Heathkit AJ-1510 Tuner help needed. - Page 2 - diyAudio
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Old 11th September 2011, 10:33 PM   #11
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Thanks for the reprint of the RE article; I'm still a bit lost by the explanation, but it's substantially more information than I had before. I had the impression that the demodulator could handle very wide modulation with less distortion than typical L-C type detectors, and the composite output had less phase distortion insuring better multiplex decoding. I replaced all Rs and Cs with .1% metal films and caps with polystyrenes or silver mica instead of the ceramic disks, on general principle, but I'm still shooting in the dark without at least a Sound Technology 1000A or the equivalent.

Again, thanks for the information; a copy went straight into my AJ-1510A manual!
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Old 11th September 2011, 11:23 PM   #12
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If you notice, the counting detector is linear with period, not frequency. But the error is quite small. The centre frequency, 10.7 MHz is 93.4579 nanoseconds. Full positive frequency shift is 10.775 MHz with a period of 92.8074 nsec and the negative shift is 10.625 MHz with a period of 94.1176 nsec. Positive difference is 0.6505 nsec and negative difference is 0.6597 nsec. Thus, there is some harmonic distortion with a counting detector, but it is small and well-characterized. Maybe the higher frequency compensates for the smaller period when it goes high and vice versa.
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Old 11th September 2011, 11:54 PM   #13
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At this point, I've little idea on how this part of the AJ-1510s circuits could be 'improved', but I bought the thing expecting to get an interesting and perhaps significant piece of equipment that'd sound good once restored. Had I known the Sony XDR-F1HD and HD radio was around the corner, I wouldn't have bought it as the Sony is giving me excellent service and satisfaction.

But I'm still holding onto the Heathkit because it sounded pretty good itself, when the digital tuning decided to work and I think it's worth restoration and upgrades.
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Old 11th September 2011, 11:59 PM   #14
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Quote:
Originally Posted by Damon Hill View Post
At this point, I've little idea on how this part of the AJ-1510s circuits could be 'improved', but I bought the thing expecting to get an interesting and perhaps significant piece of equipment that'd sound good once restored. Had I known the Sony XDR-F1HD and HD radio was around the corner, I wouldn't have bought it as the Sony is giving me excellent service and satisfaction.

But I'm still holding onto the Heathkit because it sounded pretty good itself, when the digital tuning decided to work and I think it's worth restoration and upgrades.
In the zip on post #6, you can get a lot of ideas about how to do this. The biggest change was putting 0.01 F ceramic capacitors across each chip in the divider chain from pin 16 Vcc to pin 14 that is conveniently at ground. The designers were counting on a 10 F electrolytic to bypass a high edge-rate divider chain. I still haven't got the keyboard entry to be 100% debounced, but part of my file shows you the plan for making it better.
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Old 12th September 2011, 12:13 AM   #15
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Actually, the counting detector will probably have less distorsion than most common (Foster-Seeley, ratio) detectors without requiring any alignment. Proper alignment of the conventional FM demodulator for minimum distorsion was allways a tricky job and required specialized test equipment (sweep generator,ocilloscope...) which most home kit builders didn't have access to. Maybe this was the main reason why HEATH decided to use this kind of demodulator. It is quite remarquable that a receiver of such complexity could be aligned without any test equipment but the small built-in signal meter. Another HEATHKIT achievement...
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Old 12th September 2011, 12:26 AM   #16
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Yes, that's effectively my 'bible' for upgrades and fixes; I might have lost interest without that substantial list. As it was, just to get it working I had to replace a couple of shorted capacitors right off the bat and the glitchy digital tuning certainly suggested other problems.
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Old 26th December 2011, 06:34 AM   #17
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I have written up a blurb on the AJ1510A tuner, but it is in word format. I am not sure if I can copy it into here as it is rather long. And you are right, there are several design flaws, very unusual for a Heathkit product.

It does not cover the original poster's problem of changing the tuning, but it does cover a number of flaws. If you have enough information to contact me, I can send it via e-mail.
Wow, nice write up. I have an unbuilt AJ1510A which I am planning to start building next year. I will change out all resistors from the beginning as well as caps. Any ideas of what you might do if you started from a bare bones kit?

Thanks
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Old 11th December 2012, 03:55 PM   #18
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Originally Posted by tomb18 View Post
Wow, nice write up. I have an unbuilt AJ1510A which I am planning to start building next year. I will change out all resistors from the beginning as well as caps. Any ideas of what you might do if you started from a bare bones kit?

Thanks
Just now noticing this.

Really?! Wow... That might go a very large box of pennies on eBay.

Apart from the list of modifications, I'd replace all carbon film resistors with 1% metal film, tantalum coupling caps with film (they'll be much larger), and consider buying new electrolytic caps for the power supply as the units in the kit are likely unformed by age and may quickly fail. If you have a variable DC supply, bring them up slowly over a period of hours.

Also replace the (likely) corroded RCA audio output jacks with gold-plated
parts.

Hope you'll still got the extender board; that's a useful part to have while troubleshooting and modifying.
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Old 15th December 2012, 01:27 PM   #19
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I got the kit for $800 with the cabinet.
I also have the matching 4 channel power supply which I started a while ago but then built a HW-101 instead.
I was thinking of redoing the circuit boards as well, adding places for the additional caps etc.
Should be fun!
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