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The AM and FM bands share the same IF amps, ruling out Q6 and Q7.

I'm not an electronics engineer or even very gifted in theory, so I'll ask a slight OT question because I've always wondered.  When tuners use the same IF amps for AM and FM (different IF transformers, obviously), how much efficiency (sensitivity) is lost by having the "wrong" IF transformers in the circuit?  That is, when on FM, the 455kc IF cans aren't working, but they are there.  Same with AM and the 10.7 mHz cans.  Are the wrong ones sufficiently untuned that it's the equivalent of being switched out of the circuit?  High-end tuners usually have completely separate IF circuits.

Chris Campbell
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Introductions / Re: New to the game (San Diego)
« Last post by Smariom on July 18, 2019, 04:49:18 PM »
Serial number.
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Introductions / Re: New to the game (San Diego)
« Last post by Smariom on July 18, 2019, 04:28:05 PM »
Text for picture. (Inside the amp)
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Introductions / Re: New to the game (San Diego)
« Last post by Smariom on July 18, 2019, 02:53:54 PM »
Text for picture.
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Introductions / Re: New to the game (San Diego)
« Last post by Smariom on July 18, 2019, 02:53:21 PM »
Text for picture.
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Introductions / Re: New to the game (San Diego)
« Last post by Smariom on July 18, 2019, 02:52:05 PM »
So I dug around and found more paperwork. Think my model is the 1-ST682.
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Introductions / Re: New to the game (San Diego)
« Last post by Smariom on July 18, 2019, 02:46:53 PM »
Good info Minion. I'm trying to figure out which compactors to replace or which are the filter compactors, or should I just replace them all. There is amazing sound but the hum is also quite amazing. Not to sound silly but this is a solid state? There is a warm up period before sound actually comes out.

Is the A590-01-00 the model number or what I'd use to get schematics?
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Update - replaced those transistors  and all the resistors except one on the drive board, and thankfully, Channel 2 audio has returned.

Channel 2 audio is distorted and much lower in volume level than Channel 1.  Audio was from the FM section and also through the Tape In jacks, just to be sure. This was on the work bench, not reinstalled in the cabinet, so cannot blame the speaker selector switch.

Quit working on it pretty late last night, will go through and test transistors again, and also the Selector switch.  A radio station engineer/ham radio friend here mentioned if I have lost AM but have FM, it could be the selector switch.   May as well set up the oscilloscope again and try tracing the audio signal through Channel 2 to see what else I might find.

Any suggestions, hints, tips, caveats?

Losing AM can also be due to an open AM antenna connection, a ground and two windings. The AM and FM bands share the same IF amps, ruling out Q6 and Q7.
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My Astro's stereo light barely comes on unless its a real strong signal. That is a special lamp, not 6.3v like a #47 or #1847.

Correction, this chassis uses an #1867 lamp for a stereo indicator, same as the dial lamps. Stereo lamps rarely burn out though.
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The power supply is 36 volts, the maximum replacements should be no more than 100 volts, like you confirmed.

50 mf and 5 mf @ 25 or 50 volts is common in this chassis. Speaker coupling are a pair of 400 mf, but that is not a standard value. I see Mouser has a 390 mf 1t I would use 470 mf as its a standard value and may improve bass response. The 8 mf non-polarized caps that feed/protect the horns do not need to be any more than that but could be lower, say 6.8 mf which is available in 100 volt, non-polar.

For capacitors, JustRadios is who I deal with mainly because they cater to restorers, with all values on an excel spreadsheet to order. I have used Allied, Digi-key and RadioDaze also. Mouser has a very difficult website, too many capacitor choices and most are overkill and expensive.
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