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January 1, 2012 / billo44

Trio W-46K Restoration

Here is a short blog relating the joys of twiddling with a Trio W-46K.

In pursuit of aural pleasure, I purchased this 1966 amp at an online auction.

First job was to find some space on the bench….. Here is the bench ‘after’.

In antici……….pation of the arrival of the postman!  Note liquid refreshment (local Sake), and also an earlier 1962 (older than me!) Trio W-38 receiver/amp lurking.

Below is the Trio W-46K with the top removed, the thing was not working on arrival.

Some information about the amp according to Audio Heritage (great site and a mine of useless information)   http://www.audio-heritage.jp/TRIO-KENWOOD/amp/w-46.html

(Jap-lish (bad English) translation courtesy of Google chrome auto translator)

‘As high-end home, Amplifier was developed for companies such as coffee shops and also played on.
W-46 as a kit model was also sold W-46K.`

No to be deterred (either by the bad translation, or the not working amplifier) I set about restoring the thing…

After a good general cleaning.  I noticed one of the input wires from pre-amp stage to power amp stage was no longer attached.

Fixed that and also went around the worst looking bits of ‘dry’ solder fixing them up…  Checked the valves and replaced three of five 12AX7 in the pre-amp stage (had some to hand).  In one socket there was a 12AT7 (might have been a deliberate de-rate?).  After that I still only had sound from one channel and plenty of hum.

Removed, stripped down and cleaned the `source` and `stereo/mono` switches… avoid stripping these down if you can!  Very fiddly to get back together and I could have cleaned them well enough without dismantling.

Now I had sound from both channels.  `Snap crackle pop` from the potentiometers was cured to a large extent by liberal applications of `de-oxit`, but I will look to replace these in good time.  Does any one know where to find 1 Meg Ohm A and 1 Meg Ohm C dual gang potentiometers?

The schematic is courtesy of Kenwood Japan.

W-46K schematic.jpg

Next I started replacing capacitors, the large triple cap and one other large can I left in place bypassed and grafted their replacements out of sight underneath.

Finally found the cause of the hum (98% of it anyway) was two leaky electrolytic caps C211 and C311.

Went ahead and replaced pretty much all the other electrolytcs, used cheap yellow polyester film caps (Cricklewood electronics) in the signal path…, excellent value for money.

Sounding pretty good by this stage.  I also found 4 good quality 7198A output tubes online which was quite lucky, these made another noticeable improvement in sound quality.

I replaced a few signal wires, and grafted better quality RCA plugs onto the AUX input.

Finally I fitted a modern AC power lead (with an earth!).

Had all these `bits` left over when I had finished…. also a couple of fast recovery diodes….

Now the amp sits on top of a trusty old Marantz CD-80 and sounds great considering it all cost bu–er-all.  Doing double duty as a room heater since it does give off quite a lot of heat.  Speakers are currently Crysler CE-1acII, which are very late 60’s and rated at 101 dB/W and sound good with tube gear.  Seems like a good match.

It would probably be worthwhile to try a direct input to the power amp stage and shorten the tortuously long signal paths, but it sounds pretty good for now.

I expect I bored you now, though if you got this far, you likely have similar problems too.

Happy New Year Folks!

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