Re: Tuner problem Kenwood kt 8300


Herb Ward
 

Menahem,

There was a time when I did a lot of tuner work . Some of the older ALPS front ends have trimmer caps that don't age so well as Bob mentioned. Also many of the front ends of that period had a neutralization trimmer cap in the RF amp section that often would cause the problem described by your customer if disturbed during an alignment. I have on several occasions found that those tiny trimmer caps would fail ( go open ) when disturbed. One other thing... the KT8300 is one of those tuners that can develop a whole menu of quirks due to poor PCB grounding. All of the PCB's in that unit are grounded to the chassis and power supply by the mounting screws around the perimeter of the PCB's. I have aligned more than a few tuners and receivers of that period by tightening the PCB mounting screws . ( and by installing internal lock washers between the PCB ground traces and chassis ) That might explain your experience of the tuner working well in the shop, but not so well after your customer installed it into his system. BTW many tuners have a sweet spot for antenna input that is just slightly above full quieting. If the antenna input is many thousands of microvolts, I suspect Bob's comments are right on the money. I once had to add a
 " ghost " eliminator on my first high end tuner after I added a rotor and Channel Master Stereo Probe antenna. It was just a variable attention device .

HRW

On Thu, Oct 28, 2021, 3:09 AM M Yachad <yachadm@...> wrote:
I'm the guilty man, who did the alignment.
I have worked on many of Mike Kline's tuners, all TOTL,
This is the first time I had such a super-sensitive machine - a pleasure to work on, and I did my regular alignment procedure, with absolutely perfect results in the lab.
I do remember one of the inductors having a double-bell waveform, with a trough in the center, while adjusting from bottom to top, inside the inductor shell.
Perhaps choosing the 2nd bell peak would be better?

One of my standard procedures during alignment, is to peak the waveform signal on my scope, while monitoring the THD, and then drop the generator signal strength to almost unreadable, and peak the waveform again. That way, I get the machine sensitive to very weak signals also.
I normally adjust for lowest THD, while keeping the waveform as peaked as possible.
I have found that customers prefer to listen to a CLEAN signal, as opposed to a peaked signal, and sometimes they don't coincide.

The end result was that the machine exceeds all the original factory specs, especially distortion:
1KHz
Narrow Mono = 0.060% vs Factory spec 0.15%;
Narrow Stereo = 0.254% vs Factory spec 0.4% 

So it left the lab, IMO in the best condition possible.
And I connected a little pigtail wire antenna to the machine to demonstrate normal reception performance.
No problems, no ghosting, no stereo noise.

Mike Kline, being a radio lover has a super duper outdoor antenna - he can tell us the exact model, which picks up everything.
When Mike got home, he connected the machine to his super antenna, and that's where the ghost harmonic signal problems showed up.

So, keeping things professional, any suggestions where I need to deviate from my standard alignment procedures to identify and prevent this ghost signal appearing?
Or is it really a factor of a super sensitive machine, optimally aligned, being connected to a super strong antenna?

All suggestions welcomed.

Menahem

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