Kenwood Trio 600T IF display

[steveUK]

The centre section (signifying narrow mode) of the IF bandwidth display on a Kenwood Trio 600T does not light up. Ive only just acquired the set so I haven't even taken the cover off yet to investigate. But before I do, does anyone know if the five sections of that IF display are individual lamps or LEDs, or is it a specially made illumination strip of some kind? Narrow mode itself does work, it's just the lamp that doesn't. Of course, it may be the drive to the lamp that is not be getting through.

 

[Punker X]

They are LED's. Been quite some time since I have had one of these units that far a part, but if memory serves me correct they are individual LED's mounted on a small board. Maybe someone with more recent experience can help further. May want to clean the switch contacts first.

 

[steveUK]

Thanks Mike. I managed to get hold of a schematic today and yes, it does appear to be discrete LEDs. Like you say I first of all need to clean all switch contacts.

 

[Bob@FM]

Those old LEDs do go bad, I had one do that. They can be tested with a multimeter diode test function, which will show voltage drop and dimly light a good one. To replace, I would replace all the LEDS for both narrow and wide if you want to match brightness. Older ones are less bright. Or install a resistor in front to try and match brightness.

 

[steveUK]

Thanks Bob. Again, having not taken the top off the set yet, what is the spec of the LEDS? I presume they're 'white' for starters, what else? Brighter would be nicer, the original ones are not glaringly bright.

 

[Bob@FM]

I replaced those LEDs a long time ago, just matched shape and color. They are green, rectangular is my recall.

 

[steveUK]

Yes they're visibly green and rectangular at the front panel, but is that just a green filter for regular white LEDs positioned behind, or are they special, shaped LEDS or a combined LED panel purpose made for the job? That's the question, because obtaining either is a totally different task, one is easy the other probably not possible.

 

[rcs16]

It would not be a white LEDs as we know them now but what are called a diffused lens LED vs a clear lens type.
You could put a voltmeter on the lead that drives the LED to determine if you have a switch or LED issue to begin with.

Look at a Lumex SSL-LX4673GD-LA20
https://www.mouser.ca/datasheet/2/244/SSL-LX4673GD-LA20-95504.pdf
6mcd is not very bright, if you want brighter, keep on looking ...

Would like to hear what you think of the 600T performance vs your other tuners. I bet that it has issues like my KT-8300 does with adjacent channels, I have a many station in my FM band area and a high gin antenna.
The 600T has a 3rd IF filter path, so it would be better, but how much?

 

[steveUK]

Thanks everyone. Ok, I found the culprit, one of the middle (narrow mode) LEDs is o/c. They're actually a small green LED. I guess I'd be better changing all of them to the same small green LEDs so as to maintain a balance as was suggested earlier. Standard 'modern' LEDs will be ok yeah?

 

[steveUK]

I'm looking at these but I notice that the different colours use different voltages. The measured voltage across each LED on the board was around 2.1V, but here it says that the green LEDs are 3.0v to 3.4v 20mA. Hmm.. no good is it...?

https://www.ebay.co.uk/itm/5mm-3mm-...g:9AkAAOSwlv9blVx0:rk:7:pf:0&var=521951104271

 

[rcs16]

So those originals are clear tinted lens, I guess 5mm? So I think you want a wide beam angle clear point source type not diffused as your link shows.
They get diffused by another filter, I assume clear translucent. Could try to match or figure out the beam angle to match exactly.
I do not think that the LED V drop of the replacement is that important, you might have to change the V drop R in series with the LED depending on what you choose and the brightness you want to achieve.
Really any LED will work, even blue and white types ( alter V drop R however) but choice of LED and the colour it produces are quite varied. I like the emerald green coloured LEDs myself.

Are those LEDs in series or parallel?, since it looks like there are 2 per IF

 

[steveUK]

Thanks.

