is worrying me. It looks like a small output transformer, but it looks like something was spilled on the transformer, but I could be wrong I'll post a pic of what I'm talking about
Click to expand...

A lot of these older open case transformers/chokes are coated/sealed in a wax compound. Looks like the wax it was coated in melted off. This happens quite frequently with open transformers. Test it with an ohmmeter to make sure it's not shorted or open. Someone will be able to tell you exactly how with the maggie transformers.
 
That does sound like what might have happened. It's kinda wax like too, & I have to use my fingernail to get it off. thank you for telling me
 
cademan said:
hat's just a choke coil for smoothing out ripple current. It is associated with the rectifier tube and main power filter capacitor so if it looks melted, it could be bad but you would have to measure it just to be sure. It looks ok to me from the top side.
Click to expand...
Thank you I'll measure it just to be sure
 
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