Need advice/ KT-7500/ antenna issue?

[ErikPSmith]

Hello all,

I have a few questions regarding setup and operation of a Kenwood KT-7500 tuner.

I bought this vintage tuner on eBay more than a year ago, but until last weekend I never plugged it in. Now I'm finally getting around to assembling that all-Kenwood stereo I lusted after in high school, with the matching high-end KA-9100 amp and KX-1030 cassette and numerous other vintage Kenwood components from approximately the same era (the most unusual being a Kenwood reel-to-reel and the Kenwood oscilloscope). I'll admit, it's the look of Kenwood components from the late '70s that gets me -- all those knobs and switches and dials and meters, against brushed-aluminum faceplates. But way back then, the top-end stuff had a pretty good rep for sound quality as well, and I can see there are plenty of fans on this forum. Anyway, at long last, I got around to hooking up the tuner and glory be, it works. That's the good news.

But I wonder if I have the right antenna set-up, or if I've hooked something up wrong. Or maybe something is wrong with the tuner after all.

I am using an amplified external indoor FM antenna. I connected the two 300 ohm wires to the two 300 ohm antenna posts.

FM stations came in clear as a bell -- they actually sounded better than on most modern tuners I've heard, and comparable to the ancient Hallicrafters SX-62 tube boatanchor radio I have in the living room (though I'll admit, I haven't gone out and listened to Macintoshes or any other legendary-type equipment).

A couple of things have me puzzled, though.

One of them is that after I tune into a local FM station, broadcasting in stereo, it takes a while for the stereo indicator light to turn on -- oh, maybe 30 seconds, a minute, something like that. Every other tuner I've had indicated "stereo" instantly when tuned to a stereo broadcast. Is something wrong here or is this just the way this tuner works?

There's an "output" control knob on the faceplate. But when I turn it, the volume stays the same. It doesn't make sense to me that a volume control would be bypassed when the only output is through the RCA jacks on the back.

And the weirdest idiosyncracy I notice is this. I also get reception on the AM band. But the volume is much, much lower than the FM band -- maybe half as loud. I've never noticed anything like this before on any other tuner I've used. Could it be that this is because I am using an amplified FM antenna, and only the FM signals are amplified? Could it be that something is wrong with the tuner?

Or could it be that I also need to get an AM loop antenna and hook that up as well? And if I hook up a second antenna, how do I do it? Does one wire go to the single antenna post labeled AM and does the other go to the post labeled "ground?"

I figure those of you who are more knowledgeable about such things will be able to offer me guidance. From the tone of the questions I'm asking here, you can probably guess I am far from an expert. So be gentle.

Erik Smith
Olympia, WA

 

[Lesterbest]

You need a separate AM antenna. Loops are the most common. Amplified FM antennas amplify the noise as well as the signal. As for the stereo lite, leave well enough alone unless you want to pay for an alignment which is not a DIY job. There's an FM tuner site which will give you all you want to know. Try not to OD there.

 

[musichal]

It wasn't clear to me whether you were hearing a stereo signal before the light came on, but sounds like you need a better antenna, preferably not amplified unless outside. Play with positioning a common dipole.

I'm no expert, but it doesn't seem unusual to me that FM comes in hotter than AM. But those little rectangular loops that come with many receivers are almost useless. And then there's the whole issue of your home likely having quite a few devices which interfere with AM reception (average household has 78,419 sources) - I have better luck with portables for AM with their battery PS, and easy to move around to find a spot with less RFI.

 

[rcs16]

Fortunately the tuner is a nice one and most parts are very common. So you should be able to use it for years to come, once it is cleaned up and checked for adjustement.
Messing with tuners does require specialized test equipment and knowledge in most cases.

One of them is that after I tune into a local FM station, broadcasting in stereo, it takes a while for the stereo indicator light to turn on -- oh, maybe 30 seconds, a minute, something like that. Every other tuner I've had indicated "stereo" instantly when tuned to a stereo broadcast. Is something wrong here or is this just the way this tuner works?

Yes there is something wrong. If the FM signal strength is strong, then it should not take that long to detect stereo. It should take less than a few seconds. It could be a number of possibilities, The parts are aged, so it could be some ecaps out of tolerance. The ecaps do not necessarily control the stereo decoder but could throw it off. There is only one adjustment to make, step 8 of the procedure, adj VRb4 pot, to set the free running vco frequency in the HA1196 part. Lets hope it is only that. You are to measure and set the free running vco freq, at pin 16, as close to 76KHz. Without a freq counter, others have done the adjustment, by first marking on the pot the original position, then slowly turn the pot one way til the stereo lamp turns off, then the other way until the lamp is off again, set the pot mid position to where the lamp turns off, crude, but I am told it works. Might want to spray some fader lube in the pot first, to clean it up and let it dry up.

I suggest to read the owners manual to understand how to hook up an ext AM antenna. The AM audio o/p is dependent on the antenna signal strength.

Expecting a tuner that is this old to perform perfectly, is a bit of hit and miss. To get the best out of it, I suggest to clean all the switches with deoxit, pots with fader lube, change all the old ecaps and check/adj alignment. Problem is, service $ might be more than what you paid for it.

 

[goat67]

One of them is that after I tune into a local FM station, broadcasting in stereo, it takes a while for the stereo indicator light to turn on -- oh, maybe 30 seconds, a minute, something like that. Every other tuner I've had indicated "stereo" instantly when tuned to a stereo broadcast. Is something wrong here or is this just the way this tuner works?

Try to switch the mode to wide opposed to narrow or vice versa

There's an "output" control knob on the faceplate. But when I turn it, the volume stays the same. It doesn't make sense to me that a volume control would be bypassed when the only output is through the RCA jacks on the back.

You need to hook the rca cables to the other set of output jacks it has two sets one for fixed and one for varable

 

[ErikPSmith]

Thanks, all! Based on the responses here, it seems to me that the best thing to do is to take it into a shop for a checkup -- I lack the skills for an alignment, much less the equipment, if that is what is necessary. I hadn't realized that a separate AM antenna was something you could use if an FM antenna was already attached. And I hadn't thought about the fact that there is more than one set of RCA output jacks on the back -- but sure enough, there they are. The funny thing about this tuner is that even with it "out of spec," it seems to sound a little better than the positively-ancient Dynaco FM-3 tube tuner I have hooked up to my living-room stereo -- probably a sign that my Dynaco tuner needs to be gone-through as well. Thanks so much for your help!

 

[goat67]

One of them is that after I tune into a local FM station, broadcasting in stereo, it takes a while for the stereo indicator light to turn on -- oh, maybe 30 seconds, a minute, something like that. Every other tuner I've had indicated "stereo" instantly when tuned to a stereo broadcast. Is something wrong here or is this just the way this tuner works?

Try to switch the mode to wide opposed to narrow or vice versa