Nicest built Harman Kardon A50K kit ever?

[buickguy62]

Take a look at the construction of this HK A50K amp kit. This was done by a craftsman, (or craftswoman). Essentially every wire and component runs N-S or E-W.

The first pic is of a typical A50K and the following pics are of this remarkable amp. I have the A50K build manual, and it does not show the components oriented 'true' as this was built-nor are the factory built versions. I don't think this was the first kit this person built. Having built several kits myself, to construct it this way probably would have tripled the build time.

I'm going to recap it, and endeavor to keep the build quality as it is now. Would be nice to put a pexiglas bottom on it and run it upside down just to appreciate the work!

Interesting the amount of extra work when likely no one would ever see it--maybe we are losing the 'craftsman' edge that America once had.

Anyhow, it's just beautiful!!

 

[ferninando]

isn't it nice to see something built with care and pride. all it takes is time.

 

[Bluelobster]

I'm going to recap it, and endeavor to keep the build quality as it is now. Would be nice to put a pexiglas bottom on it and run it upside down just to appreciate the work!

I agree that it real nice work on the wiring. That is something that takes a good bit of skill and practice.
I do hope you don't plan on replacing the American Radionic coupling caps. Those are some decent film/foil caps and are the reason for the voicing of the amp.

 

[Patrice B]

I agree that it real nice work on the wiring. That is something that takes a good bit of practice as well as skill.
I do hope you don't plan on replacing the American Radionic coupling caps. Those are some decent film/foil caps and are the reason for the voicing of the amp.

Huh! Isn't a good thing to replace the old caps with something recent?

I've put a mix of Solen's and OD's in my own A500 with good results.

 

[Bluelobster]

Huh! Isn't a good thing to replace the old caps with something recent?

I've put a mix of Solen's and OD's in my own A500 with good results.

Patrice
Here is a link to another thread where I posted. Look to the bottom of the page.
http://www.audiokarma.org/forums/showthread.php?t=359831

 

[Tube Radio]

Replace those caps. I had them in my Scot Lk-72 amp and was advised to replace them which was good cause after replacing the caps on the bass control that cured the lack of bass in one channel. I used Solen caps where possible, Mallory 150s for the rest and silver mica caps for the real small values that the other two caps couldn't do. Once I replaced those caps I noticed that the amp sounded better.

 

[Big & Pink]

The build quality is superb; some one really knew what they were doing.

If you want to be able to have an up skirt view you could build some sort of stand to raise it then place a mirror on the underside at an angle.

 

[Bluelobster]

Replace those caps. I had them in my Scot Lk-72 amp and was advised to replace them which was good cause after replacing the caps on the bass control that cured the lack of bass in one channel. I used Solen caps where possible, Mallory 150s for the rest and silver mica caps for the real small values that the other two caps couldn't do. Once I replaced those caps I noticed that the amp sounded better.

Those caps you replaced in your LK72 were "Ceracap" quite another animal and not to be confused.

 

[Bluelobster]

The build quality is superb; some one really knew what they were doing.

If you want to be able to have an up skirt view you could build some sort of stand to raise it then place a mirror on the underside at an angle.

Good idea!

 

[Patrice B]

Those caps you replaced in your LK72 were "Ceracap" quite another animal and not to be confused.

That's it, I had them also in my LK-72 and confused them with Radionic ones. However, they're long gone in my HK A500 so no possibility to to compare...

 

[mpholland]

It is nice looking work, but if they were truly concerned with sound quality I think they should have bypassed half the switches, the contour circuit, and the headphone circuit.

 

[Patrice B]

It is nice looking work, but if they were truly concerned with sound quality I think they should have bypassed half the switches, the contour circuit, and the headphone circuit.

The speakers aren't completely silent when you use the headphone jack. Talk about a flaw!

I had to build an external switchbox (with big power resistors) to completely kill the sound on the speakers.

 

[mpholland]

If you ever have noises that you can't directly attribute to out of spec caps, suspect one or more of the switches. The pots can even be problematic in these. I am not downing them by the way, I will never get rid of mine. Spent too much on the NOS quad of 7355's.

 

[Patrice B]

If you ever have noises that you can't directly attribute to out of spec caps, suspect one or more of the switches. The pots can even be problematic in these. I am not downing them by the way, I will never get rid of mine. Spent too much on the NOS quad of 7355's.

My A500 was plagued with random "clicks" and "pops" right after the rebuild...

I've chased down the bug a couple of months (replaced all caps and resistors twice, replaced two sockets, swapped all the little signal tubes, Deoxit several times) until I discovered that a 7355 on the right channel was the culprit!

It was testing fine but I had to put a pair of El-Menco's on this side instead of the original HK labeled tubes. I have another quad of spares BTW...

This one had also a miswired balance pot: turning CW shifted the balance to left and CCW, to right. Strange for a factory unit. Maybe someone had played inside before though...

Wonderful sounding with a pair of Realistic MC2001.

 

[GordonW]

That first pic (the "typical" one) looks more like what you see in the factory-built A500s.

The second one? They didn't go to that level of care, even on the factory assembly line!

I would replace all those American Radionics caps, as well as the electrolytics, regardless. Last A500 I reworked, had lots of leaky AR caps...

BTW: I tend to "obsess" with component layout and wiring like that, when I'm doing speaker crossovers:

That's before I soldered all the connections... but that's exactly the layout it wound up being... :thmbsp:

Regards,
Gordon.

 

[voltcontrol]

Neat-o-philes. :thmbsp:

 

[buickguy62]

I agree that it real nice work on the wiring. That is something that takes a good bit of skill and practice.
I do hope you don't plan on replacing the American Radionic coupling caps. Those are some decent film/foil caps and are the reason for the voicing of the amp.

My plan is to replace all the electrolytic and coupling caps. If I were to keep it, I might take a chance on not replacing the coupling caps, but I expect to sell it, and I want it to be as reliable as possible. From recommendations on this forum, I've been using Sprague/Vishay 716P coupling caps, and have had good result with them.

 

[buickguy62]

This one had also a miswired balance pot: turning CW shifted the balance to left and CCW, to right. Strange for a factory unit. Maybe someone had played inside before though....

On these amps, the A speakers are the LH channel, and the B speakers are the RH channel. If the balance pot seems backwards, swapping the speaker wires makes the balance behave properly. This is more often a problem on the A300, as the A channel speaker terminals are on the RH side (as you face the amp) and B channel terminals on the LH side), so that the speaker wires 'cross' from what would be their logical connections. That's not to say that your amp may have been wired backwards, only that it is easily corrected.

 

[buickguy62]

Completed recapping of the A50K, with due diligence in keeping orientation of components N-S and E-W per original. Lot's of pre-planning and extra time, but I didn't want to detract from efforts the original builder displayed.

 

[kpaxfaq]

Looks great buickguy! Your A-300's that have shown up on flea bay are always top notch as well.