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Old 10th Aug 2023, 10:31 am   #1
Luxman1050
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Default Kenwood TK150U solid state amplifier is this corrosion?

Hi all
Just got this little beauty and boy does it pack a punch for its size.
Sound wise not dissimilar to a valve amp.
Got a few hiccups,
Firstly you have the balance control attached to volume but as you increase volume the balance turns with it is this normal? So you start with balance fully off to the left then turn up. I tried the balance at mid point volume at zero and it was way to loud even with volume at zero. Turn balance to zero and slowly increas volume then you get a balanced sound? Not sure what's going on there?
Also in last picture you can see whitish blemishes on the rear of the front panel is this corrosion? Never seen that before only a white powder coating usually on aluminium. Any ideas how to remove it?
Otherwise nice little amp this was kenwoods first transistor amp bought onto the market. Date around 1968.
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Old 10th Aug 2023, 10:56 am   #2
paulsherwin
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Default Re: Kenwood TK150U solid state amplifier is this corrosion?

That's not a balance control, it's separate but linked left and right volume controls. They're supposed to rotate together.

Not sure what the 'corrosion' is.
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Old 10th Aug 2023, 11:47 am   #3
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Default Re: Kenwood TK150U solid state amplifier is this corrosion?

Thanks Paul must admit it threw me.
No not seen anything quite like it.
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Old 10th Aug 2023, 10:51 pm   #4
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Default Re: Kenwood TK150U solid state amplifier is this corrosion?

I had one of these, a reliable and good sounding amplifier. The marks in last picture is the aluminium oxidising, cleaning it will encourage it to come back fairly quickly unless the metal is cleaned and then either primed or lacquered.
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Old 11th Aug 2023, 9:08 am   #5
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Default Re: Kenwood TK150U solid state amplifier is this corrosion?

Quote:
Originally Posted by paulsherwin View Post
That's not a balance control, it's separate but linked left and right volume controls. They're supposed to rotate together.

Not sure what the 'corrosion' is.
Yes, they rotate together, but can also be independently, and finely, adjusted to correct any LH and RH Channel unbalance.
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Old 11th Aug 2023, 9:29 am   #6
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Default Re: Kenwood TK150U solid state amplifier is this corrosion?

the corrosion is on the metal chasis not on the ali face plate. That's why it's thrown me not seen that colour on a chasis before.
Yeah I'm impressed with the unit all original and sounds pretty good. The only thing now I've run it in for a while is that typical thud on switch on/off and a slight hum through the speakers. I'll change that 630wv pio cap for a safety cap not sure that will cure the thud though. I'll no doubt do a full recap at some stage although the caps checked so far are all in spec and the resistors. Those 2sd91 transistors are pretty good.
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Old 11th Aug 2023, 9:33 am   #7
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Default Re: Kenwood TK150U solid state amplifier is this corrosion?

Must admit I thought it was initially balance wonder why they decided to install the volume that way. Dual pot. Space saving?
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Old 11th Aug 2023, 9:41 am   #8
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Default Re: Kenwood TK150U solid state amplifier is this corrosion?

It was quite a common arrangement in the early years of stereo amps before a separate balance control became standard. Lots of cassette decks had similar level controls into the 90s.

A switchon thump is completely normal with transistor amps of the 60s and 70s, but there shouldn't be a significant hum.
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Old 11th Aug 2023, 9:57 am   #9
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Default Re: Kenwood TK150U solid state amplifier is this corrosion?

No significant hum just slight.
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Old 11th Aug 2023, 12:13 pm   #10
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Default Re: Kenwood TK150U solid state amplifier is this corrosion?

I think it's the same as a Kenwood KA-2000 (it's certainly very very similar).
The service manual for KA-2000 is on 'hifiengine' if you need it, and there's a pretty good write-up of it on the AK forum https://audiokarma.org/forums/index....ration.845076/

Alan
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Old 11th Aug 2023, 1:21 pm   #11
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Default Re: Kenwood TK150U solid state amplifier is this corrosion?

Oh well there's me thinking I did alright on this one. Then it just slowly died on me today. Anyone got any ideas on why the fuse have gone? Picture attached it looks like it's slowly overheated and blown. It's a 1amp quick blow fuse although it did not just pop obviously slowly burnt out. Any pointers most welcome.
Cheers Chris
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Old 11th Aug 2023, 1:22 pm   #12
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Default Re: Kenwood TK150U solid state amplifier is this corrosion?

By the way thanks for the info Alan.
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Old 11th Aug 2023, 1:42 pm   #13
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Default Re: Kenwood TK150U solid state amplifier is this corrosion?

An electrolytic in the power supply may have failed with excess leakage. Let's hope the output transistors are OK - they can be difficult to replace, and there can be a cascade of failures through the driver stages.
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Old 11th Aug 2023, 1:56 pm   #14
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Default Re: Kenwood TK150U solid state amplifier is this corrosion?

Hi
Unfortunately quite common now for earlier transistor amps to fail not long after bringing them on after a long sleep. I concur that the smoothing capacitors could be the issue but also a component failure in the DC coupled stages, hope not as it can be a nightmare to fix and of course find decent equivalent transistors to the now obsolete types. Good luck.
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Old 11th Aug 2023, 1:57 pm   #15
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Default Re: Kenwood TK150U solid state amplifier is this corrosion?

Cheers Paul got a couple of caps that will fit. Drivers hope not!!!! Oh deary me.
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Old 11th Aug 2023, 4:08 pm   #16
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Default Re: Kenwood TK150U solid state amplifier is this corrosion?

There's a mains filter capacitor (0.01uF ?) soldered to the fuse holder... that's the first suspect !

It should be swapped in any case, as it isn't a proper X2 rated component. Or just snipped out.

Pete
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Old 11th Aug 2023, 6:03 pm   #17
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Default Re: Kenwood TK150U solid state amplifier is this corrosion?

That's the safety cap fitted. New fuse and we have power again. I'll still do the psu caps waiting on some new resistors there although the originals are all within spec except the one going to mains switch about 40% out.
Interesting the coupling caps on the output transistors now this guy fitted 2200uf caps as opposed to the original 1000uf to improve the bottom end? Any merit in this? Only ask as the bass on this amp as it is is more than good enough.

Cheers for input everyone.

Chris
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Old 11th Aug 2023, 6:53 pm   #18
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Default Re: Kenwood TK150U solid state amplifier is this corrosion?

Should be OK if the caps are healthy and good quality. These amps were never marketed as superfi devices though, and changing the cap values is unlikely to make an audible difference with the type of speakers normally used.
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Old 12th Aug 2023, 10:43 am   #19
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Default Re: Kenwood TK150U solid state amplifier is this corrosion?

So in essence there's no benefit to be had if the coupling caps are increased from 1000uf to 2200uf?
They've used Elna caps throughout.
I think just to be on the safe side I'll switch the filter caps and coupling caps. It appears to have been stored for who knows how long in it's box. Just a shame with that corrosion.

Chris
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Old 12th Aug 2023, 10:46 am   #20
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Default Re: Kenwood TK150U solid state amplifier is this corrosion?

Forgot I've also managed to source the original service manual for it which will be helpful.
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