Author Topic: New to the game (San Diego)  (Read 3488 times)

Smariom

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Re: New to the game (San Diego)
« Reply #15 on: July 18, 2019, 02:53:54 PM »
Text for picture.

Smariom

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Re: New to the game (San Diego)
« Reply #16 on: July 18, 2019, 04:28:05 PM »
Text for picture. (Inside the amp)

Smariom

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Re: New to the game (San Diego)
« Reply #17 on: July 18, 2019, 04:49:18 PM »
Serial number.

Motorola Minion

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Re: New to the game (San Diego)
« Reply #18 on: July 19, 2019, 04:03:39 PM »
Solid State = all transistors and diodes, so no warm up. If it does not say solid state, its got tubes like my 1962 and earlier Magnavox consoles.

Magnavox sold their most expensive models as Astrosonic 100, with lower models called Astrosonic averaging 20-40 watts, finally the lowest priced units simply labeled "SOLID STATE", that's it. the catalog shows them all as you can see.

The BEST thing about Magnavox, RCA and Zenith solid state models was that RCA made their transistors ;D, hence the code "274" I see on yours. I have rarely needed to replace a transistor, another great thing about Magnavox.

Yours has iei and Nichicon capacitors, many dated the 40th week of 1962 that will cause issues (none that make smoke and destroy transformers, thankfully), that picture is good and I count a total of 16 on your amp chassis, which includes 12 black and a 3-cap can (upper right) and a 1-cap can next to it. Just one of those caps, over on the right including that 300mf iei, can cause hum that cannot be controlled with the volume control.

At a Magnavox TV dealer, I worked on the bench repairing what the road man pulled out and brought back to the shop, it was more serious than a hum or scratchy controls, more like a dead channel that he confirmed by swapping speaker leads. The road-guys that charged $35-up for a tv/stereo house call did not want to pull it into the shop, that was double because of a return trip. Customers would still spend a few $$$ to fix a Magnavox that was 15 years old, a testament to their initial quality...and price.

If there was just a hum, they would have a selection of caps in their road case, and "jump" the leads of a new 500 mf cap across the suspected cap, and the hum went away, they soldered it in and packed it up. Sometimes, I saw past repairs where the "open" cap was not removed from the circuit, a sloppy practice. 

Have a good weekend, gotta go keep my records from melting.  8)

Tubes - Magical - Tubes

Dave

Smariom

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Re: New to the game (San Diego)
« Reply #19 on: July 22, 2019, 12:54:37 AM »
Motorola, so which caps would you recommend I replace? It is just a hum so far. I'm looking for a starting point on what to replace / repair. You're a wealth of knowledge it seems and I will appreciate whatever youd like to suggest.

TC Chris

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Re: New to the game (San Diego)
« Reply #20 on: July 22, 2019, 08:34:13 PM »
Well, I'll jump in here and make a suggestion.  In a transistorized device, the capacitors tend to be larger-value, low-voltage as compared with tube devices.  And most of those large-value, low-voltage devices are electrolytic capacitors, which are by nature polarized (they make nonpolarized electrolytics, but those are 2 caps reversed). So I'd focus on replacing the caps with + and - marked on them.  They are chemically based devices and age can catch up with them.  The little reddish discs are ceramic caps and they almost never age-out.  Don't worry about them--unless they're in the signal path, and some think that their audio quality is poor compared with film capacitors in that service.

For the polarized capacitors, be very careful to maintain correct polarity (replace them one by one and maybe draw out + and - in case your phone rings or the house catches on fire while you're working.  The schematic is your friend, of course.

That is a handsome amplifier, well built and with those nice transistor sockets.

Chris Campbell

Smariom

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Re: New to the game (San Diego)
« Reply #21 on: July 24, 2019, 09:29:55 PM »
These then? I'll look in the parts list on the download and find out what to swap them with. I'd like to keep as much original as I can, but also upgrade where I can too. Thanks all for the help. I'll get a soldering iron and all that junk this weekend. Lost mine in a move. I'll share before and after images. :)

Smariom

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Re: New to the game (San Diego)
« Reply #22 on: August 09, 2019, 07:47:37 PM »
I replaced the 250MFD 25v caps with 250uF 50vdc caps and now.....the hum is still there and the sound out of the speakers is crazy low. Thoughts anyone?

The new caps are the smaller circled ones the original are the much fatter ones. I havent replaced the other 4 because I wanted to do things in process. I'm kinda stuck. Anyone have any thoughts?  Anyone in the SD area?

Just cerified, volume knob doesnt make it go loud or soft. It's the same soft sounds no matter where the volume knob is turned a stead hum and the music is a stead low volume. ...anyone had this issue?

Smariom

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Re: New to the game (San Diego)
« Reply #23 on: August 09, 2019, 09:37:49 PM »
I'm a dummy. After I swapped the 250mfd and tested it and was getting the faint noise...I wasn't turning the volume button. It's not the same knob as power like you think it would be. Dummy.

Anyway new caps are in. Same hum so it's not those. Waiting on the other new caps to come in.

Picture for image porn.

Bill

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Re: New to the game (San Diego)
« Reply #24 on: August 10, 2019, 07:10:22 AM »
Unless I'm not seeing how you did it in your photos, you have not replaced the can type electrolytic capacitors yet?  They sit side by side, sticking up on the topside of the chassis.  One is metal and other is paper looking.  Those two need to be replaced!  They are one of the biggest cause of hum. I believe Dave mentioned that previously.  Do you plan on replacing all caps?  Are you checking resistors as you go?  A total restoration takes time, it's done in baby steps.  Sometimes there are snags, whoops, oh S..., and lots of frustration.  :( >:( :o ??? :-[ :-\ ::) ;)  In the end, it will all be worth it.  :) :) :)  And like Chris said, a schematic is your friend.  If you have not printed it out, do so, and then follow it as you go along.

Bill