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Magnavox AstroSonic with 9300 amp

M

MagnaZach

New Member
Hello Audiokarma. I just picked up what I believe is a 1961 Magnavox AstroSonic record player with a "9304-10" amp. I have recapped most of the capacitors on this unit but I am hung up on the two .047 MFD capacitors in the amplifier. On my unit, one is 600WV and the other is 1600WV. I do have a SAMS manual for this and it has them listed as 400V. I have successfully recapped and restored a 1965 solid state Magnavox recently so I have some experience but this Tube unit is a whole new animal! I was hoping someone had some experience with these amps, as I believe they are pretty popular as stand alone units for the guitar guys. I need information on what to do with those 2 capacitors!!IMG_6570 (1).jpg IMG_6586.jpg IMG_6587.jpg IMG_6588.jpg
 
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MagnaZach said:
... I just picked up what I believe is a 1961 Magnavox record player with a "9304-10" amp. I was hoping someone had some experience with these amps, as I believe they are pretty popular as stand alone units for the guitar guys.
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They are very popular as stand alone units for stereo enthusiasts, having had a few and read TONS of threads on them I don't ever recall someone utilizing it for guitar duty.

Nice amp and congrats on your acquisition of it!!!
 
yeah, they're not original. I'd be OK with leaving them in place. Those are an epoxy dipped film cap, good just about forever. I've got some from the 1960s that I ran through a dishwasher as an experiment, perfectly good.

if you really want to change them, I think the original were a 400 volt part. Anything beyond that is just overkill but it won't harm anything either.
 
Actually, I think they are original but I could be wrong. My 175-67 amp came with these types of capacitors. They were uneven on each channel that has something to do with frequency response or something like that. I think Dave G. explained it at one time but most Magnavox amps were built like this from the factory.
 
cademan said:
Actually, I think they are original but I could be wrong. My 175-67 amp came with these types of capacitors. They were uneven on each channel that has something to do with frequency response or something like that. I think Dave G. explained it at one time but most Magnavox amps were built like this from the factory.
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That’s my concern. I have read somewhere that they should have different voltages. My SAMS says they are both 400 but I’m not certain that I have the right SAMS. They have a weird way of labeling these 9300 amp manuals but most everything else on the unit matches with the closest SAMS I could find.
 
they don't need to have different voltages, and its definitely not different channel to channel. Its the value that is not the same. Notice the ceramic cap feeding the other tube in that channel and it's value. Thats the difference. Both see about the same voltage though.
 
From what I understand, which isn't much, WV would be the "working voltage" of the capacitor. That's the max voltage you want the capacitor to handle safely. As stated, probably fine leaving it in, but if it were me, I would change to a 400v.
 
Change them with modern 630v film caps. It wouldn’t hurt to change out the disc caps as well—the ones I see usually test 10-30% lower than their marked ratings.
 
Nice

I believe that the micromatic name references the turntable itself... I've seen that record player in lots of different models of Magnavox...

IMG_20211205_150541

IMG_20211205_150541

Magnavox Console record player and radio Astrosonic??

As to the Astrosonic name they used it alot of years and on many different consoles I was told mine is a Astrosonic by it's prior owner but I don't know...

But while I was looking in my Maggie I found something interesting to me... This wiring flow chart has a patent license from RCA on it...

Magnavox Console inside flow chart

Magnavox Console inside flow chart

This had a tidbit of information I was unaware of the design used is patented by RCA in this...

I thought they magnavox were the original designers apparently Magnavox was a OEM manufacturer in this instance...
 
Micromatic is the turntable, some solid state models were AstroSonic, some of the tub models were MagnaSonic

The turntables were actually made by Collaro but branded for Magnavox. I think later on Magnavox did actually buy Collaro but there wasn't really any change to the machine.

RCA had patents on a ton of stuff. Not sure which specific one but quite possibly its the superhet tuner circuit. Everything used it and RCA had patent rights to it.
 
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gadget73 said:
Micromatic is the turntable, some solid state models were AstroSonic, some of the tub models were MagnaSonic

The turntables were actually made by Collaro but branded for Magnavox. I think later on Magnavox did actually buy Collaro but there wasn't really any change to the machine.

RCA had patents on a ton of stuff. Not sure which specific one but quite possibly its the superhet tuner circuit. Everything used it and RCA had patent rights to it.
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That similarity of naming conventions is probably why there's so much confusion about the different models... Magnasonic

So I was searching for the wrong name... Very helpful Thank You

RCA was definitely a powerful corporate entity it's not really surprising they held some of the design patents it's too bad the patent numbers are in a tear...

I've been trying to figure out a way to preserve that paper since I got the console...
 
Thank you all for your help! I used this forum extensively on my last project but never had to ask for help but its awesome to see all the knowledge when I needed it! I had some time today to work on this piece a bit and gather some more information. I found out I have:

Magnavox Imperial Micromatic
Model 3ST622A
Amplifier 9304-10
Tuner 7909-10
Multiplex 7002-00

I have recapped everything so far except one capacitor in the tuner. Its labeled .022 MFD/400 VDC. I have always order capacitors from digi-key and justradios but I am unable to locate anything close to this one. That seems to be a very low capacitance. Any ideas on what to do here would be great! Also, if anyone has any literature or schematics on the Amp, Tuner, or Multiplex that they want to share, that would be great. After learning from you guys that this unit has had at least some capacitors replaced before, I would like to check my work as I went straight off the values of the existing caps in replacing them.
IMG_6700.jpg IMG_6703.jpg IMG_6704.jpg IMG_6705.jpg IMG_6706.jpg IMG_6708.jpg IMG_6709.jpg
 
Umm the piece of paper above the model number "the wiring flow chart" is it possible for you to get a readable picture of it posted please...

You should be able to find something close enough to it have you searched for the .022mfd cap by it's alternative names 22nf or 22000pf Or 223k ???

Or tried a higher standard voltage like 630 volts

A .025mfd cap would be close enough too
 
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guitargrump said:
Umm the piece of paper above the model number "the wiring flow chart" is it possible for you to get a readable picture of it posted please...

You should be able to find something close enough to it have you searched for the .022mfd cap by it's alternative names 22nf or 22000pf Or 223k ???

A .025mfd cap would be close enough too
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guitargrump said:
Umm the piece of paper above the model number "the wiring flow chart" is it possible for you to get a readable picture of it posted please...

You should be able to find something close enough to it have you searched for the .022mfd cap by it's alternative names 22nf or 22000pf Or 223k ???

A .025mfd cap would be close enough too
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the “wiring flow chart” really just shows how the components are connected to each other..speakers multiplex, amps, etc. It doesn’t show anything particular about the components or capacitors. I have been able to find film capacitors which I believe are called orange drops with matching MFD and V but from what little I understand about these, they aren’t polarized.
 
MagnaZach said:
I have recapped everything so far except one capacitor in the tuner. Its labeled .022 MFD/400 VDC. I have always order capacitors from digi-key and justradios but I am unable to locate anything close to this one. That seems to be a very low capacitance.
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thats a common paper capacitor. Modern equivalent would be film of some flavor. Bump it to 630v if you have to but there shouldn't be any trouble finding an 0.022 uf film cap.


Most of the coupling caps in this are going to be in some decimal number of microfarads, usually in the 0.1 to 0.01uf / mfd range. All of them can be subbed with film with no issues.
 
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