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Who is using a Harman Kardon HK250 amp ?

MisterDK

MisterDK

Addicted Member
Hey folks, just wondering if the HK250 has a following and what most of you think of them. I just bought one that looks a little - aged - but it’s complete. Supposedly, it’s not in working order so I’m hoping the transformers are OK.. I won’t know ‘till it gets here.
I do have the repair manual and schematic from hifiengine, as well as a “corrected” schematic

BTW - are the chassis on these plated steel or copper sheet metal?

Thanks.
 
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Hello - I have had a HK-250 for 10-15 years. It goes in rotation around once a year and I have always been pleased with the performance and it has been 100% trouble free. It seems to have plenty of power for my needs.... I listen to wide variety of music at reasonable volumes using speakers that are ~88dB efficient. I like that it has 4, 8, and 16 taps and provisions for running as a monoblock. It is very understated looking, which I like. I honestly never checked the chassis construction... I assumed it was copper clad, but never even thought to put a magnet to it, lol.

When I bought it all I did was I recap it and replace some worn tubes. I may have replaced a couple of out-of-spec resistors. I remember it being a little crowded under the hood, but it was manageable.

FWIW, I find it to be an enjoyable amplifier to own and use, and that is putting it up against some stiff competition. I have always thought that if another one came up for sale locally I would buy it and try running a pair as monoblocks.

In any event, it's well worth restoring, IMHO.

Good luck with it.

Mark
 
Haven't used that particular model, but I would expect it to perform well with the requisite restoration. Everything about it is common topology for HK's pentode amplifiers. The power supply is a low impedance voltage doubler, and the amplifier driver consists of a cathodyne splitter preceded by a nested positive feedback loop. If the transformers are all good, the project should be pretty straightforward.

Jack
 
I had a pair here (on lone) and was impressed. These used 6fq7's input and driver & a pair of 6L6s... What I found interesting was they used ceramic coupling caps. Yes copper plated steel. Not real common.
 
I have two HK-250 amplifiers, identically restored, running dual monoblock. 100W of Tube Power, baby!

And, yes, I am the source of the aforementioned "corrected" schematic, showing how mine was (and remains) actually wired up, ever so slightly differently from the official schematics.

One of the pair is currently having power supply (I suspect) issues, so in an attempt to get it working again I am at long last replacing the original Astron capacitors with new Vishays. Those new Vishays are $20 each! what the heck? Anyway, I think I'll keep the old Astron cardboard tubes, just replacing their innards, for the sake of appearances.

As for the HK250 in general, TBH, I haven't been using the stereo much, this past half-decade, mostly because there are now four teens in this house and none of them really wants to hear Dad's music anymore; they have their own music and do me the courtesy of listening to it through their headphones.

That said, the old stereo does get a workout at Christmastime, playing universally popular and appropriate Holiday music. I gave the one working HK250 a good audial scrutiny session last week and was reminded why I loved it in the first place. Vocals are so realistic you'd swear the crooner was sitting right in front of you. And that's what motivated me to get the full pair running again, teens be damned.
 
pbnelson said:
Vocals are so realistic you'd swear the crooner was sitting right in front of you.
Click to expand...
I've only heard a few systems in my entire life like that. In addition to requiring really transparent speakers, they have to be matched to the room, and overall system Q (amp plus speakers) has to be exactly right. Would you mind describing the speakers you're using?

Jack
 
My original restoration post was here:

Harman Kardon HK250 Corrected Schematic and Restoration Photos

These photographs of my Harman Kardon HK250 restoration were on the web in 2006, but my free hosting service recently died and so I have moved them to Flickr. I have just finished restoring another HK250, and now run them both in "parallel" mode, as a dual mono-block, giving me 50 watts per...
audiokarma.org

The "Alon Adriana Mini-Monitor" speakers can be seen in this photo set (linked in above post). Room placement has remained the same all these years (there's no better arrangement). Here:

www.flickr.com

Harman Kardon HK250 Tube Amplifier Restoration and Schematics

Photos from my 2006 restoration project. Not shown are any photos of an identical restoration done in 2009. I now run them as a dual mono-block pair. Harman Kardon HK250 Tube Amplifier Restoration and Schematics HK-250
www.flickr.com www.flickr.com

I bought them new, back in the late 90's, and kept them all this time. A thorough review of them, far more than I could add, is here:

 
pbnelson said:
The "Alon Adriana Mini-Monitor" speakers can be seen in this photo set
Click to expand...
Those particular speakers are terribly inefficient (87 dB). That characteristic seems to accompany the majority of otherwise excellent speakers. The first speaker I ever heard that was truly lifelike was the Genesis 44. I've often thought about acquiring a pair to restore, but at 88 dB, they're also not suitable for lower power amplifiers. Oh well, the search goes on. :)

Jack
 
Any Klipsch Heritage speaker should work wonders with low powered tube amps. For my tv room I have a pair of Heresy speakers and in my theater room a pair of Klipschorn’s in the corners powered by a 1.6 watt per channel Alan Eaton type 45 SET amp.
 

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Didn't realize so many here had one (or two) of these great amps, its great to hear as I don't see or hear about many out in the wild. Here's my HK250 with a matched quad of (TS) RCA 5881's (4/'72), and pair of RCA 6CG7 clear top/black plate; sounds really nice with them, but I have yet to hear the amp with 6L6's in it, which I need to try.
My amp came from a fellow (& nice) AK member, and had been serviced under the hood, with 5 way binding posts, and on/off switch added; I've had to replace some of the orig. resistors in the past, and reflowed some of the soldering.
Recently, one of the bias pots started to drift, not hold bias properly, so I changed both of them out; if I remember correctly, they're 100ohm? if replacing (recommend checking them), I would replace both and make sure the two new ones measure closely to each other (something you can ask the part seller to check when buying), the space is a tight fit, so make sure you find the right ones and measure dia. Also recommend making some contact points on top of chassis for your meter to check the bias while adjusting, to avoid having to always go inside to measure when biasing.

Great imaging and soundstage, musical; nothing glaring to complain about. It holds its own in very good company. I say it's a sleeper.

Enjoy your amp!

PS: I can't say for sure but I believe it's copper coating over steel chassis.

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