Circa '66 Magnavox Astro-Sonic console - Videokarma.org TV - Video

radiotvnut · #1 09-16-2013, 10:40 PM

I need this like I need a hole in the head; but, it still came home with me after I saw it at the flea market. This is a circa '65-'66 Magnavox solid state Astro-Sonic console that I think will clean up OK. It produces audio on all sources; but, I think it could use a recap and the controls certainly need to be cleaned. The stylus was shot; so, I replaced it with one I had on hand and it now plays records. I think all the changer will need is some minor cleaning and adjusting. Besides cleaning/lubricating the motor/center bearing, and cleaning the idler wheel; my approach on record changers is "if it ain't broke, don't fix it." The radio works on both bands; but, the FM band is a lot weaker than the AM band and the sound is a little muddy (probably due to old capacitors). I noticed that this unit uses those black-cased electrolytic capacitors that like to either dry out or measure 5 times their rated value. As far as speakers, it uses side firing 12" woofers and front firing horns. I think it will be a decent unit once it's fixed up.

After seeing console after console priced at some insane price, it's refreshing to see one that's priced somewhat reasonable. They wanted $50 for this one; but, I talked them down to $40.

http://www.youtube.com/watch?v=HUvhQ3b-RKI

mstaton · #2 09-16-2013, 11:04 PM

Your pup seems to like it

truetone36 · #3 09-17-2013, 09:22 PM

That's more likely a '64-65 model since it's got the older style Micromatic changer inside.

davet753 · #4 09-18-2013, 06:23 PM

I just restored one almost like that one. The cabinet is a little larger, but I'd say it's the same chassis.

I don't remember the exact number, but I'd say I replaced about 20 of those small, black low-voltage electrolytics.....it made all the difference in the world in the sound quality.

radiotvnut · #5 09-26-2013, 10:45 PM

Once I tore into this thing, I discovered that it was actually made in April, '65.

I recapped the chassis, with one cap testing open and the rest testing anywhere between two to five times their stated value. After replacing the caps and cleaning the tuner/controls, the thing came to life with decent sound; but, I'm still not happy with the FM performance. It does fairly well on the stronger local stations; but, I still have to turn the volume up higher to get the same amount of volume as I get on AM. The weaker stations around here are faint to non-existent. I adjusted the RF trimmers on the tuning cap and got it slightly better; but, it's still not where I think it should be (based on other Magnavox models that I've had).

I checked some things and found the germanium FM RF amp and converter transistors to be suspect. Both of them check as expected in the forward direction; but, in reverse, I'm reading about 1.8 V on the meter when I normally should not be getting anything (this is with the transistors out of circuit). Anyway, NTE126 is listed as a sub for both transistors and I'm going to try replacing them.

davet753 · #6 09-27-2013, 07:40 PM

The FM performance is not all that great on mine, either. My mother has one like it, and I remember as a kid that it wasn't all that hot on FM (and that was when it was a heck of a lot newer).

If replacing those 2 transistors helps any, let me know and I'll tear mine back apart and check them.

radiotvnut · #7 09-27-2013, 08:53 PM

Well, the local parts house didn't have anything; so, in order to get the correct transistors, I'm going to have to order them. According to the web, Radio Shack still sells a pack of general purpose PNP transistors; but, they probably won't have them here. The only problem is my unit uses germanium transistors and what RS has is silicon. I know there's a chance that the silicon ones won't work; but, I'm willing to give it a try before paying almost $10 + shipping for the NTE126 transistors.

old_tv_nut · #8 09-28-2013, 08:36 PM

Quote:

Originally Posted by radiotvnut

Well, the local parts house didn't have anything; so, in order to get the correct transistors, I'm going to have to order them. According to the web, Radio Shack still sells a pack of general purpose PNP transistors; but, they probably won't have them here. The only problem is my unit uses germanium transistors and what RS has is silicon. I know there's a chance that the silicon ones won't work; but, I'm willing to give it a try before paying almost $10 + shipping for the NTE126 transistors.

VERY likely the silicons will not work (or not work well), as any biasing or AGC probably will be wrong, but not too expensive to try just in case.

Don't understand your test (reading volts rather than ohms)? Some ohmmeters may apply too much voltage for testing b-e junction of germaniums, I think.

DavGoodlin · #9 09-30-2013, 12:13 PM

Good Score radiotvphononut - I have the complete guts to an 08/64 dated AstroSonic whose cabinet was re-purposed and the FM seems OK, so I will check the FM RF amp in mine and report back.

I have lots of loose transistors too.

[/QUOTE]
Don't understand your test (reading volts rather than ohms)? Some ohmmeters may apply too much voltage for testing b-e junction of germaniums, I think.[/QUOTE]

Newer Digital Multi-meters read in volts on the "diode" range. about .6v for Silicon and .3v for Germanium. Even the one I got at Harbor Dredge has a transistor socket.
I always used a VOM or VTVM on the RX1 ohms range before and it took some getting used to.

old_tv_nut · #10 09-30-2013, 11:07 PM

Quote:

Originally Posted by DavGoodlin

Good Score radiotvphononut - I have the complete guts to an 08/64 dated AstroSonic whose cabinet was re-purposed and the FM seems OK, so I will check the FM RF amp in mine and report back.

I have lots of loose transistors too.

Don't understand your test (reading volts rather than ohms)? Some ohmmeters may apply too much voltage for testing b-e junction of germaniums, I think.[/QUOTE]

Newer Digital Multi-meters read in volts on the "diode" range. about .6v for Silicon and .3v for Germanium. Even the one I got at Harbor Dredge has a transistor socket.
I always used a VOM or VTVM on the RX1 ohms range before and it took some getting used to.[/QUOTE]

These would be forward voltage drop, not reverse - reverse should be an open circuit, and if your meter were reading voltage in reverse, would just read the applied voltage (unless it was too high and was breaking down the junction). So, not sure where the 1.8 could come from - are you sure you had the right pin-out on those devices?

DavGoodlin · #11 10-01-2013, 08:19 AM

I pulled out a Sams 836-9 to check the first RF stage in the Mag, listed as "AM-FM RF amp"
It shows a germanium PNP "61P1D" the base voltage is -0.9 v, emitter -0.7 v, collector -13.9 v.

What is possibly affecting only FM is the balun and bandswitch. Measure from each antenna terminal to ground to verify continuity. The one antenna terminal then runs thru the band selector wafer to the dual-tuned (AM and FM) network feeding the base of the subject transistor.

Of course, the transistor could be crapping out on higher frequency, which may be what you are already on to.

radiotvnut · #12 10-03-2013, 08:20 PM

OK, I touched up the alignment with the old transistor and got it working to an acceptable level. Then, I put it all back together and was listening to a certain station when it suddenly dropped off to next to nothing. I pulled it back apart and found the RF amp transistor to be intermittent. It would give me a reading one minute and then nothing the next. I tried a general purpose silicon PNP transistor and much to my surprise, the thing worked better than it ever had.