They're actually 3mm LEDs. I didn't buy those in the link above, I got these, they're 2.1V, 10mA a bit brighter and are (sold as!) Avago ones which I understand are better than the run of the mill cheap stuff. https://www.ebay.co.uk/itm/HLMP-1521-Avago-Technologies-LED-3mm-Green/131702630553?ssPageName=STRK:MEBIDX:IT&_trksid=p2057872.m2749.l2649

In the tuner they are configured 3 x sets of two LEDs connected in series. I'll put just one pair in at first to see how they compare brightness wise and take it from there re changing the series V drop R. It wouldn't hurt to go a tad brighter TBH, but saying that I'm not a fan of making vintage sets look as if they've got Christmas tree lights on them, just a tad brighter would be nice. I'll report back when I have some more news.

 

[steveUK]

I fitted the six new green LEDs and it works and looks great. The current in each LED measures 14mA which is fine. The array is a tad brighter than it was before which as I said above , is what I had hoped for.

 

[rcs16]

Looks good, hows it sound? I looked at the schematics, quite the monster, RC4558 opamps, same st decoder as in the KT-8300. TI is still making RC4558 but I think your 600T might deserve better

 

[steveUK]

Looks good, hows it sound? I looked at the schematics, quite the monster, RC4558 opamps, same st decoder as in the KT-8300. TI is still making RC4558 but I think your 600T might deserve better

Yes some time ago I replaced the many TL072 ICs in my Quad 44 preamp with OPA2134s. I suppose it could be done with the 600T (the 4558s) but I don't know if I'll bother presently as I have many projects on the go, it's an available time issue.

It's a lovely tuner to use, in particular, the tuning knob has a very heavy, extremely smooth feel to it. Not fully evaluated yet, the audio is certainly good and the selectivity and sensitivity seem good so far but changing weather patterns here make comparisons unreliable until it's been in use for a longer period. It's a cracking looker with its long dial and centre tuning knob. Very well built too.

 

[steveUK]

Looks good, hows it sound? I looked at the schematics, quite the monster, RC4558 opamps, same st decoder as in the KT-8300. TI is still making RC4558 but I think your 600T might deserve better

If I do get around to upgrading the opamps, what would you use? I've read that although some are considered 'drop in' replacements, they can lead to instability?

 

[rcs16]

There are lots of possibilities, even a NE5532AP would be fine. Instability is probably supply decoupling in the old single sided layout, is insufficient, long ground return traces. You want to add some better supply decoupling right at the supply pins, for faster devices.
My Yamaha T-85 used NJM2068, they are fine imo, I do not think I will upgrade them. OPA2134 if you like what they do in your quad44.

 

[steveUK]

I have been comparing it to a Pioneer TX-9800 which is quite a well thought of tuner and the last of the analogue tuners from Pioneer. In terms of the quality, integrity and clarity of the sound produced, I can hear no difference between the two. I have set up a passive switching unit into my amplifier and set up the outputs of the tuners to be exactly the same. Switching from one to the other I can hear no discernible difference in any quarter. I am a musician, some time sound engineer and electronics engineer may I add, and I can generally hear a difference if there is one to be heard. In terms of their DXing ability, again it's very close. There is one particular station where I live (in the UK) that I use for DXing tests. Basically, it is extremely hard to pull this station in at all, never mind with any degree of fidelity. Nonetheless, it sorts the men out from the boys in terms of how close a tuner can get to it. If anything, the Pioneer had an extremely slight edge. Quite a surprise to me really as the Trio 600T is probably thought of as being a superior - certainly more collectable/desirable - than the Pioneer TX-9800. The name on something bothers me not, it's the performance that counts - unless you're selling it, then the going rate is the going rate. I am currently working on a Tandberg 3001A (not finished), and results so far indicate to me that this tuner may be better than both the Trio and the Pioneer and may well top my Onkyo 9090 mkII. We'll see.

 

[rcs16]

It could be possible that the 600T (or any of them) needs a front end alignment. I had a SX-1250 in for an alignment recently, it was one trim cap that was off, it made a big difference in quieting sensitivity.

 

[steveUK]

It could be possible that the 600T (or any of them) needs a front end alignment. I had a SX-1250 in for an alignment recently, it was one trim cap that was off, it made a big difference in quieting sensitivity.

So true.